Pos(DSU2015)032 (On Behalf of the XENON Collaboration) † ∗ Diglio@Subatech.In2p3.Fr Speaker

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PoS(DSU2015)032 http://pos.sissa.it/ (on behalf of the XENON collaboration) † ∗ [email protected] Speaker. We gratefully acknowledge support from Region des Pays de la Loire The understanding of the natureof of the the biggest mysterious challenges Dark infrom Matter frontier astrophysics in science and our today. cosmological Universe measurements. There represents A areput number one strong of forward proposed evidences over candidates for have time: its been (WIMPs). existence one The of XENON the dark matter mostWIMPs project compelling with aims target are at nuclei finding Weakly in direct Interacting anber evidence ultra-low Massive (TPC) for background based the Particles dual-phase detector. scattering xenon of After Time thegeneration Projection successful Cham- XENON1T operation is of ready the to XENON100National start instrument Laboratory. data the taking next at the italianIn this Gran proceeding Sasso an underground introduction INFN tothe the latest direct results dark matter of detectionlenges the methods related XENON100 will to be a experiment reviewed; ton-scale will liquidXENON1T be xenon experiment detector as firstly will well revised, as be its discussed then prospects and and the the projected current special physics status reach chal- of will the be presented. ∗ † Copyright owned by the author(s) under the terms of the Creative Commons c Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). 11th International Workshop Dark Side of14-18 the December Universe 2015 2015 Yukawa Institute for Theoretical Physics, Kyoto University Japan Sara Diglio XENON1T: the start of a newDark era Matter in the search for Subatech, École des Mines de Nantes,E-mail: CNRS / IN2P3, Université de Nantes, Nantes, France PoS(DSU2015)032 Sara Diglio 5% while the remainder is accounted for by dark 2 ∼ -ray telescopes. Finally, evidence for WIMPs may also come from γ 26%, baryonic matter makes up ∼ ]. The existence of DM is at present one of the strongest pieces of evidence that the current 1 There are several complementary methods used to determine the particle nature and properties In the past decade, breakthroughs in cosmology have transformed our understanding of the collider searches. The Large Hadron Colliderthey have experiments excellent are ability already for exploring seeing theeither the weak be missing scale produced energy as directly signals or characteristic of via WIMP decays that of could other new matter states. of DM. Direct detection experimentsas examine they the elastically scatter interaction off ofing nuclei WIMP evidence in of particles the WIMP with target. pairs a annihilatingsignals DM detector somewhere are may in important the also targets galactic be for neighborhood. abased discovered anti-matter vast These indirectly searches array indirect by and of find- experiments, including neutrino telescopes, space- theory of fundamental particles andphysics, forces, is incomplete. summarized by The nature thelution of Standard of this Model non-baryonic the (SM) component "Dark is of Matter stillelementary particle puzzle" unknown, particle is and physics. of the fundamental reso- A importanceone number to possibility of motivated cosmology, by proposed astrophysics, other candidates considerations and in haveof elementary been particle undiscovered put physics elementary is forward particles that over that DM consists time: arisethe most naturally compelling in candidates are many Weakly theories Interacting Massive beyondare Particles the (WIMPs). well SM. These motivated, particles One not of onlyneously because solve they longstanding resolve problems the associated DMnaturally with in puzzle, the many but SM model also of frameworks because designed particlemetric they to physics. theories, simulta- understand theories the WIMPs weak with appear force, extrato including spatial be supersym- dimensions, formed and in others. thebaryonic early matter. These universe WIMPs particles and are are subsequently