IDM 2018 - Identification of Dark Matter Conference Brown University, July 23-27, 2018 - CERN Indico
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IDM 2018
Identification of Dark Matter Conference
1
Brown University, July 23-27, 2018
Rare Events Searches
LUX
(TAUP 2017)
Rick Gaitskell (gaitskell@brown.edu)
Co-Spokesperson, LUX Collaboration
Ex-Spokesperson, LZ Collaboration
Particle Astrophysics Group, Brown University, Department of Physics
(Supported by US DOE HEP)
see information at
http://particleastro.brown.edu/
2
http://luxdarkmatter.org
TAUP 170726v2 Gaitskell / Brown University
Taking The Lottery Out of Rare Event Searches
BBC, Nov
3 2014
Gaitskell / Brown University
p-value = 40%
(BG only)
LUX 332 live-day WIMP search run
Open Black Circles - Events outside fiducial cuts
/ surface events
Solid Black - Backgrounds and Candidate
WIMP events expected between red dotted lines
4
Establishing Signal
✿ Most Effective Way to establish sensitivity to WIMP (rare event)
signals of all kinds - is through likelihoods which requires
absolute calibration + limited additional modeling
✿ To realize True Discovery potential requires us to characterize
responses completely
✿ Monolithic detectors really help
✿ (Self) shielding, low bg construction and minimizing intrinsic
contamination to reduce fiducial event rates
✿ Maximize Discrimination of different types of interaction - but
degrades as signals get smaller / lower energies
5
LUX Impact 2013/17 6
✿ LUX First Science Run in 2013
Second Science Run 2014-2016
Full exposure: 47.5 tonne.days
(427 live-days)
✿ Improved Spin-Indep. WIMP Sensitivity by
Factor 20x since state prior to 2013.
Also Neutron Spin-Dep. Sensitivity.
✿ Axion/ALP Search
✿ Full self-consistent models for all
backgrounds events and detector
response
✿ In parallel: Major program improving LXe
ER and NR calibration over wide energy
range (including sub keV) with high
statistics and low systematics.
Allowed significant improvement in
accuracy of Xe response models.
Also clearly establishes sensitivity to 8B
coh. scattering.
✿ LZ: Kim Palladino Tues 15:30
LZ: Christine Ignarra, Tues 15:45
LUX: Rick Gaitskell Wed 14:00
p SPIN DEPENDENT COUPLINGS
LUX - Phys. Rev. Lett. 118, 251302 (2017)
C3F8
p
n
n
7
XENON1T / 1 month exposure
- Anomalous Flat Background
• [arxiv:1705.06655]
• 0.2x10-3 evts/keVee/kg/day -
Very Low ~1/10th of LUX
• ~60 Events in ER band for
1.0 tonne Fiducial Mass
• (Red Point) S1 68 phe
“Anomalous Flat
Background Component”
• Important to understand all
events if discovery potential
is to be realized
• Signal associated with
WIMP + HE Form Factor?
• If background then next
one may appear at lower
Plot Jelle Aalbers / TAUP Talk 2017 energy.
