Searching for Dark Matter with Liquid Xenon

Searching for dark matter with liquid xenon

Masaki Yamashita Masaki Yamashita Kamioka observatory, ICRR, The University of Tokyo Contents

•Introduction to direct dark matter search •Search by two phase Xe detector (WIMP) •Search by single phase Xe detector (Non-WIMP) •Future prospects

Masaki Yamashita 2 History of Dark Matter Mystery

www.nasa.gov

F. Zwicky Vera Cooper Rubin •1933 F. Zwicky Factor 400 of Discrepancy of mass estimation via Doppler Redshift of 8 galaxies in Coma Cluster. ー＞”Dark Matter” •1970’ Progress on radio astronomy. Rotation curve for the spiral galaxy via 21cm emission from neutral hydrogen gas by Vera Rubin and others. 1990’ CMB observation (COBE, WMAP, Planck)

ESA/Planck © M33 Image: NOAO, AURA, NSF, T.A.Rector. Masaki Yamashita Approaches to look for dark matter χ χ

Colliders - indirect SM SM LHC, ILC ... SK, CTA, AMS02 ...

3 ρdm = 0.3 GeV/cm

a few dark matter particle around us ! direct only direct search can tell us about dark XMASS, XENON, LZ … matter around us. Masaki Yamashita WIMP(dark matter candidate) Dark Matter is required to be • Neutral ➡ can not see ... • Non-baryonic astrophysics ➡ weakly interacting • Cold (non-relativistic) ➡ structure formation favorite candidate predicted by

SUSY particle physics M. Blanton and the SDSS ⇒ One of the favored scenario beyond standard model: The lightest SUSY particle is stable and likely becomes a dark matter candidate Linear combination of SUSY particles 0 B! W! H! 0 H! 0 χ1 = α1 + α 2 + α 3 u + α 4 d Masaki Yamashita How to detect WIMP ? a needle in a haystack

beta above ground without shield 106 counts/kg/day

neutron WIMP!

alpha neutrino WIMP event gamma <10-6 counts/kg/day

Effort to reduce radioactive background in the under ground laboratory

Masaki Yamashita Detection principle WIMPs elastically scatter target nuclei

WIMP Erecoil ~ <100 keV

χ + N → χ + N nuclei WIMP θ For example, assuming θ Mw = 100 GeV/c2 , MT = 100 GeV/c2 , r = 1 WIMP velocity: v~ 0.75 X 10-3 = 220 km/sec 1 data E = M 2 c 2 light R 2 W 2 -3 2 heavy = 1/2 x 100 x GeV/c (0.75 x 10 ) c rate = 30 keV energy Masaki Yamashita Diferential Rate Measuring the deposited energy due to elastic scattered nuclei by WIMP. Expected spectrum: WIMP

2 dR R0F (ER) k0 1 vmax 1 3 ! f v, vE d v dER = E0r k 2πv0 vmin v ( )

motion dynamics

R0: Event rate @ F: Form Factor V :velocity onto target, zero momentum (depends on atomic VE: Earth’s motion around the Sun transfer nuclei） Maxwellian distribution for DM velocity is assumed. Spin independent 2 2 µT σ0 = A 2 σχ−p µp

Masaki Yamashita 8 Differential spectrum 5GeV Mass 100GeV Mass 2 5GeV:1e-41cm2 100GeV:1e-45cm 10 Xe Xe I I 10−3 Ge Xe Ge 1 I Na Na Integral[events/day/kg] 10−1 Integral[events/day/kg] Ge 10−4 Na 10−2

10−5 10−3 Ge Xe I Na 10−4 0 2 4 6 8 10 10−6 Energy[keVnr] 0 10 20 30 40 50 Energy[keVnr]

Energy threshold is important Detector mass is important for low mass WIMPs. for high mass WIMPs.

Masaki Yamashita 9 2 30 years

Evolution of the WIMP-Nucleon sSI Ge 10-40 ‡ ‡ ‡ 10-41 ‡ Cryogenic ÊÊÊÊ 10-42 ÊÚ WIMP

2 -43 Ê c

ê 10 Ú Xe10Ú ÊÚÊ DarkSide-50 10-44 Ú GeV Xe100 Ì -45 Ú Á 10 LUX Ì 50 Ì a 10-46 100GeV Noble liquid Û ı

for LUX -47 Û Á D 10

2 Ì 10-48 Û @ cm

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s 10 Coherent Neutrino Scattering 1985 1990 1995 2000 2005 2010 2015 2020 2025 Year from arXiv:1310.8327v1

Figure 1. History and projected evolution with time of spin-independent WIMP-nucleonMasaki Yamashita 10 cross section limits for a 50 GeV WIMP. The shapes correspond to technologies: cryogenic solid state (blue circles), crystal detectors (purple squares), liquid argon (brown diamonds), liquid xenon (green triangles), and threshold detectors (orange inverted triangle). Below the yellow dashed line, WIMP sensitivity is limited by coherent neutrino-nucleus scattering.

of material screening, radiopure passive shielding and active veto detectors, has resulted in projected background levels of 1 event/ton of target mass/year. Innovations in all of these areas are continuing, and promise to increase the⇠ rate of progress in the next two decades. Ultimately, direct detection experiments will start to see signals from coherent scattering of solar, atmospheric and di↵use supernova neutrinos. Although interesting in their own right, these neutrino signals will eventually require background subtraction or directional capability in WIMP direct detection detectors to separate them from the dark matter signals.

A Roadmap for Direct Detection Discovery Search for WIMPS over a wide mass range (1 GeV to 100 TeV), with at least an order of magnitude improvement in sensitivity in each generation, until we encounter the coherent neutrino scattering signal that will arise from solar, atmospheric and supernova neutrinos Conﬁrmation Check any evidence for WIMP signals using experiments with complementary technologies, and also with an experiment using the original target material, but having better sensitivity Study

If a signal is conﬁrmed, study it with multiple technologies in order to extract maximal information about WIMP properties R&D Maintain a robust detector R&D program on technologies that can enable discovery, conﬁrmation and study of WIMPs.

Community Planning Study: Snowmass 2013 Why Liquid Xenon ?

High Atomic mass Xe (A~131) good for SI case (cross section ∝ A2)

Odd Isotope (Nat. abun: 48%, 129,131) with large SD enhancement factors High atomic number (Z=54) and density (ρ=3g/cc): compact, ﬂexible and large mass detector. High photon yield (~ 46000 UV photons/MeV at zero ﬁeld) Easy to purify for both electro-negative and radioactive purity by recirculating Xe with getter for electro-negative Distillation for Kr removal No long lifetime radioisotope. (127Xe, 36 days)

Masaki Yamashita 11 Liquid Xenon

Aluminum block floating in liquid xenon (picture)

boiling point −108℃

density 3g/cc

KEK, Haruyama Picture by Tom Haruyama, KEK Al(2.7g/cc）is block ﬂoating in liquid xenon

Masaki Yamashita 12 Dark Matter Searches

LXe detector for dark matter XENON100@LNGS • S1: direct scintillation light • S2: secondary light (ionization) Two-phase Xe TPC PMT array

Gas Xe S2 Indirect search: AMS, Fermi…Eg Liquid Xe • strong particle ID by S2/S1 - e • ﬁne spacial resolution (< 1mm) Collider search: LHC (Atlas and CMS) S1 Ed Direct search: XENON, LUX,Panda-X, CDMS, DAMA, CoGeNT… PMT array 3

XMASS-I@Kamioka Single-phase LXe scintillator • Easy for scalability • High light yield (4π PMT) S1

Liquid Xe

PMT array Masaki Yamashita 13 PHYSICAL REVIEW LETTERS week ending PRL 97, 081302 (2006) 25 AUGUST 2006

PMT) is estimated from Monte Carlo calculations to be the neutron data there are distributions of events from more than 50%, and uniform to within 5%. An internal blue neutron inelastic scattering on 129Xe, giving 40 keV gam- light-emitting diode (LED) is used to calibrate and monitor mas, and from inelastic scattering on 131Xe and 19F con- the gain of the two PMTs. The Case detector uses a single tained in Teflon, giving higher energy gammas. By PMT in the gas, with an S1 light collection efficiency of contrast, only the electron recoil band is seen when the 16%. The PMT gain is monitored using the S1 light from detectors are exposed to gammas. At low energies, the 5.3 MeV alphas from a source described below. The PMT difference in shape of the elastic nuclear recoil bands for signals were digitized with multiple analog-to-digital con- the two data sets is due to the different thresholds and light verters sampling at 5 MHz–1 GHz. The trigger threshold sensitivities of the two detectors. for the Case detector was 4.5 electrons for the S2 signal, Both detectors used the same method to calibrate the and the single photoelectron (pe) acceptance for S1 was drift-field-dependent S1 and S2 signals. The energy of 50%. For the Columbia detector the trigger was either the electron recoils, Ee, is based on S1 assuming a linear coincidence of the S1 signals from the two PMTs (at the scaling from the signals of 122 keV gammas from 57Co. level of a few photoelectron) or the S1 signal from the PMT The energy of nuclear recoils, E , is then given by E r r in the liquid (at the level of 6 spe). EeLeffSe=Sr, where Leff is the effective Lindhard factor Both detectors are housed in temperature-controlled [13] that relates the scintillation yields of nuclear and liquid nitrogen-cooled cold-finger cryostats. The detectors electron recoils at zero field. Sr and Se are the fractions were operated with Xe vapor pressures between 2.0 and of scintillation light at a given electric field, E,relativeto 2.8 atm, stabilized to better than 1% during data taking. the scintillation light at zero field for nuclear and electron The Case detector also uses a triple parallel-plate capacitor recoils, respectively, and are equal to S E =S0 for the system [10] toBrief align the liquid history surface with the grids of and Tworespective particlesphase in Fig. 3. RecentXe measurements gamma at monitor the level and stability of the liquid surface, which Columbia University give Leff for nuclear recoils with was stable to within 20 m over two months. The xenon energy as low as 10.4 keV and S for 56.5 keV recoils

r l l a a was puriﬁed with a high temperature commercial getter to [14]. Other experiments [15–18] haven measured atn o Leff o i i • 1973 Two phase liquid noble gas detector B.A. t t 2 2 r 10 r 10 minimize trapping of the drifting electrons by electroneg- higher and lower energies. The Columbiao and other data,o p p

o 0:169 o ative impurities.Dolgoshein The Columbia detector et al. accomplished (JINR, p167) this except [17], were parameterized by Lr eff 0:0984Er .r p p with a continuous gas circulation system developed for the Because the Columbia-measured value of Sr is close to first XENON• prototype1990’s [11R&D,12], whileby ICARUS the Case detector group unity,at CERN as seen in Fig. 3, we assume for simplicity that it has used a similar recirculation system only at the start of its no energy dependence. Following convention, nuclear re- two-month run. coil energies calculated in this way are denoted ‘‘keVr’’, The detectors• ~ were2000 calibrated Double with externalphase gamma Xe in ray Japan.and electron S2 recoil energies basedS2 on the10 linear S1 scale are 10 sources, includingobservation57Co, 133Ba, and from137Cs .nuclear The Case detec- recoil.denoted First ‘‘keVee’’.underground In the Case and Columbia detectors, the tor also had an internal 210Po source deposited on the center S1 calibration gives, respectively, 1:5 penuclear=keVee and recoil of the cathode plate,run providing(XMASS). 5.3 MeValpha particles. For 5 pe=keVee at zero electric field, which correspond to neutron data, external 5 Ci AmBe (Columbia) and 25 Ci 0:28 pe=keVr and 1 pe=keVr for 56 keVr nuclear recoils. 252 Cf (Case)• sources2006 were Quantitative used. study S2 signal.(PartCalibration of of the S2 ionization signal1 is also based on 1 57 0 50 100 150 0 50 100 150 Figures 1 andXENON2 show the detectors’group) responses and particle to neutron Co 122 keV gammas, but, as there is no publisheddirec datat(keV) of direct(keV) and low energy Compton scattering events. The logarithm charge yield at these low energies, separate direct charge Am-Be of the ratio S2•=S20071 is plotted First as aPhysics function of Result nuclear recoil of XENON10calibrations in the liquid phase were made in both detec- energy. In both detectors, the elastic nuclear recoil band is tors. The amount of S2 light perM. electron Yamashita is a function et al. Astropart. of Phys. 2003, 79 clearly separated from the band of electron recoil events. In gas pressure and electric field in the gas phase [4], with the ….