expectedthe predicted gravitationally to weak clustered scale interact (100 in weakly GeV with association – normal with 1 matter TeV). and have mass near Universe. A wide variety ofand observations gas now in support all a galaxies, unifiedmatter including picture which our in outweighs own, which the are luminous the immersedthe component visible in existence by stars a of at much Dark least larger Matter an cloud (DM)astronomer order in of Fritz of the non-luminous Zwicky magnitude. Universe found has Evidence that steadily for additionalto accrued matter, since explain beyond the that gravitational 1930s, which binding when is ofusually the luminous, clusters was exhibit needed of a galaxies. characteristicthe flattening In visible out particular, galaxy rotation at disk, curves large implyingrotation of distances the curves, galaxies existence towards gravitational of and lensing, a beyond hot DMCosmic the Microwave halo. gas Background edge in and Since of measurements galactic then, of clusters, evidence largeport precision from scale the structure measurements galactic existence in of of the DM. the Universe allof By sup- baryons combining as these deduced data from sets Bigin with Bang the many nucleosynthesis Universe others and – – various current including measurementsUniverse estimates the of at put density Dark the Energy DM fraction of mass-energy density of the observable XENON1T: the start of a new era in the search for Dark Matter 1. Introduction energy [ PoS(DSU2015)032 Sara Diglio ]. 2 3 ]. An experimental technique which demonstrated to be very effective 3 ultra-low background experimental environment; large detector mass to enhance thelow interaction energy probability threshold inside to the detect target; thegood smallest discrimination recoil power energies; against particle interactionsstable that detector might performance mimic over WIMP time collisions; scales of a few years. Noble gas detectors are relatively simple, and the liquids can be purified in situ. The higher As detector media, noble gases present interesting advantages such as the possibility to create Large efforts have been pursued to develop experiments which are able to directly test the In the following sections the DM direct detection principle will be described, with a particular In order to maximize the possibility to observe a DM signal, it is requested that the detectors Different technologies have been explored so far to fulfill the above requirements, a detailed • • • • • operating temperatures of noble liquids allow more straightforward and less expensive cryogenic homogeneous detection volumes at a reasonableadvantage cost of liquid with noble high gas particle detectors stoppingfast is powers. the scintillation Another accurate response interaction and position ionisation reconstructiondiffusion signal thanks for to in drifting presence electrons. of ashielding With drift to adequate avoid field, the position and surface resolution the contamination the problems lowthe that detectors transverse exploitation plague of can solid a state employ detectors. good self- fiducialisation Thiswithin allows in the order active to volume of reduce the background detector. exposition for final search 2.1 Noble gas detectors for the direct DM detection consists ofin a the target following. made of liquefied noble gases, as it will be discussed particle nature of DM. Givenability the low of interaction multiple strength collisions expected withinspectrum for a of the detector DM single particle, is scattering the negligible, events.measure prob- thus the In the nuclear the signature recoils most results energytarget common produced in nuclei. approach, by a Another the collisions possible recoil experiments between DM signature attempt DMAs is candidates consequence to represented of and by the detectors the Earth so-calledWay rotation "annual halo modulation". around relative to the the Sun, Earth thepossibility is speed largest to of around measure June the the 2nd DM direction and particlesexperiments, smallest of since in in the a the December. recoils strong Milky Moreover, angular