We establish a simple yet general parameterization of Higgs-muon interactions within the effective field theory frameworks, including both the Higgs Effective Field Theory (HEFT) and the Standard Model Effective Field Theory (SMEFT). We investigate the potential of a muon collider, operating at center-of-mass energies of 3 and 10 TeV, to probe Higgs-muon interactions. All possible processes involving the direct production of multiple electroweak bosons ($W$, $Z$, and $H$) with up to five final-state particles are considered. Our findings indicate that a muon collider can achieve greater sensitivity than the high-luminosity LHC, especially considering the independence of the Higgs decay branching fraction to muons. Notably, a 10 TeV muon collider offers exceptional sensitivity to muon-Higgs interactions, surpassing the 3 TeV option. In particular, searches based on multi-Higgs production prove highly effective for probing these couplings.
Jun 07 2024
hep-ph arXiv:2406.04040v1
Electroweak Precision Measurements are stringent tests of the Standard Model and sensitive probes to New Physics. Accurate studies of the Z-boson couplings to the first-generation quarks could reveal potential discrepancies between the fundamental theory and experimental data. Future lepton colliders offering high statistics of Z bosons would be an excellent tool to perform such a measurement based on comparison of radiative and non-radiative hadronic decays of the Z boson. Due to the difference in quark charge, the relative contribution of the events with final-state radiation (FSR) directly reflects the ratio of up- and down-type quark decays. Such an analysis requires a proper distinction between photons coming from different sources, including initial-state radiation (ISR), FSR, parton showers and hadronisation. In our talk, we will show how to extract the values of the Z couplings to quarks and present preliminary results of the analysis for ILC.
Feb 29 2024
hep-ph arXiv:2402.18460v2
We study the discrimination power of future multi-TeV muon colliders for a large set of models with extended gauge symmetries and additional neutral gauge bosons ("$Z'$-models"). Our study is carried out using a $\chi^2$-analysis of leptonic observables of s-channel scattering in effective $Z'$-models. We make use of angular and chiral asymmetries induced in such models to find the discovery reach of a given muon collider setup in terms of the $Z'$ mass and to discriminate between the different scenarios. In this context, we discuss how polarized beams - should they become available at muon colliders - or polarization measurements can help in the discrimination. Our results show that typical muon collider setups which are currently under consideration can give a significantly higher reach compared to existing bounds and projections for high-luminosity LHC.
We study the capabilities of a muon collider, at 3 and 10 TeV center-of-mass energy, of probing the interactions of the Higgs boson with the muon. We consider all the possible processes involving the direct production of EW bosons ($W,Z$ and $H$) with up to five particles in the final state. We study these processes both in the HEFT and SMEFT frameworks, assuming that the dominant BSM effects originate from the muon Yukawa sector. Our study shows that a Muon Collider has sensitivity beyond the LHC, as it not only relies on the Higgs-decay branching fraction to muons. A 10 TeV muon collider provides a unique sensitivity on muon and (multi-) Higgs interactions, significantly better than the 3 TeV option. We find searches based purely on multi-Higgs production to be particularly effective in probing these couplings.
Dec 11 2023
hep-ph arXiv:2312.05223v1
In this paper we investigate how well the nature of heavy neutral leptons can be determined at a future lepton collider, after its potential discovery. Considered in a simplified model are prompt decays of the neutrino in the mass range from 100 GeV to 10 TeV. We study event selection and application of multivariate analyses to determine whether such a newly discovered particle is of the Dirac or Majorana nature. Combining lepton charge and kinematic event variables, we find that the nature of a heavy neutrino, whether it is a Dirac or a Majorana particle, can be determined at 95% C.L. almost in the whole discovery range. We will briefly speculate about other than the studied channels and the robustness of this statement in more general models of heavy neutral leptons, particularly on the complementarity of high-energy electron-positron vs. muon colliders on resolving the flavor structure of heavy neutrinos.
We give a status report on new developments in the WHIZARD event generator, including NLO electroweak automation for $e^+e^-$ colliders, loop-induced processes, POWHEG matching, new features in the UFO interface and the current development for matching between exclusive photon radiation and fixed-order LO/NLO electroweak (EW) corrections. We report on several bug fixes relevant for certain aspects of the ILC250 Monte Carlo (MC) mass production, especially on the normalization of matching EPA samples with full-matrix element samples. Finally, we mention some ongoing work on efficiency improvements regarding parallelization of matrix elements and phase space sampling, as well as plans to revive the top threshold simulation.
May 23 2023
hep-ph arXiv:2305.12814v1
Muon colliders offer the possibility to go to very high energies with relatively small circular colliders, energies up to 10 or 14 TeV are envisioned. Due to their very clean collider environment they provide a fantastic tool to search for new physics in the electroweak sector, especially through the production of multiple EW vector and Higgs bosons, and they allow to measure the Higgs-muon coupling very precisely. I will elucidate the physics capabilities from these processes and also discuss issues on precision predictions for SM backgrounds at high-energy lepton colliders.
Luc Darmé, Céline Degrande, Claude Duhr, Benjamin Fuks, Mark Goodsell, Gudrun Heinrich, Valentin Hirschi, Stefan Höche, Marius Höfer, Joshua Isaacson, Olivier Mattelaer, Thorsten Ohl, Davide Pagani, Jürgen Reuter, Peter Richardson, Steffen Schumann, Hua-Sheng Shao, Frank Siegert, Marco Zaro We present an update of the Universal FeynRules Output model format, commonly known as the UFO format, that is used by several automated matrix-element generators and high-energy physics software. We detail different features that have been proposed as extensions of the initial format during the last ten years, and collect them in the current second version of the model format that we coin the Universal Feynman Output format. Following the initial philosophy of the UFO, they consist of flexible and modular additions to address particle decays, custom propagators, form factors, the renormalisation group running of parameters and masses, and higher-order quantum corrections.
Carlotta Accettura, Dean Adams, Rohit Agarwal, Claudia Ahdida, Chiara Aimè, Nicola Amapane, David Amorim, Paolo Andreetto, Fabio Anulli, Robert Appleby, Artur Apresyan, Aram Apyan, Sergey Arsenyev, Pouya Asadi, Mohammed Attia Mahmoud, Aleksandr Azatov, John Back, Lorenzo Balconi, Laura Bandiera, Roger Barlow, et al (277) A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.
Neutrinos are the most elusive particles known. Heavier sterile neutrinos mixing with the standard neutrinos might solve the mystery of the baryon asymmetry of the universe. In this letter, we show that among all future energy frontier accelerators, muon colliders will provide the farthest search reach for such neutrinos for mass ranges above the $Z$ pole into the multi-TeV regime. We compare the performance of muon with electron colliders of the same machine energy and briefly discuss the complementarity in flavor space between the two types of accelerators.
Dec 05 2022
hep-ph arXiv:2212.01323v1
We explore the sensitivity of directly testing the muon-Higgs coupling at a high-energy muon collider. This is strongly motivated if there exists new physics that is not aligned with the Standard Model Yukawa interactions which are responsible for the fermion mass generation. We illustrate a few such examples for physics beyond the Standard Model. With the accidentally small value of the muon Yukawa coupling and its subtle role in the high-energy production of multiple (vector and Higgs) bosons, we show that it is possible to measure the muon-Higgs coupling to an accuracy of ten percent for a 10 TeV muon collider and a few percent for a 30 TeV machine by utilizing the three boson production, potentially sensitive to a new physics scale about $\Lambda \sim$ 30-100 TeV.
