DirectSearchforDarkMa/erWIMPswithDepletedLiquidArgon

attheGranSassoLaboratory:

Dark‐SideAldoIanni,DarkSideCollabora2on

INFNGranSassoLaboratory

Padova,Sept.18th,2012

EvidenceofDarkMa/er

•  Spiralgalaxiesrota2oncurves:Ωhalo~10Ωstars

•  Clusters:galaxymo2on,gravita2onallensingandX‐rayemission:ΩmaLer~0.2‐0.3

•  CMBanisotropy:ΩmaLer~0.27,Ωbaryons~0.04–  ~84%ofmassintheUniversedarkandnon‐baryonic

•  Usingearlyuniversenucleosynthesis:Ωbaryons~0.04•  LargeScaleStructures:–  Forma2onofstructuresbygravita2onalclustering–  Comparisonofobserva2onswithnon‐rela2vis2c(cold)darkmaLerclusteringagreewell

WIMPs:WeaklyInteracEngMassiveParEcles

•  Ageneralclassof weaklyinterac2ngmassivepar2clesnotfromtheStandardModel

•  Assuming thermal equilibrium in the early Universeandnon‐rela2vis2cdecoupling, theenergydensity fortheserelicpar2clesispredictedtobe:–  Ωχ~10‐36cm2/<σv>–  annihila2oncrosssec2on~picobarns–  relicabundancerightorder(i.e.Ω∼1)

•  This circumstance: a par2cle non‐rela2vis2c atdecoupling with weak‐scale mass and cross sec2onwhich gives the right order for the relic abundance isgiventhenameofWIMPmiracle

DirectSearchforWIMPs:nuclearrecoiltagging

χ χ

N N

€

dRdE

= Nt

ρχmχ

mN

µn2 A

2σχnF2(E) d3v

f v( )vv≥vmin (E )∫

f (v) =1Ne−

vχ +vsun +vEarthv0

2

, vχ +vsun +vEarth <vesc

0 , elsewhere

• 170km/s<v0<270km/s• 450km/s<vesc<650km/s• ρχ~0.3Gev/cm3

• F(E)=nuclearformfactor• f(v)=velocitydistribu2onofWIMPsinthegalaxy

€

Erecoil =mNMχ

2

mN + Mχ( )2 v

2(1− cosθ*)

v ~ 300 km/sErecoil ~ 1−100 keV

ExpectedWIMPsSignalinLAr

100GeV/c2WIMPmass10‐45cm2WIMP‐nucleoncrosssec2on~10‐4interacEons/day/kg

CommentsonexpectedWIMPsignal

•  Nospecificfeature•  Lownuclearrecoilenergy•  10‐100eventsfor1ton‐yearexposure•  GOALofWIMPssearch:–  IfDarkMaLerismadeofWIMPsweneed:•  Strongsuppressionofbackground•  Aslowaspossiblesensi2vitytoWIMP‐nucleoncrosssec2on

ScinEllaEoninLAr

•  Minimumionizingpar2clesproduce~4×104γ/MeV

•  Fast(~7ns)andslow(~1.6µs)decaycomponents

•  Fornuclearrecoil:fastcomponent~70%•  Forelectron recoil:fastcomponent~30%

•  Scin2lla2onlightpeakedat128nm

•  Needwavelengthshigerto~400nmtomatchPMTsQuantumEfficiency

BackgroundsforLAr

•  β/γ radioac2vity•  γ radioac2vityfromsurfaceclosetosensi2vemass

•  Radiogenicneutrons:(α,n)andspontaneousfissions

•  Cosmogenicneutronsfrommuons

Neutronscanmimicanuclearrecoil

Double‐PhaseArgonTPC

Liquid

GasLayer

Cathode

DrigField(~1kV/cm)

FieldCage

Extrac2onGrid

Anode

Extrac2onField(~3kV/cm)

Photodetectors

Wavelengthshiger

RemarksonLArtargetforWIMPssearch

•  Advantages– Goodscin2llator– Moderatecryogenicrequirements:at1atmliquifiesat87K

–  1%abundanceinatmosphere(butwith39Arseelater)

•  Disatvantages– Needwaveshigerto~400nmfrom128nm– Mustremove39Ar:useundergroundAr(moredifficulttechnology)

LArTPCatWork[1]

gas

liquid

UpperPMTsarray

LowerPMTsarray

S1promptsignalfromLAr

UpperPMTsarray

LowerPMTsarray

Drigoffreee‐anddelayedsignalingasS2

S1measuresenergyand2meofeventS2measuresposi2onofeventinLArandispropor2onaltofrac2onofchargethatescapesrecombina2on

Efield

LArTPCatWork[2]

FigurefromWARP(Astropart.Phys.28,6

(2008)495‐507)

PulseShapeParameter

Log(S2/S1)

Backgroundreduc2onperformedbyexploi2ng

a)  PulseshapeofS1throughaparameterwhichmeasuresthefrac2onoffasttoslowcomponentinscin2lla2on

b)S2/S1

ElectromagneEcEvents

NuclearRecoils

DatafromDS‐10(seelater)

