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Status of the XENON100 Dark Matter Search
Guillaume Plante
Columbia University
on behalf of the XENON Collaboration
Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011
XENON100 Collaboration
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 2 / 37
Columbia Rice UCLA Zurich Coimbra LNGS SJTU
Mainz Bologna MPIK NIKHEF Subatech Munster WIS
Direct Detection
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 3 / 37
Heat
ScintillationIonization
ZEPLIN II, IIIXENONLUXWARPArDMDarkSide
CRESST-ISIMPLEPICASSOCOUPP
IGEXGEDEONGENIUSGERDACoGeNT
ZEPLIN IDEAPCLEANXMASSDAMA/LIBRAKIMS
CDMS I, IISuperCDMSEDELWEISS I, II
CRESST-IIROSEBUD
Why Xenon?
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 4 / 37
• Large mass number A (∼131), expecthigh rate for SI interactions (σ ∼ A2)if energy threshold for nuclear recoilsis low
• ∼50% odd isotopes (129Xe, 131Xe)for SD interactions
• No long-lived radioisotopes, Kr can bereduced to ppt levels
• High stopping power (Z = 54, ρ =3g cm−3), active volume is self shield-ing
• Efficient scintillator (∼80% light yieldof NaI), fast response
• Scalable to large target masses
• Nuclear recoil discrimination with si-multaneous measurement of scintilla-tion and ionization
10−5
10−4
10−3
Tot
alR
ate
[evt/
kg/
day
]
0 10 20 30 40 50
Eth - Nuclear Recoil Energy [keV]
Si (A = 28)
Ar (A = 40)
Ge (A = 73)
Xe (A = 131)
σχN = 1 × 10−44 cm2
Principle
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 5 / 37
Eionization
excitation
Xe++ e−
+Xe
Xe+
2
+e−
Xe∗∗+XeXe∗
+Xe
Xe∗2
2Xe
178 nmsinglet (3 ns)
2Xe
178 nmtriplet (27 ns)
• Bottom PMT array below cathode, fully immersed in LXeto efficiently detect scintillation signal (S1).
• Top PMTs in GXe to detect the proportional signal (S2).
• Distribution of the S2 signal on top PMTs gives xy coordi-nates (∆r < 3mm) while drift time measurement providesz coordinate (∆z < 300µm) of the event.
• Ratio of ionization and scintillation (S2/S1) allows dis-crimination between electron and nuclear recoils.
XENON100: Design
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 6 / 37
PMT HV and Signal Lines ❛❛❛❛❛❛❛❛❛❛❛❛
❆❆❆❆Anode Feedthrough ❝
❝❝❝❝❝❝❝❝❝❝
Tube to
Cooling
Tower
Top Veto
PMTs
Top Array
PMTs✭✭✭✭✭✭
PTFE
Panels✭✭✭✭✭✭✭✭✭
Side Veto
PTFE Lining✱✱✱
Lower Side
Veto PMTs✏✏✏✏✏
Bottom Array PMTs ✑✑✑✑✑✑✑✑✑✑✑✑
Double-Wall
Cryostat
✔✔
✔✔
✔✔
✔✔
✔✔
✔✔
✔✔
✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄
Upper Side
Veto PMTs��
���
Bell✭✭✭✭✭✭✭✭
Top Mesh✘✘✘✘✘✘✘✘Anode
Bottom Mesh❳❳❳❳❳❳❳
Field
Shaping
Rings
✭✭✭✭✭✭✭✭
Cathode❤❤❤❤❤❤❤❤❤
Bottom Veto PMTs
❧❧
❧❧
❧❧
• Goal was to build a detector with a ×10 increasein fiducial mass and a ×100 reduction in back-ground compared to XENON10.
• All detector materials and components werescreened in a dedicated low-background count-ing facility
• 161 kg LXe total mass consisting of a 62 kg tar-get surrounded by a 99 kg active veto. 15 cmradius, 30 cm drift length active volume.
• TPC inner volume defined by 24 interlockingPTFE panels. Drift field uniformity ensured by40 double field shaping wires, inside and outsidethe panels.
