Direct detection of light dark matter. Joachim Kopp. IDM 2012, Chicago. Fermilab. Joachim Kopp Direct detection of light dark matter 1

Direct detection of light dark matter Joachim Kopp IDM 2012, Chicago Fermilab Joachim Kopp Direct detection of light dark matter 1

Outline 1 Why light WIMPs? 2 Experimental techniques for direct detection of light dark matter 3 Theoretical interpretation of direct detection data Material-dependent scattering cross sections Dependence on the WIMP velocity distribution Light WIMPs and annual modulation Neutrinos as WIMP impostors 4 Conclusions Joachim Kopp Direct detection of light dark matter 2

Hints for light dark matter On the Earth... WIMPnucleon cross section Σ SI cm 2 39 10 10 40 10 41 10 42 CDMS Xe 10 low thr. Limits : 90 10 43 Countours: 90, 3Σ Plot based on JK Schwetz Zupan 1110.2721 DAMA q ± 10 Xe 100 2012 v 0 220 km s v esc 550 km s CoGeNT no surface BG CoGeNT small surface BG CoGeNT large surface BG CRESST 4 6 8 10 20 30 40 506070 WIMP mass m Χ GeV Several intriguing direct detection signals But severe tension with null results... and in the skies An tentative γ ray excess from the Galactic Center Hooper Goodenough 0912.2998, 1010.2752, 1201.1303 Morphology point source Radio filaments Linden Hooper Yusef-Zadeh 1106.5493 Isotropic radio background Hooper Belikov Jeltema Linden Profumo Slatyer 1203.3547 Joachim Kopp Direct detection of light dark matter 4

Theoretical motivation for light DM Conventional DM paradigm: DM has electroweak scale mass, weak scale couplings Thermal production The WIMP Miracle But note: Thermal production also possible for lighter DM An interesting alternative: Asymmetric dark matter Based on the observation that ΩDM 5 Ω baryon Suggests related production mechanisms Baryon abundance determined by matter antimatter asymmetry If DM carries baryon number and m DM 10m p, the observed ΩDM could be explained. Many model-building and phenomenology papers related to this idea: Kaplan Luty Zurek 0901.4117, Cai Luty Kaplan 0909.5499, Frandsen Sarkar Schmidt-Hober 1103.4350, Frandsen Sarkar 1003.4505, Feldstein Fitzpatrick 1003.5662, An Chen Mohapatra Nussinov Zhang 1004.3296, Cohen Phalen Pierce Zurek 1005.1655, Shelton Zurek 1008.1997, Haba Matsumoto 1008.2487, Davoudiasl Morrissey Sigurdson Tulin 1008.2399, Buckley Randall 1009.0270, Chun 1009.0983, Gu Lindner Sarkar Zhang 1009.2690, Blennow Dasgupta Fernandez-Martinez Rius 1009.3159, McDonald 1009.3227, Hall March-Russell West 1010.0245, Allahverdi Dutta Sinha 1011.1286, Dutta Kumar 1012.1341, Kouvaris Tinyakov 1012.2039, Falkowski Ruderman Volansky 1101.4936, Graesser Shoemaker Vecchi 1103.2771, McDermott Yu Zurek 1103.5472, Kouvaris Tinyakov 1104.0382, Buckley 1104.1429, Iminniyaz Drees Chen 1104.5548, Bell Petraki Shoemaker Volkas 1105.3730, Chang Goodenough 1105.3976, Cheung Zurek 1105.4612, Del Nobile Kouvaris Sannino 1105.5431, Masina Sannino 1106.3353, March-Russell McCullough 1106.4319, Davoudiasl Morrissey Sigurdson Tulin 1106.4320, Profumo Ubaldi 1106.4568, Cui Randall Shuve 1106.4834, Graesser Shoemaker Vecchi 1107.2666, Arina Sahu 1108.3967, Kane Shao Watson Yu 1108.5178, Buckley Profumo 1109.2164, Lewis Pica Sannino 1109.3513, Cirelli Panci Servant Zaharijas 1110.3809, Zentner Hearin 1110.5919, Lin Yu Zurek 1111.0293, Cui Randall Shuve 1112.2704, Kamada Yamaguchi 1201.2636, Tulin Yu Zurek 1202.0283, Walker 1202.2348, Davoudiasl Mohapatra 1203.1247, March-Russell Unwin West 1203.4854, Fan Yang Chang 1204.2564, Ellwanger Mitropoulos 1205.0673, Masina Panci Sannino 1205.5918, Okada Seto 1205.2844, Blennov Fernandez-Martinez Mena Redondo Serra 1203.5803,... Joachim Kopp Direct detection of light dark matter 5

