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

Energy budget of the universe

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!

Cosmology/astrophysics/particle physics

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 A0, sign()

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: , At, Ab (and perhaps several more…)

H. Baer, A. Belyaev, T. Krupovnickas, J. O’Farrill, JCAP

0408:005,2004

Detection of WIMP

Collider Indirect detection DM increases in Galaxies, annihilatio

n 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.

Direct detection

p

e+

_indirect detection

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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.

)()( cos moSUSY

EdE

d

dE

d

f

fSUSY

BdE

dN

m

v

dE

d224

1

dlrddVrd sol

mo )()(1

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GC and Subhalos for indirect detection The fluxes of the annihilation products are proportional to the a

nnihilation 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.

2v

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?

Predicted number

Observed number of luminous satellite galaxies

• The predicted number of substructures exceeds the luminous satellite galaxies: dark substructures?

• Satellite galaxies are seen in Milky Way, e.g. Saggittarius, MCs

20km/s 100km/s10km/s

Universal Density ProfileNFW profile

Navarro, Frenk, White 1997

CuspDark matter distribution—Density profile

Observation of rotation curve favors cored profile strongly

Nature of dark matter or astrophysics process?

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:

2s

1)(

)(

ss rr

rr

r ＝

5.15.1

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1)(

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ss rr

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10 rrNFW

5.10 rrMoore

Uncertainties from the distribution of the DM

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.

No opportunity for GLAST with cored profile

-rays from the subhalosReed et al, MNRAS357,82(2004) -rays from subhalos-rays from subhalos

-rays from smooth bkg-rays from smooth bkg

source

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 det

ermined 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 EGRE

T 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 /P, low threshold energy.

EAS ARGO/MILAGRO/HAWC observatories, have large field of view, (low identification efficiency of /P), while large effective area ~104-105m 2 , high threshold energy and high sensitivity.

Cerenkov telescopes have high angular resolution, high identification efficiency of /P, large effective area ~104 m 2 , small filed of view.

Complementary capabilities

ground-based space-based ACT EAS Pair 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

Gamma ray detection experiments

HAWC~0.04ICRAB

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

ASand 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.

Sensitivity at ARGO for DM detection （ 10yr ）

Sensitivity at HAWC for DM detection （ 5yr ）

Constrant by EGRET/GLAST

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.