• Cathode at -16 kV, drift field of 0.533 kV/cm.Anode at 4.5 kV, proportional scintillation re-gion with field ∼12 kV/cm. Custom-made lowradioactivity HV feedthroughs.
• Aprile et al., arXiv:1107.2155
XENON100: Design
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 6 / 37
PMT HV and Signal Lines ❛❛❛❛❛❛❛❛❛❛❛❛
❆❆❆❆Anode Feedthrough ❝
❝❝❝❝❝❝❝❝❝❝
Tube to
Cooling
Tower
Top Veto
PMTs
Top Array
PMTs✭✭✭✭✭✭
PTFE
Panels✭✭✭✭✭✭✭✭✭
Side Veto
PTFE Lining✱✱✱
Lower Side
Veto PMTs✏✏✏✏✏
Bottom Array PMTs ✑✑✑✑✑✑✑✑✑✑✑✑
Double-Wall
Cryostat
✔✔
✔✔
✔✔
✔✔
✔✔
✔✔
✔✔
✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄✄
Upper Side
Veto PMTs��
���
Bell✭✭✭✭✭✭✭✭
Top Mesh✘✘✘✘✘✘✘✘Anode
Bottom Mesh❳❳❳❳❳❳❳
Field
Shaping
Rings
✭✭✭✭✭✭✭✭
Cathode❤❤❤❤❤❤❤❤❤
Bottom Veto PMTs
❧❧
❧❧
❧❧
• Goal was to build a detector with a ×10 increasein fiducial mass and a ×100 reduction in back-ground compared to XENON10.
• All detector materials and components werescreened in a dedicated low-background count-ing facility
• 161 kg LXe total mass consisting of a 62 kg tar-get surrounded by a 99 kg active veto. 15 cmradius, 30 cm drift length active volume.
• TPC inner volume defined by 24 interlockingPTFE panels. Drift field uniformity ensured by40 double field shaping wires, inside and outsidethe panels.
• Cathode at -16 kV, drift field of 0.533 kV/cm.Anode at 4.5 kV, proportional scintillation re-gion with field ∼12 kV/cm. Custom-made lowradioactivity HV feedthroughs.
• Aprile et al., arXiv:1107.2155
XENON100: PMT Arrays
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• 242 low activity Hamamatsu R8520-06-Al 1” squarePMTs,
• 98 tubes on top (QE ˜23%), in concentric circles andenclosed in a PTFE structure,
• 80 high QE (˜33%) tubes on bottom, on a rectangulargrid to maximize photocathode coverage,
• 64 tubes in the LXe veto, in two rings, alternatinginward and down (up) to allow them to view the top,bottom and sides of the veto volume.
XENON100: Shield
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• XENON100 installed in a passive shield to suppress external backgrounds:
• 20 cm of H2O to moderate neutrons produced in the cavern rock
• 20 cm Pb (inner 5 cm with low radioactivity Pb) to stop gamma rays
• 20 cm polyethylene to moderate neutrons produced in the Pb
• 5 cm Cu to stop gamma rays from the polyethylene
• Shield cavity continuously purged with N2 to keep 222Rn level < 1Bq/m3.