See also Manfred Lindner Thurs. Plenary Talk Gaitskell / Brown University
p-value = 40%
(BG only)
LUX 332 live-day WIMP search run
Open Black Circles - Events outside fiducial cuts
/ surface events
Solid Black - Backgrounds and Candidate
WIMP events expected between red dotted lines
9
Estimation of Backgrounds
✿ Perform a full likelihood analysis
for all S1,S2 signal space, so
these numbers are simply to give
you a sense of the relative
contributions
✿ Bulk volume, but leakage at all
energies
✿ Low-energy, but confined to the
edge of our fiducial volume
❀ Our likelihood analysis includes
position information, so these
events have low WIMP(signal)
likelihood
✿ In the bulk volume, low- energy,
in the NR band
10Low Energy Electron Recoil (ER) Response using in situ 3H
•Very High Stats / High Accuracy ER Calibrations
◆Tritium provides very high statistics electron recoil calibration (>>103 events/phe)
Physical Review D 93 (2016), 072009
Dispersed tritium calibration
In situ measurement of ER response to low energies
Tritiated methane
Log(S2/S1) vs S1
3H
1H
1H
1H
Dark Matter Searches 11 Rick Gaitskell, Brown University, LUX / LZ / DOEXenon-127 (Decaying Cosmogenic) EC Events in Data Scatter plot of 127Xe events with area of first vertex S2 Fig. - X-rays’ ER charge spectrum versus are of second vertex S2; “First Vertex” is the first S2 ordered by drift time Dongqing Huang - Brown University, LUX 12
LUX Xenon-127 Qy along with Tritium and NEST v98
Preliminary
Dongqing Huang - Brown University, LUX 13top hit pattern:
x-y localization
Δt
S2[1y’] S2[2y’]
Monochromatic
2.5 MeV neutrons S1[1y’] Δt : z’ separation
e e- -e- -
ee
-
θ S1[2y’]
ee-e- -e- -
ee-e-e- -e
θ : energy calculation
Samuel Chan, Carlos Faham for the LUX CollaborationNeutron Beam (ADELPHI in Active Region
0 0
1.5
1
50 50
1
0.5
log10(cts / 6.4 µs / 1.0 cm)
log10(cts / 6.4 µs / 1.0 cm)
100 100
Drift time [µs]
Drift time [µs]
0.5
150 150 0
0
200 200
-0.5
-0.5
250 250
-1 -1
300 300
0 10 20 30 40 50 -20 -10 0 10 20
′ ′
y distance into LXe [cm] x perpendicular to neutron beam [cm]
• Neutron generator/beam pipe assembly aligned 16 cm (adjustable) below liquid surface in
LUX active region to maximize usable single / double scatter events
• Beam leveled to ~1 degree
• 107 live hours of neutron tube data used for analysis
• Historically, NR calibrations have significant systematics associated with neutrons scattering
in passive material.
arXiv:1608.05309
Dongqing Huang - Brown University, LUX 15
arXiv:1608.05381Surprisingly…. Lindhard All The Way Down
NEST used to provide model fits
LUX Dark Matter Experiment / Sanford Lab Rick Gaitskell (Brown)LUX Dark Matter Experiment / Sanford Lab Rick Gaitskell (Brown)
Expected Neutrino Signals (and then Backgrounds)
•Neutrino-nucleus coherent scattering (solar) could be observed in Xe TPC
⌫ ⌫
Z
N
⌫+N !⌫+N N
+08
10 2 -45 2
+12 pp pp WIMP signal: mχ = 6 GeV/c , σχ-n = 4.4x10 cm
10 pp
pep
pep
hep 10+06
Neutrino Flux [cm-2.s-1.MeV-1]
10+10
hep
Event rate [(ton.year.keV) ]
-1
7Be384.3keV 7Be384.3keV
7Be861.3keV
7Be861.3keV
10+08
8B
8B 8B 10+04 13N
13N 15O
10+06 15O 17F
dsnbflux8
17F 10+02 dsnbflux5
dsnbflux8 dsnbflux3
10+04 dsnbflux5 AtmNue
AtmNuebar
+02
dsnbflux3 10+00 AtmNumu
10 DSNB AtmNue AtmNumubar
AtmNuebar total
10+00 atm AtmNumu 10-02
AtmNumubar
10-02
10-04
10-04
0.1 1 10 100 1000 0.001 0.01 0.1 1 10
Neutrino Energy [MeV] Recoil energy [keV]
F. Ruppin et al., 1408.3581 Laura Baudis et al., JCAP01 (2014) 044
FIG. 1: Left: Relevant neutrino fluxes to the background of direct dark matter detection experiments: Solar, atmosphe
