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 nonbaryonic. 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
H. Baer, A. Belyaev, T. Krupovnickas,
J. O’Farrill, JCAP 0408:005,2004
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…)
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

_
p
g

indirect
detection
e+ n
 Direct detection of WIMP at terrestrial detectors
via scattering of WIMP of the detector material.

  ll  l  l

Direct
detection
Flux of the annihilation products
d d SUSY
 Flux is determined by

( E )   cos mo ( )
dE
the products of two factorsdE
 The first factor is the strength of the
interaction, determined completely by
particle physics d SUSY 1 v
dN f
dE

4 2m
2

dE
Bf
 The second by the distribution of DM
1
cos mo

 2   2 (r )dV   d   2 (r )dl
( ) l .o. s
d
 The flux depends on both the
astrophysics and the particle aspects.
GC and Subhalos for indirect
2
  v 
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?
Cusp
Dark matter distribution—Density profile
Observation of
rotation curve
favors cored
profile strongly
Universal Density Profile
NFW profile
Navarro, Frenk, White 1997
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:
  (r )＝
s


( r ) 1   r 
rs   rs 
0
 NFW r
 r 1
Moore:
  (r )＝
s
1.5

1.5 


r
r
(
) 1  
rs
rs  



0
 Moore r
 r 1.5
2
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
g-rays from the subhalos
Reed et al,
MNRAS35
7,82(2004)
g-rays from subhalos
source

sun
GC
g-rays from smooth bkg
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 GammaRay 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
HAWC~0.04ICRAB
angular resolution
duty cycle
area
field of view
ground-based
ACT
EAS
good
fair
low
high
large
large
small
large
energy resolution
good
fair
space-based
Pair
good
high
small
large+
can reorient
good, with
smaller
systematic
uncertainties
ASg and ARGO：
~100GeV
(High Duty cycle,Large F.O.V)
~TeV
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
ARGO hall, floored by
RPC. Half installed.
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 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 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.
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.