XENON100: Gran Sasso
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✑✑✑
❤❤❤❤❤❤❤❤❤❤❤❤
Outside Buildings
Tunnel
Lab
XENON100: Typical Low Energy Event
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 10 / 37
s]µDrift Time [0 20 40 60 80 100 120 140 160 180
Am
plitu
de [V
]
0.0
0.5
1.0
1.5
Veto
Am
plitu
de [V
]
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
TPC
-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6
0.00
0.05
0.10
0.15S1: 14.1 pe
170 171 172 173 174 175 176 177
0.0
0.1
0.2
0.3 S2: 926.1 pe
XENON100: Typical Low Energy Event
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 11 / 37
1
2
3
4
5
67
8 910
11
12
13
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15
16
17
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20
2122232425
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28
29
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34
3536 37 38
39
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46
47484950
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5859 60 61
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68697071
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848586
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97 98179
180
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185186 187 188
189
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200
201202203204
205
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209
210
99 100 101 102
103 104 105 106 107 108 109
110 111 112 113 114 115 116 117 118
119 120 121 122 123 124 125 126 127 128
129 130 131 132 133 134 135 136 137 138
139 140 141 142 143 144 145 146 147 148
149 150 151 152 153 154 155 156 157 158
159 160 161 162 163 164 165 166 167
168 169 170 171 172 173 174
175 176 177 178
211
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217218 219 220
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233234235236
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[pe]
PM
Ti
S2
0
20
40
60
80
100
120
140
XENON100: ER Background
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Energy [keV]0 500 1000 1500 2000 2500 3000
]-1
keV
-1 d
ay-1
Rat
e [e
vent
s kg
-410
-310
-210
data (Fall 2009, no veto cut)
MC (total)
Kr, 120 ppt)85MC (
Bq/kg)µRn, 21 222MC (
y)2110×=2.111/2
, Tββ νXe 2136MC (
Pb214
Ac228
Bi214
Bi214
Cs137 Co60
Co60
K40Tl208
Tl208
Mn54
Energy [keVee]1 2 3 4 5 6 7 8 910 20 30 40 50 100
]-1
d-1
kg
-1R
ate
[eve
nts
keV
ee
-310
-210
-110
1
10
210
CRESST
DAMA/LIBRA
CDMSCoGeNT
IGEX
XENON10
XENON100(target volume)
XENON100(fiducial volume)
XENON100 keVee scale needed below 9 keV
• Measured and predicted ER background without veto cut and for a 30 kg fiducial volume.
• Measured ER background (9.6× 10−3 events keV−1 kg−1d−1) is in good agreement with MonteCarlo predictions (no tuning). Background from materials is dominated by PMTs.
• ER background level in fiducial volume (< 6× 10−3 events keV−1 kg−1d−1, with vetocoincidence cut) is ×100 lower than XENON10 (0.6 events keV−1 kg−1d−1).
• Details in Aprile et al., Phys. Rev. D 83, 082001, 2011
XENON100: Calibration
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• Electronic recoil band calibration per-formed with high energy gammasfrom 60Co (1.17 Mev, 1.33 MeV).
• Background in the energy region ofinterest is due to low energy Comp-ton scatters from high energy gammarays or β decays.
• Nuclear recoil band calibration per-formed with 3.7 MBq (220 n/s)AmBe neutron source.
• Since WIMPs are expected to elasti-cally scatter off of nuclei understand-ing the behavior of single elastic nu-clear recoils in Xe is essential.
]nr
Nuclear Recoil Equivalent Energy [keV0 5 10 15 20 25 30 35 40
(S2/
S1)
10lo
g
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.00 5 10 15 20 25 30 35 40
(S2/
S1)
10lo
g
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
60Co
AmBe
Nuclear Recoil Equivalent Energy
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• Nuclear recoil equivalent energy Enr isobtained from the S1 signal
Enr =S1
Ly,er
1
Leff(Enr)
Ser
Snr
• Ly,er, light yield of electron recoilsfrom 122 keV γ rays
• Ser, Snr, scintillation light quenchingdue to drift field
• Relative scintillation efficiency Leff
Leff (Enr) =Ly,nr (Enr)
Ly,er (Eee = 122 keV) Nuclear Recoil Energy [keV]1 10 100
eff
L
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Sorensen 2009
Lebedenko 2009
Arneodo 2000
Akimov 2002
Aprile 2005
Aprile 2009
Bernabei 2001
Chepel 2006
Manzur 2010
• The uncertainty in Leff at low energies is the largest systematic uncertainty in the reported resultsfrom LXe WIMP searches at low WIMP masses.
• Recent measurement performed at Columbia University, lowest energy measured 3 keV.