Semiconductor detectors Binding energy of electrons in semiconductor detectors is very small (3 ev in Ge) Already a very feeble nuclear recoil leads to excitation Practical limitation: Electronic noise Possible solution: Reduce capacitance of the device Make them smaller for instance CCDs (DAMIC) DAMIC collaboration 1105.5191 Change the electrode geometry Point-contact detectors (CoGeNT) Luke Goulding. Madden Pehl IEEE Trans. Nucl. Sci. 36 (1989) 926 Barbeau Collar Tench nucl-ex/0701012 CoGeNT Super-CDMS Joachim Kopp Direct detection of light dark matter 7

Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Joachim Kopp Direct detection of light dark matter 8

Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 Primary recoil ion hits Xe atom at rest Outer electrons rearrange themselves under the influence of both nuclei. Some of them may end up in excited or unbound states Joachim Kopp Direct detection of light dark matter 8

Ionization (S2) signals in liquid Xenon Ionization energy in LXe: O(12 ev) Actual experimental energy threshold depends on kinematics: Threshold energy for WIMP nucleus scattering depends on Leff Difficult to measure (requires experiments with low-e neutrons) Difficult to calculate (interactions of primary recoil nucleus with other Xe atoms requires complicated many-body dynamics) Brenot et al. Phys. Rev. A 11 (1975) 1245; Ovchinnikov et al. Phys. Rept. 389 (2004) 119 WIMP electron scattering very inefficient for O(100 GeV) dark matter JK Niro Schwetz Zupan 0907.3159... but an ideal process for MeV GeV DM Essig Mardon Volansky 1108.5383, Essig Manalaysay Mardon Sorensen Volansky 1206.2644 Σe cm 2 10 34 10 35 10 36 10 37 10 38 Hidden Photon models Excluded by XENON10 data 1 electron 2 electrons 3 electrons 10 39 1 10 100 10 3 Dark Matter Mass MeV Joachim Kopp Direct detection of light dark matter 8

Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? WIMPnucleon cross section Σ SI cm 2 39 10 10 40 10 41 10 42 CDMS Xe 10 low thr. DAMA q ± 10 Limits : 90 10 43 Countours: 90, 3Σ Xe 100 2012 v 0 220 km s 550 km s v esc CoGeNT no surface BG CoGeNT small surface BG CoGeNT large surface BG CRESST 4 6 8 10 20 30 40 50 6070 WIMP mass m Χ GeV Plot based on JK Schwetz Zupan 1110.2721 Joachim Kopp Direct detection of light dark matter 11

Material-dependent scattering cross sections How can the tension in the global data set when interpreted in terms of dark matter scattering be resolved? Isospin-violating DM Feng Kumar Marfatia Sanford 1102.4331 Different couplings to protons and neutrons switch off xenon Inelastic DM Tucker-Smith Weiner hep-ph/0101138 Inelastic scattering prefers heavy targets (CRESST!) WIMPnucleon cross section Σeffcm 2 10 37 10 38 10 39 10 40 CRESSTII DAMA IVDM, fn fp 0.7 Limits: 90 Contours: 90, 3Σ KIMS CRESST comm. run CDMS lowthr CDMSSi Xenon100 CDMS WIMPnucleon cross section ΣSIcm 2 10 37 10 38 10 39 10 40 CRESST comm. run Xenon100 CRESSTII KIMS idm, 90keV Limits: 90 Contours: 90, 3Σ DAMA 10 41 v0 220 kms, vesc 550 kms 10 1 10 2 10 3 mχ GeV 10 41 v0 220 kms, vesc 550 kms 30 40 50 mχ GeV Plot: JK Schwetz Zupan 1110.2721 Plot: JK Schwetz Zupan 1110.2721 Joachim Kopp Direct detection of light dark matter 11

Dependence on the WIMP velocity distribution Conventional assumption: f (v) ( exp [ v 2 /v 2 0 ] exp [ v 2 esc /v 2 0 ] ) Θ(v esc v) However, N-body simulations predict deviations from this simple form v 2 v 2 f(v) fv10 10 3 3 5.00 1.00 0.50 0.10 0.05 0.01 4 3 2 1 0 0 100 200 300 400 500 600 Via Lactea vesc ~ 550 km/s 200 250 300 350 400 450 500 550 200 300 v kms 5.00 Lisanti Strigari Wacker Wechsler 1010.4300 5.00 GHALO vesc ~ 433 km/s 1.00 1.00 Joachim Kopp Direct detection of light dark matter 13 Also: Streams and debris flow Lisanti Spergel 1105.4166, Kuhlen Lisanti Spergel 1202.0007 v fv10 5.00 1.00 0.50 0.10 0.05 0.01 4 3 2 1 0 0 100 200 300 400 500 6