would the dependence improve of the WIMP discriminating interactions power is of expected [ the 2. Dark Matter direct detection focus on the XENON project. meet the following conditions: summary can be found in [ XENON1T: the start of a new era in the search for Dark Matter PoS(DSU2015)032 Sara Diglio . This is about 2 50 GeV/c ∼ . ], consisting of 25 kg of LXe, 5 3.1 , 4 3.5 ton, XENON1T is the first multi- ∼ , recent results from XENON100 will be dis- 3.1 for a WIMP mass of 4 2 . -rays, betas), which is an important method to reduce cm γ 3.3 47 − ] has been inaugurated in November 2015. First science data 9 ], consisting of 161 kg of LXe. After the successful operation , 7 8 , 6 and an overview of status of the XENON1T detector including design characteristics ). These detectors usually use either Argon (Ar) or Xenon (Xe), and eventually Neon reported characteristics and expectations of the different XENON experiments. 2 1 3.2 ]. To achieve another order of magnitude in sensitivity, the XENON Collaboration plan to 9 Table At present, the XENON Collaboration consists of 21 institutions and about 130 collaborators The XENON Collaboration is working on the search for DM and has chosen the dual-phase In the following sections the focus will be on the XENON project: the functioning of the 10 GeV/c build and install in thethe same LXe vacuum mass cryostat and acryogenic with new plants even detector, and lower data XENONnT, background. acquisition with systemis more of set The than XENON1T, to new making twice start rapid experiment operating realization. by will XENONnT 2019. use the same shield, and its scientific reach will be presented in of the XENON100 experiment – forthe many next years generation the XENON1T most [ sensitiveare WIMP expected detector by in end of the spring world 2016. – With total Xe mass of cussed in from all over the world.del Gran The Sasso XENON (LNGS) detectors in haveXENON Italy been Collaboration at operating completed an first at average the the depth XENON10then Laboratori of detector the Nazionali 3600 [ XENON100 m detector water [ equivalent since 2006. The ton LXe experiment for DM searchesWIMP-nucleon world-wide. cross section It close has to aa 10 design sensitivity factor for 100 spin-independent below theyear XENON100 [ best limit and will be reached with an exposure of 2 ton per (Liquid-Gas) Xe TPC as detecting medium. the background of the experiment as it will be discussed in section 3. The XENON project XENON dual-phase TPC will be described in sec XENON1T: the start of a new era in the search for Dark Matter systems with respect to otherbility technologies. inside the With target their is large∼ increased, detector allowing mass for a the better interaction sensitivity proba- at large WIMP masses (above (Ne), in liquid phasegle (LAr phase or (XMASS, LXe, DEAP, CLEAN) eventually orin LNe) dual-phases this as (WARP, XENON, latter target DarkSide, case, material. LUX, amaterial ArDM), Time will They Projection be can used. Chamber be (TPC) Thepulse either first with shape category sin- liquid discrimination exploit to and the select gaseous nuclear scintillationtechniques phase recoils. light with of Dual-phases in the detectors ionization the the may charge liquid, same measurements combine possibly resulting thetween in using above nuclear a recoils more and efficient electronic discrimination recoils be- ( PoS(DSU2015)032 2 ] 9 and cm γ 1 t [ 4 47 2 − − × Sara Diglio 10 10 × × 1.8 1.6 ∼ ∼ @50 GeV/c ] in 2 years 7 34 kg [ × 2 3 cm 2 − 45 10 − × 10 × 5.3 ∼ 2.0 @55 GeV/c . An interaction in the liquid Xe target gener- 1 5 ] in 224.6 live days 4 5.4 kg [ × 2 cm 2 44 − 10 × 1 D=25, H=1589 1" PMTs(R8520) D=30, H=3060 242 1"∼ PMTs (R8520)4.5 @30 GeV/c D=96, H=95 248 3" PMTs 65 (R11410) 10 XENON10 XENON100 XENON1T in 58.6 live days day) · kg · Comparison of characteristics among the XENON experiments. Measurements are reported for The detection principle is presented in Fig. The XENON detectors consist in Time Projection Chambers (TPCs) filled with Xe in liquid Rn/Xe Bq/kg) Kr/Xe (ppt) 5000 20 0.2 interactions (electronic recoils, ER) and nuclear