New Measurement of Leff : Detector
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 15 / 37
• Built a new special purpose LXe detec-tor with maximized scintillation light de-tection efficiency
• Cubic sensitive volume with six 2.5 x 2.5 cm Hama-matsu R8520-406 SEL High QE PMTs
• Calibration with 122 keV γ rays from a 57Cosource gives a light yield of Ly = 24.14 ±0.09(stat)± 0.44(sys) pe/keVee with a resolution(σ/E) of 5%
• Very high light yield, enables a measurement witha low energy threshold
New Measurement of Leff : Setup
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LXe
d
2H(d, n)3Heϕ = π
2
EJ301
EJ301
n
θ
θ
• Record fixed-angle elastic scatters of monoenergeticneutrons tagged by organic liquid scintillators with n/γdiscrimination
• Use 2H(d, n)3He 2.5 MeV neutrons from a compactsealed-tube neutron generator
• Recoil energy is fixed by kinematics
Er ≈ 2EnmnMXe
(mn +MXe)2(1− cos θ)
Time of Flight [ns]-50 0 50 100 150
]-1
d-1
Rat
e [e
vent
s ns
0
50
100
150
200
250
300
n
γ o = 34.5θ 1.0 keV±6.5
Accidentals Accidentals
Scintillation Signal [pe]0 10 20 30 40 50 60 70
]-1
d-1
Rat
e [e
vent
s pe
0
20
40
60
80
100o = 34.5θ
1.0 keV±6.5
New Measurement of Leff : Result
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Nuclear Recoil Energy [keV]1 10 100
eff
L
0.00
0.05
0.10
0.15
0.20
0.25
0.30Sorensen 2009Lebedenko 2009Horn 2011 (FSR)Horn 2011 (SSR)Aprile 2005Aprile 2009Chepel 2006
Manzur 2010Plante 2011
• Lowest energy (3 keV) and most precise Leff direct measurement achieved to date.
• For details see Plante et al., Phys. Rev. C 84, 045805, 2011
XENON100: Data Taking 2009/2010
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Date [mm/dd]10/27 11/26 12/26 01/25 02/24 03/26 04/25 05/25
Live
Day
s
0
20
40
60
80
100
120Science Data (run_08)
Science Data (run_07) Co)60Calibration (Calibration (AmBe)
• Results from 11.2 days unblinded data in Aprile et al., Phys. Rev. Lett. 105, 131302, (2010).
• Data taken in the first half of 2010, blinded region of interest, 100.9 live days
• Results from the blind 100.9 days in Aprile et al., Phys. Rev. Lett. 107, 131302, 2011
XENON100: Data Selection
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Basic quality cuts
Designed to remove noisy events, events with un-physical parameters. Very high acceptance.
• S1 coincidence cut
• S2 threshold cut
• S2 saturation cut
• Signal/Noise cut
Fiducial volume cut
Because of the high stopping power of LXe, fidu-cialization is an extremely effective way of reduc-ing background. Fiducial volume chosen:
• 48 kg super-ellipsoid
Scatter cuts
Designed to remove events with multiple inter-actions (multiple S2s), with delayed coincidences(multiple S1s) or misidentified S1s.
• S1 single peak cut
• S2 single peak cut
• Veto cut
Advanced cuts
Designed to remove events which fail consistencychecks, e.g. mismatch in positions from differentalgorithms, or with S1 PMT patterns not consis-tent with their position in the TPC
• S1 PMT pattern cut
• S2 width consistency cut
• Position reconstruction cut
XENON100: Leff Parametrization
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Energy [keVnr]1 2 3 4 5 6 7 8910 20 30 40 100
Leff
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
Energy [keVnr]1 2 3 4 5 6 7 8910 20 30 40 100
Leff
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35 Arneodo 2000Bernabei 2001Akimov 2002Aprile 2005Chepel 2006Aprile 2009Manzur 2010Plante 2011
• Leff parametrization is an average of the direct fixed angle neutron scattering Leff measurements
• New measurement of Leff at low energies added to the data used to obtain the parametrization
XENON100: Nuclear Recoil Acceptance
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• Keep acceptance high (think discovery)
• Data quality cuts acceptance estimatedfrom AmBe and 60Co calibration data, MCsimulations, and ERs outside the WIMPsearch energy range
• Decided a priori to use Profile Likelihoodapproach and test both background onlyand signal+background hypotheses
• No S2/S1 rejection cut in the Profile Like-lihood approach
• Define a benchmark WIMP region for a par-allel cuts-based analysis
• 99.75% ER rejection line
• S2 threshold
• NR band lower 3-σ
Energy [keVnr]10 20 30 40 50
Acc
epta
nce
0
0.2
0.4
0.6
0.8
1
S1 [PE]5 10 15 20 25 30 35
Energy [keVnr]10 20 30 40 50
/S1)
-ER
mea
nb
(S2
10lo
g
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
99.75% rejection
NR acceptanceσ-3
S1 [PE]2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
mχ ≥ 50GeV
mχ = 10GeV
mχ = 7GeV
XENON100: Nuclear Recoil Acceptance
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WIMP spectrum
3 pe 4 pe
Photoelectron spectrum
Efficiency corrected
• Resolution near threshold is dominated bystatistics in photon detection efficiency.
