WIMPS & Axion searches with EDELWEISS

Rencontres de Blois May 2013

Thibault de Boissière (CEA Saclay) 1 Outline

EDELWEISS : introduction WIMP searches with EDELWEISS Axions in a nutshell Axions: new results

Thibault de Boissière (CEA Saclay) 2 EDELWEISS primary goal: WIMP direct detection

= 0.3 GeV/cm³

Weak scale σ = Cross section (Spin independent part dominates with Ge target nuclei)

R= σ Φ N Φ= Incoming WIMP flux

N= Target nuclei R ≈ 10⁻ ³ events/kg/day

Er: typically ~ keV to ~10keV We need low thresholds, ⇒ low backgrounds and high mass targets! Thibault de Boissière (CEA Saclay) 3 EDELWEISS Ge bolometers

neutron calibration d l e i y

n o i t a z i n o I

= Q

● Interdigit Bolometers working underground @ LSM, cooled @ 18 mK. Recoil energy [keV]

● Simultaneous measurement of Heat (NTD thermometer) and WIMP search results d

Ionization (Al electrodes) l e i y ●

Select events in fiducial volume from ionization (segmented n o

electrodes). i t a z i n o

● I Discriminate events with Q= Eionization / Erecoil ● Q=1 for electron recoils (mostly due to gammas and = Q possible axions) ● Q=0.3 for nuclear recoils (due to neutrons and possible WIMP candidates) WIMP search region 4

Recoil energy [keV] EDELWEISS II WIMP search (1 year, 384 kg.days)

1 year, 10 detectors limit from Physics Letters B 702 (2011) 329-335. σ = 4.4x10⁻⁸ pb at 85 GeV

Also shown are the dedicated low-mass analysis results from Phys. Rev. D 86, 051701 (R) (2012)

EDW III (40 detectors of 800g) is in commissionning. Goal: 3000 kg.d. and σ ≈ 10⁻⁹ pb.

Long term project: EURECA, a Ge ton-scale experiment. CDR written. Possible collaboration with CDMS

5 Low mass WIMPS

Work in progress to improve sensitivity on low mass WIMPS

Ongoing R & D to improve threshold.

CDMS II (Si detectors) 3 events over a background of 0.4 EDELWEISS II arXiv:1304.4279 Thibault de Boissière (CEA Saclay) Phys. Rev. D 86, 6 051701(R) (2012) Electronic recoil and axions

EDW is also ⁶⁸Ge sensitive to ⁶⁵Zn electronic recoils down to 2.5 keV 0.25 counts/kg.d.keV at 12 keV Excellent electron 0.8 keV FWHM recoil background at 2.5 keV threshold low energies (use fiducial volume discrimination)

Axions can generate ⁴⁹V ⁵⁵Fe an electronic recoil: we can detect or constrain axions

Thibault de Boissière (CEA Saclay) 7 Axions in a nutshell

Axions are elementary particles first theorized by Peccei and Quinn to solve the strong CP problem

In this framework, axions interact with SM particles: there are model dependent couplings. Axion field and decay constant

Axions, being charge-neutral and weakly interacting, are also a prime candidate to explain dark matter in the Universe

We work with effective couplings:

Axion nucleon Axion electron Axion photon coupling coupling coupling

gaN gae ga γ

Thibault de Boissière (CEA Saclay) 8 Axion searches: 4 channels

Production Detection Statistical method

Solar Primakov Primakov (Bragg Energy dependence and scattering) time correlator ga γ ga γ Solar Compton Axio electric effect Bremsstrahlung Energy dependence g (Spectral bump) gae ae Solar ⁵⁷ Fe deexcitation Axio electric effect Energy dependence g g aN ae (Spectral line @ 14.4 keV) Assume axion (with mass Axio electric effect m ) make up all of Energy dependence a g galactic dark matter ae (Spectral line @ ma)

9 Solar axion search: Primakov effect

Axion Production Axion Detection

−E 14 g ×108 2 a Typical transferred momentum has d Φ 6.02×10 aγ 2.481 1.205 wavelength close to interatomic = 2 ( −1 ) Ea e dEa cm . s.keV GeV spacing. A Bragg pattern arises ⇒ strong enhancement of the signal.

2 Bragg: E = G⃗ axion 2u⃗⋅G⃗

Outgoing Incoming u photon solar axion G Germanium electric field

10 Expected count rate during 1 day

−8 −1 ga γ=1×10 GeV

Thibault de Boissière (CEA Saclay) 11 Statistical analysis: time correlation

Axion count rate Build the time correlator: averaged over χ ∝∑ R(E ,t )−〈R〉 time ⇒ Obtain g a γ at a given CL events This depends on the azimuthal orientation!

g ×108 4 Combine all 10 detectors with unknown Distribution of λ=( a γ ) orientations: GeV −1 → MC simulation of the experiment

Real data gaγ=0 GeV⁻ ¹ → Scan over orientations and possible couplings

→ Rule out coupling from the comparison between simulation and real data. g =4.10⁻⁹ GeV ⁻ ¹ aγ −9 −1 g <2.3×10 GeV a γ 12 Primakov Solar Axions: limit on gaγ (448.5 kg.days)

EDW II b 1/8 preliminary ga γ ∝( ) limit (95% CL) MT ¹ ⁻ L V C e

G %

5 n i 9

L C

% 5 9

t a

γ a g

Thibault de Boissière (CEA Saclay) 13 Axion mass in eV Constraints on Dark Matter axions (448.5 kg.days)

Assume axions make up all of dark matter and have a PRELIMINARY mass in the keV range.