We summarize the status of automated NLO SM corrections for hadron and lepton collider processes in the multi-purpose event generator WHIZARD. The focus will be on NLO EW and QCD-EW mixed corrections at the LHC. Also, recent progress on the inclusion of EW corrections in future lepton collider processes and on the POWHEG-matched event generation in the NLO automated setup will be discussed.
M. Begel, S. Hoeche, M. Schmitt, H.-W. Lin, P.M. Nadolsky, C. Royon, Y-J. Lee, S. Mukherjee, C. Baldenegro, J. Campbell, G. Chachamis, F.G. Celiberto, A. M. Cooper-Sarkar, D. d'Enterria, M. Diefenthaler, M. Fucilla, M. V. Garzelli, M. Guzzi, M. Hentschinski, T. J. Hobbs, et al (30) This report was prepared on behalf of three Energy Frontier Topical Groups of the Snowmass 2021 Community Planning Exercise. It summarizes the status and implications of studies of strong interactions in high-energy experiments and QCD theory. We emphasize the rich landscape and broad impact of these studies in the decade ahead. Hadronic interactions play a central role in the high-luminosity Large Hadron Collider (LHC) physics program, and strong synergies exist between the (HL-)LHC and planned or proposed experiments at the U.S. Electron-Ion Collider, CERN forward physics experiments, high-intensity facilities, and future TeV-range lepton and hadron colliders. Prospects for precision determinations of the strong coupling and a variety of nonperturbative distribution and fragmentation functions are examined. We also review the potential of envisioned tests of new dynamical regimes of QCD in high-energy and high-density scattering processes with nucleon, ion, and photon initial states. The important role of the high-energy heavy-ion program in studies of nuclear structure and the nuclear medium, and its connections with QCD involving nucleons are summarized. We address ongoing and future theoretical advancements in multi-loop QCD computations, lattice QCD, jet substructure, and event generators. Cross-cutting connections between experimental measurements, theoretical predictions, large-scale data analysis, and high-performance computing are emphasized.
Tulika Bose, Antonio Boveia, Caterina Doglioni, Simone Pagan Griso, James Hirschauer, Elliot Lipeles, Zhen Liu, Nausheen R. Shah, Lian-Tao Wang, Kaustubh Agashe, Juliette Alimena, Sebastian Baum, Mohamed Berkat, Kevin Black, Gwen Gardner, Tony Gherghetta, Josh Greaves, Maxx Haehn, Phil C. Harris, Robert Harris, et al (302) This is the Snowmass2021 Energy Frontier (EF) Beyond the Standard Model (BSM) report. It combines the EF topical group reports of EF08 (Model-specific explorations), EF09 (More general explorations), and EF10 (Dark Matter at Colliders). The report includes a general introduction to BSM motivations and the comparative prospects for proposed future experiments for a broad range of potential BSM models and signatures, including compositeness, SUSY, leptoquarks, more general new bosons and fermions, long-lived particles, dark matter, charged-lepton flavor violation, and anomaly detection.
Alberto Belloni, Ayres Freitas, Junping Tian, Juan Alcaraz Maestre Aram Apyan, Bianca Azartash-Namin, Paolo Azzurri, Swagato Banerjee, Jakob Beyer, Saptaparna Bhattacharya, Jorge de Blas, Alain Blondel, Daniel Britzger, Mogens Dam, Yong Du, David d'Enterria, Keisuke Fujii, Christophe Grojean, Jiayin Gu, Tao Han, Michael Hildreth, et al (48) The precise measurement of physics observables and the test of their consistency within the standard model (SM) are an invaluable approach, complemented by direct searches for new particles, to determine the existence of physics beyond the standard model (BSM). Studies of massive electroweak gauge bosons (W and Z bosons) are a promising target for indirect BSM searches, since the interactions of photons and gluons are strongly constrained by the unbroken gauge symmetries. They can be divided into two categories: (a) Fermion scattering processes mediated by s- or t-channel W/Z bosons, also known as electroweak precision measurements; and (b) multi-boson processes, which include production of two or more vector bosons in fermion-antifermion annihilation, as well as vector boson scattering (VBS) processes. The latter categories can test modifications of gauge-boson self-interactions, and the sensitivity is typically improved with increased collision energy. This report evaluates the achievable precision of a range of future experiments, which depend on the statistics of the collected data sample, the experimental and theoretical systematic uncertainties, and their correlations. In addition it presents a combined interpretation of these results, together with similar studies in the Higgs and top sector, in the Standard Model effective field theory (SMEFT) framework. This framework provides a model-independent prescription to put generic constraints on new physics and to study and combine large sets of experimental observables, assuming that the new physics scales are significantly higher than the EW scale.
Aug 22 2022
hep-ph arXiv:2208.09438v1
We present results on NLO electroweak (EW) corrections to multiple massive boson production processes at a future muon collider. Inclusive cross sections with $\mathcal{O}(\alpha)$ corrections for processes for up to four bosons in the final state as well as differential distributions for $HZ$ production are computed for $\sqrt{s}=3$, $10$ and $14$ TeV by using FKS subtraction in the NLO EW automated Monte-Carlo framework WHIZARD+RECOLA. Large logarithmic effects due to collinear ISR and EW virtual correction factors as well as the impacts of an energy cut on hard photons are discussed with an emphasis on the properties of Higgsstrahlung. The potential of a proposed muon collider for studying physics of the EW sector is underlined by the EW corrections significantly affecting observables for processes at high energies and boson multiplicities.
S. Frixione, E. Laenen, C.M. Carloni Calame, A. Denner, S. Dittmaier, T. Engel, L. Flower, L. Gellersen, S. Hoeche, S. Jadach, M.R. Masouminia, G. Montagna, O. Nicrosini, F. Piccinini, S. Plätzer, A. Price, J. Reuter, M. Rocco, M. Schönherr, A. Signer, et al (8) Mar 24 2022
hep-ph arXiv:2203.12557v2
This white paper concerns theoretical and phenomenological aspects relevant to the physics of future $e^+e^-$ colliders, in particular regarding initial-state QED radiation. The contributions each contain key technical aspects, and are formulated in a pedagogical manner so as to render them accessible also to those who are not directly working on these and immediately-related topics. This should help both experts and non-experts understand the theoretical challenges that we shall face at future $e^+e^-$ colliders. Specifically, this paper contains descriptions of the treatment of initial state radiation from several Monte Carlo collaborations, as well as contributions that explain a number of more theoretical developments with promise of future phenomenological impact.