• For each WIMP mass, convert the energyspectrum to a S1 spectrum in photoelec-trons, apply the S2 acceptance function,convolve the spectrum with a Poisson dis-tribution.
Energy [keVnr]10 20 30 40 50
Acc
epta
nce
0
0.2
0.4
0.6
0.8
1
S1 [PE]5 10 15 20 25 30 35
cS1 [pe]
0 5 10 15 20 25 30
cS
2 [p
e]
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Preliminary
mχ ≥ 50GeV
mχ = 10GeV
mχ = 7GeV
XENON100: Background Prediction
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• Expected background: 48 kg fiducial mass,99.75% electronic recoil rejection, 100.9live days
• Statistical leakage (from electronic recoilevents)
• 1.14 ± 0.48 events, estimated from thenon-blinded electronic recoil band frombackground
• Dominated by 85Kr (Kr concentration∼700 ppt) due to a previous leak
• Anomalous leakage
• 0.56± 0.25 events, estimated using dataand MC from 60Co and background
• Neutron prediction from MC
• 0.11 ± 0.08 events, muon-induced fastneutrons and neutrons from (α, n) reac-tions and spontaneous fission
• Total 1.8± 0.6 events in 100.9 days
Energy [keVnr]10 20 30 40 50
Acc
epta
nce
0
0.2
0.4
0.6
0.8
1
S1 [PE]5 10 15 20 25 30 35
Energy [keVnr]10 20 30 40 50
/S1)
-ER
mea
nb
(S2
10lo
g
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
99.75% rejection
NR acceptanceσ-3
S1 [PE]2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
XENON100: Unblinding
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• 6 events in the signal region after unblinding, inspection reveals 3 are due to electronic noise
• Population of noise events near threshold, leaks into signal region
XENON100: Unblinding
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Energy [keVnr]10 20 30 40 50
/S1)
-ER
mea
nb
(S2
10lo
g
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
S1 [PE]2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
• 6 events in the signal region after unblinding, inspection reveals 3 are due to electronic noise
• Population of noise events near threshold, leaks into signal region
• Remove population with noise post-unblinding cut, 3 candidate WIMP events remain
XENON100: Event Distribution
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Energy [keVnr]10 20 30 40 50
/S1)
-ER
mea
nb
(S2
10lo
g
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
S1 [PE]2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
]2 [cm2Radius0 50 100 150 200 250
z [c
m]
-30
-25
-20
-15
-10
-5
0
Radius [cm]2 4 6 8 10 12 14 15.3
• 3 candidate events clearly inside the 48 kg fiducial volume
• Probability (Poisson) to observe 3 or more events when expecting 1.8± 0.6 is 28%
• Profile Likelihood analysis does not yield a significant signal excess either, background-onlyhypothesis has a p-value of 31%
XENON100: Profile Likelihood Approach
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 27 / 37
• Construct the Likelihood function
L = L1(σ,Nb, ǫs, ǫb,Leff , vesc;mχ)
× L2(ǫs)× L3(ǫb)
× L4(Leff)× L5(vesc)
• Main term contains only one parameter ofinterest, the signal cross-section σ, otherparameters are nuisance parameters andprofiled out
• Additional terms constrain the nuisanceparameters in the main term
• Makes use all observed events in theWIMP search data, no sharp S2/S1 dis-crimination cut, energy distribution
• Allows systematic uncertainties to be in-corporated in a consistent manner