Dependence on the WIMP velocity distribution 10 38 10 39 standard f p f n 1 v 0 270 kms v esc 500 kms q Na 0.3 Χ 2 242., 50.4 Σ SI in cm 2 DAMA 10 40 CR C Cl F 10 41 Xe Xe 10100 4 6 8 10 12 Si 14 M DM in GeV Si Xe Ge Farina Pappadopulo Strumia Volansky 1107.0715 Joachim Kopp Direct detection of light dark matter 14

Dependence on the WIMP velocity distribution 10 38 10 39 standard f p f n 1 v 0 220 kms v esc 600 kms q Na 0.3 Χ 2 255., 73.2 Σ SI in cm 2 DAMA 10 40 CR C Cl F 10 41 Xe 10 100 SiGe Si 4 6 8 10 12 14 M DM in GeV Xe Farina Pappadopulo Strumia Volansky 1107.0715 Joachim Kopp Direct detection of light dark matter 14

Dependence on the WIMP velocity distribution 10 38 10 39 standard f p f n 1 v 0 220 kms v esc 500 kms q Na 0.3 Χ 2 249., 72.0 Σ SI in cm 2 DAMA 10 40 CR C Cl F 10 41 Xe Xe 10100 Ge Si Si 4 6 8 10 12 14 M DM in GeV Xe Farina Pappadopulo Strumia Volansky 1107.0715 Joachim Kopp Direct detection of light dark matter 14

Dependence on the WIMP velocity distribution Σ SI in cm 2 10 38 10 39 10 40 CR k 3 f p f n 1 v 0 220 kms v esc 500 kms q Na 0.3 Χ 2 250., 72.3 DAMA C Cl F 10 41 Xe 100 Xe 10 4 6 8 10 12 14 M DM in GeV Si Ge Xe 10 Farina Pappadopulo Strumia Volansky 1107.0715 Joachim Kopp Direct detection of light dark matter 14

Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected ) -R Winter )/(2R (R Average Summer 0.3 0.25 0.2 0.15 0.1 Xenon Argon 10 ton*year Xenon 50 ton*year Argon 0.05 0-0.05-0.1 2 10 3 10 Mass (GeV) Arisaka et al. 1107.1295 Joachim Kopp Direct detection of light dark matter 16

Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner 1107.0717 and JK Schwetz Zupan 1110.2721 Events kev kg day 14 12 10 8 6 4 2 0 0 100 200 300 0.5 1. kev SI scattering days since 1 1 2010 1. 1.5 kev 0 100 200 300 days since 1 1 2010 1.5 2. kev 0 100 200 300 days since 1 1 2010 2. 2.5 kev 0 100 200 300 days since 1 1 2010 2.5 3. kev 0 100 200 300 400 days since 1 1 2010 Data points: CoGeNT, 1106.0650 (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + BG @ best fit) for spin-independent scattering Extra surface BG = 0 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in 0.5 1 kev bin = 73%) Joachim Kopp Direct detection of light dark matter 16

Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner 1107.0717 and JK Schwetz Zupan 1110.2721 Events kev kg day 14 12 10 8 6 4 2 0 0 100 200 300 0.5 1. kev SI scattering days since 1 1 2010 1. 1.5 kev 0 100 200 300 days since 1 1 2010 1.5 2. kev 0 100 200 300 days since 1 1 2010 2. 2.5 kev 0 100 200 300 days since 1 1 2010 2.5 3. kev 0 100 200 300 400 days since 1 1 2010 Data points: CoGeNT, 1106.0650 (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + BG @ best fit) for spin-independent scattering Extra surface BG = 12 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in 0.5 1 kev bin = 46%) Joachim Kopp Direct detection of light dark matter 16

Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner 1107.0717 and JK Schwetz Zupan 1110.2721 Events kev kg day 14 12 10 8 6 4 2 0 0 100 200 300 0.5 1. kev SI scattering days since 1 1 2010 1. 1.5 kev 0 100 200 300 days since 1 1 2010 1.5 2. kev 0 100 200 300 days since 1 1 2010 2. 2.5 kev 0 100 200 300 days since 1 1 2010 2.5 3. kev 0 100 200 300 400 days since 1 1 2010 Data points: CoGeNT, 1106.0650 (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + BG @ best fit) for spin-independent scattering Extra surface BG = 24 kev 1 day 1 exp ( E/0.3keV ) (signal fraction in 0.5 1 kev bin = 30%) Joachim Kopp Direct detection of light dark matter 16