J. M. Campbell, M. Diefenthaler, T. J. Hobbs, S. Höche, J. Isaacson, F. Kling, S. Mrenna, J. Reuter, S. Alioli, J. R. Andersen, C. Andreopoulos, A. M. Ankowski, E. C. Aschenauer, A. Ashkenazi, M. D. Baker, J. L. Barrow, M. van Beekveld, G. Bewick, S. Bhattacharya, C. Bierlich, et al (191) We provide an overview of the status of Monte-Carlo event generators for high-energy particle physics. Guided by the experimental needs and requirements, we highlight areas of active development, and opportunities for future improvements. Particular emphasis is given to physics models and algorithms that are employed across a variety of experiments. These common themes in event generator development lead to a more comprehensive understanding of physics at the highest energies and intensities, and allow models to be tested against a wealth of data that have been accumulated over the past decades. A cohesive approach to event generator development will allow these models to be further improved and systematic uncertainties to be reduced, directly contributing to future experimental success. Event generators are part of a much larger ecosystem of computational tools. They typically involve a number of unknown model parameters that must be tuned to experimental data, while maintaining the integrity of the underlying physics models. Making both these data, and the analyses with which they have been obtained accessible to future users is an essential aspect of open science and data preservation. It ensures the consistency of physics models across a variety of experiments.
Alexander Aryshev, Ties Behnke, Mikael Berggren, James Brau, Nathaniel Craig, Ayres Freitas, Frank Gaede, Spencer Gessner, Stefania Gori, Christophe Grojean, Sven Heinemeyer, Daniel Jeans, Katja Kruger, Benno List, Jenny List, Zhen Liu, Shinichiro Michizono, David W. Miller, Ian Moult, Hitoshi Murayama, et al (492) The International Linear Collider (ILC) is on the table now as a new global energy-frontier accelerator laboratory taking data in the 2030s. The ILC addresses key questions for our current understanding of particle physics. It is based on a proven accelerator technology. Its experiments will challenge the Standard Model of particle physics and will provide a new window to look beyond it. This document brings the story of the ILC up to date, emphasizing its strong physics motivation, its readiness for construction, and the opportunity it presents to the US and the global particle physics community.
Chiara Aimè, Aram Apyan, Mohammed Attia Mahmoud, Nazar Bartosik, Alessandro Bertolin, Maurizio Bonesini, Salvatore Bottaro, Dario Buttazzo, Rodolfo Capdevilla, Massimo Casarsa, Luca Castelli, Maria Gabriella Catanesi, Francesco Giovanni Celiberto, Alessandro Cerri, Cari Cesarotti, Grigorios Chachamis, Siyu Chen, Yang-Ting Chien, Mauro Chiesa, Gianmaria Collazuol, et al (105) The perspective of designing muon colliders with high energy and luminosity, which is being investigated by the International Muon Collider Collaboration, has triggered a growing interest in their physics reach. We present a concise summary of the muon colliders potential to explore new physics, leveraging on the unique possibility of combining high available energy with very precise measurements.
Jorge De Blas, Dario Buttazzo, Rodolfo Capdevilla, David Curtin, Roberto Franceschini, Fabio Maltoni, Patrick Meade, Federico Meloni, Shufang Su, Eleni Vryonidou, Andrea Wulzer, Chiara Aimè, Aram Apyan, Pouya Asadi, Mohammed Attia Mahmoud, Aleksandr Azatov, Nazar Bartosik, Alessandro Bertolin, Salvatore Bottaro, Laura Buonincontri, et al (114) In the path towards a muon collider with center of mass energy of 10 TeV or more, a stage at 3 TeV emerges as an appealing option. Reviewing the physics potential of such muon collider is the main purpose of this document. In order to outline the progression of the physics performances across the stages, a few sensitivity projections for higher energy are also presented. There are many opportunities for probing new physics at a 3 TeV muon collider. Some of them are in common with the extensively documented physics case of the CLIC 3 TeV energy stage, and include measuring the Higgs trilinear coupling and testing the possible composite nature of the Higgs boson and of the top quark at the 20 TeV scale. Other opportunities are unique of a 3 TeV muon collider, and stem from the fact that muons are collided rather than electrons. This is exemplified by studying the potential to explore the microscopic origin of the current $g$-2 and $B$-physics anomalies, which are both related with muons.
Neutrinos are among the most mysterious particles in nature. Their mass hierarchy and oscillations, as well as their antiparticle properties, are being intensively studied in experiments around the world. Moreover, in many models of physics beyond the Standard Model, the baryon asymmetry or the dark matter density in the Universe are explained by introducing new species of neutrinos. Among others, heavy neutrinos of Dirac or Majorana nature were proposed to solve open questions in High Energy Physics. Such neutrinos with masses above the EW scale could be produced at future linear e$^+$e$^-$ colliders, like the Compact LInear Collider (CLIC) or the International Linear Collider (ILC). We studied the possibility of observing decays of heavy Dirac and Majorana neutrinos in the $qq\ell$ final state with ILC running at 500 GeV and 1 TeV, and CLIC at 3 TeV. The analysis is based on the Whizard event generation and fast simulation of detector response with Delphes. Neutrinos with masses from 200 GeV to 3.2 TeV were considered. We estimated the limits on the production cross sections, interpreted them in terms of the neutrino-lepton coupling parameter $V_{\ell N}^{2}$ (effectively the neutrino mixing angle) and compared them with current limits coming from the LHC running at 13 TeV, as well as the expected limits from future hadron colliders. The limits for the future lepton colliders, extending down to the coupling values of $10^{-7} - 10^{-6}$, are stricter than any other limit estimates published so far.
We explore the sensitivity of directly testing the muon-Higgs coupling at a high-energy muon collider. This is strongly motivated if there exists new physics that is not aligned with the Standard Model Yukawa interactions which are responsible for the fermion mass generation. We illustrate a few such examples for physics beyond the Standard Model. With the accidentally small value of the muon Yukawa coupling and its subtle role in the high-energy production of multiple (vector and Higgs) bosons, we show that it is possible to measure the muon-Higgs coupling to an accuracy of ten percent for a 10 TeV muon collider and a few percent for a 30 TeV machine by utilizing the three boson production, potentially sensitive to a new physics scale about $\Lambda \sim 30-100$ TeV.
High precision experimental measurements of the properties of the Higgs boson at $\sim$ 125 GeV as well as electroweak precision observables such as the W -boson mass or the effective weak leptonic mixing angle are expected at future $e^+e^-$ colliders such as the FCC-ee. This high anticipated precision has to be matched with theory predictions for the measured quantities at the same level of accuracy. We briefly summarize the status of these predictions within the Standard Model (SM) and of the tools that are used for their determination. We outline how the theory predictions will have to be improved in order to reach the required accuracy, and also comment on the simulation frameworks for the Higgs and EW precision program.
Diogo Buarque Franzosi, Michele Gallinaro, Richard Ruiz, Thea K. Aarrestad, Flavia Cetorelli, Mauro Chiesa, Antonio Costantini, Ansgar Denner, Stefan Dittmaier, Robert Franken, Pietro Govoni, Tao Han, Ashutosh V. Kotwal, Jinmian Li, Kristin Lohwasser, Kenneth Long, Yang Ma, Luca Mantani, Matteo Marchegiani, Mathieu Pellen, et al (9) Insight into the electroweak (EW) and Higgs sectors can be achieved through measurements of vector boson scattering (VBS) processes. The scattering of EW bosons are rare processes that are precisely predicted in the Standard Model (SM) and are closely related to the Higgs mechanism. Modifications to VBS processes are also predicted in models of physics beyond the SM (BSM), for example through changes to the Higgs boson couplings to gauge bosons and the resonant production of new particles. In this review, experimental results and theoretical developments of VBS at the Large Hadron Collider, its high luminosity upgrade, and future colliders are presented.
