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Dark matter, YBJ, subhalos, detection, signals
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西藏羊八井实验探测暗物质信号 XJ Bi，IHEP（2008/4/28） 第十届高能物理年会 南京大学
Outline • Dark matter and new physics • Sites looking for DMA • GC vs subhalos • YBJ and its potential for DMA detection • conclusion
Non-baryonic DM From BBN and CMB, it has Bh2=0.02+-0.002. Therefore, most dark matter should be non-baryonic. DMh2=0.113+-0.009 Non-baryonic cold dark matter dominates the matter contents of the Universe. New particles beyond the standard model are required! New physics!
H. Baer, A. Belyaev, T. Krupovnickas, J. O’Farrill, JCAP 0408:005,2004 • mSUGRA or CMSSM: simplest (and most constrained) model for supersymmetric dark matter • R-parity conservation, radiative electroweak symmetry breaking • Free parameters (set at GUT scale): m0, m1/2, tan b, A0, sign(m) • 4 main regions where neutralino fulfills WMAP relic density: • bulk region (low m0 and m1/2) • stau coannihilation region m mstau • hyperbolic branch/focus point (m0 >> m1/2) • funnel region (mA,H 2m) However, general MSSM model versions give more freedom. At least 3 additional parameters: m, At, Ab (and perhaps several more…)
c c _ g p c c e+ n Detection of WIMP • Collider • Indirect detection DM increases in Galaxies, annihilation restarts(∝ρ2); ID looks for the annihilation products of WIMPs, such as the neutrinos, gamma rays, positrons at the ground/space-based experiments • Direct detection of WIMP at terrestrial detectors via scattering of WIMP of the detector material. indirect detection Direct detection
Flux of the annihilation products • Flux is determined by the products of two factors • The first factor is the strength of the interaction, determined completely by particle physics • The second by the distribution of DM • The flux depends on both the astrophysics and the particle aspects.
GC and Subhalos for indirect detection • The fluxes of the annihilation products are proportional to the annihilation cross section and the DM density square. Fluxes are greatly enhanced by clumps of DM. • The Galactic center and center of subhalos have high density. • There are 5%~10% DM of the total halo mass are enclosed in the clumps. • The following characters make subhalos more suitable for DM detection: • GC is heavily contaminated by baryonic processes. • Structures in CDM from hierarchically, i.e., the smaller objects form earlier and have high density. • Subhalos may be more cuspy profile than the GC. • Mass is more centrally concentrated when an object is in an environment with high density.
Problems at small scale of CDM • Galactic satellite problem and cusp at GC • Nature of dark matter or astrophysics process?
Satellite galaxies are seen in Milky Way, e.g. Saggittarius, MCs Predicted number Observed number of luminous satellite galaxies 10km/s 20km/s 100km/s • The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures?
Dark matter distribution—Density profile Cusp Observation of rotation curve favors cored profile strongly Universal Density Profile NFW profile Navarro, Frenk, White 1997
Profiles of dark matter • Two generally adopted DM profiles are the Moore and NFW profiles from N-body simulation • They have same density at large radius, while different slope as r->0 NFW: Moore:
Dark subhalos, with no baryon matter, is cuspy at the center, which is more favorable sites than GC to detect dark matter annihilation. • YBJ can not observe GC, but has advantage to search signals from subhalos.
Complexity of GC X-ray radio γ-ray
Difficulty in DM detection from GC • It is found only a narrow window is left for GLAST to probe the GC considering the strong gamma source detected by HESS.
g-rays from the subhalos Reed et al, MNRAS357,82(2004) g-rays from subhalos source y g-rays from smooth bkg sun GC
Cumulative number of gamma ray sources • Fixing the particle factor we give the cumulative number of gamma rays sources as function of their intensities. • There are large uncertainties from the subhalos profile determined by simulations. • Once the sensitivity of a detector is known, we can predict the number of sources from subhalos detected by it.
Unidentified sources of EGRET • More than half of the sources detected by EGRET are unidentified. Recent analyses show that most of the unidentified sources are not from subhalos. If none of them are from subhalos, this is translated into a constraint on the SUSY parameter space. • Similarly, GLAST in space, ARGO in Tibet, (the next generation all-sky VHE Gamma-Ray water Cherenkov telescope) HAWC can also put constraints.
Search the subhalos at different detectors • Simulation can not predict the position of subhalos we can only look for subhalos with high sensitivity and large field of view detectors. • Satellite-based experiments, EGRET, GLAST，AMS02, have large field of view, high identification efficiency of g/P, low threshold energy. • EAS ARGO/MILAGRO/HAWC observatories, have large field of view, (low identification efficiency of g/P), while large effective area ~104-105m 2 , high threshold energy and high sensitivity. • Cerenkov telescopes have high angular resolution, high identification efficiency of g/P, large effective area ~104 m 2 , small filed of view.
Gamma ray detection experiments Complementary capabilities ground-based space-based ACTEASPair angular resolution good fair good duty cycle low high high area large large small field of view small large large+ can reorient energy resolution good fair good, with smaller systematic uncertainties HAWC~0.04ICRAB
ASg and ARGO： (High Duty cycle,Large F.O.V) ~TeV ~100GeV 中意合作 ARGO实验RPC大厅 中日合作 AS γ实验区闪烁体探测器阵列 Here comes the two experiments hosted by YBJ observatory. One is call ASg, a sampling detector covering 1% of the area and have been operated for 15 years. The other full coverage one is called ARGO, still under installation. ASg use scintillation counter and ARGO use RPC to detector the arrival time and the number of secondary particles, with which the original direction and energy of CR particle can be restored. ASg has a threshold energy at a few TeV while ARGO down to about 100GeV. Both experiment have the advantages in high duty cycle and large field of view. Because for both of the experiments there is only one layer of detector, it is very difficult to separate the g ray shower from CR nucleishowers. Working in the similar energy range on mountain Jemez near Los Alamos, by using water cherenkov technique, MILAGRO has two layer of PMT, which enable it a rather good capability to separate g ray from background. Though it locates in a low altitude, has a smaller effective area, it has similar sensitivity to ASg experiment. To combine this technique with high altitude would greatly improve the sensitivity of our current EAS experiments. ARGO hall, floored by RPC. Half installed.
Conclusion • The GC has been extensively studied to search the gamma rays from DM annihilation. However, if the DM profile is cored, there is no chance to detect its DMA signal. Further there is strong gamma background detected by HESS. • Subhalos are alternative sites for DM annihilation detection. EGRET/GLAST/ARGO/HAWC are possible to detect gamma rays from these sites. No such detection implies strong constraints on the SUSY parameter space. • Satellite and ground experiments are complementary.