Theproblemof39Ar

•  Arnaturallypresentintheatmosphereat1%level

•  39Arformedbycosmicmuoninterac2ons–  40Ar(n,2n)39Ar

•  39ArisaβdecayemiLerwithQβ=565keVandT1/2=269years

•  InArfromtheatmosphere,39Arisatthelevelof1Bq/kg–  ~9×104decays/kg/day– WIMPs(100GeV,10‐45cm2)~10‐4events/kg/day

DarkSideApproach

•  DoublephaseTPC– Exploitbackgroundrejec2onpower

•  Lowbackgroundtechnology– Carefulselec2onofmaterials– AssemblinginRn‐freecleanroom

•  AcEveneutronveto– Boron‐loadedscin2llator

•  DepletedArgon–  39Arac2vityreducedto~0.6%Bq/kg

UndergroundArgon[1]

•  40Arproducedfrom40K•  TheEarthisreachin40Kinunderground•  40Armovesintotheatmosphereandmakes39Arwith

muonsinterac2ons•  Inunderground39Arisexpectedtobemuchlessdueto

lowmuonflux•  However,39Arundergroundcanbeproducedby

radiogenicneutronsinterac2ons–  39K(n,p)39Ar

•  Recipe:godeepundergroundwheresurroundingrocksarepoorinUandTh

UndergroundArgon[2]•  Inexhauststreamgas(CO2)ofcommercialminingfacili2esArat

400‐600ppmlevel–  InDSextrac2onsite:CO2plantoutput,CO2(96%)+N2(2.4%)+He(0.4%)+Ar(0.06%)

•  Makeon‐sitepreconcentra2onto~40,000ppm,thencryogenicdis2lla2onatFNAL–  Agerdis2lla2on:CO2(~0)+N2(<0.05%)+He(~0)+Ar(>99.95%)

•  Purifieddepletedargonproducedat0.5kg/day

•  39Ardepletedat<0.6%levelwrtatmosphericlevel–  ~500decays/kg/day–  ForWIMPs~10‐4interac2ons/kg/day

•  UseLArscin2lla2onproper2estoperformbackgroundreduc2on–  PromptsignalPSDshows:90%n‐recoilacceptancewith<10‐5e‐recoilleakage

UndergroundArgon[3]

39Ardeple2onfactor>100

Inprogressstudywithcoun2ngdetectorundergroundatKURF(1400m.w.e.)Virginia,USA

NeutronsfromnaturalradioacEvity•  Radiogenicneutrons–  from(α,n)andspontaneousfissionofheavyelementssuchasUandTh

– energy~afewMeV(<10MeV)

•  SourceinDarkSide:– PMTs(lowbackgroundPMTs~fewn/year/PMT)– Steelincryostatandsupportstructures

•  Recipe:– Passiveshieldingeffec2vefor~MeVenergiesbutasksformoresurroundingmaterials

– Ac2veveto

CosmogenicNeutrons

0 500 1000 1500 2000 2500 3000 3500

10!16

10!15

10!14

10!13

10!12

10!11

En !MeV"Neutronflux#cm2

s!1$

<En>~90MeV• FluxatGranSassolab: 2.4m‐2day‐1

 0.7m‐2day‐1for>10MeV• Expectedrate~3×10‐33/s/atom• WIMPSrate~10‐34/s/atom

• Neutronsfromsurroundingrocksreducedbyshielding InDS‐503mofwater~10‐3and0.04from1.5mofliquidscin2llator:~4×10‐5

Water

LS

LArTPC

µ‐inducedneutrons

NeutronVeto

•  FutureDarkMa+erDetectors@LNGS,F.Calaprice,WONDER,GranSasso,March22,2010

•  Ahighlyefficientneutronvetofordarkma+erexperiments,A.Write,P.MosteiroandF.Calaprice,NIMA644(2011)18‐26

•  Makeuseofaboron‐loadedradiopureliquidscin2llator–  10B+n‐>7Li+α(1.474MeV)+γ(0.478MeV)93.7%withσ=3837b–  α energyiscontained–  capture2me~3µs

•  1mthickvetomakesareduc2onof107againstexternalneutrons•  NeutronsfrominternalLArtargetmasscapturedin60µsin1m

thickvetowith99.5%efficiency•  WaterTankmuonveto+neutronvetoreducescosmogenic

background>>103

EsEmatedbackgroundintheDSneutronveto

•  30tonsboron‐loadedscin2llatorin1000m3watertank,100PMTs

•  Liquidscin2llator–  14C:~4Bq(Borexinolevel14C/12C~2×10‐18)–  U+Th(1ppt):~0.3Bq–  K(70ppb):~33Bq

•  StainlessSteelContainmentvessel:~30Bq(~1mBq/kginUandTh)