recoils (WIMP signal and neutron background, µ diameter, height 222 ( ER bkg in FV WIMP-nucleon TPC size (cm): Photo sensors nat (evts / keV cross section limits Total Xe mass (kg)Target Xe 25 mass (kg) 14Fiducial Xe mass (kg) 5.4 161 62 48 3500 2000 1000 β NR) is therefore possible byionization charge measuring signal. the The ratio ratio of S2/S1 prompt is scintillation about light 5 signal times bigger to for collected electron events compared to ates prompt scintillation light andtoward the ionization gaseous electrons. phase and Electronsprimary there are and detected drifted through secondary a by light process are anon of detected electric the proportional by bottom field scintillation. photomultiplier of tubes the Both (PMTs) cylinder.x, placed The y interaction on coordinates point the determined is topwhile reconstructed from and in the the three z hit dimensions, coordinate with pattern isscintillation the of deduced signal the by in means localised the of gas signalsignal the phase, on by drift called the the S2, time drift top is between time PMTsionization delayed the of array, relative whereas the two to electrons light electrons the through signals. produce S1 the athere (prompt liquid. The is diffuse scintillation) more Recoil track. recombination ions of produce electron-ion DueConsequently, pairs a to compared in dense nuclear their to region recoils different those of compared electrons, ionization tohave recoiling nuclear densities, fewer electron. recoils un-recombined produce ionization electrons. prompt scintillation Discrimination light between background but due to (LXe) and gaseous (GXe) phase. Table 1: XENON10 and XENON100 while expectations are shown for XENON1T. 3.1 The XENON detectors working principles XENON1T: the start of a new era in the search for Dark Matter PoS(DSU2015)032 . yr). 3.3 21 10 Sara Diglio ∼ τ background, ER), β and Xe, providing additional γ 131 Xe, Half-life: 136 Xe and 129 6 rays from external sources and good event position γ and 90% confidence level on spin-independent elastic WIMP- 2 at 55 GeV/c 2 cm and neutrons. In addition, the high atomic number and the large density make the inner 45 Left: working principle of the XENON liquid/gas dual-phase TPC. Right: sketch of the wave- − γ , 10 β The XENON100 detector is operative since 2008. In 2012 it has reached the sensitivity of Among the advantages of using Xe as a target detector, there are the two following: it is the XENON detectors rely on careful selection of low-background materials to suppress internal × 2.0 3.2 Results from XENON100 forms of nuclear recoils (WIMPs and neutrons, NR) and electronic recoils ( Figure 1: noble gas with the bestof stopping Xe power; found it in has nature almost are no stable, intrinsic or radioactivity, long-life since double-beta all emitter isotopes ( XENON1T: the start of a new era in the search for Dark Matter showing the different ratio of the charge (S2) and light (S1) signals for the two typesnuclear of events. events. This method allows a good discrimination of signal from background. volume of the Xe target virtuallyMore free details of about electromagnetic detector backgrounds. components and background predictions will be given in section resolution to define fiducial volume (FV). Externalreject shielding and an active veto are also required to sources of background, self-shielding against This property is crucialatomic for mass low with background respect experiments. tospin-independent other Furthermore, WIMP-nucleus noble interaction due rate gases, to is Xe proportional theand has to so much a the the higher square higher WIMP of expected signal the signalvantage should nuclear of rate. mass, be containing greatly almost In enhanced 50% fact, of for nonsensitivity the large zero to nuclei. spin spin-dependent isotopes, In WIMP addition interactions. LXeK Finally, has at Xe 1 the liquefies bar, ad- therefore at the temperaturesthan cryogenic below for system 165 lighter needed noble to gas keep that it will at request such lower temperature temperatures is for relatively their easier cryogenic. PoS(DSU2015)032 ]. 12 −

