Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for...

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Fei Gao * for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California, San Diego Oct 29th, 2015, Kashiwa, Japan * affiliated with Shanghai Jiao Tong University

Transcript of Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for...

Page 1: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Fei Gao* for the XENON collaboration

Search for Event Rate Modulation in XENON100 Electronic Recoil Data

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University of California, San Diego

Oct 29th, 2015, Kashiwa, Japan

* affiliated with Shanghai Jiao Tong University

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XENON Collaboration

2

Columbia Nikhef Mainz Muenster

MPIK

Purdue Coimbra Subatech Bologna Weizmann

UCLA

Rice

Bern

Zurich

LNGS Torino

RPI

NYUAD

Stockholm

Chicago

UCSD

~130 Scientists from 21 institutes

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Annual modulation and DAMA/LIBRADark matter (DM) signal rate is expected to be annually modulating

A key feature to distinguish signals from overwhelming backgrounds

DAMA/LIBRA:

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peak phase 152 days (June 1)

9.3 sigma significance

Phase (144 +- 7) days

only for single hit

No signal above 6 keV

Seems to be a convincing evidence, HOWEVER…

Freese et al., Rev. Mod. Phys. 85, 1561 (2013)

Bernabei et al., Eur. Phys. J. C 73, 12 (2013)

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Nuclear Recoil Interpretation

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Nuclear recoil interpretations of DAMA/LIBRA modulation have been challenged by several more sensitive experiments with background rejection power

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How about Leptophilic DM?❖ DAMA/LIBRA annual modulation can be interpreted

as signals from Leptophilic DM models

❖ We tested three representative models in XENON100 using the electronic recoil data:

❖ 1, DM-electron scattering through axial-vector coupling

❖ 2, Mirror DM model

❖ 3, Luminous DM model

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Page 6: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Light Response in XENON100

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light response is determined with low energy measurements interpolated by NEST v0.98, uncertainties are from NEST and spread of measurements

DAMA/LIBRA 2-6 keV Electronic recoil (ER) corresponds to 3-14 PE in XENON100

Baudis et al., Phys. Rev. D 87, 115015 (2013) Aprile et al., Phys. Rev. D 90, 062009 (2014)

Szydagis et al., J. Instrum. 6, P10002 (2011)

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❖ DAMA/LIBRA rate converted to XENON100 spectrum assuming leptophilic DM model, axial vector coupling

❖ Energy response, resolution and cut acceptance applied

❖ Compare XENON100 average rate with DAMA/LIBRA modulation amplitude

❖ Constraints on DM interpretation of DAMA/LIBRA (assuming 100% modulation):

❖ WIMPs-electron scattering 4.4-sigma

❖ Mirror dark matter model 3.6-sigma

❖ Luminous dark matter model 4.6-sigma

DAMA/LIBRA Comparison

S1 (PE)0 5 10 15 20 25 30

Rat

e (c

ount

s/PE

/tonn

e/da

y)

0

2

4

6

8

10

12

Mean electronic recoil energy (keV)1 2 3 4 5 6 7 8 9 10

DAMA/LIBRA annually modulated spectrum (2-6)keV interpreted asleptophilic DM, axial-vector couplingmirror DMXENON100 70 summer live days

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S1 [PE]5 10 15 20 25 30

Cut A

ccep

tanc

e

00.10.20.30.40.50.60.70.80.9

1

2.0 - 5.8 keV 5.8 - 10.4 keV

Energy [keV]2 4 6 8 10

Science 349, 851 (2015)

Energy [keV]0 2 4 6 8 10 12

Rate

[cou

nts/k

eV/to

n/da

y]

10−

0

10

20

30

40

DAMA/LIBRA Modulation

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Search for Modulations❖ The first LXe TPC with more than one year of stable

running conditions

❖ The first modulation search for DM at Gran Sasso Lab after DAMA/LIBRA

❖ Demonstration for future XENON modulation searches

❖ Search for leptophilic DM signals

❖ Require good understand the stability of detector and backgrounds

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Page 9: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Stability of the Detector

Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

C]oT

[∆

-0.15-0.1

-0.050

0.050.1

0.150.2

0.250.3

C oT(Room) avg:20.7∆×-110C oT(Gas Xenon) avg:-86.5∆

C oT(Liquid Xenon) avg:-91.6∆

(b)

Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Liqu

id L

evel

[mm

]

2.3

2.4

2.5

2.6

2.7

2.8Level Meter 1Level Meter 2

(c)

Time Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Rate

[Cou

nts/D

ay]

0

0.5

1

1.5

2

2.5 (f)

(51.1%)σ1±

Background rate (SS) 2.0 - 5.8 keV

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PRL 115, 091302 (2015)

❖ Detector pressor (2)

❖ Room pressor

❖ LXe temperature (4)

❖ PTR temperature

❖ Room temperature

❖ Purification flow rate

❖ LXe levels (2)

❖ PMT gain

❖ Radon level (2)

Very tiny absolute variations

No correlations with ER rate No significant impact on ER rate!

