International audienceThe Alpha Magnetic Spectrometer (AMS), to be installed on the International Space Station, will provide data on cosmic radiations in a large range of rigidity from 0.5 GV up to 2 TV. The main physics goals in the astroparticle domain are the anti- matter and the dark matter searches. Observations and cosmology indicate that the Universe may include a large amount of unknown Dark Matter. It should be composed of non baryonic Weakly Interacting Massive Particles (WIMP). A good WIMP candidate being the lightest SUSY particle in R-parity conserving models. AMS offers a unique opportunity to study simultaneously SUSY dark matter in three decay channels from the neutralino annihilation: e+, antiproton and gamma. The supersymmetric theory frame is considered together with alternative scenarios (extra dimensions). The expected flux sensitivities in 3 year exposure for the e+/e- ratio, antiproton and gamma yields as a function of energy are presented and compared to other direct and indirect searches

Rosier-Lees, S.

Hal - Université Grenoble Alpes

Dark Matter searches with AMS02

HAL Université de Savoie

Dark Matter searches with AMS02S. Rosier-LeesTo cite this version:S. Rosier-Lees. Dark Matter searches with AMS02. Rogelio Caballero, Juan Carlos D’Olivo,Gustavo Medina-Tanco, Lukas Nellen, Federico A. Sa´nchez, Jose´ F. Valde´s-Galicia. 30th In-ternational Cosmic Ray Conference - ICRC’07, Jul 2007, Merida, Mexico. 4 (HE part 1),pp.729-732, 2008. <in2p3-00175533>HAL Id: in2p3-00175533http://hal.in2p3.fr/in2p3-00175533Submitted on 19 Nov 2007HAL is a multi-disciplinary open accessarchive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come fromteaching and research institutions in France orabroad, or from public or private research centers.L’archive ouverte pluridisciplinaire HAL, estdestine´e au de´poˆt et a` la diffusion de documentsscientifiques de niveau recherche, publie´s ou non,e´manant des e´tablissements d’enseignement et derecherche franc¸ais ou e´trangers, des laboratoirespublics ou prive´s.30TH INTERNATIONAL COSMIC RAY CONFERENCESEARCH FOR DARK MATTER with AMS02S. ROSIER-LEES ON BEHALF OF THE AMS COLLABORATIONLAPP: In2p3 and CNRS, Universite´ de Savoie, Francerosier@lapp.in2p3.frAbstract: The Alpha Magnetic Spectrometer (AMS), to be placed on ISS, will provide data on cosmicradiations in a large range of energy from 0.5 GeV to 1 TeV. The main physics goals in the astroparticledomain are the anti-matter and the dark matter searches. The e+, p¯ and γ channels will contribute tothe dark matter indirect detection studies since they are expected to be produced in the annihilation ofthe χ˜01, one good Cold Dark Matter candidate predicted in the supersymmetry theory. The expected fluxsensitivities in 3 year exposure for gamma rays, the e+/e− ratio and p yields as a function of energy arepresented and compared to other direct and indirect searches.IntroductionCold dark matter (CDM) makes up 23 % of the en-ergy of the universe, as deduced from the WMAP[1] measurements of the temperature anisotropiesin the Cosmic Microwave Background, in combi-nation with data on the Hubble expansion and thedensity fluctuations in the universe. One WIMPs(Weakly Interacting Massive Particles) candidatemay be majorana neutralinos (χ˜01) proposed in theSupersymmetric Models in which case pair anni-hilations can occur to produce neutrinos, gammarays, electrons, positrons, protons or antiprotons.Kaluza-Klein (KK) excitation of Standard Modelfields (for example the B1 particle, the first KKexcitation of the B boson) which appear in modelsof universal extra dimensions are also good candi-date for dark matter. From these the electrons andprotons are drown in the many particles in the uni-verse, but the others may be detectable above thebackground from nuclear interactions, especiallybecause of much harder spectra expected from neu-tralino annihilation. AMS will measure preciselyp,γ, e+ and D¯ ’s spectrum from the GeV to theTeV. The identification of the particles will be akey issue to obtain a rejection against the protonbackground of, e.g, at least 104 at 200 GeV.The detectorCompare to the AMS-01 detector which operatedsuccessfully during 10 days in June 1998 on theShuttle Discovery, a significant upgrade of the de-tector AMS-02 has been planned. A complete de-scription of the full detector, as well as the exper-imental performance can been found in references[2] and [3]. The major elements of the AMS-02 de-tector consist of a superconducting magnet (MG),a gaseous transition radiation detector (TRD), asilicon tracker (TR), Time of Flight hodoscopes(ToF), a ring imaging Cerenkov detector (RICH)[4]-[5], an