10 10 (green) ×

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Sara Diglio

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2 CDMS ]. Right side: Spin-

7 2

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expected sensitivity expected expected sensitivity expected

σ σ

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XENON100 limit (2013) limit XENON100 ± ± ZEPLIN−III

Ae WIMP Mass [GeV/c Mass WIMP

XENON10

−34 −35 −36 −37 −38 −39 −40

10 10 10 10 10 10 10 SD WIMP−neutron cross section [cm section cross WIMP−neutron SD ] ]. These limits result from the analysis of 2 on the left shows that for solar axions with 10 [ 3 ]. Green (yellow) bands on both figures are the 2 10 7 on the left). The result for spin-dependent interactions 2 on the right shows the upper limit on ALPs-electron coupling ] (fig. 3 7 , values of the axion-electric coupling constant ] and to perform analysis aiming at reconciling the apparent tension between 2 11 mass range. 2 ]. The former search is well motivated by models describing axions and ALPs as 12 Left side: the XENON100 limits on solar axions (blue line) at 90% C.L. Right side: the Left side: Spin-Independent (SI) WIMP-nucleon cross section limits [ (yellow) are shown in both plots. Limits form other experiments are also shown for comparison [ ) uncertainty on the expected sensitivity. The resulting exclusion limits (90% CL) in blue are also σ σ The same XENON100 data have been used to investigate the axions and axion like particles (2 σ Figure 3: XENON100 limit (90% CL) onthat ALP ALPs coupling to constitute electrons all as theand a dark 2 function matter of in the our mass, galaxy under (blue the assumption line). The expected sensitivities at 1 are excluded (90% C.L.). Figure in the 5-10 keV/c masses below 1 keV/c XENON100 and other experiments withcollaboration the [ possible DM signal observed by the DAMA/LIBRA cold dark matter candidates whichbeen interact analyzed predominantly and with upper limits atomic have electrons: been set. ER events Figure have Figure 2: (ALPs) hypotheses [ data taken over an integrated period of 225 live-days. 1 represented. Other experimental results are also shown for comparison. XENON1T: the start of a new era in the search for Dark Matter nucleon scattering cross section [ on neutrons is reported on the right hand side of fig. Dependent (SD) WIMP-neutron cross section limits [ PoS(DSU2015)032 on the 4 Sara Diglio , as it would be seen by 2 σ σ σ . 2 15 days disfavored the interpretation of a ± confidence level. 8 σ 30 confidence level, as it can be seen in fig. 10 σ 25 9 8 20 7 ]. Right side: The XENON100 best-fit, 95% and 99.73% confidence level 13 15 6 S1 (PE) DAMA/LIBRA annually modulated spectrum (2-6)keV interpreted as leptophilic DM, axial-vector coupling mirror DM XENON100 70 summer live days ]. The measured phase of 112 5 10 14 Excluded models Confidence level WIMP axial-vector coupling to electronsKinematically mixed mirror DMLuminous DM 4.4 3.6 4.6 4 Mean electronic recoil energy (keV) band includes statistical and systematic uncertainties. The (blue) data points are XENON100 3 5 σ on the left shows the DAMA/LIBRA modulated energy spectra, interpreted as WIMPs 2 ]. A summary of the excluded models is reported in table Left side: The DAMA/LIBRA modulated energy spectra for different models (red and dark red), Exclusion limits on different leptophilic models that could have explained the DAMA/LIBRA 4 ]. 1 ]. 13 13 0 2 0 8 6 4

10 12 The other study exploited the periodic variations of the electronic recoil event rate in the (2-6) Fig. Concerning the possible DM signal observed by the DAMA/LIBRA, since the detector has no Rate (counts/PE/tonne/day) Rate keV energy range [ modulation due to standard DMright. halo In at addition, 2.5 the annual modulationof WIMPs interpreted to as electrons a was DM also signature excluded with at axial-vector 4.8 coupling data from the 70 summer liveis days also with shown their (dashed statistical cyan) uncertainty. [ The expected average XENON100 rate Figure 4: interpreted as WIMPs scattering through axial-vector interactions,tector. as The it 1 would be seen in the XENON100 de- contours as a functionyear of [ modulation amplitude and phase relative to January 1, 2011 for the period of 1 scattering through axial-vector interactions for the models listed in table Table 2: signal [ discrimination power between NR andnull-results ER, from a other experiments, possibility would to consist in reconcile assuminghypothesis, the leptophilic DM. the observed In signal XENON order to with Collaboration test the between such performed a two DM analyses candidate both andER focused electrons rate in on and the the allowed detectorsignal interaction to medium. [ exclude three The ﬁrst leptophilic study models used as the explanation overall for the DAMA/LIBRA XENON1T: the start of a new era in the search for Dark Matter the XENON100 experiment. PoS(DSU2015)032 on 5 plate PMT bases plate Field PTFE Copper bottom shaping Supports electrodes ]. Their Sara Diglio 19 , 18 , 17