S1 [PE]0 2 4 6 8 10 12 14 16 18 20 22 24
S2
[PE
]0
1000
2000
3000
4000
5000
6000
• More details in
Aprile et al., Phys. Rev. D 84, 052003, 2011
XENON100: Limit
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 28 / 37
]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000
]2W
IMP
-Nuc
leon
Cro
ss S
ectio
n [c
m
-4510
-4410
-4310
-4210
-4110
-4010
-3910
]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000
]2W
IMP
-Nuc
leon
Cro
ss S
ectio
n [c
m
-4510
-4410
-4310
-4210
-4110
-4010
-3910
]2WIMP Mass [GeV/c6 7 8 910 20 30 40 50 100 200 300 400 1000
]2W
IMP
-Nuc
leon
Cro
ss S
ectio
n [c
m
-4510
-4410
-4310
-4210
-4110
-4010
-3910
DAMA/I
DAMA/Na
CoGeNT
CDMS (2010)
CDMS (2011)
EDELWEISS (2011)
XENON10 (S2 only, 2011)
XENON100 (2010)
XENON100 (2011)observed limit (90% CL)
Expected limit of this run:
expectedσ 2 ± expectedσ 1 ±
Buchmueller et al.
Trotta et al.
• Strongest limit to date over a large WIMP mass range, challenges the interpretation ofCoGeNT and DAMA signals as being due to low mass WIMPs
• Results recently published Aprile et al., Phys. Rev. Lett. 107, 131302, 2011
XENON100: Current Data Taking Status
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 29 / 37
• Kr concentration reduced by more than ×5 (∼50% background reduction)
• Improved S2 trigger with lower trigger threshold
• New dark matter run started early 2011, ∼160 live days accumulated
• Much more ER calibration data, already ∼16 live days 60Co and ∼18 live days 232Th
Date [mm/dd]03/01 05/01 07/01 08/31 10/31
Live
Day
s
0
20
40
60
80
100
120
140
160
Science Data (run_10)
Co)60Calibration (Th)232Calibration (
Calibration (AmBe)
XENON1T: Future
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 30 / 37
• 1m3 TPC, 2.4t LXe, 1t fiducial mass
• ×100 background reduction compared toXENON100
• Low radioactivity photosensors
• 10 m water shield
• Currently in design phase, construction 2012
• Approved for construction in Hall B at LNGS
Summary
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 31 / 37
Date [mm/dd]03/01 05/01 07/01 08/31 10/31
Live
Day
s
0
20
40
60
80
100
120
140
160
Science Data (run_10)
Co)60Calibration (Th)232Calibration (
Calibration (AmBe)
• XENON100 background goal achieved, detector is taking dark matter data
• Accumulated 100 days exposure in 2010, 3 events observed with an expectation of 1.8± 0.6
• Set the most stringent limit to date on the WIMP-nucleon spin-independent cross section
• Already ∼160 days exposure accumulated with lower background level and improved triggerthreshold, stay tuned for new results
Extras
XENON100: Position Dependent Corrections
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 33 / 37
Z [mm]
-300-250
-200-150
-100-50
0Radius [mm]
0 20 40 60 80 100 120 140
rela
tive
LCE
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
histEntries 2888Mean x -178.9
Mean y 72.85
RMS x 86.59
RMS y 43.28
histEntries 2888Mean x -178.9
Mean y 72.85
RMS x 86.59
RMS y 43.28
x [mm]-150 -100 -50 0 50 100 150
y [m
m]
-150
-100
-50
0
50
100
150
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
• Corrections from measurements with 137Cs,AmBe (40 keV inelastic), 131mXe (164 keV),with agreement better than 3%.
• S1 rz and S2 xy correction due to spatial de-pendence of the light collection.
• S2 z correction due to finite electron lifetime.