Apr 23 2021
hep-ph arXiv:2104.11141v1
This article summarizes the talk given at the LCWS 2021 conference on the status and news of the WHIZARD Monte Carlo event generator. We presented its features relevant for the physics program of future lepton and especially linear colliders as well as recent developments towards including NLO perturbative corrections and a UFO interface to study models beyond the Standard Model. It takes as reference the version 3.0.0$\beta$ released in August 2020 and additionally discusses the developments that will be included in the next major version 3.0.0 to be released in April 2021.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yuanning Gao, Shinya Kanemura, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Poeschl, Juergen Reuter, Frank Simon, Tomohiko Tanabe, James D. Wells, Mikael Berggren, Esteban Fullana, Juan Fuster, Frank Gaede, Stefania Gori, Daniel Jeans, et al (15) To aid contributions to the Snowmass 2021 US Community Study on physics at the International Linear Collider and other proposed $e^+e^-$ colliders, we present a list of study questions that could be the basis of useful Snowmass projects. We accompany this with links to references and resources on $e^+e^-$ physics, and a description of a new software framework that we are preparing for $e^+e^-$ studies at Snowmass.
Michele Gallinaro, Kenneth Long, Jürgen Reuter, Richard Ruiz, Dinos Bachas, Liron Barak, Fady Bishara, Ilaria Brivio, Diogo Buarque Franzosi, Giacomo Cacciapaglia, Farida Fassi, Eirini Kasimi, Henning Kirschenmann, Chara Petridou, Harrison Prosper, Jorge Romão, Ignasi Rosell, Ennio Salvioni, Rui Santos, Magdalena Slawinska, et al (2) The high-energy scattering of massive electroweak bosons, known as vector boson scattering (VBS), is a sensitive probe of new physics. VBS signatures will be thoroughly and systematically investigated at the LHC with the large data samples available and those that will be collected in the near future. Searches for deviations from Standard Model (SM) expectations in VBS facilitate tests of the Electroweak Symmetry Breaking (EWSB) mechanism. Current state-of-the-art tools and theory developments, together with the latest experimental results, and the studies foreseen for the near future are summarized. A review of the existing Beyond the SM (BSM) models that could be tested with such studies as well as data analysis strategies to understand the interplay between models and the effective field theory paradigm for interpreting experimental results are discussed. This document is a summary of the EU COST network "VBScan" workshop on the sensitivity of VBS processes for BSM frameworks that took place December 4-5, 2019 at the LIP facilities in Lisbon, Portugal. In this manuscript we outline the scope of the workshop, summarize the different contributions from theory and experiment, and discuss the relevant findings.
Julien Baglio, Alessandro Ballestrero, Riccardo Bellan, Carsten Bittrich, Simon Brass, Ilaria Brivio, Diogo Buarque Franzosi, Claude Charlot, Roberto Covarelli, Javier Cuevas, Michele Gallinaro, Raquel Gomez-Ambrosio, Pietro Govoni, Michele Grossi, Alexander Karlberg, Aysel Kayis Topaksu, Borut Kersevan, Wolfgang Kilian, Patrick Kirchgaesser, Rafael L. Delgado, et al (31) This document summarises the talks and discussions happened during the VBSCan Mid-Term Scientific Meeting workshop. The VBSCan COST action is dedicated to the coordinated study of vector boson scattering (VBS) from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.
Waleed Abdallah, Shehu AbdusSalam, Azar Ahmadov, Amine Ahriche, Gaël Alguero, Benjamin C. Allanach, Jack Y. Araz, Alexandre Arbey, Chiara Arina, Peter Athron, Emanuele Bagnaschi, Yang Bai, Michael J. Baker, Csaba Balazs, Daniele Barducci, Philip Bechtle, Aoife Bharucha, Andy Buckley, Jonathan Butterworth, Haiying Cai, et al (122) We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data.
This summarizes the talk given at the LCWS 2019 conference in Sendai, Japan, on the progress of the WHIZARD event generator in terms of new physics features and technical improvements relevant for the physics programme of future lepton and especially linear colliders. It takes as a reference the version 2.8.2 released in October 2019, and also takes into account the development until version 2.8.3 to be released in February 2020.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yaunning Gao, Shinya Kanemura, Hyungdo Kim, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Poeschl, Juergen Reuter, Frank Simon, Tomohiko Tanabe, James D. Wells, Jaehoon Yu, Junping Tian, Taikan Suehara, Marcel Vos, Graham Wilson, et al (2) We present an overview of the capabilities that the International Linear Collider (ILC) offers for precision measurements that probe the Standard Model. First, we discuss the improvements that the ILC will make in precision electroweak observables, both from W boson production and radiative return to the Z at 250 GeV in the center of mass and from a dedicated GigaZ stage of running at the Z pole. We then present new results on precision measurements of fermion pair production, including the production of b and t quarks. We update the ILC projections for the determination of Higgs boson couplings through a Standard Model Effective Field Theory fit taking into account the new information on precision electroweak constraints. Finally, we review the capabilities of the ILC to measure the Higgs boson self-coupling.
Gauthier Durieux, Ilaria Brivio, Fabio Maltoni, Michael Trott, Simone Alioli, Andy Buckley, Mauro Chiesa, Jorge de Blas, Athanasios Dedes, Céline Degrande, Ansgar Denner, Christoph Englert, James Ferrando, Benjamin Fuks, Peter Galler, Admir Greljo, Valentin Hirschi, Gino Isidori, Wolfgang Kilian, Frank Krauss, et al (21) We propose a procedure to cross-validate Monte Carlo implementations of the standard model effective field theory. It is based on the numerical comparison of squared amplitudes computed at specific phase-space and parameter points in pairs of implementations. Interactions are fully linearised in the effective field theory expansion. The squares of linear effective field theory amplitudes and their interference with standard-model contributions are compared separately. Such pairwise comparisons are primarily performed at tree level and a possible extension to the one-loop level is also briefly considered. We list the current standard model effective field theory implementations and the comparisons performed to date.
Riccardo Bellan, Jakob Beyer, Carsten Bittrich, Giacomo Boldrini, Ilaria Brivio, Lucrezia Stella Bruni, Diogo Buarque Franzosi, Claude Charlot, Vitaliano Ciulli, Roberto Covarelli, Duje Giljanovic, Giulia Gonella, Pietro Govoni, Philippe Gras, Michele Grossi, Tim Herrmann, Jan Kalinowski, Alexander Karlberg, Kimmo Kallonen, Eirini Kasimi, et al (44) This document reports the first year of activity of the VBSCan COST Action network, as summarised by the talks and discussions happened during the VBSCan Thessaloniki 2018 workshop. The VBSCan COST action is aiming at a consistent and coordinated study of vector-boson scattering from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.