, 16 . 5

bell PTFE pillars PTFE Diving PMTs Cathode reflector 9 ]. 9 ]. In the following sections the different subsystems constituting the XENON1T 9 ]. The details of the PMT performance are described in [ 15 Left side: XENON1T experimental area in the Hall B of the LNGS. Right side: drawing of the Liquid Xenon Detector The XENON1T experiment has been designed to increase the sensitivity of XENON100 by As part of the evolution of the XENON program, in the same underground laboratory where detector will be introduced and the experiment scientific reach will3.3.1 be presented. XENON1T subsystems The dual-phase TPC has the longestIt drift consists and of largest a active cylinder mass of2 of 95 tons LXe cm of and height any instrumented and TPC 96 with builttection cm to-date. 248 of diameter scintillation 3"-inch filled light Hamamatsu with and active PMTsused ionization LXe (R11410) for charge target for via of PMTs about proportional have the been gas simultaneous carefully scintillation.as de- selected possible The in materials [ order to keep the level of their radioactivity as low Figure 5: TPC and its components [ about two orders of magnitude.ground levels with To respect do to this, previousthe a experiments XENON are larger Collaboration required. unprecedented in A target order specialmass mass to care of and fulfill has more these lower been than requirements. back- taken three by and In tons purification particular, of systems to Xe, handle were a the firstlylow special total designed intrinsic storage/recovery and radioactivity, system, all then cryogenic detector built.screened infrastructures materials and In close where addition, to chosen the in after a target ordergenic screening distillation volume to column campaign, have reach were a been constructed. very water thoroughly A Cherenkovdeveloped Monte muon to Carlo veto estimate simulation and the based detector a on sensitivity GEANT4 cryo- to hastector the been interaction medium between [ a DM candidate and the de- the left shows a picture ofof the XENON1T the experimental TPC area and in its the components Hall is B represented of on the the LNGS. right A of drawing figure XENON100 is located, the commissioningjected of to XENON1T start is by ongoing: end of science spring data-taking 2016. is The pro- construction of XENON1T started in 2013. Figure XENON1T: the start of a new era in the search for Dark Matter 3.3 Design and status of the XENON1T PoS(DSU2015)032 Sara Diglio on the right. 5 ]. of deminaralized water, will act 20 3 s and neutrons. The water system γ C and a pressure of 2 bar. The system ◦ 10 ]. In the same service building where the cryogenic system is 21 Storage and Recovery Cryogenic and Purification Systems Cryostat Water Cherenkov Muon Veto The Storage and Recovery system (ReStoX) isrify an and self-made recover cryogenic up vessel to designed 7.6 to tonsBefore store, of transferring pu- Xe both the in Xe liquid into or ReStoX, in gaseous it phase is under stored high in purity conditions. bottles: a gas handling and impurity control located, a purification system consisting ofclean the commercial Xe high-flow from hot electronegative impurities getters via has continuous circulation been of installed gas trough to heated getters. The cryogenic system has beeninside designed the to cryostat liquefy at 3500 constant Kg pressureconsists of and of Xe cold two temperature and redundant for maintain pulse long itof tube term in about refrigerator operations. liquid 200 (PTR) The form W towers: system at one LXegency PTR temperature, like long and whose term a cooling power-outage second [ power LN2 is cooling system to be used in case of emer- consists of two independent cylindrical vessels:(insulated an with inner multi-layer vessel insulators 1.5larger and m inner high vacuum) and vessel and 1.1 for an m awalled outer of and more vessel diameter vacuum massive made insulated, carries future to independent detectorand accommodate inner for (XENONnT). pipes a Xe for A filling/recovery. PMT 7.5 signals/high An m voltagevalue additional is cables separate long of line line, 150 carries kV) double- to the theThe high detector system voltage through has (whose a been maximum custom-designed optimized ultra via highminimize finite vacuum mass fiber element contributing feedthrough. method to (FEM) background stress while analysis maximizing to allowable simultaneously working pressure. An ultra vacuum, thermallyceived insulated to system host made the of LXe detector low-radioactivity at material a has temperature been of con- -95 The system will alsosources provide and detector access leveling. points and feedthroughs for water purification, calibration A water tank 10.5 m high and 9.6 m in diameter, filled with 700 m XENON1T: the start of a new era in the search for Dark Matter average quantum efficiency is of 35%resolution at is Xe of scintillation about of 30%. 