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Scientific Report 2007-2009<br />
Particle physics<br />
P29. Search of Dark Matter and Antimatter with AMS<br />
The Alpha Magnetic Spectrometer (AMS) is a highenergy<br />
particle physics experiment in space to be placed<br />
on the International Space Station (ISS). The main<br />
physics goals are the anti-matter and the dark matter<br />
searches [1]. Until now, a consistent theory of baryogenesis<br />
has not been yet proposed, as presently experimental<br />
data do not support these models. The last 20<br />
years cosmic ray searches for antinuclei have given negative<br />
results. Detection of a few anti-He nuclei will be a<br />
clear evidence of existence of antimatter domains, since<br />
their formation in conventional processes is largely suppressed.<br />
Present limits on He ¯ search are at the level of<br />
10 −6 therefore to increase the sensitivity for antimatter<br />
up to very far distances, greater than 20 Mpc, AMS has<br />
to reach a rejection factor for He of 10 −9 . High value<br />
of magnetic field B and large magnetic volume are first<br />
requirements for this goal, since momentum resolution is<br />
proportional to BL 2 . Simulation by Monte Carlo method<br />
shows that no false candidates will be found in 10 9 He<br />
events, therefore we expect to reach the limit shown in<br />
figure 1.<br />
Antihelium/Helium Flux Ratio Limit (95% C.L.)<br />
10 -2<br />
10 -3<br />
10 -4<br />
10 -5<br />
10 -6<br />
10 -7<br />
10 -8<br />
10 -9<br />
(a)<br />
(b)<br />
(e)<br />
(c)<br />
(d)<br />
AMS-02 3 Years<br />
(c)<br />
1 10 10 2<br />
Rigidity (GV)<br />
(a) Buffington et al. 1981<br />
(b) Dolden at al. 1997<br />
(c) Badhwar et al. 1978<br />
(d) Alcaraz et al. 1998<br />
(e) Sasaki et al. 2001<br />
Figure 1: Projected AMS limits on He/He ¯ flux ratio compared<br />
to previous measurements (including AMS-01).<br />
Several observations indicate that the Universe should<br />
include a large amount of unknown dark matter (DM). It<br />
should be composed of non-baryonic Weakly Interacting<br />
Massive Particles (WIMP). The Lightest Supersymmetric<br />
Particle in R-parity conserving SUSY models may be<br />
a WIMP candidate. SUSY dark matter can be searched<br />
in decay channels from neutralino annihilation. A simultaneous<br />
measurement of all channels will add confidence<br />
to the result. In the energy range 1 to 100 GeV of Cosmic<br />
Rays spectrum, ratio of proton/positron is of the order<br />
of 10 3 to 10 4 , proton/antiproton ratio varies between<br />
10 5 and 10 3 and electron/antiproton from 10 3 to 10 2 .<br />
A detector aiming to search neutralino signal through<br />
annihilation products therefore needs an excellent proton<br />
and electron identification along with good charge<br />
sign determination, of the order of 10 5 . Since AMS will<br />
take data for at least three years, it will record cosmic<br />
ray spectra with very high statistics and high precision,<br />
allowing possible discovery of new phenomena or new<br />
10 3<br />
particles.<br />
Figure 2: AMS detector in a cut-through view. USS is<br />
the support structure. See text for sub-detectors acronyms.<br />
Overall dimensions are 3m x 3m x 3m<br />
The AMS main components are:<br />
• Transition Radiation Detector (TRD) with capability<br />
to reject protons with a factor greater than 10 2<br />
up to 250 GeV/c;<br />
• the central spectrometer, magnet and silicon<br />
tracker;<br />
• Time of Flight scintillation counters (TOF);<br />
• Ring Imaging Cerenkov Counter (RICH) measuring<br />
independently speed and charge;<br />
• Electromagnetic calorimeter (ECAL) with 3D sampling.<br />
It will reject protons with a factor greater<br />
than 10 3 ;<br />
• Anticoincidence counters (ACC).<br />
Figure 2 shows a cut-through view of the detector.<br />
The Rome group, with INFN participation, has<br />
contributed mainly to the TRD construction and to<br />
the overall apparatus integration. The group will<br />
initiate data analysis on particle identification by TRD<br />
selection.<br />
References<br />
1. The AMS-02 Collaboration, Nucl. Instrum. Meth. A588,<br />
227-234 (2008)<br />
Authors<br />
A. Bartoloni 1 , B. Borgia, C. Gargiulo 1 , P. Lipari 1 , F.R.<br />
Spada 1 , E. Valente 1<br />
http://www.roma1.infn.it/exp/ams/<br />
<strong>Sapienza</strong> Università di Roma 136 Dipartimento di Fisica