•  Externalbackground<1Bq•  InnerDetectorTPC<1Bq•  PMTs~100Bq•  Randomcoincidences~160Bq•  Total~300Bqwhichgives~2%dead2mein1µsDAQ

window

DarkSideProgram

•  DarkSide‐10–  aprototypedetectorwith10kgofLAr–  currentlyopera2ngundergroundatGranSasso–  testcryogenictechnologywithdoublephaseTPC–  testLightYieldandbackgroundrejec2onpower

•  DarkSide‐50–  50kgofdepletedLArfor10‐45cm2sensi22vyfor100GeVWIMP

–  currentlyunderconstruc2on(readybyearly2013)–  Testac2vevetoconceptandlowbackgroundprocedures

•  DarkSide‐G2–  3tonstargetmassofdepletedLAr– WIMPsensi2vity10‐47cm2for100GeV

DarkSideWIMPSensi2vity

]2[GeV/c210 310

]-2

[cm

SI pσ

-4810

-4710

-4610

-4510

-4410

-4310

-4210

-4110

-4010

10χ~

m

pre LHC (68% and 95% CL contours in CMSSM)

1/fbLHC (68% and 95% CL contours in CMSSM)

DS-50

DS-G2

CDMS

XENON100

ForDS‐50(>20keVnr):1)  6pe/keVee2)  2pe/keVnr3)  0.1ton‐yearForDS‐G2(>25keVnr):1)10ton‐year

DS‐50

DS‐G2

DarkSide‐10

•  TestDarkSidetechnologies–  Controlofgaslayer–  ChargedrigandS2lightcollec2on

–  Lightyield(determinedtobe~9p.e./keVeeatzerofield)

•  Backgroundsuppressionstudies

•  Experienceopera2nganargonTPC

18”boLomPMTasin1sttestdoneatPrincetonReplacedby73”PMTsatLNGS

DarkSide‐10atLNGS

•  Inopera2onatGranSassoundergroundsincesummer2011

•  Watershieldingtoreducebackgroundrate

•  15Hzwith4PMTstriggerwithwatershielding

•  Calibra2onwithgammaandAmBesource

DS‐10:PMTscalibraEons

•  73”PMTshighQE

ateachendofsensi2vevolume

•  QE~30‐36%

DS10:light‐yield

Energy[keV] Light‐Yield[p.e./keV] ResoluEon(σ)[%]

122 8.87 5.2

511 8.78 3.4

662 9.08 3.1

1275 8.60 2.9

average 8.9±0.4

Light‐Yieldmeasuredbymeansofgammasourceslocatedoutsidethecryostatvessel

DS‐10:eventw/dri_field

DS‐10:PSDwithS1signal

•  FigureofmeritforPSD:f90=frac2onofS1lightwhicharrivesbefore90ns

DS‐10:neutroncalibraEon

Background AmBe

DatatakeninTCPmodewithAmBesource(10n/s)outsidethecryostat.Rejec2onpoweragainstthresholdunderstudy

DarkSide‐10:publicaEons

•  LightYieldinDarkSide‐10:aprototypetwo‐phaseliqidargonTPCforDarkMa+erSearches,DarkSidecoll.,arXiv:2104.6218

•  StudyoftheResidual39ArcontentinArgonfromUndergroundSources,DarkSidecoll,arXiv:1204.6011

DarkSide50

•  50kgDLArsensi2vemass•  WIMP‐nucleoncrosssec2onsensi2vity~10‐45cm2

•  Detectorunderconstruc2on•  Datatakingexpectedinspring2013•  Firststeptoward1ton‐scaledetector

TheLiquidScin2llatorContaimentVesselfortheDarkSideNeutronVetoascompletedwithintheCTFwatertank(HallCofLNGS)

Summary

•  DarkSidedetectordesignedtohaveverylowbackgroundfordirectWIMPsearchwithLAr

•  Firstuseofac2veboron‐loadedliquidscin2llatorneutronveto

•  MakeuseofBorexinofluindhandlingandpurifica2onplants

•  10kgprototypeinopera2onsincesummer2011•  50kgDS‐50fulldesigndetectorinconstruc2on•  DS‐50commissioningexpectedearly2013•  DS‐50sensi2vity~10‐45cm2

DarksideCollaboraEonAugustana College – SD, USA

Black Hills State University – SD, USA Fermilab – Il, USA

INFN Laboratori Nazionali del Gran Sasso – Assergi, Italy INFN and Università degli Studi Genova, Italy INFN and Università degli Studi Milano, Italy INFN and Università degli Studi Naples, Italy INFN and Università degli Studi Perugia, Italy

Institute for High Energy Physics – Beijing, China Joint Institute for Nuclear Research – Dubna, Russia

Princeton University, USA RRC Kurchatov Institute – Moscow, Russia

St. Petersburg Nuclear Physics Institute – Gatchina, Russia Temple University – PA, USA University of Arkansas, USA

University of California, Los Angeles, USA University of Houston, USA

University of Massachusetts at Amherst, USA