178the An nm active homogenous and volume electric their by drift single a field photoelectron cathodeof of at the 1 bottom external kV/cm and part will of a be the gate supplied TPC at inside including a its few components mm is below presented the in liquid fig. level. A sketch as an active shield around theis LXe equipped detector with against 84 low 8–inch energy identifying high quantum cosmic efficiency ray PMTs muons sensitive that tomimic WIMPs may Cherenkov interactions, light induce resulting aiming in high source at energy ofoperate background neutrons for as XENON1T. that This a system can will Water reach thus Cherenkovneutrons the Muon larger TPC Veto than with and 99.7% an in estimatedone case efficiency third also of in the the tagging parent cases) muon muon and1 induced larger is ton than hitting of 71.4% the fiducial otherwise. water volume The is tank muon estimated (this induced to happens neutron be background in less in than 0.01 per year [ PoS(DSU2015)032 Kr that is Sara Diglio 85 5% of the total ER background) ∼ 4% of the total ER background), solar ∼ 11 ], the functionality of the column has been verified. 85% of the total ER background) comes from the decay 24 , ∼ 23 –emitter contamination from the Xe is realized trough the cryogenic β Kr ]. XENON1T requires Kr concentration less than 0.2 parts-per-trillion (ppt) 85 22 Kr from which the Xe is extracted ( nat Rn daughters. Other sources of ER background are: the radioactive isotope on the left shows the spatial distribution of the ER background events from the detector 6 Xe (contained in the natural Xe) that is responsible for double–beta decays and that con- 222 Radioactivity from the different detector components will result in ER backgrounds within the Cryogenic Distillation Column Data acquisition and computing A Monte Carlo (MC) simulation fully based on GEANT4 has been developed in order to re- 136 neutrinos that scatter elastically off the electrons of the medium ( materials inside the whole activesponding volume, to in different target the masses energy are range also between indicated. 1 and 12 keV. FVs corre- tributes to about 1% of theFigure total ER background. contained in the and while commercially available Xe contains Krthe of difference about in 5 vapour pressures parts-per-billion (ppb). betweenment systems Kr The with and column sub-ppt Xe uses precision to [ remove Kr from Xe. By using measure- detector FV, whose main contribution ( of the An active removal of distillation column [ An high speed data acquisitionPMTs, system select (DAQ) interesting has events, been store developedthe data in lowest to possible order file, threshold to process and read raw totrigger data. the select on data online PC It data from farm. has using The been individual maximum designedtaking, channel DAQ while to rate readout the is and reach DM expected online trigger to is be estimatedcomputing/analysis around to facilities 1000 reach have Hz been 2 for put Hz. calibration in In data place:Concerning order to they the consist handle the in latter, total both a amount localprocess of and consistent data, remote and use systems. store of raw data sharing and resources Monte Carlo (GRID) simulations. is3.3.2 foreseen, Monte in Carlo particular simulation to produce via software the performance ofexperiment. the Inputs XENON1T from detector, screening and campaign predict from thethe sensitivity all MC. of detector The the components simulation have been hasbackgrounds used been which to used will tune to affect estimate the the discovery potential rate of of XENON1T. the different sources of ER and NR XENON1T: the start of a new era in the search for Dark Matter measures impurities level of each cylindersystem of connect Xe and gas analyze usingfilling. up a dedicated to Due Gas to four Chromatograph. the gas large This to cylinders scale improve to of the the recuperate performance XENON1T gas of detector,so the residuals the to experiment: during ReStoX dramatically it component detector shorten is is the able verycan purification strategic to also dead store time recover and it when purify the in liquiddouble detector case Xe walled, will of in be high temporary advance, filled. problems, pressure preventing Similarly, (72LN2 it losses bar) and of by vacuum Xe. an insulated internal sphere ReStoX LN-based consists of condenser. of 2.1 a meter diameter, cooled by PoS(DSU2015)032 . 1 − 100 90 keV) ]. · 9 Sara Diglio 80 day · 70 (kg 60 6 − 50 3.25 0.91 CNNS Radiogenic neutrons Muon-induced neutrons 40 30 Nuclear Recoil [keV] Energy 20 10 0 -7 -8 -9 -2 -3 -4 -5 -6 -11 -10