PRL 97, 081302 (2006) log10(S2/S1)

Masaki Yamashita 14 FIG. 1 (color). Columbia detector response to AmBe neutron and 137Cs gamma sources, at 2:0 kV=cm drift ﬁeld. 081302-2 XENON10 Spin Independent (2008)

PRL 100, 021303 (2008) 18

3.5 1 3 0.5 Calibration 2.5 S1) 0 /

(S2 2 (S2/S1) −0.5 10 10 1.5 Log

log −1 1 ∆ ~99.5% 137Cs (662 keV gamma) 137 AmBe (neutron) −1.5 Cs (662 keV gamma) 0.5 AmBe (neutron) 0 2 4 6 8 10 12 14 16 18 20 BG rejection WIMP ROI −2 S1 [keVee] (2.2 p.e./keVee) 0 2 4 6 8 10 12 14 16 18 20 S1 [keVee] (2.2 p.e./keVee) 4 FIG. 31: (Color online) The electronic and nuclear recoil whilebands the shownS1signalfromanormaleventintheactivevol- in Log10(S2/S1) vs. S1 space. FIG. 32: (Color online)The bands in figure 31 have been ume is distributed more evenly over the PMTs (smaller transformed to show the distance in Log10(S2/S1) space from the ER band center, giving the new discrimination parameter, S1RMS). A large fraction of events that leaked into Log10(S2/S1). The vertical lines indicate the WIMP region the WIMP-signal window are of this type of background of interest (ROI). andthis could range be are removed dominated by by the recombination cuts discussed fluctuations, above. The cutuntil acceptance the lowestεc energiesfor single-scatter where uncorrelated nuclear recoil statistical events, basedfluctuations on AmBe take fast over. neutron The widthcalibration of the data, electronic is listed re- in Tablecoil band I. is very important for gamma rejection because mean and sigma from the NR band Gauss fits, respec- the two bands overlap. Due mainly to the non-uniform tively. The Gauss fits were performed only to define the S1 response at di↵erent locations in the fiducial region, window bounds;ROI the NR acceptance, Anr, was calculated applying spatially-dependent corrections to S1 based on by counting the number of AmBe events that fall within the 131mXe calibration (see section VI A 3) improves the this window, for each energy bin. overall S1 resolution and thus helps to reduce the vari- ⊿ Log(S2/S1) ance of the bands. Data with the AmBe neutron source 60 were taken on December 1, 2006 for approximately 12 Nuclear Recoils (AmBe) hours, accumulating a total of about 260,000 events. The Electronic Recoils (137Cs) 50 WIMP Acceptance Window energy dependence of both bands makes it dicult to pre- FIG. 4: ResultsEnergy from 58.6 live-days of WIMP-searchkeVr in the cisely measure the discrimination power in the absence of 5.4 kg LXe target. The WIMP search window was defined extraordinarily large calibration datasets. In an e↵ort to between40 the two vertical lines (4.5 to 26.9 keV nuclear recoil remove this energy-dependence, a one-dimensional trans- equivalent energy) and blue lines (about 50% nuclear recoil formation that “flattens” the ER band is applied to all acceptance).30 data. The ER band is broken up into 1 keVee-wide, ver- Counts tical slices in S1. For each, a Gauss fit is applied to the 20 Log10(S2/S1) spectrum. The mean of each fit now rep- bin in the analysis of the WIMP search data is currently resents the center of the ER band in that particular bin. limited by available calibration statistics. To set conser- A high-order polynomial is fit to the Gauss means, which vative10 limits on WIMP-nucleon cross sections, we con- provides an analytic form for the ER band centroid as a sider all ten observed events, with no background sub- function of S1, and is subtracted from every data point in traction.0 Figure 5 shows the 90% C.L. upper limits on both bands. This procedure flattens the ER band (and −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 WIMP-nucleon cross sectionsLog (S2/S1) as a function of WIMP to a large extent, the NR band as well), and introduces 10 FIG. 3: Position distribution of events in the 4.5 to 26.9 keV mass calculated using the “maximum gap” method in a new parameter, Log10(S2/S1), which represents the nuclear recoil energy window, from the 58.6 live-days of FIG.[24] 33: and (Color using online) the standard Distributions assumptions of Log for10(S2 the/S1) galactic for WIMP-searchdistance from data. the ER (+) centroid Events in in the Log WIMP-signal10(S2/S1) space. region nuclearhalo [25]. and electronic The current recoils work in the gives range a 13.4–17.2WIMP-nucleon keVr. The cross − beforeFigure the 32 software shows the cuts. bands (⊕)EventsremainingintheWIMP- in Log10(S2/S1) space. WIMPsection acceptance 90% C.L. window upper in limit this particular of 8.8 × energy10 44 rangecm2 isat a searchAlthough region the after energy the software dependence cuts. The of the solid ER lines band indic cen-ate definedWIMP by mass the blue, of 100 shaded GeV/ rectanglec2,afactorof2.3lowerthan which is between µ and the fiducial volume, corresponding to a mass of 5.4 kg. µ 3 of the NR band. troid has been removed, the NR band centroid and width the previously best published limit [26]. For a WIMP still change with energy. Again, the flattened bands are mass of 30 GeV/c2,thelimitis4.5×10−44 cm2.Wehave brokenThe 3D up position into vertical sensitivity S1 slices, of the only XENON10 this time detec-more used a constant 19% nuclear recoil scintillation efficiency torcoarse gives binning additional is used—seven background binssuppression in the with WIMP fiducial en- toThe derive shape the of limit. the TheLog result10(S2/ variesS1) fluctuations by ±20%(± in35%) the for volumeergy region cuts of [22]. interest Due to (ROI)—in the high stoppingorder to maximize power of LXe, the ERmass band 100 (30)are “empirically” GeV/c2 WIMPs Gaussian; when varying that theis, withnuclear thestatistics background in each rate slice, in and the a central Gauss partfit is of applied the detector to the therecoil statistics scintillation available, efficiency theyL appeareff over consistent a range withof 12% isLog lower10(S2 (0.6/S1) events/keVee/kg/day) spectrum of both bands. than One that such near slice the is ato Gaussian 29%, corresponding distribution. to the As lowest previously energy stated, data points the edgesshown (3 in events/keVee/kg/day). Figure 33, for the range 13.4–17.2 The fiducial keVr volume (1 keVr is measuredLog10(S2/ inS1) [20] spectrum and in [21]. is dominated The measured by recombina- single scatter defined= 1.1 pe, to according be within to 15 [11]) to 65 ofµ nuclears(about9.3cmin recoil energy.Z The,out tionnuclear fluctuations, recoil spectrum which are from poorly the understood, AmBe calibration and thus data ofWIMP the total acceptance drift distance window of is defined 15 cm) to drift lie intime the window range moreis consistent cannot be at said the 20% in the level absence with of the a Monte larger calibra-Carlo pre- (µ 3) < Log (S2/S1) <µ,whereµ and are the tion dataset. We calculate the predicted ER rejection in and with a radius10 less than 8 cm (out of 10 cm) in XY, dicted spectrum, both in absolute event rate and spectral corresponding to a total mass of 5.4 kg (Fig. 3) [23]. The shape, when Leff is taken as 19% over the energy range cut in Z also removes many anomalous events due to the of interest. LXe around the bottom PMTs, where they happen more Although we treated all 10 events as WIMP candi- frequently compared to the top part of the detector. dates in calculating this limit, none of the events are After all the cuts were finalized for the energy window likely WIMP interactions. ∆Log10(S2/S1) values for 5 of interest, we analyzed the 58.6 live-days of WIMP- events (compared with 7 predicted) are statistically con- search data. From a total of about 1800 events, ten sistent with the electron recoil band. These are labeled events were observed in the WIMP search window after as No.’s 3, 4, 5, 7, 9 in Fig. 3 and Fig. 4. As shown in cuts (Fig. 4). We expect about seven statistical leakage Table I these leakage events are more likely to occur at events (see Table I) by assuming that the ∆Log10(S2/S1) higher energies. Aposterioriinspection of event No. 1 distribution from electron recoils is purely Gaussian, shows that the S1coincidencerequirementismetbe- an assumption which is statistically consistent with the cause of a noise glitch. Event No.’s 2, 6, 8, 10 are not available calibration data. However, the uncertainty of favored as evidence for WIMPs for 3 main reasons. First, the estimated number of leakage events for each energy they are all clustered in the lower part of the fiducial 08/13/2007 02:02 AM

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Weather Tech Life This? Sports What's Money XENON10Travel Spin Independent case Links for Gadgets Advertising News Shop Related Quote Home Dan Vergano Auto Insurance Auto Ins HolladayPRL 100, 021303 (2008) The Hartford No Hassle April AARP & On Fast, ?4 Save $303 & Space Over 50 » Science | Print | tter | Save With… ma E-mail Technologywhile the S1signalfromanormaleventintheactivevol- dark aarp.thehartford.com ume is distributed moret evenlyec overt the PMTs (smaller Payment on Dr.… o de Press Mortgage Featured S1RMS).n At large fraction of events that leaked into the New rates. s o Associated around Calculate mortgage e ithe WIMP-signal Recommend window are of this type of background Chang, low Rac | By Alicia laboratories See today's | Comment the invisible 54m agoand could be removed by the cuts discussed above. The deep underground matter, apart. lowermybills.com Updated — In dark cut acceptance~10kgεc for single-scatter nuclear recoil events, on to spot from spinning Advertisement LOS ANGELES race is galaxies based on AmBe fast neutron calibration data, high is listed-tech in to keep of globe, a believed solve one Table I. glue that's would cosmic dark matter for the of a shoo-in the nature and be discovers Whoever mysteries exercise. of greatest just a brainy science's than better understanding modern Yet it's more with a help reveal Prize. — along — could Nobel dark matter dark energy Deciphering force⊿ Log(S2/S1) called mysterious another up of the universe. have turned the fate matter research hypothetical dozen USA Today: for theFIG. 4: Results2007/08/02 someEnergy from 58.6 two live-days of tunnel WIMP-searchkeVr in the hunts deterred mines and Previous has5.4 not kg LXe target. of Theidled WIMP search window was defined AP but that between darkness the two vertical lines (4.5 to 26.9 keV nuclear recoil Elena Aprile, nothing,Researchers the use high-tech By plumbingequivalent energy) and blue lines (about 50% nuclear recoil teams from glimpse. than a fleetingacceptance). powerful Enlarge working machines for to detect are more to scientist in shafts today so far a research Detector machines has failed Yamashita, the XENON10 detecting the best bigger Masaki of lab at Columbia mysterious-matter dark even matternow building Dr. final assembly Dark but are during the of the Astrophysics generations,bin in the analysis teams of the WIMP search data is currently room" stuff. Many this? "clean York. previous of thelimited by available calibration statistics. To set conser- What's the in New a whiff University catch vative limits on WIMP-nucleon cross sections,theoretical we con- the hunt. of Technology to aid in sider all ten observed Institute events, with no background sub- features a California to happen." E-mail novel technologies Carroll,traction. Figure 5 shows the 90% C.L. upper limits on e-newsletter toying with said Sean WIMP-nucleon some breakthroughs cross sections as a function of WIMP newsletters free Tech inbox. or search," good for E-mail our in your detectors dark matter looking mass calculated using the “maximum gap” method in to receive the day FIG. 3: Position age distribution of of events in the "It's 4.5 to 26.9 keV | Detector exotic Sign up news of golden experiments. [24] and using the standard assumptions of tiny, for the galactic the top nuclear in the recoil energyrole in window, the from the 58.6 live-days of | Astrophysics made up the get "We're has no University that it's of and WIMP-search who data. (+) Events in the | WIMP-signal Columbia region halo [25]. The theory current is work gives up a WIMP-nucleon a quarter cross physicist ⊕ to make × −44 of its2 before the software cuts.IN: (Astronomers)EventsremainingintheWIMP- Thesection prevailing 90% C.L. thought upper limit of 8.8 because10 cm at a matter. matter, 2 it exists E-mail search regionSTORIES after the software cuts. The solid dark lines indicate ago.WIMP Dark mass of 100 GeV/ knowc ,afactorof2.3lowerthan FIND MORE dark about years Astronomers the fiducial volume, correspondingstill in the to a mass of 5.4 billion kg. the heat. previously best published limit [26]. For a WIMP Text are 13.7 light or − HTML Bang some give off 2 × 44 theoretical2 admittedly the Big doesn't mass of 30 GeV/c ,thelimitis4.5 10 forcm .Wehave Select one: Scientists from it searching alerts happens The left 3D over position sensitivityname because of the XENON10 detec- used a constant 19% nuclear are recoil scintillation efficiency E-mail as it particles gets its galaxies. experiments candidate. news your inbox tor gives mass, additional background stars suppressionand with fiducial toit derive is. Most the limit. The result-matter varies by ±20%(±35%) for Breaking in with what dark2 news universe's -war leading nucleus breaking this? volume cuts tug [22].-of Due to the high stopping powerknowing of LXe, mass — 100 the (30) GeV/c WIMPs when varying atomic the nuclear Get What's far cry from particles hits the gravitationalthe background rate in the central is a part of the detector recoil scintillation efficiency WIMPLeff over a range ofwith 12% exists massive when a interfering is lower (0.6 dark events/keVee/kg/day) matter interacting than that near the to 29%, moment corresponding to the rays lowest from energy data points that — or weakly the rare cosmic Advertiser Knowingedges (3 events/keVee/kg/day). WIMPS The fiducial volume is for measured to in prevent [20] and in [21]. The measured single scatter Featured called are all waiting ground particlesdefined to be within 15 to 65 µs(about9.3cminZrun,out belownuclear recoil spectrum from the AmBe calibrationneedle data in Pheromones: -built machines have to have a Athena of the total drift custom distance of 15 cm) drift time window is consistent at the 20% level with "You the Monte Carlo pre- Get discoverer's Experiments up this way: looking Theand underground with a radius less thanrecoil. 8 cm (out of 10 cm) in XY, dicted spectrum, sums both it in absolute event event rateyou're and spectral Pheromone men and an elastic England out the for andcorresponding causes to a total mass of 5.4 kg (Fig. 3) [23]. The shape, in when L is to taken pull as 19% over the energy range formulas romance University technologyeff increase results. of Sheffield better women Photo cutthe in Z also removes many anomalous Spooner events due toYou the needof interest. England, Click Neil the hay. Canada, your life. LXe around the researcher bottom PMTs, where remove they happen more Although we treated all 10 events in as WIMP candi- gold in science. matter trying to in caverns Homestake the frequentlyDark compared you're to the top part of the detector. dates in calculating and this limit, none defunct of the events than are to read and in Minnesota chose the — bigger aAfter haystack all the cuts rubbish." were finalized for the energy window iron minelikely WIMP interactions. ∆Log10( Sworld2/S1) values for 5 www.athenainstitute.com reject the an idled Foundation in the offor interest, and we analyzed the 58.6 live-days in of WIMP- events Science (compared with of its 7 kind predicted) are statistically con- are humming National labs search data. From a total of about 1800month, events, the ten sistentand deepest with the electron recoil band. These are labeled experiments Last largest events were observed inand the Russia. WIMP search window of the after as No.’s 3, 4, 5, 7, 9 in Fig. 3 and Fig. 4. As shown in Subterranean Japan site of one cuts (Fig. 4). Italy, We expect aboutto be the seven statistical ground. leakage Table I these leakage events best. are more likely to occur at France, Dakota below works silicon events (see in TableSouth I) by assuming stacked that the ∆Log10(S2/S1) higher technology energies. Aposterioriinspection uses of ultracold event No. 1 mine Buildings over which search, Newer distribution from State electron recoils is purely Gaussian, spar shows that the S1coincidencerequirementismetbe- matter collision. six Empire physicists dark a WIMP an assumption which is statistically and consistent with the cause for ofcryogenic a noise glitch. Event of No.’s 2, 6, 8, 10 chambers. are not is cutthroat CDMS telltale vibrations liquid bubble available competition calibration data. However, the uncertainty called of favored sift as out evidence for WIMPs for 3 main reasons. First, The years, puck to like superheated Juan the estimated number of leakage past events several for eacha energyhockey they are all clustered in the lower part of the fiducialsaid for the size of technologies limitations," front-runner each the or emerging quirks and The crystals as xenon have their germanium gas such All of them COUPP. and use noble team called or detector. part of a contraptions experiment and matter of Chicago dark Ahlen of no perfect at the University Steve "There's physicist said particle check. find anything," Brandeis Collar, a a reality not and be in for you may of Technology location. they may you build, Institute Page 1 of 3 realize to be determined of an experiment Massachusetts in a yet Scientists big from the year matter how next that no collaborators underground possible along with be placed "It's who that will Boston University, a prototype is building University,