A. Freitas, S. Heinemeyer, M. Beneke, A. Blondel, S. Dittmaier, J. Gluza, A. Hoang, S. Jadach, P. Janot, J. Reuter, T. Riemann, C. Schwinn, M. Skrzypek, S. Weinzierl Due to the high anticipated experimental precision at the Future Circular Collider FCC-ee (or other proposed $e^+e^-$ colliders, such as ILC, CLIC, or CEPC) for electroweak and Higgs-boson precision measurements, theoretical uncertainties may have, if unattended, an important impact on the interpretation of these measurements within the Standard Model (SM), and thus on constraints on new physics. Current theory uncertainties, which would dominate the total uncertainty, need to be strongly reduced through future advances in the calculation of multi-loop radiative corrections together with improved experimental and theoretical control of the precision of SM input parameters. This document aims to provide an estimate of the required improvement in calculational accuracy in view of the anticipated high precision at the FCC-ee. For the most relevant electroweak and Higgs-boson precision observables we evaluate the corresponding quantitative impact.
A. Blondel, J. Gluza, S. Jadach, P. Janot, T. Riemann, S. Abreu, J.J. Aguilera-Verdugo, A.B. Arbuzov, J. Baglio, S.D. Bakshi, S. Banerjee, M. Beneke, C. Bobeth, C. Bogner, S. Bondarenko, S. Borowka, S. Braß, C.M. Carloni Calame, J. Chakrabortty, M. Chiesa, et al (66) The Future Circular Collider (FCC) at CERN, a proposed 100-km circular facility with several colliders in succession, culminates with a 100 TeV proton-proton collider. It offers a vast new domain of exploration in particle physics, with orders of magnitude advances in terms of Precision, Sensitivity and Energy. The implementation plan foresees, as a first step, an Electroweak Factory electron-positron collider. This high luminosity facility, operating between 90 and 365 GeV centre-of-mass energy, will study the heavy particles of the Standard Model, Z, W, Higgs, and top with unprecedented accuracy. The Electroweak Factory $e^+e^-$ collider constitutes a real challenge to the theory and to precision calculations, triggering the need for the development of new mathematical methods and software tools. A first workshop in 2018 had focused on the first FCC-ee stage, the Tera-Z, and confronted the theoretical status of precision Standard Model calculations on the Z-boson resonance to the experimental demands. The second workshop in January 2019, which is reported here, extended the scope to the next stages, with the production of W-bosons (FCC-ee-W), the Higgs boson (FCC-ee-H) and top quarks (FCC-ee-tt). In particular, the theoretical precision in the determination of the crucial input parameters, alpha_QED, alpha_QCD, M_W, m_t at the level of FCC-ee requirements is thoroughly discussed. The requirements on Standard Model theory calculations were spelled out, so as to meet the demanding accuracy of the FCC-ee experimental potential. The discussion of innovative methods and tools for multi-loop calculations was deepened. Furthermore, phenomenological analyses beyond the Standard Model were discussed, in particular the effective theory approaches. The reports of 2018 and 2019 serve as white papers of the workshop results and subsequent developments.
P. Azzi, S. Farry, P. Nason, A. Tricoli, D. Zeppenfeld, R. Abdul Khalek, J. Alimena, N. Andari, L. Aperio Bella, A.J. Armbruster, J. Baglio, S. Bailey, E. Bakos, A. Bakshi, C. Baldenegro, F. Balli, A. Barker, W. Barter, J. de Blas, F. Blekman, et al (206) Feb 13 2019
hep-ph arXiv:1902.04070v3
The successful operation of the Large Hadron Collider (LHC) and the excellent performance of the ATLAS, CMS, LHCb and ALICE detectors in Run-1 and Run-2 with $pp$ collisions at center-of-mass energies of 7, 8 and 13 TeV as well as the giant leap in precision calculations and modeling of fundamental interactions at hadron colliders have allowed an extraordinary breadth of physics studies including precision measurements of a variety physics processes. The LHC results have so far confirmed the validity of the Standard Model of particle physics up to unprecedented energy scales and with great precision in the sectors of strong and electroweak interactions as well as flavour physics, for instance in top quark physics. The upgrade of the LHC to a High Luminosity phase (HL-LHC) at 14 TeV center-of-mass energy with 3 ab$^{-1}$ of integrated luminosity will probe the Standard Model with even greater precision and will extend the sensitivity to possible anomalies in the Standard Model, thanks to a ten-fold larger data set, upgraded detectors and expected improvements in the theoretical understanding. This document summarises the physics reach of the HL-LHC in the realm of strong and electroweak interactions and top quark physics, and provides a glimpse of the potential of a possible further upgrade of the LHC to a 27 TeV $pp$ collider, the High-Energy LHC (HE-LHC), assumed to accumulate an integrated luminosity of 15 ab$^{-1}$.
Andy Buckley, Frank Krauss, Simon Plätzer, Michael Seymour, Simone Alioli, Jeppe Andersen, Johannes Bellm, Jon Butterworth, Mrinal Dasgupta, Claude Duhr, Stefano Frixione, Stefan Gieseke, Keith Hamilton, Gavin Hesketh, Stefan Hoeche, Hannes Jung, Wolfgang Kilian, Leif Lönnblad, Fabio Maltoni, Michelangelo Mangano, et al (23) Feb 06 2019
hep-ph arXiv:1902.01674v1
Monte Carlo event generators (MCEGs) are the indispensable workhorses of particle physics, bridging the gap between theoretical ideas and first-principles calculations on the one hand, and the complex detector signatures and data of the experimental community on the other hand. All collider physics experiments are dependent on simulated events by MCEG codes such as Herwig, Pythia, Sherpa, POWHEG, and MG5_aMC@NLO to design and tune their detectors and analysis strategies. The development of MCEGs is overwhelmingly driven by a vibrant community of academics at European Universities, who also train the next generations of particle phenomenologists. The new challenges posed by possible future collider-based experiments and the fact that the first analyses at Run II of the LHC are now frequently limited by theory uncertainties urge the community to invest into further theoretical and technical improvements of these essential tools. In this short contribution to the European Strategy Update, we briefly review the state of the art, and the further developments that will be needed to meet the challenges of the next generation.
J. de Blas, R. Franceschini, F. Riva, P. Roloff, U. Schnoor, M. Spannowsky, J. D. Wells, A. Wulzer, J. Zupan, S. Alipour-Fard, W. Altmannshofer, A. Azatov, D. Azevedo, J. Baglio, M. Bauer, F. Bishara, J.-J. Blaising, S. Brass, D. Buttazzo, Z. Chacko, et al (83) The Compact Linear Collider (CLIC) is a mature option for the future of high energy physics. It combines the benefits of the clean environment of $e^+e^-$ colliders with operation at high centre-of-mass energies, allowing to probe scales beyond the reach of the Large Hadron Collider (LHC) for many scenarios of new physics. This places the CLIC project at a privileged spot in between the precision and energy frontiers, with capabilities that will significantly extend knowledge on both fronts at the end of the LHC era. In this report we review and revisit the potential of CLIC to search, directly and indirectly, for physics beyond the Standard Model.
We describe a new parallel approach to the evaluation of phase space for Monte-Carlo event generation, implemented within the framework of the WHIZARD package. The program realizes a twofold self-adaptive multi-channel parameterization of phase space and makes use of the standard OpenMP and MPI protocols for parallelization. The modern MPI3 feature of asynchronous communication is an essential ingredient of the computing model. Parallel numerical evaluation applies both to phase-space integration and to event generation, thus covering the most computing-intensive parts of physics simulation for a realistic collider environment.