10 10 10 10 10 10 10 10

NR Rate [(kg [(kg Rate NR ] keV) day

⋅ ⋅ -1

day day kg ( [ Rate keV ) keV

] 12 ⋅ ⋅ -1 Xe + Solar neutrinos -4 -5 -6 -1 -2 -3 136 10 10 10 10 10 10 3 10 × . Events with S2 > 150 PE are selected assuming a 99.75% Kr + 7 220 85 200 180 Rn + 160 222 ] 140 2 120 [mm 2 R 100 ]. 80 Electron Recoils : Nuclear Recoils : Background Sourcesmaterials + radiogenic neutrons + muon-induced neutrons + CNNS Events 9 the predicted backgrounds in XENON1T assuming 99.75% ER discrimination with 60 3 40 Left side: Spatial distribution of the ER background events from the detector materials inside on the right shows the energy spectrum of each contributor of the total NR background Expectation values of events in XENON1T in 2 years exposure, within the 1 ton FV and in the S1 20 6 0 In table The separate contributions of ERs and NRs together with the total background spectrum as a 0

300 200 100 400 -100 -200 -300 -400 Z [mm] Z Table 3: range between 3 and 70 PE assuming 99.75% ER discrimination with a flat 40% NR acceptance [ a flat 40% NR acceptanceFV and are in summarized. the S1 Thebetween range reported 4 between numbers and 3 50 have and keV) been 70 considering evaluated a PE in 2 (on years 1 average, exposure. it ton corresponds to the NR energy range function of S1 is represented inER figure rejection with acorresponding flat to 40% three different NR masses acceptance. and expected cross Event sections rates are also for shown. three examples of WIMP signals Figure 6: the active LXe volume, inFV. Additional the FVs 1–12 corresponding to keV 800 energybrown kg, lines, range. 1250 respectively. kg The The and white 1530 regions thick present kgRight black a are side: background line also rate Energy indicated indicates smaller spectrum by than the the of 10 figures reference purple, the are red 1 from different and [ ton contributions to the NR background events in 1 ton FV. Both listed above, in 1 ton FV. XENON1T: the start of a new era in the search for Dark Matter Neutrons can produce NRs via elastic scatteringtering. off Among Xe the nuclei, main mimicking contributors the to WIMP-nucleondetector the scat- components, NR neutrons backgrounds that we are can produced list:and by radiogenic concrete the neutrons around interaction from the of cosmic undergroundinduced muons laboratory neutrons) with and and the with finally rock NRs the resulting detector fromFigure the materials coherent (so neutrino-nucleus called scattering (CNNS). muon- PoS(DSU2015)032 ] 9 ]. 9 Sara Diglio 80 70 2 2 2 cm cm -46 cm 60 -47 -46 . For comparison results from other = 2 10 = 2 10 2 σ = 2 10 , σ 2 σ , 50

2 , ν 2 40 S1 [PE] 13 = 50 GeV/c χ 30 m Total (ER+NR) backgroundTotal ER background from neutrons NR background NR background from m = 10 GeV/c WIMP, m = 100 GeV/c WIMP, m = 1000 GeV/c WIMP, 20 10 0 -4 -5 -6 -7 -8 -9 -11 -10

10 10 10 10 10 10

PE) day (kg [ Rate Event ]

⋅ ⋅ is achieved for a mass -1 2 XENON1T sensitivity (90% C.L.) to spin-independent WIMP-nucleon interaction [ shows the sensitivity expected by the XENON1T experiment to spin-independent cm 8 47 Spectrum of the total background and of its components as a function of S1. Event rates for − 10 Figure 8: Figure × WIMP-nucleon interaction after 2 years1.6 of exposure in 1experiments ton as FV. well The as minimum prediction for cross XENONnT section are of shown in the same figure. Figure 7: three examples of WIMPalso signals shown. corresponding The to vertical three dashedwith different blue S2 masses lines > and delimit 150 PE the expected are S1 cross selected region sections assuming used a are in 99.75% the ER sensitivity rejection calculation. with a Events flat 40% NR acceptance [ XENON1T: the start of a new era in the search for Dark Matter PoS(DSU2015)032 . . Phys. C73 G43 Sara Diglio Astropart. Springer (1988) 1353 J. Phys. , . . D37 Eur. Phys. J. , . arXiv:0706.0039 . . 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