PAMELA detector
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| Organization | PAMELA group |
|---|---|
| Mission Type | Cosmic Ray |
| Host Satellite | Resurs DK1 |
| Launch | June 15, 2006 |
| Launch vehicle | Soyuz-FG |
| Launch site | Baikonur Cosmodrome |
| Mission duration | 3 years |
| Mission elapsed time | 18 years and 5 months |
| Mass | 470 kg |
| Max length | 1300 mm |
| Power consumption | 335 Watts |
| Webpage | PAMELA homepage |
| Orbital elements (Resurs DK1) | |
| Inclination | 70 degrees |
| Orbit | quasi-polar elliptical |
| Min altitude | 360 km |
| Max altitude | 604 km |
| Period | 94.02 min |
PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics), is an operational cosmic ray research module attached to an Earth orbiting satellite. PAMELA was launched on 15 June 2006, is the first satellite-based experiment dedicated to the detection of cosmic rays, with a particular focus on their antimatter component, in the form of positrons and antiprotons. Other objectives include long-term monitoring of the solar modulation of cosmic rays, measurements of energetic particles from the Sun, high-energy particles in Earth's magnetosphere, and Jovian electrons. It is also hoped that it may detect evidence of dark matter annihilation.[1]
Development and launch
PAMELA is the largest device yet built by the Wizard collaboration, which includes Russia, Italy, Germany and Sweden and has been involved in many satellite and balloon-based cosmic ray experiments such as Fermi-GLAST. The 470 kg, US$32 million (EU€24.8 million, UK£16.8 million) instrument will make observations for at least three years.
PAMELA is mounted on the upward-facing side of the Resurs-DK1 Russian satellite.[1] It was launched by a Soyuz rocket from Baikonur Cosmodrome on 15 June 2006, PAMELA has been put in a polar elliptical orbit at an altitude between 350 and 610 km, with an inclination of 70°.
Design
The apparatus is 1.3 m high, has a total mass of 470 kg and a power consumption of 335 W. The instrument is built around a permanent magnet spectrometer with a silicon microstrip tracker which provides rigidity and dE/dx information. At its bottom is a silicon-tungsten imaging calorimeter, a neutron detector and a shower tail scintillator to perform lepton/hadron discrimination. A Time of Flight (ToF), made of three layers of plastic scintillators is used to measure the beta and charge of the particle. An anticounter system made of scintillators surrounding the apparatus is used to reject false triggers and albedo particles during off-line analysis.[2]
| Particle | Energy Range |
|---|---|
| Antiproton flux | 80 MeV - 190 GeV |
| Positron flux | 50 MeV - 270 GeV |
| Electron flux | up to 400 GeV |
| Proton flux | up to 700 GeV |
| Electron/positron flux | up to 2 TeV |
| Light nuclei (up to Z=6) | up to 200 GeV/n |
| Light isotopes (D, 3He) | up to 1 GeV/n |
| Antinuclei search | sensitivity better than 10−7 antiHe/He |
Results
Preliminary data (released Aug 2008, ICHEP Philadelphia) shows an excess of positrons in the range 10-60 GeV. This is thought to be a sign of dark matter annihilation:[3][4] hypothetical WIMPs colliding with and annihilating each other to form gamma rays, matter and antimatter particles.
The first two years of data were released in October 2008 in three publications.[5] The positron excess was confirmed and found to persist up to 90 GeV. Surprisingly, no excess of antiprotons was found. This is inconsistent with predictions from most models of dark matter sources, in which the positron and antiproton excesses are correlated.
Sources of error
Between 1 and 100 GeV PAMELA is exposed to one hundred times as many electrons as antiprotons. At 1 GeV there are one thousand times as many protons as positrons and at 100 GeV ten thousand times as many. Therefore, to correctly determine the antimatter abundances, it is critical that PAMELA is able to reject the matter background. The PAMELA collaboration claimed in The electron hadron separation performance of the PAMELA electromagnetic calorimeter that less than one proton in 100,000 is able to pass the calorimeter selection and be misidentified as a positron when the energy is less than 200 GeV.
The ratio of matter to antimatter cosmic rays of energy less than 10 GeV that reach PAMELA from outside the solar system depends on solar activity and in particular on the time in the 22 year solar cycle. The PAMELA team has invoked this effect to explain the discrepancy of their low energy results with results obtained by CAPRICE, HEAT and AMS-01 which were obtained during the half of the cycle when the solar magnetic field had the opposite polarity. In particular the PAMELA experiment has contradicted an earlier claim by the HEAT experiment of anomalous positrons in the 6 GeV to 10 GeV range.
See also
- AMS-02 is a research module with similar goals scheduled to be attached to the International Space Station in 2011.
- List of space telescopes
References
- ^ a b c Vincenzo Buttaro (ed.). "The Space Mission PAMELA". Retrieved 2009-09-04.
- ^ P.Picozza et al., "Launch of the space experiment PAMELA", http://arxiv.org/abs/0708.1808
- ^ Physicists await dark-matter confirmation, Nature, 13 August 2008
- ^ The PAMELA Positron Excess from Annihilations into a Light Boson, Arxiv.org, 30 October 2008
- ^ Two years of flight of the Pamela experiment: results and perspectivesA new measurement of the antiproton-to-proton flux ratio up to 100 GeV in the cosmic radiationObservation of an anomalous positron abundance in the cosmic radiation, arXiv.org, 28 October 2008