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