The International Linear Collider is now proposed with a staged machine design, with the first stage at $\sqrt{s}=250$ GeV and an integrated luminosity goal of 2 ab${}^{-1}$. One of the questions for the machine design is the importance of positron polarization. In this report, we review the impact of positron polarization on the physics goals of the 250 GeV stage of the ILC and demonstrate that positron polarization has distinct advantages.
Nov 12 2018
hep-ph arXiv:1811.03950v1
The threshold scan at future lepton colliders is the most precise known method to determine the top quark mass (well below 100 MeV), a fundamental parameter of the Standard Model that co-determines the stability properties of the electroweak vacuum. We present a new method to match the continuum next-to-leading order QCD corrections with the next-to-leading logarithmic resummation of the Coulomb singularities of the quasi-toponium bound state at threshold where fixed-order perturbation theory is invalid. This matching is performed at the level of the fully exclusive $W^+bW^-\bar{b}$ final state. It allows to study all kinds of differential distributions at or close to threshold. The top mass dependence of these distributions opens up new possibilities for the top mass determination that might be competitive with the inclusive threshold scan.
Nov 07 2018
hep-ph arXiv:1811.02268v1
Little Higgs models - which can most easily be thought of as a variant of composite Higgs models - explain a light Higgs boson at 125 GeV as an pseudo-Nambu-Goldstone boson of a spontaneously broken global symmetry. The mechanism of collective symmetry breaking shifts the UV scale of these models to the 10 TeV scale and higher. T-parity is introduced as a discrete symmetry to remove tree-level constraints on the electroweak precision data. Still after run 1 of LHC, electroweak precision observables gave stronger constraints than Higgs data and direct searches. We present a full recast of all available 13 TeV searches from LHC run 2 to show that now direct searches supersede electroweak precision observables. The latest exclusion limits on the LHT model will be presented, as well as an outlook on the full high-luminosity phase of LHC.
We report on the precision determination of the top-quark mass to next-to-next-to-leading order in QCD in well-defined renormalization schemes using data from the Large Hadron Collider for single-top and top-quark pair production. We also discuss the calibration of the so-called Monte Carlo top-quark mass parameter which is determined from a comparison to events with top-quark decay products. The implications of the measured value of the top-quark mass for conclusions about the stability of the electroweak vacuum state of our Universe are illustrated. At future lepton colliders, we provide for the first time matched exclusive calculations valid both at the top threshold and in the continuum, also fully differentially. In addition, we calculate fully off-shell top-pair production (also with an associated Higgs boson) at next-to-leading order in QCD, which allows to extract the top-Yukawa coupling with an unprecedented precision.
A high-energy $e^+e^-$ Linear Collider has been considered since a long time as an important complement to the LHC. Unprecedented precision measurements as well as the exploration of so far untouched phase space for direct production of new particles will provide unique information to advance the limits of our understanding of our universe. Within this project, the physics prospects of such a collider as well as their interplay with design of the accelerator and the detectors have been investigated in a quantitative way. This kind of study required a close collaboration between theory and experiment, always taking into account results of the LHC and other relevant experiments. In this article we will summarize some of the most important developments and results, covering all core areas of the physics progamme of future $e^+e^-$ colliders.
Processes where $W$ and $Z$ bosons scatter into pairs of electroweak bosons $W$, $Z$, and Higgs, are sensitive probes of new physics in the electroweak sector. We study simplified models that describe typical scenarios of new physics and parameterize the range of possible LHC results between the Standard-Model prediction and unitarity limits. Extending the study beyond purely longitudinal scattering, we investigate the role of transversally polarized gauge bosons. Unitarity becomes an essential factor, and limits on parameters matched to the naive perturbative low-energy effective theory turn out to be necessarily model-dependent. We discuss the implications of our approach for the interpretation of LHC data on vector-boson scattering and Higgs-pair production.
Alessandro Ballestrero, Benedikt Biedermann, Simon Brass, Ansgar Denner, Stefan Dittmaier, Rikkert Frederix, Pietro Govoni, Michele Grossi, Barbara Jäger, Alexander Karlberg, Ezio Maina, Mathieu Pellen, Giovanni Pelliccioli, Simon Plätzer, Michael Rauch, Daniela Rebuzzi, Jürgen Reuter, Vincent Rothe, Christopher Schwan, Hua-Sheng Shao, et al (4) Mar 22 2018
hep-ph arXiv:1803.07943v3
Vector-boson scattering processes are of great importance for the current run-II and future runs of the Large Hadron Collider. The presence of triple and quartic gauge couplings in the process gives access to the gauge sector of the Standard Model (SM) and possible new-physics contributions there. To test any new-physics hypothesis, sound knowledge of the SM contributions is necessary, with a precision which at least matches the experimental uncertainties of existing and forthcoming measurements. In this article we present a detailed study of the vector-boson scattering process with two positively-charged leptons and missing transverse momentum in the final state. In particular, we first carry out a systematic comparison of the various approximations that are usually performed for this kind of process against the complete calculation, at LO and NLO QCD accuracy. Such a study is performed both in the usual fiducial region used by experimental collaborations and in a more inclusive phase space, where the differences among the various approximations lead to more sizeable effects. Afterwards, we turn to predictions matched to parton showers, at LO and NLO: we show that on the one hand, the inclusion of NLO QCD corrections leads to more stable predictions, but on the other hand the details of the matching and of the parton-shower programs cause differences which are considerably larger than those observed at fixed order, even in the experimental fiducial region. We conclude with recommendations for experimental studies of vector-boson scattering processes.
We describe recent additions to the WHIZARD 2 Monte-Carlo event generator which improve the physics description of lepton-collider event samples and speed up the calculation time required for cross sections and event generation.
Jan 25 2018
hep-ph arXiv:1801.08083v1
We review exclusive top pair production including decays at a future high-energy lepton collider, both in the threshold region and for higher energies. For the continuum process, we take complete QCD next-to-leading order matrix elements for the $2\to 6$ process with leptonic W decays into account. At threshold, we match the fixed-order relativistic QCD-NLO cross section to a nonrelativistic cross section with next-to-leading logarithmic (NLL) threshold resummation implemented via a form factor.
We exploit all LHC available Run 2 data at center-of-mass energies of 8 and 13 TeV for searches for physics beyond the Standard Model. We scrutinize the allowed parameter space of Little Higgs models with the concrete symmetry of T-parity by providing comprehensive analyses of all relevant production channels of heavy vectors, top partners, heavy quarks and heavy leptons and all phenomenologically relevant decay channels. Constraints on the model will be derived from the signatures of jets and missing energy or leptons and missing energy. Besides the symmetric case, we also study the case of T-parity violation. Furthermore, we give an extrapolation to the LHC high-luminosity phase at 14 TeV as well.