Aprile et al., Astropart. Phys., 35, 573-590 (2012)

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❖ Stability of cut acceptance is derived from weekly ER calibrations sources

❖ The acceptance variation further accounts for the variation of the detector parameters like LXe level.

❖ The dips of acceptance are due to increment of noise level.

❖ The fluctuation of acceptance is taken into account for the event rate modulation analysis.

Stability of Cut Acceptance

Time Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Rate

[Cou

nts/D

ay]

0

0.5

1

1.5

2

2.5 (f)

(51.1%)σ1±

Background rate (SS) 2.0 - 5.8 keV

Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Cut A

ccep

tanc

e

0.60.65

0.70.75

0.80.85

0.90.95

1 (e)

(3.8%)σ1±

Average Cut Acceptance2.0 - 5.8 keV

10

PRL 115, 091302 (2015)

Page 11: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

❖ Co60 (T1/2 = 5.3 year) gamma background is time dependent, but the absolute contribution is negligible.

❖ Radon and krypton background concentration are time dependent due to tiny air leak

❖ Radon contributes to the overall background by less than 20%. Hence the absolute contribution to fluctuation is negligible.

❖ No correlation between radon and ER rate.

❖ Krypton concentration varies in time due to air leak. The size of its variation is taken into account.

Stability of Backgrounds

Time Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Rate

[Cou

nts/D

ay]

0

0.5

1

1.5

2

2.5 (f)

(51.1%)σ1±

Background rate (SS) 2.0 - 5.8 keV

Mar/11 May/11 Jul/11 Sep/11 Nov/11 Jan/12 Mar/12

Bq/k

g]µ

Rado

n Le

vel [

50

60

70

80

90

100 (d)

(8.6%)σ1±

Radon inside LXe

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Page 12: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Profile Likelihood Analysis

f(t) = ✏(t)

✓C +Kt+A cos

✓2⇡

(t� �)

P

◆◆

L =

nY

i=1

˜f(ti)

!Poiss (n|N

exp

(E))L✏LKLE

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Cut acceptance constant background

krypton variation due to air leak

modulation

observed number of events

energy response

Constraints

We performed an unbinned profile likelihood analysis to search for modulation signal

Event Rate:

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Discovery Potential

Period [Days]8 10 20 30 40 100 200 300 10000

2468

101214161820

P = 100P = 365P = 500

(local)σ2

(local)σ3

0.0010.0020.010.020.1Frequency [1/Days]

-2log(L 0

/L1)

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Simulated modulation signals

A=2.7 events/(keV · tonne · day) ~ best fit value for P=365.25 days

Average significance of 3 sigma assuming ~25% DAMA/LIBRA modulation

Characteristic plateau

no rise at large periodgood resolution on period

no resolution on period

PRL 115, 091302 (2015)

The data is only sensitive to modulation with period < 500 days

Page 14: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

❖ No evident peak crossing the 1-sigma global significance threshold!

❖ SS in the Low-E (2.0-5.8 keV) range shows increasing significance at long period region. 2.8-sigma local significance at one year period

❖ MS background only control sample in Low-E range shows similar power spectrum as SS. This disfavors an WIMPs interpretation of the SS spectrum

❖ SS in high-E (5.8-10.4 keV) does not show high significance at long period region

Modulation Search Results

Period [Days]7 8 910 20 30 40 50 100 200 300 400

2468

10121416

(local)σ2

(local)σ3

(global)σ1

1 ye

ar

Frequency [1/Days]

SS, 2.0 - 5.8 keV

0.0020.010.020.030.1

Period [Days]

7 8 9 10 20 30 40 50 60 100 200 300 400

2468

10121416

(local)σ2

(local)σ3

(global)σ1MS, 2.0 - 5.8 keV0.0020.0030.010.020.030.040.1

Period [Days]7 8 910 20 30 40 50 100 200 300 400

2468

10121416

(local)σ2

(local)σ3

(global)σ1SS, 5.8 - 10.4 keV0.0020.010.020.030.1

-2log(L 0

/L1)

-2log(L 0

/L1)

-2log(L 0

/L1)

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PRL 115, 091302 (2015)

Signal, Low-E

Background, Low-E

Side band, high-E

Page 15: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

❖ The phase (112+-15) days (April 22) is not consistent with the standard halo model (June 2) at 2.6-sigma

❖ The amplitude of is also too small (only ~25%) compared with the expected DAMA/LIBRA modulation signal in XENON100.

