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Searching for signatures of dark matter in the cosmic ray spectrum measured by AMS-01
Available online at www.sciencedirect.com
Nuclear Physics B (Proc. Suppl.) 221 (2011) 335 www.elsevier.com/locate/npbps
Searching for signatures of dark matter in the cosmic ray spectrum measured by AMS-01 G. Carosi1∗ , S. Xiao1 , P. Fisher1 , G. Rybka1 and F. Zhou1 1 ∗
Massachusetts Institute of Technology: 77 Massachusetts Ave, Cambridge, MA, USA 02139 Now at: LLNL, L-270, 7000 East Ave, Livermore, CA, USA 94550
E-mail: [email protected] Abstract. A search for signatures of WIMP dark matter annihilating to charged cosmic rays via W+ W− production was performed using data from the AMS-01 magnetic spectrometer, which flew for 10 days on the space shuttle Discovery in 1998. A brief description of the detector along with the analysis method and results is given.
If dark matter consists of majorana Weakly Interacting Massive Particles (WIMPs) one can look for them annihilating with each other to charged cosmic rays in the galactic halo. Direct annihilation to an e± or p± pair is highly helicity suppressed so we focused our search on annihilation through W+ W− bosons (requiring MW IM P > 80 GeV). The W+ W− then decay to stable charged particles (e± and p± ) with characteristic spectra correlated to M W IM P . Even after propagation through the galaxy these decay products could show up as anomalous features in the flat power-law spectrum from astrophysical sources [1]. The AMS-01 experiment consisted of a permanent magnet with a uniform 0.14 Tesla field in a 1 m3 volume, a scintillator time of flight system, a 6 layer silicon tracker, an aerogel cerenkov detector and an anti-coincidence counter. Its maximum detectable rigidity was ≈ 360 GV. For detector and mission details see [2]. Though annihilation signals would be clearer in the lower background e + spectra AMS-01 couldn’t distinguish e+ from the large p+ background at energies > 3 GeV. Instead we utilized the Z = -1 spectrum. PYTHIA was used to generate Z = -1 decay spectra for W + W− bosons decaying at various center of mass energies. These spectra were then convolved with Green’s functions of particles transported to earth using the GALPROP galactic propagation software The final e+ and p¯ spectra for each WIMP mass was then convolved with an AMS acceptance matrix (from Monte-Carlo) and added. These expected signals from WIMPs of various masses were then compared with data with and without an additional astrophysical power-law background. The results showed that the dark-matter alone could not describe the data, that the power-law alone was a good fit and that the addition of WIMP annihilation did not improve the fit. As a result we could place limits on the rate of W + W− production in the galaxy and, subsequently on the cross-section of WIMP annihilation through this channel. For further details see [3]. [1] G. Jungman, M. Kamionkowski and K. Griest, Physics Reports, 267:195–373, 1996 [2] M. Aguilar et al. (AMS Collaboration). Physics Reports, 366(6):331-405, 2002 [3] G. Carosi. Ph.D dissertation. MIT, Dept. of Physics, 2006: http://web.mit.edu/gcarosi/www/gp thesis.pdf 0920-5632/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2011.09.034
Nuclear Physics B (Proc. Suppl.) 221 (2011) 335 www.elsevier.com/locate/npbps
Searching for signatures of dark matter in the cosmic ray spectrum measured by AMS-01 G. Carosi1∗ , S. Xiao1 , P. Fisher1 , G. Rybka1 and F. Zhou1 1 ∗
Massachusetts Institute of Technology: 77 Massachusetts Ave, Cambridge, MA, USA 02139 Now at: LLNL, L-270, 7000 East Ave, Livermore, CA, USA 94550
E-mail: [email protected] Abstract. A search for signatures of WIMP dark matter annihilating to charged cosmic rays via W+ W− production was performed using data from the AMS-01 magnetic spectrometer, which flew for 10 days on the space shuttle Discovery in 1998. A brief description of the detector along with the analysis method and results is given.
If dark matter consists of majorana Weakly Interacting Massive Particles (WIMPs) one can look for them annihilating with each other to charged cosmic rays in the galactic halo. Direct annihilation to an e± or p± pair is highly helicity suppressed so we focused our search on annihilation through W+ W− bosons (requiring MW IM P > 80 GeV). The W+ W− then decay to stable charged particles (e± and p± ) with characteristic spectra correlated to M W IM P . Even after propagation through the galaxy these decay products could show up as anomalous features in the flat power-law spectrum from astrophysical sources [1]. The AMS-01 experiment consisted of a permanent magnet with a uniform 0.14 Tesla field in a 1 m3 volume, a scintillator time of flight system, a 6 layer silicon tracker, an aerogel cerenkov detector and an anti-coincidence counter. Its maximum detectable rigidity was ≈ 360 GV. For detector and mission details see [2]. Though annihilation signals would be clearer in the lower background e + spectra AMS-01 couldn’t distinguish e+ from the large p+ background at energies > 3 GeV. Instead we utilized the Z = -1 spectrum. PYTHIA was used to generate Z = -1 decay spectra for W + W− bosons decaying at various center of mass energies. These spectra were then convolved with Green’s functions of particles transported to earth using the GALPROP galactic propagation software The final e+ and p¯ spectra for each WIMP mass was then convolved with an AMS acceptance matrix (from Monte-Carlo) and added. These expected signals from WIMPs of various masses were then compared with data with and without an additional astrophysical power-law background. The results showed that the dark-matter alone could not describe the data, that the power-law alone was a good fit and that the addition of WIMP annihilation did not improve the fit. As a result we could place limits on the rate of W + W− production in the galaxy and, subsequently on the cross-section of WIMP annihilation through this channel. For further details see [3]. [1] G. Jungman, M. Kamionkowski and K. Griest, Physics Reports, 267:195–373, 1996 [2] M. Aguilar et al. (AMS Collaboration). Physics Reports, 366(6):331-405, 2002 [3] G. Carosi. Ph.D dissertation. MIT, Dept. of Physics, 2006: http://web.mit.edu/gcarosi/www/gp thesis.pdf 0920-5632/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2011.09.034