C.F. Anders, A. Ballestrero, J. Balz, R. Bellan, B. Biedermann, C. Bittrich, S. Braß, I. Brivio, L.S. Bruni, J. Butterworth, M. Cacciari, A. Cardini, C. Charlot, V. Ciulli, R. Covarelli, J. Cuevas, A. Denner, L. Di Ciaccio, S. Dittmaier, S. Duric, et al (94) This document summarises the talks and discussions happened during the VBSCan Split17 workshop, the first general meeting of the VBSCan COST Action network. This collaboration is aiming at a consistent and coordinated study of vector-boson scattering from the phenomenological and experimental point of view, for the best exploitation of the data that will be delivered by existing and future particle colliders.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yuanning Gao, Shinya Kanemura, Hyungdo Kim, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Pöschl, Jürgen Reuter, Frank Simon, Tomohiko Tanabe, James D. Wells, Jaehoon Yu, Mikael Berggren, Moritz Habermehl, Robert Karl, Gudrid Moortgat-Pick, et al (5) The International Linear Collider is now proposed with a staged machine design, with the first stage at $\sqrt{s}=$~250 GeV and an integrated luminosity goal of 2~ab$^{-1}$. One of the questions for the machine design is the importance of positron polarization. In this report, we review the impact of positron polarization on the physics goals of the $250$ GeV stage of the ILC and demonstrate that positron polarization has distinct advantages.
We present an approach to predict exclusive $W^+bW^-\bar{b}$ production at lepton colliders that correctly describes the top-anti-top threshold as well as the continuum region. We incorporate $t\bar{t}$ form factors for the NLL threshold resummation derived in NRQCD into a factorized relativistic cross section using an extended double-pole approximation, which accounts for fixed-order QCD corrections to the top decays at NLO. This is combined with the full fixed-order QCD result at NLO for $W^+bW^-\bar{b}$ production to obtain predictions that are not only valid at threshold but smoothly transition to the continuum region. Our implementation is based on the Monte Carlo event generator WHIZARD and the code TOPPIK and allows to compute fully-differential threshold-resummed cross sections including the interference with non-resonant background processes. For the first time it is now possible to systematically study general differential observables at future lepton colliders involving the decay products of the top quarks at energies close to the pair production threshold and beyond.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yuanning Gao, Shinya Kanemura, Hyungdo Kim, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Poeschl, Juergen Reuter, Frank Simon, Tomohiko Tanabe, James D. Wells, Jaehoon Yu, Mikael Berggren, Moritz Habermehl, Sunghoon Jung, Robert Karl, et al (4) The International Linear Collider is now proposed with a staged machine design, with the first stage at 250 GeV with a luminosity goal of 2 ab-1. In this paper, we review the physics expectations for this machine. These include precision measurements of Higgs boson couplings, searches for exotic Higgs decays, other searches for particles that decay with zero or small visible energy, and measurements of e+e- annihilation to W+W- and 2-fermion states with improved sensitivity. A summary table gives projections for the achievable levels of precision based on the latest full simulation studies.
We discuss top-quark physics at the ILC with a focus on the full off-shell processes for $t\bar{t}$ and $t\bar{t}H$ production, including top-quark decays and also leptonic $W$ decays. A special focus is on the matching of the resummed vNRQCD threshold calculation and the fixed-order NLO QCD continuum calculation, where we present an update on the validation of the matching. All of the calculations have been performed in the \wz event generator framework.
P. Azzi, P. Azzurri, S. Biswas, F. Blekman, G. Corcella, S. De Curtis, J. Erler, N. Foppiani, I. Helenius, S. Jadach, P. Janot, F. Jegerlehner, P. Langacker, E. Locci, F. Margaroli, B. Mele, F. Piccinini, J. Reuter, M. Steinhauser, R. Tenchini, et al (2) This document provides a writeup of contributions to the FCC-ee mini-workshop on "Physics behind precision" held at CERN, on 2-3 February 2016.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yuanning Gao, Shinya Kanemura, Hyungdo Kim, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Pöschl, Jürgen Reuter, Frank Simon, Tomohiko Tanabe, James D. Wells, Jaehoon Yu, Howard Baer, Mikael Berggren, Sven Heinemeyer, Suvi-Leena Lehtinen, et al (5) This paper addresses the question of whether the International Linear Collider has the capability of discovering new particles that have not already been discovered at the CERN Large Hadron Collider. We summarize the various paths to discovery offered by the ILC, and discuss them in the context of three different scenarios: 1. LHC does not discover any new particles, 2. LHC discovers some new low mass states and 3. LHC discovers new heavy particles. We will show that in each case, ILC plays a critical role in discovery of new phenomena and in pushing forward the frontiers of high-energy physics as well as our understanding of the universe in a manner which is highly complementary to that of LHC. For the busy reader, a two-page executive summary is provided at the beginning of the document.
D. de Florian, C. Grojean, F. Maltoni, C. Mariotti, A. Nikitenko, M. Pieri, P. Savard, M. Schumacher, R. Tanaka, R. Aggleton, M. Ahmad, B. Allanach, C. Anastasiou, W. Astill, S. Badger, M. Badziak, J. Baglio, E. Bagnaschi, A. Ballestrero, A. Banfi, et al (356) This Report summarizes the results of the activities of the LHC Higgs Cross Section Working Group in the period 2014-2016. The main goal of the working group was to present the state-of-the-art of Higgs physics at the LHC, integrating all new results that have appeared in the last few years. The first part compiles the most up-to-date predictions of Higgs boson production cross sections and decay branching ratios, parton distribution functions, and off-shell Higgs boson production and interference effects. The second part discusses the recent progress in Higgs effective field theory predictions, followed by the third part on pseudo-observables, simplified template cross section and fiducial cross section measurements, which give the baseline framework for Higgs boson property measurements. The fourth part deals with the beyond the Standard Model predictions of various benchmark scenarios of Minimal Supersymmetric Standard Model, extended scalar sector, Next-to-Minimal Supersymmetric Standard Model and exotic Higgs boson decays. This report follows three previous working-group reports: Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002), Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002), and Handbook of LHC Higgs Cross Sections: 3. Higgs properties (CERN-2013-004). The current report serves as the baseline reference for Higgs physics in LHC Run 2 and beyond.
Oct 14 2016
hep-ph arXiv:1610.04131v1
Weak vector boson scattering at high energies will be one of the key measurements in current and upcoming LHC runs. It is most sensitive to any new physics associated with electroweak symmetry breaking. However, a conventional EFT analysis will fail at high energies. To address this problem, we present a parameter-free prescription valid for arbitrary perturbative and non-perturbative models: the T-matrix unitarization. We describe its implementation as an asymptotically consistent reference model matched to the low-energy effective theory. We show examples of typical observables of vector-boson scattering at the LHC in our unitarized framework. For many strongly-coupled models like composite Higgs models, dimension-8 operators might be actually the leading operators. In addition to those longitudinal and transversal dimension eight EFT operators, the effects of generic tensor and scalar resonances within simplified models are considered.
We present predictions for $t \bar t$ and $t \bar t H$ production and decay at future lepton colliders including non-resonant and interference contributions up to next-to-leading order (NLO) in perturbative QCD. The obtained precision predictions are necessary for a future precise determination of the top-quark Yukawa coupling, and allow for top-quark phenomenology in the continuum at an unprecedented level of accuracy. Simulations are performed with the automated NLO Monte-Carlo framework WHIZARD interfaced to the OpenLoops matrix element generator.