electromagnetic calorimeter (EMC), astar tracker system (AST) and anti-coincidenceveto counters (ACC). The momentum and sign ofthe charge Q is measured by the tracker, whilethe absolute value of the charge is measured independently by the tracker, RICH and ToF. Thevelocity of the particle is measured by the TOF,TRD and RICH, thus allowing for redundant parti-cle identification, once the charge and the momen-tum are known. Gamma ray are detected eitherby the calorimeter or by the pair conversion out-side the tracker. The large acceptance of the de-tector (∼ 0.4m2sr) combined with rigidity mea-surements of charged particles up to the multi-TeVrange and redundant and performing particle iden-tification will allow for a good understanding of thecosmic rays in our galaxy.Indirect searchesAMS, through the precise spectrum measurementsof the positron, anti-proton, gamma and antideuteron will perform indirect searches of DM;Those searches will be sensitive to both the lo-cal (positrons) and the galactic (anti proton andgamma) or extragalactic (gamma) Dark Matter.The search sensitivity will depend on differentmodel assumptions related to the nature and thedensity of the Dark Matter candidate, his annihila-tion rate and on the the cosmic rays propagation inthe galaxy for the charged annihilation products. Anew spectrum generator (for positron ,anti-proton,gamma, anti-deuton and neutrinos) has been usedand developed, interfacing MicrOMEGAS [6],which estimates the relic density for different mod-els, with PYTHIA [7] for the decay and the hadro-nisation of the DM annihilation products. Chargedparticles are propagated with a semi analyticalmodel, using the positron or anti-proton propagatorwith cylindrical conditions [8]- [10]. In additiondifferent Halo profile models are assumed like theNavarro, Frenk and White (NFW) [9] halo profilein which the DM density is distributed followingan isothermal spherical symmetric profile. Finallysome substructure models naturally providing highboost factors ( 1000) exits without specific fine tun-ing [11]. In what follows, these so called IMBHmodels have been used to estimate the boost factor,necessary to fit excess seen in the HEAT data [12].Positron FluxAMS-02 will be able to measure the positron fluxin the energy range 1 to 400 GeV, with an energyresolution of about 2%, statistical uncertainty of 1% at 50 GeV and high average background rejec-tion for e+/e− and e+ /p.To identify positrons among the large physicalbackground coming from the protons flux, oneshould be able to separate positrons from protonsat a level better than 106. In AMS-02, this is ob-tained by combining information provided by sev-eral sub-detectors: the Transition Radiation detec-tor, the Tracker and the Calorimeter. The AMS-02 acceptance for positrons has been estimated tobe on average 0.045 m2.sr in the range 2 to 500GeV [13] while the effective rejection power de-fined as the inverse of proton acceptance is greaterthan 3.108 for energies above 10 GeV.The sensibility to detect a positron signal in AMS-02 from a primary source such as the annihilationof neutralinos is illustrated in the figure 1 for aneutralino mass of 150 GeV, decaying mostly intobbar pair, where the signal is originally amplifiedas mentioned above. The e+ interstellar flux hasbeen calculated by means of a standard diffusionmodel [14] to fit the HEAT data [12]. Some classof models with extra dimensions provide a parti-cle candidate to Dark Matter. The chosen exam-ple is extracted from Universal Extra Dimensionsmodels, where the stable particle can be a Kaluza-Klein photon [15]. The figure 2 shows the signalexpected in AMS-02 for the signal amplified to fitthe HEAT data; compared to a MSSM scenario,the energy spectrum is quit different; this measure-ment will be a key point to distinguish the two the-oretical hypotheses and learn more about the na-ture of the DM candidate.Antiproton fluxAntiprotons are identified by their negative chargein the tracker and a hadronic signature in the TRD.The main background originating from proton in-teractions outside the sensitive volume is removedby severe quality cuts. Acceptance for antiprotonsis 0.160 m2.sr in the range 1 to 16 geV and 0.033m2.sr up to 300 GeV [16]. At energy below fewGeVs, different uncertainties spoil the knowledgeof the p¯ spectrum of the secondary p¯ components.AMS-02 will measure accurately the p¯ spectrumup to hundred GeV with a few percent energy reso-lution and an irreducible background (coming frome− and p) to signal ratio below a few percent levelas illustrated in Figures 1 and 2. The simulation ofsecondary p¯ spectrum detected by AMS-02 in threeyears is shown in Figures 