i↵use supernovae [22–24]. Right: Neutrino background event rates for a germanium based detector. The black das
orresponds to the sum of the neutrino induced nuclear recoil event rates. Also shown is the similarity between the ev
2 45 2 8
rom
Dark aMatter
6 GeV/c
SearchesWIMP with a SI cross section on the nucleon
18 of 4.4 ⇥ 10 cm (black
Rick solid
Gaitskell, line)
Brown and the
University, LUX /B
LZneutrin
/ DOE
ate.83m
CALIBRATIONS: KR Manuscript
in preparation
83mKr; drift time 4 - 8 μs
▪ Krypton-83m is injected regularly into
the detector to characterize detector
response and monitor stability
▪ Mixes homogenously with LXe
▪ Used for:
▪ Position reconstruction
▪ Electron lifetime
▪ S1 & S2 position corrections
▪ Electric field modeling
▪ Decays by emitting 2 internal
conversion electrons
▪ 32.2 keV + 9.4 keV (T1/2 = 154 ns)
▪ Monoenergetic for our standard analysis
▪ T1/2 = 1.83 h
19PRL 118, 261301 (2017)
Axions & ALPs in LUX WS2013
Cross section for the axio-electric effect: Signal models
-- Expected energy spectrum from a
massless solar axion assuming gAe = 10-12 Massless solar axion
_ LUX expected solar axion energy
spectrum, as modeled with NEST
Mass 10 keV/c2 galactic ALP
Dark Matter Searches 20 Rick Gaitskell, Brown University, LUX / LZ / DOELUX Axion Search - Multiparameter Modeling
•The number of counts in each background component is based on independent assay results and
measurements, with no additional scaling.
LUX WS2013 Run
127Xe
85Kr+Rn-daughters
γ- rays
γ- rays additional from bottom
Dark Matter Searches 21 Rick Gaitskell, Brown University, LUX / LZ / DOEPRL 118, 261301 (2017)
Axions & ALPs in LUX WS2013
Coupling between solar axions and electrons Coupling between galactic ALPs and electrons
LUX 2013 excludes gAe > 3.5x10-12 (90% CL)
LUX 2013 excludes gAe > 4.2x10-13 (90% CL)
mA > 0.12 eV/c2 (DFSZ model)
across the range 1-16 keV/c2 in ALP mass
mA > 36.6 eV/c2 (KSVZ model)
ANALYSIS USING FULL LUX DATA WS 2014-16 IS ON-GOING
Dark Matter Searches 22 Rick Gaitskell, Brown University, LUX / LZ / DOEIn answer to another fundamental question: “Where to Dark Matter
Experiment go when they have finished searching ?…”
The Museum …
23… or they give birth to an instrument with 50x the sensitivity … LZ
24LZ Detector - 10 tonnes Xe
Replacing LUX at the Sanford Underground Research Facility (SURF)
Technical Design Report arXiv:1703.09144 260 Authors, 400 Pages
DOE Project, ConstrucOon Fully Underway > CD4
Commissioning April 2020, Physics in 2021, Goal 1000 days
Baseline WIMP sensiOvity @ 40 GeV is 2.3 x 10-48 cm2
Other promising science targets:
ββ0n, pp & 8B solar neutrinos,
coherent neutrino sca_ering
✿ LZ: Kim Palladino Tues 15:30
25
LZ: Christine Ignarra, Tues 15:45
LUX: Rick Gaitskell Wed 14:00Conclusion
✿ Direct in-situ calibrations have been used in LUX to
unambiguously establish response of entire target volume to a
wide range of interactions
✿ Established exciton response of Xe over wide range of energies
using very high event statistics
✿ Must also be concerned with variations with position (high stats /
appropriate sources)
✿ Eliminate other possible systematics such as DAQ/Electronics/
Code glitches
✿ Enables high confidence in Rare Event Searches
Minimize FALSE POSITIVES / MAXIMIZE SIGNAL IDENTIFICATION
✿ LUX Continues to Exploit Data for additional rare event searches
which will be reported in 2017/18
26IDM 2018
Identification of Dark Matter Conference
27
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