Keisuke Fujii, Christophe Grojean, Michael E. Peskin, Tim Barklow, Yuanning Gao, Shinya Kanemura, Hyungdo Kim, Jenny List, Mihoko Nojiri, Maxim Perelstein, Roman Poeschl, Juergen Reuter, Frank Simon, Tomohiko Tanabe, Jaehoon Yu, James D. Wells, Adam Falkowski, Shigeki Matsumoto, Takeo Moroi, Francois Richard, et al (5) If the gamma-gamma resonance at 750 GeV suggested by 2015 LHC data turns out to be a real effect, what are the implications for the physics case and upgrade path of the International Linear Collider? Whether or not the resonance is confirmed, this question provides an interesting case study testing the robustness of the ILC physics case. In this note, we address this question with two points: (1) Almost all models proposed for the new 750 GeV particle require additional new particles with electroweak couplings. The key elements of the 500 GeV ILC physics program---precision measurements of the Higgs boson, the top quark, and 4-fermion interactions---will powerfully discriminate among these models. This information will be important in conjunction with new LHC data, or alone, if the new particles accompanying the 750 GeV resonance are beyond the mass reach of the LHC. (2) Over a longer term, the energy upgrade of the ILC to 1 TeV already discussed in the ILC TDR will enable experiments in gamma-gamma and e+e- collisions to directly produce and study the 750 GeV particle from these unique initial states.
We present a new study of quasi-elastic $W$ and $Z$ scattering processes in high-energy $e^+e^-$ collisions, based on and extrapolating the low-energy effective theory which extends the Standard Model with a 125 GeV Higgs boson. Besides parameterizing deviations in terms of the dimension-8 operators that arise in the effective theory, we also study simplified models of new physics in $W/Z$ scattering in terms of scalar and tensor resonance multiplets. The high-energy asymptotics of all models is regulated by a universal unitarization procedure. This enables us to provide benchmark scenarios which can be meaningfully evaluated off-shell and in exclusive event samples, and to determine the sensitivity of an $e^+e^-$ collider to the model parameters. We analyze the longitudinal vector boson scattering modes, where we optimize the cuts for the fiducial cross section for different collider scenarios. Here, we choose energy stages of 1.0, 1.4 and 3 TeV, as motivated by the extendability of the ILC project and the staging scenario of the CLIC project.
Jun 01 2016
hep-ph arXiv:1605.09594v1
Vector boson scattering is (together with the production of multiple electroweak gauge bosons) the key process in the current run 2 of LHC to probe the microscopic nature of electroweak symmetry breaking. Deviations from the Standard Model are generically parameterized by higher-dimensional operators, however, there is a subtle issue of perturbative unitarity for such approaches for the process above. We discuss a parameter-free unitarization prescription to get physically meaningful predictions. In the second part, we construct simplified models for generic new resonances that can appear in vector boson scattering, with a special focus on the technicalities of tensor resonances.
M. Vos, G. Abbas, M. Beneke, S. Bilokin, M. Costa, S. De Curtis, K. Fujii, J. Fuster, I. Garcia Garcia, P. Gomis, A. Hoang, A. Irles, Y. Kiyo, M. Kurata, L. Linssen, J. List, M. Nebot, M. Perello Rosello, R. Poeschl, N. Quach, et al (8) A summary is presented of the workshop "top physics at linear colliders" that was held at IFIC Valencia from the 30th of June to the 3rd July 2015. We present an up-to-date status report of studies into the potential for top quark physics of lepton colliders with an energy reach that exceeds the top quark pair production threshold, with a focus on the linear collider projects ILC and CLIC. This summary shows that such projects can offer very competitive determinations of top quark properties (mass, width) and its interactions with other Standard Model particles, in particular electroweak gauge bosons and the Higgs boson. In both areas the prospects exceed the LHC potential significantly - often by an order of magnitude.
In this talk I summarize the physics case of the International Linear Collider (ILC) focusing on its potential towards discovery, discrimation or disentanglement of new physics beyond the Standard Model (BSM).
In this talk we summarize the top physics setup in the event generator WHIZARD with a main focus on lepton colliders. This includes full six-, eight- and ten-fermion processes, factorized processes and spin correlations. For lepton colliders, QCD NLO processes for top quark physics are available and will be discussed. A special focus is on the top-quark pair threshold, where a special implementation combines a non-relativistic effective field theory calculation augmented by a next-to-leading threshold logarithm resummation with a continuum relativistic fixed-order QCD NLO simulation.
State-of-the-art algorithms generate scattering amplitudes for high-energy physics at leading order for high-multiplicity processes as compiled code (in Fortran, C or C++). For complicated processes the size of these libraries can become tremendous (many GiB). We show that amplitudes can be translated to byte-code instructions, which even reduce the size by one order of magnitude. The byte-code is interpreted by a Virtual Machine with runtimes comparable to compiled code and a better scaling with additional legs. We study the properties of this algorithm, as an extension of the Optimizing Matrix Element Generator (O'Mega). The bytecode matrix elements are available as alternative input for the event generator WHIZARD. The bytecode interpreter can be implemented very compactly, which will help with a future implementation on massively parallel GPUs.
Feb 22 2016
hep-ph arXiv:1602.06270v2
We give a status report on the automation of next-to-leading order processes within the Monte Carlo event generator WHIZARD, using GoSam and OpenLoops as provider for one-loop matrix elements. To deal with divergences, WHIZARD uses automated FKS subtraction, and the phase space for singular regions is generated automatically. NLO examples for both scattering and decay processes with a focus on e+e- processes are shown. Also, first NLO-studies of observables for collisions of polarized leptons beams, e.g. at the ILC, will be presented. Furthermore, the automatic matching of the fixed-order NLO amplitudes with emissions from the parton shower within the POWHEG formalism inside WHIZARD will be discussed. We also present results for top pairs at threshold in lepton collisions, including matching between a resummed threshold calculation and fixed-order NLO. This allows the investigation of more exclusive differential observables.
Jan 12 2016
hep-ph arXiv:1601.02459v2
We present the status of the automation of NLO processes within the event generator WHIZARD. The program provides an automated FKS subtraction and phase space integration over the FKS regions, while the (QCD) NLO matrix element is accessed via the Binoth Les Houches Interface from an externally linked one-loop program. Massless and massive test cases and validation are shown for several e+e- processes. Furthermore, we discuss work in progress and future plans. The second part covers the matching of the NRQCD prediction with NLL threshold resummation to the NLO continuum top pair production at lepton colliders. Both the S-wave and P-wave production of the top pair are taken into account in the resummation. The inclusion in WHIZARD allows to study more exclusive observables than just the total cross section and automatically accounts for important electroweak and relativistic corrections in the threshold region.
Motivated by the recent diphoton excesses reported by both ATLAS and CMS collaborations, we suggest that a new heavy spinless particle is produced in gluon fusion at the LHC and decays to a couple of lighter pseudoscalars which then decay to photons. The new resonances could arise from a new strongly interacting sector and couple to Standard Model gauge bosons only via the corresponding Wess-Zumino-Witten anomaly. We present a detailed recast of the newest 13 TeV data from ATLAS and CMS together with the 8 TeV data to scan the consistency of the parameter space for those resonances.
Braneshop, and
the US National Science Foundation.
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