❖ The DM interpretation of DAMA/LIBRA annual modulation as being due to WIMPs electron scattering through axial vector coupling is disfavored at 4.8-sigma from a PL analysis

DAMA/LIBRA Comparison (2D)

Phase [Days]20 40 60 80 100 120 140 160 180 200A

mpl

itude

[eve

nts/

(keV

·tonn

e·da

y)]

0

2

4

6

8

10

12 Expected

expectedphase fromDM halo

XENON10095% C.L.99.73% C.L.best fit

20 40 60 80 100 120 140 160 180 200

24681012

σ1

σ2

σ3

2 4 6 810120

2

4

6

8

10

12

σ1 σ2 σ3

-2lo

g(L 1/L

max

)

-2log(L1/Lmax)

DAMA/LIBRA

C = (5.5± 0.6) events/(keV · tonne · day),

A = (2.7± 0.8) events/(keV · tonne · day),

� = (112± 15) days

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PRL 115, 091302 (2015)

DAMA/LIBRA(expected) = 11.5± 1.2stat± 0.7syst

Page 16: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Summary❖ The first stable LXe TPC sufficient for modulation searches.

❖ No significant modulation is found in the XENON100 electronic recoil data.

❖ The increasing significances at long period in both SS and MS samples does not favor a dark matter interpretation

❖ Leptophilic DM models to interpret DAMA/LIBRA modulation have been challenged by XENON100

❖ WIMPs-electron scattering 4.4-sigma

❖ Mirror dark matter model 3.6-sigma

❖ Luminous dark matter model 4.6-sigma

❖ More data is ready for modulation searches.

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PRL 115, 091302 (2015)

Science 349, 851 (2015)

Page 17: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

XENON100 ER background

ER background:Beta decay from krypton

Beta decay from radon

Gammas from materials

Very good data/MC absolute matching inside fiducial volume!!!

Radioactivity from screening values, no turning!

Need XENON1T to suppressPMT background

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E. Aprile et al. (XENON100), Phys. Rev. D83, 082001 (2011)

Page 18: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

WIMP-electron scattering Requirement: no loop-induced nuclear recoil - axial vector interaction

Advantage: natural model with coupling to electrons

Disadvantage: bad spectrum match with DAMA/LIBRA

Kopp et.al, PRD 80, 083502 (2009)18

Page 19: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Mirror electron scattering❖ Multi-component mirror models

❖ DM halos are composed of a multi-component plasma of mirror particles (same mass as their partners)

❖ Mirror electron scatters on electron through kinematically mixed coupling

❖ Scatter rate proportional to number of loosely bound electrons (binding energy < 1 eV)

❖ Constant scaling of 0.89 between XENON100 and DAMA/LIBRA

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. R. Foot, Int.J.Mod.Phys. A29, 1430013 (2014)

Page 20: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Luminous Dark Matter

❖ Upper scattering inelastic dark matter scattering, the interaction rate is determined by dipole moment

❖ ~keV mass splitting produce X-rays

❖ Interaction in the earth besides the detector, and produce X-rays inside the detector

❖ 3.0 keV mass splitting fits well with the DAMA/LIBRA modulation

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. B. Feldstein et.al, Phys.Rev. D82, 075019 (2010)

Page 21: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Radon Correlation Analysis

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M. Weber, PhD Dissertation, University of Heidelberg (2013) www.ub.uni-heidelberg.de/archiv/15155

Page 22: Search for Event Rate Modulation in XENON100 …...Fei Gao* for the XENON collaboration Search for Event Rate Modulation in XENON100 Electronic Recoil Data 1 University of California,

Calibration between radon and krypton

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Leak rate is calculated fromthe correlation analysis between external and internal radon

three RGMS measurements of kryptonacross the run

Perfect linear correlation betweenkrypton levels and air leak