http://www.usatoday.com/tech/science/space/2007-08-12-dark-matter-hunt_N.htm 2

Evolution of the WIMP-Nucleon sSI Ge 10-40 ‡ ‡ ‡ 10-41 ‡ Cryogenic ÊÊÊÊ 10-42 ÊÚ WIMP

2 -43 Ê c

ê 10 Ú Xe10Ú ÊÚÊ DarkSide-50 10-44 Ú GeV Xe100 Ì -45 Ú Á 10 LUX Ì 50 Ì a 10-46 100GeV Noble liquid Û ı

for LUX -47 Û Á D 10 2 270kg Ì 10-48 Û @ cm

SI -49

s 10 Coherent Neutrino Scattering 1985 1990 1995 2000 2005 2010 2015 2020 2025 Year from arXiv:1310.8327v1 Figure 1. History and projected evolution with time of spin-independent WIMP-nucleonMasaki Yamashita cross section limits for a 50 GeV WIMP. The shapes correspond to technologies: cryogenic solid state (blue circles), crystal detectors (purple squares), liquid argon (brown diamonds), liquid xenon (green triangles), and threshold detectors (orange inverted triangle). Below the yellow dashed line, WIMP sensitivity is limited by coherent neutrino-nucleus scattering.

Community Planning Study: Snowmass 2013 Interaction with dark matter nuclear recoil electronic recoil

fast neutron -U/Th/40K etc background WIMP (SUSY, KK …)

Masaki Yamashita nuclear recoil electronic recoil

fast neutron -U/Th/40K etc background WIMP -WIMP-electron (SUSY, KK …) -Super WIMP (bosonic) -Axion/Axion like particle -Mirror DM The signal is in electron recoil ? -Luminous DM … Masaki Yamashita XMASS experiment

Masaki Yamashita 20 Y. Suzuki for XMASS collab. XMASS arXiv:hep-ph/0008296 (2000) Multi purpose experiment by using LXe Xenon MASSive detector for Solar neutrino Xenon neutrino MASS detector Xenon detector for Weakly Interacting MASSive Particles

T T T

neutrino mass Masaki Yamashita The XMASS collaboration: Kamioka Observatory, ICRR, the University of Tokyo: Yokohama National University: K. Abe, K. Hiraide, K. Ichimura, Y. Kishimoto, K. S. Nakamura Kobayashi, M. Kobayashi, S. Moriyama, M. Nakahata, Miyagi University of Education: N. Kato, H. Ogawa, H. Sekiya, S. Tasaka, A. Takeda, Y. Fukuda M. Yamashita, B. Yang STEL, Nagoya University: Kavli IPMU, the University of Tokyo: Y. Itow, K. Kanzawa, K. Masuda K.Martens, Y. Suzuki, X. Benda Institute for Basic Science: Kobe University: N. Y. Kim, Y. D. Kim K. Hosokawa, K. Miuchi, Y. Ohnishi, N. Oka, Y. KRISS: Takeuchi Y. H. Kim, M. K. Lee, K. B. Lee, J. S. Lee Tokai University: Tokushima University: K. Nishijima K.Fushimi

Masaki Yamashita XMASS experiment M

832kg LXe Kamioka mine Gifu, Hida city, Ikenoyama

Kamland super Kamiokande

ICRR, UTokyo Masaki Yamashita

Masaki Yamashita 23 Water Shield

10 m

-φ10m x 10m ultra pure water shield with 20 inch x 70 PMTs for muon veto

Masaki Yamashita 24 XMASS Detector R10789

Activity per 1PMT(mBq/ PMT) 238U-chain 0.70+/-0.28

232Th-chain 1.51+/-0.31 ~ 40cm 40K <5.1

60Co 2.92+/-0.16

- 642 ultra low background 2 inch PMTs - 62% photo coverage - Largest detector: 832 kg of LXe for sensitive volume. Masaki Yamashita Challenge for low Radioactivity PMT

e.g. 40K case 4000 Bq/human

15 Bq/banana

0.01 Bq/PMT 6.42 Bq/642 PMTs

MasakiMasaki Yamashita Yamashita History of XMASS PMTs

XMASS PMT HISTORY PMT

YEAR 2000 2002 2008 2015- Size 2inch 2inch 2inch 3inch Model Prototype R8778 R10789 R13111 Material:Body glass Kovar Kovar QE 25% 25% 27-39% U [mBq/PMT] 50 18±2 0.70 +/- 0.28 goal is Th [mBq/PMT] 13 6.9±1.3 1.5 +/- 0.31 1/10 of 40K [mBq/PMT] 610 140±20 < 5.1 R10780 60Co [mBq/PMT] <1.8 5.5±0.9 2.9 +/- 0.16

Masaki Yamashita Calibration system OFHC copper rod and source stepping motor on the tank top

guide pipe

OFHC copper rod

moved along z−axis Flange for Detector calibration source exchange

gate valve •-Inner calibration is for energy calibration. ID Injection for XMASS

Figure 5: Calibration system on top of the tank. Source placedontheedgeofthecopper

rod is inserted into the ID and can be moved along the z axis.

26 2012/12/21

SUS 0.21 side) (KRISS 68 122 57 - Co (4)

SUS 0.17 485 59.5 241 - Am (3)

brass 5 800 88 25, 22, 109 - Cd (2)

brass 5 350 5.9 55 - Fe (1)

material Outer [mm] Dia. [Hz] Intensity ] keV [ energy

Table 7: Calibration sources and energies. The 8 keV (*1) in the 109Cd and 59.3 keV (*2)5 Gate 57 in the Co source are Kα X-rays from the copper and tungsten, respectively, used for ~5m valve

source housing.

0 3 0 Isotopes Energy [keV] Shape 3 55Fe 5.9 cylinder Co source

109

Cd 8(*1), 22, 58, 88 cylinder 57

241 Am

Am 17.8, 59.5 thin cylinder241

57Co 59.3(*2), 122 thin cylinder 20

137Cs 662 cylinder 57

sources by Korean collaborator KRISS by made 0.21mm φ for were sources Theses Masaki Yamashita

Sources 3.

21 Energy calibration •High Photoelectron Yield ~15 PE/keV •Good agreement between data and. •Evaluated absorption length 4-11 m, scatter 52cm

TotalK. Abe etPE al. / Nuclear Instruments and Methods in Physics Research A 716 (2013) 78–85 85 57Co source energy and vertices for 122 keV gamma rays are reproduced well 1 1 real data by the MC. real data 2013. Dec 31 2014. Jul 02 2014. Dec 31 0.8 0.8 simulation (MC) simulation (MC) 16 16 0.6 0.6 57Co 14. Conclusion

0.4 0.4 15PE/keV NPE/122 14 PE/keV The construction14 of the XMASS detector was completed in 0.2 September 2010 and commissioning runs were conducted from

Events (normalized) 0.2 @122keV Events (normalized) October 2010 to June 2012. power cut Events (normalized) 0 ' 0 0 20 40 60 80 100 120 140 The10 XMASS detector is the world s largest (ton scale) single- 0 500 1000 1500 2000 2500 phase liquid xenon detector for dark matter searches. The key idea reconstructedReconstructed energy [keVee] energy [keVee] total nPEs for BG reduction is self-shieldingAbsorption using vertex reconstruction. The PE positionAbs.(m) 5 and energy resolution along the z-axis inside the detector Fig. 7. Observed n PE spectrum using the 57Co source at z 0 cm (red dots). 0.8 ¼ were measured with radioactive sources and are well reproduced Simulated 0.7 spectrum is shown as blue histogram. (For interpretation of the references to color in this ﬁgure caption, the reader is referred to the webreal version data of this article.) by MC. The observed position and energy resolution for 122 keV 0.6 simulation (MC) gamma1.02 rays are 1.0 cm at z 720 cm and 4% (rms) at z 0 cm, 0.5 ¼ ¼ 1.2 respectively. 0.4 Ahighlightyield,141.00 :771:2PE=keV, was obtained owing to the 0.3

Normalized large photocoverage (462%)andsmallamountofimpuritiesinthe 1.1 0.2 0.98 0.1 liquid xenon. This wasLight achieved Yield bystability careful control0.5% of dust and radon

Events (normalized) fi fi 0 during Relative deduced scintillation light yield construction0 and puri 100cation by liquid200 collection and300 lling 400 1 -40 -30 -20 -10 0 10 20 30 40 with purified gas. The concentrations of radon (8:270:5mBqDay= from835 kg 2014. Jan. 1 222 220 reconstructedReconstructed z [cm] position (z) [cm] for Rn and o0:28 mBq=835 kg for Rn) and krypton (o2:7 ppt) in liquid xenon are also the lowest among liquid xenon detectors 0.9 for dark matter searches. ~500 daysMasaki Yamashita 29 Figure 9: Energy spectra 0.8 reconstructed using the 57Co source at z = 0cm (upper) and ver- Acknowledgments Calibration data/ Simulation tex distributions reconstructed 0.7 using the same source at z = −40, −30,...,40 cm (lower). We gratefully acknowledge the co-operation of Kamioka Fitted Mining and Smelting Company. This work was supported by 0.6 the Japanese Ministry of Education, Culture, Sports, Science and 0 20 40 60 80 100 120 Technology, Grant-in-Aid for Scientific Research, and partly sup- Electron equivalent energy [keVee] ported by the National Research Foundation of Korea Grant funded Fig. 8. Comparison of energy scales in calibration data and MC. by the Korean Government (NRF-2011-220-C00006).