Date [mm/dd/yy]12/31/10 03/02/11 05/02/11 07/02/11 09/01/11
s]µE
lect
ron
Life
time
[
300
350
400
450
500
550
600
eq.]2
Concentration [ppb O
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
New Measurement of Leff : Extracting Leff
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 34 / 37
Time of Flight [ns]10 20 30 40 50 60 70 80 90 100 110
]-1
d-1
Rat
e [e
vts
ns
1
10
210
310
410
Time of Flight [ns]10 20 30 40 50 60 70 80 90 100 110
]-1
d-1
Rat
e [e
vts
ns
1
10
210
310
410
o = 34.5θ 1.0 keV±6.5
Energy [keV]0 2 4 6 8 10 12 14 16 18 20
]-1
d-1
Rat
e [e
vts
keV
1
10
210
310
410
Energy [keV]0 2 4 6 8 10 12 14 16 18 20
]-1
d-1
Rat
e [e
vts
keV
1
10
210
310
410
o = 34.5θ 1.0 keV±6.5
• Transform the MC recoil energy spectrum into a simu-lated scintillation spectrum g using S1 = Ly ·Leff,j ·Er,
with gaussian energy resolution σ = R√Er, PMT gain
fluctuations, and applying trigger efficiency
• Extract the energy dependence of Leff by minimizingthe χ2 between the measured and simulated spectra,h and g
χ2(
Leff,j , Rj
)
=
N∑
i=0
[
hi − gi(
Leff,j , Rj
)]2
σ2
h,i+ σ2
g,i
(
Leff,j , Rj
)
effL0.105 0.110 0.115 0.120 0.125 0.130 0.135 0.140
Res
olut
ion
Par
amet
er R
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
4049
5973
89109
133162
198
o = 34.5θ 1.0 keV±6.5
Scintillation Signal [pe]0 10 20 30 40 50 60 70
]-1
d-1
Rat
e [e
vent
s pe
0
20
40
60
80
100o = 34.5θ
1.0 keV±6.5 = 32.12χ
Uncertainty in Leff
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 35 / 37
σ2
Leff= σ2
Leff ,fit+
( ∂Leff
∂Ly
)2σ2
Ly+
( ∂Leff
∂Enr
)2σ2
Enr
+(
∆Leff
∆ǫ
)2σ2ǫ +
(
∆Leff
∆rg
)2σ2rg
+(
∆Leff
∆rs
)2σ2rs
• The total uncertainty on Leff is computed from
• σLeff ,fit, uncertainty from the fit
• σLy, uncertainty 57Co light yield
• σEnr, spread in nuclear recoil energies
• σǫ, liquid scintillator cut efficiency uncertainty
• σg , neutron generator position uncertainty
• σs, liquid scintillator position uncertainty
• ∂Leff/∂Enr is computed from a logarithmic fit to the measured values
• ∆Leff/∆ǫ, ∆Leff/∆rg , and ∆Leff/∆rs are calculated from MC simulations
• At all energies, the dominant contribution is from σEnrBelow 6.5 keV, the second largest
contribution is from σǫ. At 6.5 keV and above, the second largest contribution is fromσLeff ,fit
XENON100: Anomalous Leakage
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 36 / 37
• Two types of leakage from the ER band, statis-tical leakage and anomalous leakage
• We assume the ER band is Gaussian inlog (S2/S1), fixed discrimination at 99.75%gives the expected statistical leakage
• Events with low non-Gaussian S2/S1 also ingamma calibration data, e.g. 60Co
• One source for those “anomalously leaking”events is multiple scatter events where one ormore scatter occurs in a charge insensitive regionof the detector
• Use the S1 Pattern likelihood cut to removeevents likely due to two energy deposits
• Compute the expected anomalous leakage inbackground using 60Co as reference
GXe
LXe
Eg
Ed
S1
S2
e-e-e-
S11
2
Example Noise Event
Guillaume Plante Exploring Low-Mass Dark Matter Candidates - PITT PACC - November 14-16, 2011 37 / 37
s]µDrift Time [0 2 4 6 8 10 12 14
Am
plitu
de [V
]
0.0
0.1
0.2
0.3
0.4 TPC
s]µDrift Time [-200 -150 -100 -50 0 50 100 150
Am
plitu
de [V
]
0.0
0.2
0.4TPC
-10 -5 0 5 10
0.00
0.01
S1: 3.7 pecS1: 5.6 pe