1 and 2 together withprevious measurements for both scenarios (MSSMor Extra dimension). The different spectra shapereflects the difference mass assumptions made ineach case.Gamma fluxThe AMS potential for the DM detection in thechannels with γ in final state has been performedincluding two detection modes presented previ-ously, the ”conversion mode ” [17] and the ”singlephoton” [18]. In the conversion mode, gamma areconverted in the .25 radiation lengths of the TRDand are identified but 2 opposite charged trackswith low invariant mass. In the calorimeter, pho-tons shower directly with no other activity in thedetector. These methods have complementary ac-ceptances, the first one being efficient down to 2GeV with a maximum acceptance of 0.06 m2.sr at30 GeV while the second one is efficient to highenergy with a maximum 0f 0.097 m2.sr at 200GeV. Both methods have a similar time integratedsensitivity to the galactic Center.Gamma rays might be a possible signature ofdark matter processes through annihilation like andχ˜01χ˜01 → γγ, and χ˜01χ˜01 → γγ the continuum pho-ton flux mainly through the pi0 mesons produced injets from annihilation products, a typical spectrumincluding all the gamma sources is given in figures1- 2. Different extragalactic sources based on theIMBH models [11], but at different distance (2 or20 kpc), have been considered in Figure 1 (top) forneutralino mass of 150 GeV (left) or for Kaluza-Klein photon of 50 GeV(right), after three years ofdata taking.ConclusionsAMS has a unique opportunity to measure simul-taneously the gamma, antiprotons ans positronsspectra, increasing its sensitivity to Dark Mattersearch or leading to better constraints on the mod-els. The combination of the precise energy spec-trum measurements of the 3 channels will rendpossible (in few optimistic cases of hints) the de-termination of the nature of dark matter and whynot his decay modes.References[1] Wilkinson Microwave Anisotropy Probe(WMAP) three year results: implications forcosmology. By WMAP Collaboration (D.N.Spergel et al.) Mar 2006. Astrophys.J. astro-ph/0603449[2] V. Bindi et al, ICRC proceedings, 2007.[3] A. Oliva et al, ICRC proceedings, 2007.[4] F. Barao et al, ICRC proceedings, 2007.[5] A. Malinine et al, ICRC proceedings, 2007.[6] G. Belanger et al. MicrOMEGAs 2.0:A Program to calculate the relic den-sity of dark matter in a generic model.Comput.Phys.Commun.176:367-382 2007[7] T. Sjostrand et al. Computer Phys. Com-mun. 135 238 (2001). LU TP 00-30, hep-ph/0010017[8] P.Brun Recherche inclusive de matiere noireavec AMS-2 PhD Thesis (2007).[9] J.F Navarro et al, Astrophys. J 462 (1996)563 [arXiv:astro-ph/9508025][10] G. Belanger et al. in preparation[11] P.Brun et al. astro-ph arXiv:0704.2543.[12] Positron measurements with HEAT-pbar in-strument. S. Coutu et al.. Proceedings ofICRC 2001.[13] Mesures du spectre de positons cosmiquesavec l’expe´rience AMS-02 et recherche designaux exotiques.Jonathan Pochon PhD Thesis.[14] P.Ullio et al. astro-ph/990[15] G. Servant et T. Pait.[16] D.Caraffini PhD Thesis INFN Perugia 2005.4086.[17] I.Sevilla PhD Thesis CIEMAT Madrid 2005.Nucl. Phys. B650 391-419 (2003)[18] L. Girard, detection with AMS02, proceed-ings Moriond 2005 and PhD thesis, Decem-bre 2004.Energy  [ GeV ]1 10 210 ]-1.sr-1.s-2  [ GeV.cmγΦ2 E-710-610-510-410-310-210 Extra-Galactic backgroundSusy signalAMS02 projection (3 y.) case 1AMS02 projection (3 y.) case 2Proton backgroundEnergy  [ GeV ]10 210 ]-1.sr-1.s-2.cm2  [ GeVe+Φ3 E -410-310-210Standard signalSusy signalTotalAMS02 projection (3 y.)AMS01HEATKinetic energy  [ GeV ]10 210 ]-1.sr-1.s-2.cm2  [ GeVpΦ3 T -410-310-210Standard signalSusy signalTotalWIZARD-MASS 91CAPRICE 98BESS 98BESS 99BESS 00AMS02 projection (3 y.)Figure 1: Indirect searches assuming a 150 GeVχ˜01 mass in respectively the gamma (top), the posi-ton (medium) and the anti-protons (bottom) after 3years of data taking in AMSEnergy  [ GeV ]1 10 210 ]-1.sr-1.s-2  [ GeV.cmγΦ2 E -610-510-410-310Extra-Galactic backgroundKaluza-Klein signalAMS02 projection (3 y.) case 1AMS02 projection (3 y.) case 2Proton backgroundEnergy  [ GeV ]10 210 ]-1.sr-1.s-2.cm2  [ GeVe+Φ3 E-410-310-210Standard signalKaluza-Klein signalTotalAMS02 projection (3 y.)AMS01HEATKinetic energy [ GeV ]10 210 ]-1.sr-1.s-2.cm2  [ GeVpΦ3 T-510-410-310-210-110 Standard signalKaluza-Klein signalTotalWIZARD-MASS 91CAPRICE 98BESS 98BESS 99BESS 00AMS02 projection (3 y.)Figure 2: Indirect searches assuming a 50 GeV KKboson mass in respectively the gamma (top), thepositon (medium) and the anti-protons (bottom) af-ter 3 years of data taking in AMS

Dark Matter searches with AMS02

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