References

[1] Y. Suzuki, arXiv:hep-ph/0008296. [2] K.G. Begeman, A.H. Broeils, R.H. Sanders, Monthly Notices of the Royal Astronomical Society 249 (1991) 523; J. Dunkley, et al., Astrophysical Journal Supplement 180 (2009) 306; R.A. Knop, et al., Astrophysical Journal 598 (2003) 102; S.W. Allen, et al., Monthly Notices of the Royal Astronomical Society 334 (2002) L11; M. Tegmark, et al., Physical Review D 69 (2004) 103501. [3] H.C. Cheng, et al., Physical Review Letters 89 (2002) 211301; A. Birkedal-Hansen, J.G. Wacker, Physical Review D 69 (2004) 065022; A. Bottino, et al., Physical Review D 69 (2004) 037302; 26 J. Ellis, et al., Physical Review D 71 (2005) 095007. [4] K. Ueshima, et al., the XMASS Collaboration, Nuclear Instruments and Methods in Physics Research Section A 659 (2011) 161. [5] M. Laubenstein, G. Heusser, Applied Radiation and Isotopes 67 (2009) 750. [6] K. Abe, et al., the XMASS Collaboration, Astroparticle Physics 31 (2009) 290. [7] K. Abe, et al., the XMASS Collaboration, Nuclear Instruments and Methods in Physics Research Section A 661 (2012) 50. [8] I. Lawson, B. Cleveland, in: the Proceedings of the Low Radioactivity Techni- ques, LRT2010, AIP Conference Proceedings, Sudbury, Canada, 28–29 August 2010, pp. 68–77. [9] Y. Takeuchi, et al., Nuclear Instruments and Methods in Physics Research Section A 421 (1999) 334. [10] H. Ikeda, et al., Nuclear Instruments and Methods in Physics Research Section A 320 (1992) 310; S. Fukuda, et al., Nuclear Instruments and Methods in Physics Research Section A 501 (2003) 418. 57 Fig. 9. Energy spectra reconstructed using the Co source at z 0cm(upper)and [11] K. Abe, et al., the XMASS Collaboration, Physics Letters B 719 (2013) 78–82. ¼ vertex distributions reconstructed using the same source at z −40, −30,…,40cm [12] K. Abe, et al., the XMASS Collaboration arXiv:1212.6153. ¼ (lower). [13] S. Agostinelli, et al., Nuclear Instruments and Methods in Physics Research Section A 506 (2003) 250. vertices for various 57Co source positions. The observed position [14] T. Doke, et al., in: the Proceedings of the International Workshop on Technique and Application of Xenon Detectors, Xenon01, World Scientiﬁc, the University resolution (rms) is 1.4 cm at z 0 cm and 1.0 cm at z 720 cm for ¼ ¼ of Tokyo, Japan, 3–4 December 2001, pp. 17–27. 122 keV gamma rays. The distributions of the reconstructed [15] Y. Endo, et al., JSAP: The 72th Autumn Meeting, 2011, 30a-T-8. Comparison of background rate before particle ID

■ Background rate in the fiducial volume before separation of nuclear recoils from e/γ. XMASS ■ XMASS achieved O(10-4) event/day/kg/keVee at a few 10’s keV. XMASSXMASS

■ Advantage for DM search via electron recoil.

Added to D.C.Malling thesis (2014) Fig.

Masaki Yamashita PTEP 2014,063C01 H.Uchidaetal.

Table 1. Signal efficiencies with their systematic errors for deriving the limit shown in Figs. 4 and 7.Therowstartingfrom(a)isbasedonRef.[29], and the one starting from (b) on Ref. [33]. WIMP mass (GeV) 20 50 100 300 1000 3000 5000 (a) signal efficiency (%) 23 7 29 4 26 2 19 1 16 1 15 1 15 1 ±6 ±5 ±4 ±3 ±3 ±3 ±3 (b) signal efficiency (%) 24 7 30 2 29 2 26 2 25 2 25 2 25 2 ±6 ±5 ±4 ±5 ±5 ±5 ±5

used in Ref. [29], it can be seen in Fig. 1 that the shape of this distribution for a 50 GeV WIMP does not change much with the use of the more modern form factors. These cut values and the signal Downloaded from window optimized for the 50 GeV WIMPs were also used to obtain the limits for the other WIMP masses. Our signal efficiency is defined as the ratio between the number of simulated events remaining after all cuts in the 36–48 keV signal region and the number of simulated events generated within K. Abe et al. / Physics Letters B 719 (2013) 78–82 the fiducial81 volume (radius less than 15 cm, containing 41 kg of LXe). As shown in Table 1, signal efficiency ranges from 29% for 50 GeV WIMPs to 15% for 5 TeV WIMPs for the nuclear form http://ptep.oxfordjournals.org/ factors given in Ref. [29].

5. Results and discussion As clearly visible in Fig. 3,thecutsdiscussedintheprevioussectionalmosteliminateallbackground in and around the signal window. After all cuts, 5 events remain in our 36–48 keV signal region. The main contribution to the remaining background in this energy region stems from the 222Rn daughter at Kokusai Hoken Keikakugaku (UNIV OF TOKYO) on June 6, 2014 214Pb. From our simulation we estimate this background alone to contribute 2.0 0.6 events. As ± other background contributions are smaller but less certain, we do not subtract background when calculating our limits. Our detector’s low background allows us to directly use the event count in Fig. 6. WIMP signal acceptance efficiency after data reduction for the analysis. the signal region to extract our limit on the inelastic scattering cross section of WIMPs on 129Xe select these events a time-of-flight correction is made to the tim- nuclei. Using Eq. 6 and taking into account the nuclear form factor and our signal efficiency we ing distribution of each event assuming the event vertex is on derive a 90% C.L. upper limit for this cross section, which in Fig. 4 is compared to the result from the surface of the PMT closest to the charge-weighted center of gravity of the event. After this correction the timing distribution XMASSRefs. [12,13]. The grayexperiment@Kamioka band reflects our systematic uncertainties. The systematic uncertainty on Fig. 7. Simulated WIMP energy spectra in the XMASS detector assuming the maxi- of Cherenkov-like events is found to be narrower than that for mum cross section that provides a signal rate no larger than the observation in any scintillation-like events. Events with more than 60% of their PMT bin abovelight 0.3 keVee. mass WIMP Solar axion hits occurring within the first 20 ns of the event window are re- Inelastic scattering moved as Cherenkov-like. The ratio of the number of PMT hits ) [p b ] 2 within the first 20 ns relative to the total number of hits in the as I 10 129 + 129Xe* event window for all events (head-to-total ratio) is shown in Fig. 4. σ χ + Xe à χ Each step of the data reduction is shown in Fig. 5. The expected WIMP acceptance efficiency of these cuts was estimated with the detector simulation. In the simulation WIMP recoil energy spectra were generated for each WIMP mass and MC events were distributed uniformly throughout the detector volume 10 using a liquid scintillation decay constant of 25 ns [16]. Fig. 6 shows the resulting signal acceptance efficiency at energies below 1 keVee. The size of the error bars comes primarily from the systematic uncertainty in the xenon scintillation decay constant, Asymptotic cross section ( 25 1ns,whichisestimatedbasedonthedifferencebetweenthe ± XMASS model [16] and the NEST model [17] based on [18].Asys- 1 Phys. Lett. B 724 (2013) 46 tematic error on the selection efficiency is determined based on 102 103 the error resulting from a linear fit to the points in the figure. At Phys. Lett. B 719 (2013) 78 WIMP mass [GeV] the 0.3 keVee analysis threshold this error is 6.1%. as Fig. 4. The black solid line is our 90% C.L. upper limit on the asymptotic cross section σI for inelastic scat- 4. Results and discussion 129 PTEP 2014, 063C01 tering on Xe using the same form factors as DAMA. The gray band covers its variation with our systematiccoherent ν-n scattering Fig. 8. Spin-independent elastic WIMP-nucleon cross section as a functionuncertainty. of WIMP The dotted line is the limit obtained by the DAMA group [12,13]. It was derived after statisti- Fig. 7 shows simulated WIMPs energy spectra overlaid on the mass. All systematic uncertainties except that from are taken into account in Leff cally subtracting background. Our low background allows us to derive this limit without such background observed spectrum after the data reduction was applied. WIMPs the XMASS 90% C.L. limit line. The effect of the uncertainty on the limit is Leff are assumed to be distributed in an isothermal halo with v shown in the band. Limits from other experiments and favored regionssubtraction. are also o = 220 km/s, a galactic escape velocity of v 650 km/s, and an shown [4–9]. esc = average density of 0.3GeV/cm3.Inordertosetaconservative upper bound on the spin-independent WIMP-nucleon cross sec- nuclear-recoil and electronic events, and many events remain in 7/11 tion, the cross section is adjusted until the expected event rate the analysis sample, the present result excludes part of the param- in XMASS does not exceed the observed one in any energy bin eter space favored by other measurements [4–6] when those data Supernova above 0.3 keVee. Implementing the systematic errors discussed in are interpreted as a signal for light mass WIMPs. Finally, we are the text above, the resulting 90% confidence level (C.L.) limit de- workingsuper-WIMPs(ALPs) on modifications to the inner surface of XMASS, especially rived from this procedure is shown in Fig. 8.Theimpactofthe around the PMTs, to improve the detector performance. uncertainty from eff is large in this analysis, so its effect on the Astroparticle Physics 89 (2017) 51 limit is shown separatelyL in the figure. Acknowledgements After careful study of the events surviving the analysis cuts, their origins are not completely understood. Contamination of 14C We gratefully acknowledge the cooperation of Kamioka Mining Rare decay search in the GORE-TEX® sheets between the PMTs and the support struc- and Smelting Company. This work was supported by the Japanese ture may explain a fraction of the events. Light leaks through this Ministry of Education, Culture, Sports, Science and Technology, Double electron capture material are also suspect. Nonetheless, the possible existence of a Grant-in-Aid for Scientific Research, and partially by the National WIMP signal hidden under these and other backgrounds cannot Research Foundation of Korea Grant funded by the Korean Govern- K-shell X-ray be excluded. Although no discrimination has been made between ment (NRF-2011-220-C00006). ν

Nuclear Recoil Energy [keVnr] 5 10 15 20 25

] 0.15 Co

57 Electron Equivalent Energy [keVee] 1 2 3 4 5 6 0.1 method 1 Expected ± 1σ 0.05 method 2 Expected ± 2σ 0

0.8 -0.05 0.6

0.4 -0.1 Efficiency 0.2 0 1 2 3 4 5

Amplitude[events/day/kg/keV Energy[keV ] Modulation 57Co -0.15 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 ν K-shell X-ray Energy[keV ] Phys. Rev. Lett. 113 (2014) 121301 57Co Phys. Lett. B759 (2016) 64-68 editor’s suggestion Phys Lett. B (2016), pp. 272 Masaki Yamashita, ICRR, Univ of Tokyo Search for Bosonic super-WIMPs Phys. Rev. Lett. 113 (2014) 121301 v or a

• Motivated by Warm Dark Matter • sterile neutrino, gravitino … • However, it can be pseudoscaler or vector Vector case boson and in this case, it can be detected by absorption of the particle, which is similar to the photoelectric effect. • Search for mono-energetic peak at the mass of the particle( 40-120 keVee) • Our limit excludes the possibility that such particles constitute all of dark matter. Pseudoscalar • The most stringent direct constraint on gaee.

