Indirect dark matter search with YBJ-AS Observatory Outline Introduction Status of ground-based observations Data analysis with AS experiment Results 5. Conclusions Wu hanrong on behalf of YBJ-ASg collaboration 2008.09.24 TeVPA-IV@IHEP

Indirect Dark Matter search Astrophysics : Dark matter halo Gamma-ray flux from WIMP annihilation: Particle Physics From Observation

Target of indirect search Galactic Halo external galaxies galaxy clusters substructures Galactic Center(GC) Local Group galaxies Mini-spikes around IMBH

Indirect DM search—ground based observatory IACT arrays Advantage: Good angular resolution; gamma/hadron discrimination Disadvantage: limited FOV and duty cycle Advantage: large FOV, 90% duty cycle Disadvantage: no good gamma/hadron identifintification EAS arrays

Data analysis with AS experiment

Tibet AS Observatory a.s.l. 4300 m (YBJ , Tibet) 606g/cm2 Large field of view Duty cycle (>90%) Mode Energy: ASγ(~3TeV) ARGO ASγ

Schematic map of the array and data using in analysis Tibet-II Tibet-IIIB4 Run period space Mode Energy Angular resolution area Tibet-III 1999.11~2004.10 7.5m ~3TeV ~0.90 ~22050m2 Statistic (after selection): ~1.86*10^10

analysis method Equal 迭代 This method is developed to fit simultaneously the relative cosmic ray intensity from all directions over the sky. The principle is that at any moment, for all directions , if we scale down(or up) the observed event number by divide them by their relative CR intensity, then statistically, those scaled observed event number in an zenith belt should be equal anywhere.Here we define relative CR. Intensity as I. So, for some moment, at some zenith angle,we get an on-source window, and then we obtain some off-sources window with the same shape, the same size and the same zenith angle as on-source window, For the on source window, there are observed event number Non and relative intensity Ion, according for off-sources, Noff and Ioff.then statistically, Non/Ion and the average value of Noff/Ioff should be approximately equal, so a ki-square function can be built, this is for some certain direction and on-source window, and then for all direction and all moment, in the same way, we can get all ki-square function and then sum them,so a large ki-square function is constructed.by minimizing the function, we can get CR relative Intensity at all directions.

全天图以及M31显著性 1.M31(10.7,41.3) Non: 2876965 Noff: 2875325.3 Nexc: 1639.7 Significance: 0.97 M31 2. No high siginificant point (>5sigma) except known source crab and Mrk421 is detected

1. 90%C.L. limit— M31

2. 90%C.L. limit— substructure Significance for BKG Significance for BKG+DM signal

2. 90%C.L. limit— substructure preliminary

Conclusions Detect no any substructure in the field of YBJ ASgamma observatory Detect no DM from M31 90% C.L. upper limit on “thermally averaged annihilation cross section” between 10^-19cm^3s^-1 and 10^-22cm^3s^-1 is given Future search, ARGO-YBJ(~300GeV)

Thanks!

1. 90%C.L. Flux limit— M31 90%C.L. flux limit： DM spectrum From Observation Monte Carlo

2. 90%C.L. Flux limit— substructure -----Number of substructure for 800 toy MC trials BKG BKG+DM signal