Light WIMPs and annual modulation For light WIMPs, detectors are probing the tail of the velocity distribution Larger fractional annual modulation expected What would reduced annual modulation in the new CoGeNT data mean for the DM interpretation? Plot based on Fox JK Lisanti Weiner 1107.0717 and JK Schwetz Zupan 1110.2721 Events kev kg day 14 12 10 8 6 4 2 0 0 100 200 300 0.5 1. kev SI scattering days since 1 1 2010 1. 1.5 kev 0 100 200 300 days since 1 1 2010 1.5 2. kev 0 100 200 300 days since 1 1 2010 2. 2.5 kev 0 100 200 300 days since 1 1 2010 2.5 3. kev 0 100 200 300 400 days since 1 1 2010 Data points: CoGeNT, 1106.0650 (after subtraction of known cosmogenic peaks) Red curve: Prediction (signal + BG @ best fit) for spin-independent scattering When surface backgrounds are accounted for, reduced modulation in CoGeNT would make the data more consistent with a WIMP hypothesis Joachim Kopp Direct detection of light dark matter 16

Neutrinos as WIMP impostors Solar neutrinos are a well-known background to future direct DM searches: see e.g. Gütlein et al. arxiv:1003.5530 dσ SM (νn νn) = G2 F m NF 2 (E r ) [ de r 2πEν 2 A 2 Eν 2 + 2AZ (2Eν 2 (sw 2 1) E r m N sw) 2 ] + 4Z 2 (Eν 2 + sw(2e 4 ν 2 + Er 2 E r (2E ν + m N )) + sw(e 2 r m N 2Eν 2 )), countsnakevyear 10 2 10 1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11 10 12 10 13 10 14 pp 7 Be 13 N 15 O pep CoGeNT SM total rate Components 17 F electron recoil DAMA 8 B hep 10 1 10 0 10 1 10 2 10 3 10 4 Erec kev XENON100 e Borexino countstonkevyear 10 8 10 7 10 6 10 5 10 4 10 3 10 2 10 1 10 0 10 1 pp 7 Be 13 N 15 O pep hep Nuclear recoil Ge 8 B 17 F SM total rate Components 10 2 10 4 10 3 10 2 10 1 10 0 10 1 Erec kev CoGeNT CDMSII Plots from Harnik JK Machado 1202.6073 Joachim Kopp Direct detection of light dark matter 18

Enhanced neutrino scattering from BSM physics Harnik JK Machado 1202.6073 countsnakeveeyear 10 2 10 1 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 B C A CoGeNT Standard model DAMA D Line M A g eg Ν A Μ Ν 0.32 10 10 Μ B B 10 kev 4 10 12 C 50 kev 4 10 12 D 250 kev 6 10 12 10 1 10 0 10 1 10 2 10 3 rec ee XENON100 e Borexino A: ν magnetic moment B, C, D: kinetically mixed A + sterile ν s: L 1 4 F µνf µν 1 4 FµνF µν 1 2 ɛf µνf µν + ν si / ν s + g ν sγ µ ν sa µ (ν L ) c m νl ν L (ν s) c m νs ν s (ν L ) c m mix ν s Enhanced scattering at low E r for light A Negligible compared to SM scattering at energies probed in dedicated neutrino experiments Various mechanisms for daily and annual modulation Pospelov 1103.3261, Harnik JK Machado 1202.6073 Joachim Kopp Direct detection of light dark matter 19

Enhanced neutrino scattering from BSM physics countsnakeveeyear 10 2 10 1 10 0 10 1 10 2 10 3 10 4 B C A CoGeNT DAMA D rec ee XENON100 e Harnik JK Machado 1202.6073 Nuclear recoil Ge 10 5 Standard model 10 1 Line M A g eg Ν Line M Borexino A g Ng Ν sin 2 Θ 24 10 6 A Μ Ν 0.32 10 10 Μ B 10 0 A Μ Ν 0.32 10 10 Μ B active 10 7 B 10 kev 4 10 12 B 100 MeV 9 10 8 active C 50 kev 4 10 12 10 1 C 100 MeV 8 10 7 0.02 10 8 D 250 kev 6 10 12 D 10 MeV 10 2 10 6 0.02 10 1 10 0 10 1 10 2 10 3 10 4 10 3 10 2 10 1 10 0 10 1 countstonkevnryear 10 8 10 7 10 6 Standard model 10 5 10 4 10 3 10 2 A E rec kev nr D B C CoGeNT CDMSII A: ν magnetic moment A: ν magnetic moment B, C, D: kinetically mixed A + sterile ν s B: U(1) B L boson C: kinetically mixed U(1) + sterile ν D: U(1) B + sterile ν charged under U(1) B Pospelov 1103.3261, Pospelov Pradler 1203.0545 Enhanced scattering at low E r for light A Negligible compared to SM scattering at energies probed in dedicated neutrino experiments Various mechanisms for daily and annual modulation Pospelov 1103.3261, Harnik JK Machado 1202.6073 Joachim Kopp Direct detection of light dark matter 19