Masaki Yamashita XMASS annual modulation search

Masaki Yamashita 33 606 KLYPIN, ZHAO, & SOMERVILLE Vol. 573

8 examined in a future paper. In this model, typical parametersoftheMaxwelliandistribution 8 for our location in the Milky Way are σSHM =270km/sandvesc =650km/s,thelatterbeing the speed necessary to escape the Milky Way (WIMPs with speedsinexcessofthiswould examinedhave in escaped a future the paper. galaxy, In hence this the model, truncation typical of the parameter distributionsoftheMaxwelliandistribution in Eqn. (15)). Unlike the for ourGalactic location disk in (along the Milky with Way the Sun), are σ theSHM halo=270km/sand has essentially vnoesc rotation;=650km/s,thelatterbeing the motion of the the speedSun relative necessary to this to escapestationary the halo Milky is Way (WIMPs with speedsinexcessofthiswould have escaped the galaxy,Annual hence the truncationmodulation of the distrib signalution in Eqn. (15)). Unlike the v ,SHM = vLSR + v ,pec , (24) Galactic disk (along with the Sun), the⊙ halo has essentially⊙ no rotation; the motion of the rotation velocity Fig. 3. Sun relative to this stationary halo is —Mass distribution of the MW galaxy for model A1 ( full curve) where vLSR =(0, 220, 0) km/s is the motion of the Localand Standard model B1 (dashed of curve Rest). The large and dots withv error,pec bars are= observational constraints. From small to large radii the constraints⊙ are basedMilky on the Way We are here! following: stellar radial velocities and proper motions in the Galactic cen- (10, 13, 7) km/s is the Sun’s peculiar velocity. The Earth’s speedter; radial rel velocitiesative of OH/IR to stars; the modeling halo, of thevobs bar using(t), DIRBE and v ,SHM = vLSR + v ,pec , stellar velocities; rotational velocity at the solar radius; and dynamics(24) of is maximized around June 1. The⊙ local dark matter density⊙ satellites.ρ0 is taken to be the estimated average density in the local neighborhood, 0.3 GeV/cm3. where vLSR =(0, 220,2000) km/s is the motion of the Local Standard of Rest and v ,pec = from the motions of satellite galaxies discussed in 3. The ⊙ x (10, 13, 7) km/s is the Sun’s peculiar velocity. The Earth’s speedcentral data rel pointsative were not to used the either halo, in our ﬁttingvobs or(t in), C. Annual Modulation the analysis of the bulge (Zhao 1996b). Nevertheless, they is maximized around June 1. Thehalo local dark matter densitycomeρ fairly0 is close taken to the extrapolation to be the of our estimated model into the 3 very center of our Galaxy. The theoretical curves for our average density in the local neighborhood, 0.3 GeV/cm . favored models A1 and B1 are very close to each other, It is well known that the count rate in WIMPdisk detectors willwhich exp is noterience surprising an because annual they ﬁt themodu- same data and Sun have the same global dark matter content. The largest devia- lation as a result of the motion of the Earth around the Suntion des ofcribed the models above from the [4, data 5]. is for In the some mass inside 100 cases, but not all, the count rate (Eqn. (1)) has an approximapc, wherete time the observational dependence estimate is twice larger than the C. Annual Modulationprediction of the models. Even at this point the disagree-

velocity[km/s] NASA/JPL-Caltech/R. Hurt (SSC/Caltech) bulge ment is not alarming because the observational data are dR likely more uncertain than the formal error. (E,t) S0(E)+Sm(E)cosω(t Whattc) is, remarkable about Figure 3 is that(25) it spans more It is well known that the countdE rate≈ in WIMP detectorsthan− will 5 orders exp oferience magnitude in an radius annual and mass. It modu- is encour- aging that, without fine-tuning, our models are consistent Fig. 2.—Rotation curve forradius(kpc) our favorite models A1 (no exchange of lation as a result of theangular motion momentum) of and Bthe1 (with the Earth exchange). Note around that the dark the matter Sunwith des observationscribed of the above dynamical [4, mass 5]. of the In MW some over where tc is the timedominates of only year in the outer at part which of the Milkyvobs Way.( Symbolst)isatitsmaximum. showKLYPIN observa- et al. thisAPJ huge 2002 range. S0(E)istheaverage cases, but not all, the counttional data from rate H i measurements (Eqn. of Knapp (1)) et al. has (1985; circles an)andKerr approximaFindingte an time acceptable dependence model for M31 was relatively easy differential recoil rateet al. (1986; overtriangles a). year and Sm(E)isreferredtoasthemodulationamplitudebecause there are much232 less data. km/s In particular, we do not (which may, in fact, be negative). The above equation is a reahavesonable kinematic approximation constraints for the disk, for which the wouldSun be ities anddR proper motions in the Galactic center. Squares are equivalent to constraints at the solar position in our Galaxy. SHM we are consideringbased on kinematicsin(E,t this) of paper, OH/IRS ( starsE but)+ (Lindqvist isS not et(E al. valid)cos 1992). forω(Our allt model halot ) seems, models, to reproduce particularly reasonably well the at dynami-(25) The point at 3.5 kpc is based0 on the Zhao (1996a,m 1996b) cal mass ofc M31 from 100 pc to 100 kpc. Our model does 30 km/s some recoil energiesmodel fordE of dark the bar. matter Because≈ the streams; model was compared see Ref. with the [53] fornot− produce a discussion. the very large For wiggles the exhibited60 SHM,° by the observed data on stellar kinematics (inner rotation curve and radial rotation curve. The wiggles at 5 and 9 kpc are likely due to Earth velocity dispersion), it gives a constraint on the total mass: noncircular motions induced by the bar and, thus, as dis- where tc is the time of4 year1010 M ,withanuncertaintyofabout20%.Forthe at which1 dR vobs(t)isatitsmaximum.dR cussed before, cannotS be0( reproducedE)istheaverage by any axisymmetric nextÂ S datam( pointE )= at 8.5 kpc we simply(E, assumeJune that 1) the circular(E,model.Dec The 1) bulge. of M31 is almost twice as(26) massive as the differential recoil rate over a year2 and1dE Sm(E)isreferredtoasthemodulationamplitudedE velocity is 220 20 km sÀ ,whichcoversthewholerangeof− bulge of our Galaxy. It is also slightly (30%) more compact. reasonable values.Æ We! then estimate the mass as The disk of" M31 is also more massive, but it is more (which may, in fact, beM negative).v2r=G.Thelastobservationalpointistheconstraint The above equation is aextended. reasonable As a result, approximation in the central 5 kpc of the for M31 the the Masaki Yamashita 34 SHMExperiments we are considering such as DAMA¼ in this will paper, often but give is the not average valid amplitu for allde halo over models, some interval, particularly at some recoil energies for dark matter streams;1 seeE2 Ref. [53] for a discussion. For the SHM, S = dES (E). (27) m E E m 1 dR 2 − 1 #E1 dR S (E)= (E, June 1) (E, Dec 1) . (26) m 2 dE − dE ! D. Parameter Space " Experiments such as DAMA will often give the average amplitude over some interval, Many of the parameters that factor into the expected recoil rates for a scattering detector are unknown, including the WIMP mass,1 fourE WIMP-nucleon2 couplings (SI and SD couplings to each of protons andSm neutrons),= the locald WIMPESm( densiE). ty, and the WIMP velocity (27) distribution in the halo. In this paper,E2 weE shall1 E fix1 the halo model to the SHM and the local 3 − # density to 0.3 GeV/cm .Inaddition,weshalltakefp = fn (equal SI couplings) so that there are only three independent scattering couplings; the SI coupling will be given in terms D. Parameter Space of the SI scattering cross-section off the proton, σp,SI.Theparameterspaceweexaminewill then consist of the four parameters m, σp,SI, ap,andan. Many of the parameters that factor into the expected recoil rates for a scattering detector are unknown, including the WIMP mass, four WIMP-nucleon couplings (SI and SD couplings to each of protons and neutrons), the local WIMP density, and the WIMP velocity distribution in the halo. In this paper, we shall fix the halo model to the SHM and the local 3 density to 0.3 GeV/cm .Inaddition,weshalltakefp = fn (equal SI couplings) so that there are only three independent scattering couplings; the SI coupling will be given in terms of the SI scattering cross-section off the proton, σp,SI.Theparameterspaceweexaminewill then consist of the four parameters m, σp,SI, ap,andan. Energy spectrum直接検出 1year Jun Dec

10GeV WIMP June Xe target 2-10% difference Dec cross over point

10 difference keVr

Masaki Yamashita 35 Page 8 of 11 Eur. Phys. J. C (2013) 73:2648

ith time interval, !E is the chosen energy bin, ϵjk is the than 1. Although this can be still ascribed to statistical fluc- overall efficiency. Moreover, the signal can be written as tuations (see before), let us ascribe it to a possible system- Sik S0,k Sm,k cos ω(ti t0),whereS0,k is the con- atics. In this case, one would derive an additional error to = + · − stant part of the signal and Sm,k is the modulation am- the modulation amplitude measured in the (2–6) keV energy 4 plitude. The usual procedure is to minimize the function interval: 3 10− cpd/kg/keV, if quadratically combining ≤ × 5 yk 2ln(Lk) const for each energy bin; the free param- the errors, or 2 10 cpd/kg/keV, if linearly combining = − − ≤ × − eters of the fit are the (bjk S0,k) contributions and the Sm,k them. This possible additional error: 3%or 0.2%,re- + ≤ ≤ parameter. Hereafter, the index k is omitted for simplicity. spectively, on the DAMA/LIBRA–phase1 modulation am- In Fig. 8 the obtained Sm are shown in each consid- plitude is an upper limit of possible systematic effects com- ered energy bin (there !E 0.5keV)whenthedataof ing from the detector to detector differences. = DAMA/NaI and DAMA/LIBRA–phase1 are considered. Among further additional tests, the analysis of the mod- It can be inferred that positive signal is present in the ulation amplitudes as a function of the energy separately (2–6) keV energy interval, while Sm values compatible with for the nine inner detectors and the remaining external ones Page 4 of 11 Eur. Phys. J. C (2013) 73:2648 zero are present just above. In fact, the Sm values in the has been carried out for the entire DAMA/LIBRA–phase1. Fig. 2 Experimental residual rate of the single-hit scintillation (6–20) keV energy interval have random fluctuations around events measured by 2 DAMA/LIBRA–phase1 in the zero with χ equal to 35.8 for 28 degrees of freedom (up- (2–4), (2–5) and (2–6) keV energy intervals as a function of per tail probability of 15 %). All this confirms the previous the time. The time scale is maintained the same of the analyses. As previously done for the other data releases [2, previous DAMA papers for coherence. The data points 3, 7], the method also allows the extraction of the Sm val- present the experimental errors as vertical bars and the ues for each detector, for each annual cycle and for each associated time bin width as energy bin. The S horizontal bars.The m are expected to follow a normal dis- superimposed curves are the tribution in absence of any systematic effects. Therefore, cosinusoidal functions Sm Sm behaviours A cos ω(t t0) with the variable x −⟨ ⟩ has been considered to verify aperiodT 2π 1yr,aphase− σ = ω = = t0 152.5day(June2nd)and that the Sm are statistically well distributed in all the seven modulation= amplitudes, A, equal to the central values DAMA/LIBRA–phase1 annual cycles, in all the sixteen en- obtained by best fit on the data DAMA/LIBRApoints of the entire Eur. Phys.J.ergy bins C(2013) (!E 0.25 73, keV JINST in the (2–6) 2012 keV 7 energyP03009 interval) DAMA/LIBRA–phase1. The = dashed vertical lines correspond and in each detector. Here, σ are the errors associated to Sm to the maximum expected for the DM signal (June 2nd), while and Sm are the mean values of the Sm averaged over the Model Independentthe dotted vertical lines Annual⟨ ⟩ Modulation Result correspond to the minimum detectors and the annual cycles for each considered energy •DAMA/ DAMA(~100NaI + DAMA/LIBRA-phase1 kg) + LIBRA (~250 Total exposure:kg) 487526 kg×day = 1.33 ton×yr bin. The distributions and their Gaussian fits obtained for Single-hit residuals rate of scintillation events vs time in 2-6 keV EPJC 56(2008)333, EPJC 67(2010)39, EPJC 73(2013)2648 •14cycle -> 1.33ton x yr the detectors are depicted in Fig. 9. continuous line: t = 152.5 d, T =1.0 y •Annual Modulation 9.2 σ Defining χ2 x2—where the sum is0 extended over = A=(0.0110±0.0012) cpd/kg/keV •Fit with all the parameters free: all the 112 (32 for the detectorχ2/dof restored = 70.4/86 after 9.2 the σ C.L. upgrade ! 2 –A = (0.0112 ± 0.0012) cpd/kg/keV in 2008) x values—χ /d.o.f.Absence values rangingof modulation? from 0.72No to –t0 = (144±7) days(152 d SHM) 1.22 are obtained (see Fig. 10χ2–top/dof);=154/87 they areP(A=0) all = below 1.3×10 the-5 –T = (0.998±0.002) y 95 % C.L. limit. Thus the observedFit with all annual the parameters modulation free: effect is well distributed in allA the = (0.0112 25 detectors ± 0.0012) at cpd 95 %/kg/ C.L.keV t = (144±7) d - T = (0.998±0.002) y The mean value of the 25 χ 2/0d.o.f. is 1.030, slightly larger

