Electron Recoil Dark Matter Direct Detection Qing Wang

Electron Recoil & Dark Matter Direct Detection Qing Wang Tsinghua Univ. Beijing

Background and Status of ER Our present understanding 2

Cosmology, Astrophysics Search DM particle physics 3

Cosmology & Astrophysics： Found ！ 4

Particle Physics： Not Found ！ No unambiguous evidence has been obtained to date Collider Experiment Direct Detection Indirect Detection 5

Nuclear Recoil & Electron Recoil 6

Electron Recoil not considered at very beginning ! 7

m，v 0, M, vˊ Estimation of Recoil Energy v，v 0ˊ Theory & Exp not prefer electron recoil Target recoil v target initial v 0’ Angle between incident particle & target DM initial v 0 CM frame traditional threshold For M>>m rest nucleon DM final v’ Lower detection bound ER~2 v 02 m 2/M~ 2 ke. V ×(m/10 Ge. V)2× 100 Ge. V/M m reduce from 10 Ge. Vto 1 Ge. V，NR reduce from 2 ke. V to 20 e. V，ER keep 1 e. V ！ v 0~10 -3； for electron m>>M ER~2 v 02 M~1 e. V Chemistry & Biology Too small for electron recoil energy

1 st rise up ER energy~ke. V 9

Bounded electron of Na. I(Tl) has 10 -4 probability v 2>1/2（p>0. 5 Me. V） 10 Sodiumiodide

Theory & Exp not prefer ER again ! Phys. Rev. D 80 (2009) 083502 DAMA signal was explained as ERavoid contradiction with other exps Assume But And DM only interact with leptons Leptons loop induce enough leptophilic NR electroncannot seen as free particle Phys. Rev. D 81 (2010) 042002 with some velocity distribution While CDMS analysis on ER spectrum gives no signal 11

A new gauge boson X, couples to SM particles and the WIMP through kinetic vector boson mixing with properties: 2 me ≤ m. X ≤ mχ β ≤ mχ αDM Typical values： m. X = 0. 1– 1 Ge. V, mχ = 0. 1– 1 Te. V ， αDM = αem mχ = 100 Ge. V 2 nd rise up mχ = 10 Ge. V mχ = 1000 Ge. V pick back small recoil energy~10 e. V hydrogenic atom；massless mediator 12

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Recoil energy~1 -10 e. V 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 14

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Recoil energy: ke. V region: NR dominant ！ e. V region: ER dominant ! 10~several hundred e. V region: ? That’s CDEX most interested region ! 17

Static free electron If R 0 Universal 0. 245, 0. 433, 0. 571 ER spectrum Phase B：> NR spectrum Phase A：> ER spectrum Event rate Static target： Recoil energy Incident kinetic energy Incident particle mass Needs initial momentum distribution and bounded states effects! 18

Free electron with some momentum distribution Impact of electron Initial velocity 19

Free electron with some momentum distribution Energy<0 Phase B Too big energy ？ Phase A Effect of initial velocity Phase B 20

Free electron with some momentum distribution 4. 3, 7× 10 -7 4. 7, 5× 10 -8 21

Free electron with some momentum distribution 0. 37, 0. 33 2. 8, 3× 10 -5 4. 3, 7× 10 -7 22

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When dark matter mass become small More steep R e d u c e l i ttl e b i t increase 24

At 10~several hundred e. V 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 ! 25

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