electron recoil & dark matter direct detection qing wang tsinghua univ. beijing
TRANSCRIPT
Electron Recoil &
Dark Matter Direct Detection
Qing Wang Tsinghua Univ. Beijing
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Background and Status of ER
Our present understanding
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Cosmology, Astrophysics
Search DM
particle physics
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Cosmology & Astrophysics ： Found ！
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Particle Physics ： Not Found ！
Direct D
etection
Indirect Detection
Collider Experiment
No unambiguous evidence has been obtained to date
6Nuclear Recoil & Electron Recoil
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Electron Recoil not considered at very beginning !
Target recoil v target initial v0’ DM initial v0 DM final v’
For M>>m rest nucleon ER~2v02m2/M~ 2keV ×(m/10GeV)2×100GeV/M
v0~10-3 ； for electron m>>M ER~2v02M~1eV Chemistry & Biology
Estimation of Recoil Energy M, v ， v0ˊ
m ， v0, vˊ
Angle between incident particle & target CM frame
m reduce from 10GeVto 1GeV ， NR reduce from 2keV to 20eV ， ER keep 1eV ！
Theory & Exp not prefer electron recoil
traditional threshold Lower detection bound
Too small for electron recoil energy
~
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1st rise up ER energy~keV
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Bounded electron of NaI(Tl) has 10-4 probability v2>1/2 （ p>0.5MeV ）
Sodiumiodide
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DAMA signal was explained as ERavoid contradiction with other exps
Assume DM only interact with leptons leptophilic
But Leptons loop induce enough NR
And electroncannot seen as free particle
While CDMS analysis on ER spectrum gives no signal
Phys.Rev. D81 (2010) 042002
Phys.Rev. D80 (2009) 083502
with some velocity distribution
Theory & Exp not prefer ER again !
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2nd rise up
A new gauge boson X, couples to SM particles and the WIMP through kinetic vector boson mixing with properties: 2me ≤ mX ≤ mχ β ≤ mχ αDM
Typical values ： mX = 0.1–1 GeV, mχ = 0.1–1 TeV ， αDM = αem
pick back small recoil energy~10eV
mχ = 10 GeV mχ = 100GeV
mχ = 1000 GeV
hydrogenic atom ； massless mediator
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Recoil energy~1-10eV
Free electron with momentum distribution change to bound state wave function ，
effect of large momentum tail change to ：
★ larger contribution from initial larger momentum state phase space
★ smaller contribution due to overcome ionization energy
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Recoil energy:
keV region: NR dominant ！
eV region: ER dominant !
10~several hundred eV region: ?
That’s CDEX most interested region !
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ER spectrum
Phase B ： >
NR spectrum
Static target ：
If R0 Universal
Needs initial momentum distribution and bounded states effects!
0.245, 0.433,0.571
Event rate
Recoil energy Incident kinetic energy
Incident particle mass
Static free electron
NR spectrum
Phase A ： >
ER spectrum
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Impact of electron
Initial velocity
Free electron with some momentum
distribution
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Effect of initial velocity
Energy<0
Too big energy ？
Phase A
Phase B
Phase B
Free electron with some momentum
distribution
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4.7, 5×10-8
4.3, 7×10-7
Free electron with some momentum
distribution
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4.3, 7×10-7
2.8, 3×10-5
0.37, 0.33
Free electron with some momentum
distribution
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More steep
Red
uce little b
it
increase
When dark matter mass become small
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At 10~several hundred eV region:
Competation result of ER and NR is still not clear
May or may not produce measurable event rate
More nuclear & atomic
calculation is needed !
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