Principal mode Comparison between single hit residual rate (red points) and multiple 2.737×10-3 d-1 ≈ 1 y-1 hit residual rate (green points); Clear modulation in the single hit events; 2π Table 3 Modulation amplitude, A, obtained by fitting the single-hit the formula: A cos ω(t t0) with T 1yrandt0 152.5day No modulation in the residual rate of the multiple− hit= eventsω = = residual rate of the entireA=-(0.0005±0.0004) DAMA/LIBRA–phase1 (Fig. cpd2), and/kg/ in- keV(June 2nd) as expected by the DM annual modulation signature. The cluding also the former DAMA/NaI data [22] for a total cumulative correspondingAmplitudeχ 2 value of each fit and the confidence level (C.L.) are exposure of 1.33 ton yr. It was obtained by fitting the data with also reported × Multiple hits events = Energy interval DAMA/LIBRA–phase1Dark Matter particle “switched off” DAMA/NaI & DAMA/LIBRA–phase12-6 keV (keV) (cpd/kg/keV) (cpd/kg/keV)

2–4 A (0.0167 0.0022) 7.6σ C.L. A (0.0179 0.0020) 9.0σ C.L. = ± → = ± → χ2/d.o.f. 52.3/49 χ 2/d.o.f. 87.1/86 Sm Sm Power spectrum Power spectrum = = Fig. 9 Distributions (histograms) of the variable −⟨ ⟩ ,whereσ are 2–5 A (0.0122 0.0016) 7.6σ C.L. A (0.0135 0.0015) 9.0σ C.L. σ = ± → = ± → the errors associated to the S values and S are the mean values of χ 2/d.o.f. 41.4/49 χ 2/d.o.f. 68.2/86 m m = = ⟨ ⟩ 2–6 A (0.0096 0.0013) 7.4σ C.L. A (0.0110 0.0012) 9.2σ C.L. the modulation amplitudes averaged over the detectors and the annual = ± → = ± → χ 2/d.o.f. 29.3/49 χ 2/d.o.f. 70.4/86 cycles for each considered energy bin (here !E 0.25 keV). Each No systematics or side reaction able to = = = Fig. 8 Energy distribution of the S variable for the total cumulative 36 panel refers to a single DAMA/LIBRA detector (the detector 16 was account for the measured modulation This result offers an additional strong support form the presenceMasaki of DM particles Yamashita in the amplitude and to satisfy all the galacticexposure halo further 1.33 excluding ton yr. any The side energy effect bin either is 0.5from keV. hardware A clear or from modulation software out of trigger for the first five annual cycles [3]). The entries of each procedures or from background× peculiarities of the signature is present in the lowest energy region, while Sm values compatible with histogram are 112 (the 16 energy bins in the (2–6) keV energy interval zero are present just above. In fact, the Sm values in the (6–20) keV and the seven DAMA/LIBRA–phase1 annual cycles) except for detec- 2 The data favor the presence of aenergy modulated interval have behaviour random fluctuations with aroundall the zero proper with χ equal to tor 16 (32 entries); the r.m.s. values are reported in Fig. 10—bottom. 35.8 for 28 degrees of freedom (upper tail probability of 15 %) The superimposed curves are Gaussian fits features for DM particles in the galactic halo at about 9.2σ C.L. Annual Modulation search 2013/11/20 - 2015/03/29 WIMP signal efficiency -We carried out the analysis without particle ID for 359.2 days WIMP case and model independent case. -Large mass (832 kg) - Data set live time 2013/11/20 - 2015/03/29 (359.2 live days) # 1 year data of XMASS (0.82 ton x year) vs. 14 years data of DAMA/LIBRA (1.33 ton x year) live time 359.20 days x 832 = 298854.40 kg days 3 ] 10 ID Trig :(34272303, 1.000, 1.000) Co

57 dT(pre)>10 ms:(29894332, 0.872, 0.872) =>Current staisics is already half of DAMA/LIBRA data. T-RMS<100ns:(28631832, 0.835, 0.958) 2 10 Cherenkov cut :(1630021, 0.048, 0.057) -Low energy threshold: 0.5 keV by 122keV Max/PE cut :( 349135, 0.010, 0.214) 1. ID trigger 10 => 4.8keVnr (estimated by Aprile et al. PRL(2011) ) 2. dT cut (> 10ms) 3. Timing RMS 1.1 keVee (15% difference from NEST 1

Rate [counts/day/kg/keV 4. Cherenkov cut -Systematic error due to time dependence of light 10-1 yield (~ 10%) was treated by two method 10-2 5. Max/PE cut keVee 1 2 3 4 5 6 10-3 0 1 2 3 4 5 Energy [keV ] 57Co Masaki Yamashita 89 If we normalized this eciency at 8 m absorption length, the eciency change from 0.96

90 to 1.2 in the range of 5 m to 11 m. Uncertainties coming from the position dependency of

91 the detector were taken into account as a systematic errors and those were the dominant 89 If we normalized this eciency at 8 m absorption length, the eciency change from 0.96 92 systematic errors in this analysis. 90 to 1.2 in the range of 5 m to 11 m. Uncertainties coming from the position dependency of 93 91 the detector were taken into account as a systematic errors and those were the dominant 94 To retrieve the annual modulation amplitude in our data, the method of least squares for 92 systematic errors in this analysis. 95 binned data was used in our analysis. The dataset is divided into time bins with roughly 93 96 10 days of live time and each of them was divided into energy bins with a 0.1 keV57Co.Our 94 To retrieve the annual modulation amplitude in our data, the method of least squares for 97 Fitting57 time variation data software energy threshold was set to 0.5 keV Co. Two independent analysis were performed 95 binned data was used in our analysis. The dataset is divided into time bins with roughly 98 with di↵erent treatmentTwo independent for systematic uncertaintyanalysis andto treat both of systematic them ﬁt all energy error. and time 96 10 days of live time andMain each systematic of them was dividederror intocomes energy from bins withlight a yield 0.1 keV2 change57Co.Our during the search 99 bins simultaneously. A method-1 introduced ’pull term’ parameter ↵ and was deﬁned as,

97 software energy thresholdperiod was and set to the 0.5Ebins keVerrortbins57Co .wasdata Two independentestimatedex 2 analysis by MC were after performed tuning by calibration (R R ↵iKi,j) 2 = i,j i,j + ↵2 (1) sourcemethod1 data. (< +- 5%) 2 i 98 with di↵erent treatment for systematic uncertainty and(stat) bothj of them fit all energy and time Xi Xj method1: Pull method (pull term α) 2 99 bins simultaneously.data A method-1ex introduced ’pull term’ parameter ↵ and was defineddata as, 100 where Ri(j) and Ri(j) and (stat are the data, expected event rate and the statisticalR error: observed data Ebins tbins data ex 2 ex 101 in the i-th energy2 and j-th time bin,(R respectively.i,j Ri,j K↵ii,jKi,representsj) 2 the 1 systematicRLight: error Yield expected of LXe rate method1 = 2 + ↵i (1) i j (stat)j Nbins:Ebins x tbins 102 on the expected event rate.X A methode-2X uses a covariance matrix to include e↵ects of data ex 100 where R and R and (stat2 are the data, expected event rate and the statistical error 103 systematici(j) errori(j)method2: and the Covariancewas defined as Matrix systematic term 101 in the i-th energy and j-th timeN bin,bins respectively. Ki,j represents the 1 systematic error 2 data ex 1 data ex method2 = (Ri Ri )(Vstat + Vsys)ij (Rj Rj ) , (2) size 102 on the expected event rate. A methode-2 uses a covariance matrix to include e↵ects of Xi,j 2 obs (a) 0.5 1 Co

Abs.(m) 5 ⇥ 1.051.05 2.1 < E[keVee] 105 are108 theIn dataorder and to extract expected the event amplitude rate in in the a modeli-th ( independentj-th) 2-dimensional way, the bin. expectedVstat eventrepresents rate was 1.02 57Co source 1 Relative cut efficiency Relativecut efficiency 106 the109 statisticalcalculated error as and V1.00sys is the covariance matrix for systematic uncertainties which we

relative efﬁciency uncertainty 0.950.95 0.98 ex absorption length[m] 107 evaluated using Monte Carlo simulation.R (Ei,tj)=Ci + Ai cos 2⇡(tj t0)/T (3) Relative deduced scintillation light yield 5 6 7 8 9 10 11 0 100 200 300 400 Absorption length [m] Day from 2014. Jan. 1 108 Masaki Yamashita In110 orderwhere to extractCi and A thei are amplitude unmodulated in a model event independent rate and modulated way, the amplitude expected event free parameters rate was to

109 calculated111 be determined as by the method of least squares in the i-th energy bin. T and t0 are the period ex 112 and phase of the modulation,R (Ei,t respectively.j)=Ci + Ai cos 2⇡(tj t0)/T (3)

110 where113 ForCi theand caseAi are of model unmodulated dependent event case, rate we and assumed modulated WIMP amplitude dark matter. free Theparameters expected to rate

114 111 be determinedwas modiﬁed by the as method of least squares in the i-th energy bin. T and t0 are the period

ex 112 and phase of the modulation,R (E ,t respectively.)=C + A (m ,E)cos2⇡(t t )/T , (4) i i j i n ⇥ i i n 0 113 For the case of model dependent case, we assumed WIMP dark matter. The expected rate 5 114 was modiﬁed as

Rex(E ,t )=C + A (m ,E)cos2⇡(t t )/T , (4) i i j i n ⇥ i i n 0 5 3 tillation light as well as the intrinsic light yield of the was used. The data set was divided into 40 time-bins 57 liquid xenon scintillator are extracted from the Co cal- (tbins) with roughly 10 days of live time each. The data ibration data the Monte Carlo simulation [17]. With that in each time-bin were then further divided into energy- we found that we can trace the observed photoelectron bins (Ebins) with a width of 0.5 keVee.Twofitting meth- change in the calibration data as a change as the absorp- ods were performed independently. Both of them fit all tion length, while the scattering length remains stable energy- and time-bins simultaneously. Method 1 used a at 52 cm with a standard deviation of 0.6%.Wethen ‘pull term’ ↵ with 2 defined as: re-evaluate the absorption length and the± relative intrin- Ebins tbins data ex 2 sic light yield to see the stability of the scintillation light (R R ↵Ki,j) 2 = i,j i,j + ↵2, (1) response by fixing the scattering length at 52 cm. The (stat)2 + (sys)2 i j i,j i,j ! absolute absorption length varied from about 4 m to 11 X X m, but the relative change in the intrinsic light yield stay- where Rdata, Rex , (stat) and (sys) are data, ex- ing within 0.6% over the entire data taking period. i,j i,j i,j i,j ± pected event rate, statistical and systematic error, re- The time dependence of the photoelectron yield a↵ects spectively, of the (i-th energy- and j-th time-) bin. The the eciency of the cuts. Therefore, we evaluate the ab- time is denoted as the number of days from January 1, sorption length dependence of the relative cut ecien- 2014. Ki,j represents the 1 correlated systematic error cies through Monte Carlo simulation. If we normalize on the expected event rate based on the relative cut ef- the overall eciency at an absorption length of 8 m, this ficiency in that bin. Method 2 used a covariance matrix eciency changes from 4% to +2% over the relevant 2 to propagate the e↵ects of the systematic error. Its absorption range. The position dependence of the e- was defined as: ciency was taken into account as a correlated system- Nbins atic error ( 2.5%). This is the dominant systematic 2 data ex 1 data ex ⇠ ± = (R R )(V +V ) (R R ), (2) uncertainty in the present analysis. The second largest k k stat sys kl l l contribution comes from a gain instability of the wave- Xk,l form digitizer (CAEN V1751) between April 2014 and where Nbins(= Ebins tbins) was the total number of bins September 2014 due to a di↵erent textcolorredoperation ⇥ and Rdata(ex) is the event rate where k = i t +j.The method used in that period. This e↵ect contributes an k bins matrix V contains the statistical uncertainties· of the uncertainty of 0.3% to the energy scale. Other e↵ects stat bins, and V is the covariance matrix of the systematic from LED calibration, trigger threshold stability, timing WIMPsys case Abe et al. (XMASS collaboration ) Phys Lett. B (2016)272 uncertainties as derived from the relative cut eciency. calibration were negligible. The observed count rate after We performed two analyses, one assumed WIMP in- cuts as a function of time in the energy region between teractions, the other one was independent of any specific 1.1 and 1.6 keV is shown in Fig. 2. The systematic er- ee dark matter model. Hereafter we call the former case as

rors caused by the relative cut eciencies are also shown. ] a WIMP model and the latter case for a model indepen-ee •2013 Nov - 2015 March 1.05 7GeV dent analysis. 1.1-1.6 keVee (4.8 - 6.8 keVnr)