Axions are non relativistic: look for a line at the axion

mass in the recoil spectrum e

a

g

−12 gae <1.05×10

(@ ma= 12.5 keV)

Axion mass (ma) in keV

Thibault de Boissière (CEA Saclay) 14 EDW II Constraints on gae (448.5 kg.days)

S o ( la Z m r S PRELIMINARY o ⁵ F d ⁷F D e e l d d Z e e V p ex S en c K d it e e at a n io

t) n

g

Solar Compton Bremmstrahlung

Dark Matter

Axion mass (m ) in keV a 15 Constraints on gae (448.5 kg.days)

B o r ex in o D er C b Z in S PRELIMINARY uo F re D R & Z D V S

K

e

a g

Derbin

Xmass

Solar neutrinos CoGent

CDMS Red giant EDW

Dotted lines are model dependent Axion mass (m ) in keV constraints. a 16 Red curves are EDELWEISS limits Conclusion

● Dark Matter search with EDELWEISS (EDW):

– EDWII data constraints potential “low mass signals”. – EDWIII in commissioning, goal: σ ≈ 2.10⁻⁹ pb

● New results for axion searches:

17 Back up

Thibault de Boissière (CEA Saclay) 18 Conclusion

Production Detection Statistical method Result @ ma<< keV

Solar Primakov Primakov (Bragg Energy dependence −9 −1 scattering) and time correlator gaγ <2.3×10 GeV ga γ ga γ Solar Compton Axio electric effect Bremsstrahlung Energy dependence g <2.8×10−11 gae (Spectral bump) ae gae Solar ⁵⁷ Fe Axio electric effect deexcitation Energy dependence g ×g <4.7×10−17 g ae aN gaN ae (Spectral line @ 14.4 keV)

Assume axion make Axio electric effect −12 up all of galactic Energy dependence gae<1.05×10 dark matter gae (Spectral line @ ma) (for ma=12 keV axions)

EDELWEISS setup

In LSM underground laboratory Cryogenics at 18 mK Various shieldings: muon veto, lead and PE shield, clean room and deradonized air

Thibault de Boissière (CEA Saclay) 20 Axion results

The sun should be an intense source of (relativistic) axions through various processes:

Production in low lying (eg Fe at 14.4 keV) magnetic transitions (gaN)

Primakoff effect: photon axion conversion γ + γ → A (gaγ)

Axion Bremsstrahlung е⁻ + Z → e ⁻ + Z + A (gae)

Axion Compton scattering process γ + е⁻ → е ⁻ + А (gae)

Galactic (Dark Matter) axions could be detected if they have a mass in the keV range. They are non relativistic.

Detection: axio electric effect or Primakov effect

Thibault de Boissière (CEA Saclay) 21 Background model

Thibault de Boissière (CEA Saclay) 22 Axion detection (1) : the axio electric effect

Axio electric effect: A + e + Z → e + Z

=> Detect the electron

g2 3 E2 β σ (E )=σ ae a (1− ) A a PE β 2 16 π α me 3

Photo electric cross section Thibault de Boissière (CEA Saclay) 23 Axion results: 14.4 keV axions

Axions can be produced in magnetic transitions. A prime candidate is 57Fe (abundant and easily excited in the sun)

k a Expected Φ =β3 Φ (geff )2 β= Flux in cm².s⁻ ¹ a 0 aN k γ

Count rate R14.4=Φa×σa×W ×ϵ

Detector resolution function

Thibault de Boissière (CEA Saclay) 24 14.4 keV axions: statistical analysis

Assume a Poisson background and construct a likelihood function

th N (E)=B(E)+R14.4 (E)

2 2 Background Axion signal ∝gae×gaN

Extract limit and confidence interval (ML) + Cross check with MC

−17 Preliminary result: gae gaN <4.7×10

Thibault de Boissière (CEA Saclay) 25 Solar axion search: 14.4 keV and Compton-Bremsstrahlung

90% CL signal for 14.4 keV solar axions Only use the energy ma =0 keV dependence.

We are looking for possible line features in the spectrum.

In the absence of a signal, derive limits on axion couplings

−11 gae <2.8×10 (CB @ ma= 0 keV)

−17 gae×gaN <4.7×10

(14.4 keV @ ma= 0 keV)

Thibault de Boissière (CEA Saclay) 26 Limit for one detector

8 −1 4 λ=ga γ γ×(10 /GeV )

Error bars are 1.64 σ

α is the unknown azimuth orientation

Most conservative limit: pick the worst case orientation.

−9 −1 ga γ γ<2.7×10 GeV

Thibault de Boissière (CEA Saclay) 27 Combining several detectors

Idea: use the tail and the top to discriminate

Thibault de Boissière (CEA Saclay) 28