Summary and conclusions Several intriguing experimental hints for 10 GeV DM Theoretical motivation in asymmetric DM scenarios, but can be accomodated in many popular DM models Direct detection of light dark matter requires new experimental techniques Currently, data from different experiments contradict each other CoGeNT, DAMA, CRESST see unexplained signals Strong exclusion from Xenon-100, CDMS,... (under standard assumptions) Note: Reduced modulation removes tension within the CoGeNT data Ways out: Material-dependent scattering cross sections? (isospin-violating DM, inelastic DM) New physics in the neutrino sector can fake WIMP signals Joachim Kopp Direct detection of light dark matter 21

Thank you!

Bonus slides

Example: A model with a 4th neutrino Introduce a 4 th neutrino ν s and a light U(1) gauge boson A (hidden photon) Harnik JK Machado 1202.6073 related model with gauged U(1) B first discussed by Pospelov 1103.3261 see also Pospelov Pradler 1203.0545 ν s charged under U(1) direct coupling to A SM particles couple to A only through kinetic mixing L 1 4 F µνf µν 1 4 F µνf µν 1 2 ɛf µνf µν + ν s i / ν s + g ν s γ µ ν s A µ (ν L ) c m νl ν L (ν s ) c m νs ν s (ν L ) c m mix ν s A small fraction of solar neutrinos can oscillate into ν s ν s scattering cross section in the detector given by dσ A (ν s e ν s e) ɛ 2 e 2 g 2 m e [ = 2E 2 de r 4πpν(M 2 A 2 + 2E r m e ) 2 ν + Er 2 2E r E ν E r m e mν 2 ] Joachim Kopp Direct detection of light dark matter 24

Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Active sterile neutrino oscillations: For oscillation lengths 1 AU, sterile neutrino appearance depends on the time of year. Sterile neutrino absorption: For strong ν s A couplings and not-too-weak A SM couplings, sterile neutrino cannot traverse the Earth. lower flux at night. And nights are longer in winter. Joachim Kopp Direct detection of light dark matter 25

Temporal modulation of neutrino signals Signals of new light force mediators and/or sterile neutrinos can show seasonal modulation: The Earth Sun distance: Solar neutrino flux peaks in winter. Active sterile neutrino oscillations: For oscillation lengths 1 AU, sterile neutrino appearance depends on the time of year. Sterile neutrino absorption: For strong ν s A couplings and not-too-weak A SM couplings, sterile neutrino cannot traverse the Earth. lower flux at night. And nights are longer in winter. Earth matter effects: An MSW-type resonance can lead to modified flux of certain neutrino flavors at night. And nights are longer in winter. Joachim Kopp Direct detection of light dark matter 25

Hidden photons L 1 4 F µνf µν 1 4 F µνf µν 1 2 ɛf µνf µν + ν s i / ν s + g ν s γ µ ν s A µ Kinetic mixing Ε 10 24 10 21 10 18 10 15 10 12 10 9 10 6 10 3 1 g2μ Atomic Physics Atomic Physics 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 g Ν 2 sin 2 2Θ 10 12 g Ν 2 sin 2 2Θ 10 4 CMB Kinetically Mixed Gauge Boson CMB LSW Fixed target 10 24 10 21 10 18 10 15 10 12 10 9 10 6 10 3 1 Dark Photon Mass M A' GeV CAST Borexino in models with U1'charged sterile Ν SunGlobular Clusters, energy loss via Ν s in models with 10 kev sterile neutrinos A' capture in Sun partly allowed Sun Globular Clusters g2e SN1987A 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 Constraints from Jaeckel Ringwald 1002.0329, Redondo 0801.1527, Bjorken Essig Schuster Toro 0906.0580, Dent Ferrer Krauss 1201.2683, Harnik JK Machado 1202.6073 Joachim Kopp Direct detection of light dark matter 26