(359.2 live days)In the case of the WIMP model,theexpectedmodu- 1 8GeV, ]

ee lation amplitudes become a function of the WIMP mass 1.05 •assuming WIMP spectrum 0.95 1.1-1.6 keVee (4.8 - 6.8 keVnr) Ai(m) as the WIMP mass m determines the recoil en-

1 ergy• 2D ﬁlng (ime and energy bin ) spectrum. The expected rate in a bin then becomes: 0.9 t0 = 152.5 day (Jun. 2nd) stat error 1 ω = 2π/T (T = 365.24. day) 0.95 tj + tj 0.85 systematic error

2 Rate [events/day/kg/keV ex (t t0) Ri,j = Ci + n Ai(m)cos2⇡ dt, (3) 0.9 0 100 200 300 400 500 t 1 t · T j 2 j Day from 2014.Jan.1 Z Ai: amplitude 0.85 Rate [events/day/kg/keV where n is the WIMP-nucleonCi: constant cross section. To ob- 0 100 200 300 400 500 XENON10-S2 ±1 σ expected Day from 2014.Jan.1 tain the WIMP-nucleonσ crossχ: WIMP-nucleus section the cross data section was ﬁtted (2011) ±2 σ expected mχ:WIMP mass in the energy range of 1.1-15 keVee. We assume a stan- DAMA/LIBRA(2009 Savage) dard spherical isothermalt0:152.5 galactic day halo model with the 5sigma low mass FIG. 2. (color online) Observed count rate as a function of T : 1 year most probable speed of v0=220 km/s, the Earth’s ve- time in the 1.1 - 1.6 keVee (= 4.8 - 6.8 keVnr) energy range. •DAMA/LIBRA region is mostly XMASS(2013) The black error bars show the statistical uncertainty of the locity relative to the dark matter distribution of vE = CoGeNT (2013) CDMS-Si (2014) count rate. Square brackets indicate the 1 systematic er- 232 + 15 sin2⇡(t t )/T km/s, and a galactic escape ve- excluded by 0 annual modulaion ror for each time bin. The solid and dashed curves indicate locity of vesc = 650 km/s, a local dark matter density 2 the expected count rates assuming 7 and 8 GeV/c WIMPs of 0.3search. GeV/cm3, following [18]. In the analysis, the sig- XMASS 40 2 respectively with a cross section of 2 10 cm where the nal eciencies for-41 each WIMP2 mass are estimated from LUX(2014) XENON100(2012) WIMP search sensitivity closed to DAMA/LIBRA.⇥ <4.3 x 10 cm (90% CL) @ 8GeV Monte Carlo simulation of uniformly distributed nuclear recoil events in the liquid xenon volume. The system- To retrieve the annual modulation amplitude from the atic error of the eciencies comes from the uncertainty Masaki Yamashita 39 data, the least squares method for the time-binned data of liquid xenon scintillation decay time of 25 1 ns [5] ± 4

and is estimated as about 5% in this analysis. The ex- 2 pected count rate for WIMP masses of 7 and 8 GeV/c ±1 σ expected 40 2 XENON10-S2 with a cross section of 2 10 cm for the spin indepen- (2011) ±2 σ expected dent case are shown in⇥ Fig. 2 as a function of time after DAMA/LIBRA(2009 Savage) all cuts. This demonstrates the high sensitivity of the XMASS detector to modulation. As both methods found XMASS(2013) no significant signal, the 90% C.L. upper limit by method CoGeNT (2013) CDMS-Si (2014) 1 on the WIMP-nucleon cross section is shown in Fig. 3. The exclusion upper limit of 4.3 10 41cm2 at 8 GeV/c2 XMASS was obtained. The 1 scintillation⇥ eciency of [22] was LUX(2014) used to obtain a conservative limit. To evaluate the sen- XENON100(2012) sitivity of WIMP-nucleon cross section, we carried out a statistical test by applying the same analysis to 10,000 dummy samples with the same statistical and systematic errors as data but without modulation by the following a FIG. 3. (color online) Limits on the spin-independent elastic procedure. At first, time-averaged energy spectrum was WIMP-nucleon cross section as a function of WIMP mass. obtained from the observed data. Then, we performed The solid line shows the XMASS 90% C.L. exclusion from the annual modulation analysis. The 1 and 2 bands a toy Monte Carlo simulation to simulate time variation ± ± of event rate of background at each energy bin assum- represent the expected 90% exclusion distributions. Limits as well as allowed regions from other searches based on counting ing the same live time as data and including systematic method are also shown [2, 3, 5, 8–10, 23]. uncertainties. The 1 and 2 bands in Fig. 3 out- line the expected 90%± C.L. upper± limit band for the no- modulation hypothesis using the dummy samples. The result excludes the DAMA/LIBRA allowed region as in- in Fig. 4 represent expected amplitude coverage derived terpreted in [8] for WIMP masses higher than 8 GeV/c2. from same dummy sample above by method 1. This test This limit is consistent between two di↵erence of anal- gave a p-value of 0.014 (2.5) for method 1 and of 0.068 ysis methods (less than 10% for the cross section) and (1.8) for method 2. For both methods the model in- still excludes in di↵erent astrophysical assumptions (up- dependent amplitudes found in the data are consistent 41 2 per limit of 5.4 10 cm in the case of vesc = 544 km/s with background fluctuations. To be able to test any [24]). The best⇥ fit parameters in a wider mass range is model of dark matter, we evaluated the constraints on 42 2 a cross section of 3.2 10 cm for a WIMP mass of the positive and negative amplitude separately in Fig. 4. 140 GeV/c2. This yields⇥ a statistical significance of 2.7, The upper limits on the amplitudes in each energy bin however, in this case, the expected unmodulated event were calculated by considering only regions of positive or rate exceeds the total observed event rate by a factor of negative amplitude. They were calculated by integrating 2, therefore these parameters were deemed unphysical.3 Gaussian distributions based on the mean and sigma of Model Independent Case data (=G(a)) from zero. The positive or negative upper For the model independent case, the expected event a tillation light as well as the intrinsic light yield of the was used. The data set was divided into 40 time-bins up 1 Abe et al. (XMASS collaboration ) Phys 57Lett. B (2016)272rate was estimated as: limits are satisfied with 0.9 for 0 G(a)da/ 0 G(a)da liquid xenon scintillator are extracted from the Co cal- (tbins) with roughly 10 days of live time each. The data 0 0 ibration data the Monte Carlo simulation [17]. With that in each time-bint + 1 weret then further divided into energy- or G(a)da/ G(a)da,wherea and aup are the j 2 j (t t ) aup R R we found that we can trace the observed photoelectron binsex (E ) with a width of 0.5 keV .Twofitting0 meth- 1 Ri,j =bins Ci + Ai cosee 2⇡ dt, (4) amplitude and its 90% C.L. upper limit, respectively. change in the calibration data as a change as the absorp- ods were performed1 independently. Both of themT fit all R R Model independent analysis : tj 2 tj tion length, while the scattering length remains stable energy- andZ time-bins simultaneously.✓ Method 1 used◆ a Method 1 obtained positive (negative) upper limit of 2 • Noat sign 52 cm for with SUSY a standard particle deviation at LHC of so0 far..6% .Wethenwhere‘pull the term’ free↵ with parameters2 defined as:Ci and Ai were the unmodu- 2.1( 2.1) 10 events/day/kg/keVee between 1.1 and ± free in energy bin ⇥ re-evaluate the absorption length and the relative intrin- lated event rate and the modulation amplitude, respec- 1.6 keVee and the limits become stricter at higher en- •No sign in direct detection for more than Ebins tbins data ex 2 sic light yield to see the stability of the scintillation light (Ri,j Ri,j ↵Ki,j) decade. tively.2 t=0 and T were the phase and period+ ↵2, of(1) the mod- ergy. The energy resolution (/E) at 1.0 (5.0) keVee is response by fixing the scattering length at 52 cm. The (stat)2 + (sys)2 i j i,j i,j ! absolute absorption length varied from about 4 m to 11 ulation, andX tXj and tj was the time-bin’s center and estimated to be 36% (19%) comparing gamma ray cal- •important to look for variety candidate. Nuclear Recoil Energy [keVnr] m, but the relative change in the intrinsic light yield stay- width, respectively.data ex In the fitting procedure, the 1.1–7.6 ibrations and its Monte Carlo simulation. As a guide- where Ri,j , 5Ri,j , (stat)10 i,j and15 (sys)20 i,j are25 data, ex-30 • Annualing within modulation0.6% over signal the entire is searched data taking for period. ] 0.05 ± keVpectedee ee energy event rate, range statistical was used and systematic and the error, modulationre- pe- line, we make direct comparisons with other experi- The time dependence of the photoelectron yield a↵ects 0.04 without any model assumption. riodspectively,T was of fixed the (i to-th one energy-DAMA year and andj-th the time-) phase bin.ExpectedThet0 ± 1toσ 152.5 ments not by considering a specific dark matter model the eciency of the cuts. Therefore, we evaluate the ab- time0.03 is denoted as the number of days from January 1, • sorption Amplitude length (Ai) dependence and Constant of the relative (Ci) are cut free e cien- days ( 2nd of June) when the Earth’s velocityExpected ± 2σ relative but only count rate. The maximum amplitude of 2014.0.02⇠Ki,j represents the 1 correlated systematic error 2 ⇠ cies through Monte Carlo simulation. If we normalize to the dark matter distribution is expected to be maxi- 2.5 10 events/day/kg/keV between 2.5 and 3.0 parameter. on0.01 the expected event rate based on the relative cut ef- ee the overall eciency at an absorption length of 8 m, this mal. Figure 4 shows the best fit amplitudes as a func- keV⇥ was obtained by DAMA/LIBRA in [11] while • Slightly negative amplitude was observed. ficiency0 in that bin. Method 2 used a covariance matrix ee eciency changes from 4% to +2% over the relevant to propagate the e↵ects of the systematic error. Its 2 3 tionXe or NaI(Tl) -0.01 of energy for method 1 after correcting for the ef- XMASS obtains a positive upper limit of 3.0 10 • absorption Signifcance range. was The evaluated position dependence with test of the e- was defined as: 0.8 ⇥ ciency was taken into account as a correlated system- ficiency.-0.02 The eciency was evaluated0.6 from gamma ray events/day/kg/keVee and this limit is lower than their statistic (10,000 sample) and no N 0.4 atic error ( 2.5%). This is the dominant systematic Monte-0.03 Carlobins simulation with a flat energy spectrum uni- count rate. XENON100[16] obtained annual modu- ⇠ ± 2 data ex Efficiency 0.21 data ex uncertaintysignifcant in modulated the present analysis. signal has The been second largest = t0(R =k 152.5R dayk )( V(Jun.stat+ 2nd)Vsys)kl (Rl Rl ), (2) 3

Amplitude[events/day/kg/keV -0.04 0 formly distributed in the sensitive0 volume2 4 (Fig.6 8 4 inset).10 lation amplitude (2.7 0.8) 10 counts/day/kg/keVee k,l ω = 2π/T (T = 365.24. day) Energy[keV ] contributionobserved. comes (1.8σ from a gain instability of the wave- ee ± ⇥ 3 ） Both-0.05 methodsX are in good agreement and ﬁnd a nega- (2.0–5.8 keV ) while XMASS gives ( 4.0 1.3) 10 form digitizer (CAEN V1751) between April 2014 and 0 1 2 3 4 5 6 7 8 ee -3 -3 where Nbins(= Ebins tbins) was the total number of bins ± ⇥ •

ee lation amplitudes become a function of the WIMP mass 1.05 1.1-1.6 keVee (4.8 - 6.8 keVnr) Ai(m) as the WIMP mass m determines the recoil en-

1 ergy spectrum. The expected rate in a bin then becomes:

1 0.95 tj + 2 tj ex (t t0) Ri,j = Ci + n Ai(m)cos2⇡ dt, (3) 0.9 t 1 t · T Z j 2 j 0.85 Rate [events/day/kg/keV where n is the WIMP-nucleon cross section. To ob- 0 100 200 300 400 500 Day from 2014.Jan.1 tain the WIMP-nucleon cross section the data was ﬁtted in the energy range of 1.1-15 keVee. We assume a standard spherical isothermal galactic halo model with the FIG. 2. (color online) Observed count rate as a function of most probable speed of v =220 km/s, the Earth’s ve- time in the 1.1 - 1.6 keVee (= 4.8 - 6.8 keVnr) energy range. 0 The black error bars show the statistical uncertainty of the locity relative to the dark matter distribution of vE = count rate. Square brackets indicate the 1 systematic er- 232 + 15 sin2⇡(t t )/T km/s, and a galactic escape ve- 0 ror for each time bin. The solid and dashed curves indicate locity of vesc = 650 km/s, a local dark matter density 2 the expected count rates assuming 7 and 8 GeV/c WIMPs of 0.3 GeV/cm3, following [18]. In the analysis, the sig- 40 2 respectively with a cross section of 2 10 cm where the nal eciencies for each WIMP mass are estimated from WIMP search sensitivity closed to DAMA/LIBRA.⇥ Monte Carlo simulation of uniformly distributed nuclear recoil events in the liquid xenon volume. The system- To retrieve the annual modulation amplitude from the atic error of the eciencies comes from the uncertainty data, the least squares method for the time-binned data of liquid xenon scintillation decay time of 25 1 ns [5] ± DM - electron recoil models

•WIMP-electron scattering •Signal is not a nuclear recoil. –R. Bernabei et al. PRD, 77 02308 •e.g. (2008), • no loop-induced nuclear recoil - axial –J. Kopp et al. PRD 80, 083502 (2009) vector interaction –B.M. Roberts et al., PRL 116, 023201 •photon emission from excited DM (2016) (Luminous dark matter) •Luminous dark matter •modulation signal –B. Feldstein et al., PRD 82, 075019 •axion like particle can not be candidate (2010) because σ ~1/v , dm fux ~ v. •Mirror Dark Matter •DAMA/LIBRA vs LXe –R. Foot, Int. J. Mod. Pays. A 29, 126, •Energy deposit ~ 3 keV energy deposit. (from (2014) DAMA/LIBRA) •Plasma Dark Matter •Event rate is similar for Xe(z=54) and Iodine –J. D. Clarke at el. axXiv1512.06471v (z=53) •… •modulation analysis is not depend on the halo model.

Masaki Yamashita 41 Page 8 of 11 Eur. Phys. J. C (2013) 73:2648

B. Feldstein et al., PRD 82, 075019 (2010) DAMA/LIBRA • DM is excited by hitting the Earth rock. Fig. 9 Distributions (histograms) of the variable Sm Sm ,whereσ are • Emit photon in the detector −⟨σ ⟩ excited ground the errors associated to the Sm values and Sm are the mean values of • χ -> χ + γ (~ 3keV) the modulation amplitudes averaged over the⟨ detectors⟩ and the annual cycles for each considered energy bin (here !E 0.25 keV). Each = • Unlike axion-like particle, the signal has annual Fig. 8 Energy distribution of the Sm variable for the total cumulative panel refers to a single DAMA/LIBRA detector (the detector 16 was exposure 1.33 ton yr. The energy bin is 0.5 keV. A clear modulation out of trigger for the first five annual cycles [3]). The entries of each modulation × is present in the lowest energy region, while Sm values compatible with histogram are 112 (the 16 energy bins in the (2–6) keV energy interval • rate depends not mass but volume of the detector. zero are present just above. In fact, the Sm values in the (6–20) keV and the seven DAMA/LIBRA–phase1 annual cycles) except for detec- energy interval have random fluctuations around zero with χ 2 equal to tor 16 (32 entries); the r.m.s. values are reported in Fig. 10—bottom. • We consider only density for comparison. 35.8 for 28 degrees of freedom (upper tail probability of 15 %) The superimposed curves are Gaussian fits

ρ(NaI) 3.67 = = 1.27 Rate(Xe/NaI) = ρ(Xe) 2.88

0.08 DAMA/LIBRA in Xe.(Luminous) 0.06 CL90% 3σ χ 0.04 5σ

0.02 * 0 χ -0.02 χ γ -0.04

1 2 3 4 5 6 7 8

Amplitude [counts/day/kg/keVee] Energy [keVee] Masaki Yamashita 42 Future prospects

Masaki Yamashita43 XMASS Experiment

XMASS I XMASS 1.5 XMASS II FV:100kg FV:3tonton FV:10ton24Ton

Masaki Yamashita 44 Background 10−3 222Rn 10 μBq/kg

4 10− 2νββ 136Xe (nat)

−5 10 solar neutrino 222Rn 0.1 μBq/kg(214Pb) 10−6 Kr < 0.1 ppt(expected)

7 10− 100GeV WIMP 10-46cm2

10−8 0 10 20 30 40 50 60 70 80 90 100 Rn background is the key for any DM and neutrino physics search. (WIMP, Super-WIMP, Axion, 2nuECEC etc) Two phase reduces ~1/200 for electron recoil events. 45 Masaki Yamashita LXe detector for dark matter ﬁnal

PMT S1 Gas S Liqu E e Liquid Xe S E PMT lowest BG Rn removal PMT array PMT chamber (charcoal)

PMT array

Gas Xe S2 Eg

Liquid Xe e- surrounded by Photo sensor > 10 ton volume S1 Ed

PMT array Masaki Yamashita 46 図 6.7: Photographs of the Rn removal system for the XMASS. (1) is charcoal housings with heating wires. (2) is cryogenic system, which use pulse tube refrigerator and HFE as coolant.

102 XENONnT: Sensitivity

39 ] −

2 10 DAMA/Na XENON1T Sensitivity in 2 t⋅y −40 Expected limit (90% CL) 10 DAMA/I CDMS-Si (2013) ± 1 σ expected 10−41 ± 2 σ expected XENON10 (2013) 10−42 SuperCDMS (2014) PandaX (2014) DarkSide-50 (2015) 10−43 −44 LUX (2015) 10 XENON100 (2012) −45 model) 10 ⋅y - LUX2015 ~5ton −46 XENON1T (2 t 10 model) ~40ton LUX2015 10−47 ⋅y - XENONnT (20 t −48 neutrino ﬂoor 10 coherent scattering −49 Billard et al., Neutrino Discovery limit (2013)

WIMP-nucleon Cross Section [cm 10 6 10 20 30 100 200 1000 2000 10000 arXiv:1609.06735 2 WIMP mass [GeV/c ] SI Figure 1: Plot of rescaled spin-independent WIMP detection rate ⇠ (,p)versusm from several published results versus current and future reach (dashed) of direct WIMP detection • Spin-independent WIMP-nucleon interaction cross section sensitivity of ∼2×10−48 cm2 experiments. ⇠ =1(i.e. it is assumed WIMPs2 comprise the totality of DM) for the experimental projectionsfor WIMPs and with for all a mass models ofexcept50 GeVRNS/c and(arXiv:1512.07501) pMSSM. Masaki Yamashita 47 Guillaume Plante - XENON Dark Matter 2016 - UCLA - February 19, 2016 16 / 17 scale. The scans over parameter space typically range up to weak scale soft terms of 4 TeV and are subject to a variety of constraints including LHC sparticle search limits and that TP 2 ⌦1 h 0.12. For general projections from a three parameter model involving just electroweak- inos, see Ref. [56].

3 Spin-independent direct detection

We ﬁrst examine a grand overview of prospects for spin-independent SUSY WIMP direct detection. In this case, the neutralino-nucleon scattering cross section is dominated by Higgs and squark exchange diagrams. (Here, most results do not include extensive QCD corrections so theory predictions should be accepted to within a factor two unless otherwise noted [57]. Since squark mass limits are now rather high from LHC searches, the Higgs exchange h dia- gram usually dominates the scattering amplitude. The results are presented in Fig. 1 in the SI ⇠ (,p)vs.m plane. We leave the factor ⇠ in the y-axis to account for a possible depleted local abundance of WIMPs. For the experimental projections and for all models except RNS and pMSSM, it is assumed that ⇠ =1(i.e. it is assumed that WIMPs comprise the totality of

7 low background liquid xenon detector

• WIMP 1x10-47cm2 • > x 10 lower background for DM search via electron recoil Rn • pp solar (~ SK) • With this detector, carrying out Super Kamiokande those physics search (models SK 13 solar nu events/day are welcome) in XMASS. 18 ~10pp /5 7Be events/day/10ton 3.5 1

3 = 0.5 pp neutrino 2.5 S1) 0 /

(S2 2 (S2/S1) −0.5 10 10 1.5 Log

log −1

∆ WIMP 25 kton Fid 1 137Cs (662 keV gamma) 137 AmBe (neutron) −1.5 Cs (662 keV gamma) 0.5 AmBe (neutron) 0 2 4 6 8 10 12 14 16 18 20 plot from Xe10 WIMP ROI ideal case −2 S1 [keVee] (2.2 p.e./keVee) 0 2 4 6 8 10 12 14 16 18 20 S1 [keVee] (2.2 p.e./keVee)Masaki Yamashita 48 FIG. 31: (Color online) The electronic and nuclear recoil bands shown in Log10(S2/S1) vs. S1 space. FIG. 32: (Color online)The bands in figure 31 have been transformed to show the distance in Log10(S2/S1) space from the ER band center, giving the new discrimination parameter, Log10(S2/S1). The vertical lines indicate the WIMP region of interest (ROI). this range are dominated by recombination fluctuations, until the lowest energies where uncorrelated statistical fluctuations take over. The width of the electronic re- Super Kamiokande coil band is very important for gamma rejection because mean and sigma from the NR band Gauss fits, respec- the two bands overlap. Due mainly to the non-uniform tively. The Gauss fits were performed only to define the S1 response at di↵erent locations in the fiducial region, window bounds; the NR acceptance, Anr, was calculated applying spatially-dependent corrections to S1 based on by counting the number of AmBe events that fall within the 131mXe calibration (see section VI A 3) improves the this window, for each energy bin. overall S1 resolution and thus helps to reduce the vari- ance of the bands. Data with the AmBe neutron source 60 were taken on December 1, 2006 for approximately 12 Nuclear Recoils (AmBe) hours, accumulating a total of about 260,000 events. The Electronic Recoils (137Cs) energy dependence of both bands makes it dicult to pre- 50 WIMP Acceptance Window cisely measure the discrimination power in the absence of extraordinarily large calibration datasets. In an e↵ort to 40 remove this energy-dependence, a one-dimensional trans- formation that “flattens” the ER band is applied to all 30 data. The ER band is broken up into 1 keVee-wide, ver- Counts tical slices in S1. For each, a Gauss fit is applied to the 20 Log10(S2/S1) spectrum. The mean of each fit now represents the center of the ER band in that particular bin. A high-order polynomial is fit to the Gauss means, which 10 provides an analytic form for the ER band centroid as a function of S1, and is subtracted from every data point in 0 both bands. This procedure flattens the ER band (and −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 Log (S2/S1) to a large extent, the NR band as well), and introduces 10 a new parameter, Log10(S2/S1), which represents the FIG. 33: (Color online) Distributions of Log10(S2/S1) for distance from the ER centroid in Log10(S2/S1) space. nuclear and electronic recoils in the range 13.4–17.2 keVr. The Figure 32 shows the bands in Log10(S2/S1) space. WIMP acceptance window in this particular energy range is Although the energy dependence of the ER band cen- defined by the blue, shaded rectangle which is between µ and µ 3 of the NR band. troid has been removed, the NR band centroid and width still change with energy. Again, the flattened bands are broken up into vertical S1 slices, only this time more coarse binning is used—seven bins in the WIMP en- The shape of the Log10(S2/S1) fluctuations in the ergy region of interest (ROI)—in order to maximize the ER band are “empirically” Gaussian; that is, with statistics in each slice, and a Gauss fit is applied to the the statistics available, they appear consistent with Log10(S2/S1) spectrum of both bands. One such slice is a Gaussian distribution. As previously stated, the shown in Figure 33, for the range 13.4–17.2 keVr (1 keVr Log10(S2/S1) spectrum is dominated by recombina- = 1.1 pe, according to [11]) of nuclear recoil energy. The tion fluctuations, which are poorly understood, and thus WIMP acceptance window is defined to lie in the range more cannot be said in the absence of a larger calibra- (µ 3) < Log (S2/S1) <µ,whereµ and are the tion dataset. We calculate the predicted ER rejection in 10 Summary • Both two phase liquid xenon detector and single phase detector play main role for direct dark matter search. • XMASS-I carried out variety of candidate dark matter • low-mass WIMP, modulation search, Super-WIMP + solar Axion and 2nuECEC. •Future liquid xenon experiment will be able to detect pp solar neutrino, double beta decay. •Keys for future DM search are the light sensor and Rn background and XMASS group has strong points for these challenges. •With this detector, not only WIMP but also variety of DM search and neutrino physics study will be conducted in XMASS. Higgs GW Dark Matter

Masaki Yamashita 50