The 2nd workshop of air shower detection at high LHAASO detection of dark matter and astrophysical gamma ray sources Xiao-Jun Bi IHEP, CAS Feb. 17 – 19, 2011

Outline Detection of dark LHAASO Diffuse gamma rays detection Crab Nebula– a standard candle or variable γ-ray source Concluding remarks

Standard cosmology DM exists. Particle nature is unclear. It is the key problem of particle physics and cosmology. Non-gravitional methods to detect DM particles

Indirect detection of dark matter -- Gamma rays  Monoenergetic spectrum Continuous spectrum Smoking gun of dark matter, while low flux Flux is large, not definitive signal

Dark matter detection at YBJ

China-Italy ARGO hall for RPC China-Japan AS γ array AS  and ARGO ： (High Duty cycle,Large F.O.V) ~TeV ~100GeV ARGO hall, floored by RPC. Half installed. Here comes the two experiments hosted by YBJ observatory. One is call AS , 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. AS  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. AS  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  ray shower from CR nuclei showers. 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  ray from background. Though it locates in a low altitude, has a smaller effective area, it has similar sensitivity to AS  experiment. To combine this technique with high altitude would greatly improve the sensitivity of our current EAS experiments.

The LHAASO project

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.

Possibilities of DM detection at YBJ Gamma rays from the GC （ almost impossible ） From the DM subhalos in the MW From the Local group (satellite dwarf galaxies and nearby galaxies)

ARGO constraints on DM annihilation Yu Z., Chen S., Bi X., 2010

LHAASO vs local group For DM mass >~500GeV ， LHAASO > Fermi

 -rays from the subhalos– large F.O.V, high sensitivity, high duty circle (compare Fermi, HESS) Reed et al, MNRAS35 7,82(2004)  -rays from subhalos  -rays from smooth bkg source sunGC  ARGO sensitivity

Sensitivities of LHAASO and Fermi on subhalo detection LHAAOS threshold ~100GeV ， ~10 ％ Crab For DM mass >~ 700GeV, LHAASO > Fermi

Diffuse gamma rays at LHAASO

Anomalous cosmic electron/positron spectrum at PAMELA 、 ATIC 、 Fermi

Different models can work well Adjusting parameters, DM decay/annihilation, pulsars can all explain PAMELA and ATIC Zhang, Bi, et al

We recalculated the diffuse gamma ray spectrum according to the Fermi/ATIC electron spectrum, for different theoretical models to explain the anomalous electron spectrum Ground detctor 1Crab/Sr

Crab flares (~3F crab over ~1yr)

Variability of Crab Nebula gamma ray flux The electrons are accelerated in a series of knots, whose sizes follow a power-law distribution The maximal electron energy is assumed to be proportional to the size of the knot Fluctuations at the highest energy end of the overall electron distribution will result in variable gamma-ray emission via the synchrotron process Larger knots are rarer than smaller knots, the model predicts that the variability of the synchrotron emission increases with the photon energy We realize such a scenario with a Monte-Carlo simulation and find that the model can reproduce both the largest gamma-ray flares over a period of ~1 year and the monthly scale gamma-ray flux fluctuations as observed by the Fermi/LAT by proper parameters Yuan, Bi, et al. arXiv:

Variability of Crab Nebula gamma ray flux The model predicts corresponding IC fluctuation at ~100TeV. The LHAASO can monitor Crab at high energies. This is crucial for the mechanism of the gamma ray flares.

Conclusion Besides some traditional topics at LHAASO, ie, searching the steady gamma ray sources, flares of AGNs, cosmic ray spectrum measurements, there are some other interesting topics, such as DM signal detection, phenomena with new physics. More topics are under study, quantum Pl A large F.O.V. detector with high sensitivity like LHAASO is an important and necessary complementary to the ACTs.

Thanks!