Post on 24-Mar-2022
S
DanMcKinsey,Sco/HertelUCBerkeley,LBNL
SuperfluidHeliumforLightDarkMa7erDetec9on
DarkSectorsWorkshopSLAC
April29,2016
OutlineThistalk:• Somehistory,context• Someadvantagesofsuperfluidhelium• Signalsinsuperfluidhelium• EnergyparOOoning• SomedetectorconceptsNexttalk(Sco/Hertel)• SomerecentTESmeasurementswithsuperfluidhelium• Phonon/rotonreflecOonanddetecOon• Light/heatbasedERvsNRdiscriminaOon• Darkcounts
4/29/16 D.McKinseyCPADWorkshop
DanMcKinsey,LBNLDarkMa/er
Liquified Noble Gases: Basic Properties
LHe
LNe
LAr
LKr
LXe
Liquid density(g/cc)
0.145
1.2
1.4
2.4
3.0
Boiling pointat 1 bar
(K)
4.2
27.1
87.3
120
165
Electronmobility(cm2/Vs)
low
low
400
1200
2200
Dense and homogeneousDo not attach electrons, heavier noble gases give high electron mobility
Easy to purify (especially lighter noble gases)Inert, not flammable, very good dielectrics
Bright scintillators
Scintillationwavelength
(nm)
80
78
125
150
175
Scintillation yield
(photons/MeV)
19,000
30,000
40,000
25,000
42,000
Long-lived radioactiveisotopes
none
none
39Ar, 42Ar
81Kr, 85Kr
136Xe
Triplet moleculelifetime
(µs)
13,000,000
15
1.6
0.09
0.03
Superfluidhelium-4asadetectormaterial
• Used to produce, store, and detect ultracold neutrons.
• Production based on “superthermal effect”: direct production of phonons by cold neutrons, allowing the neutrons to scatter to 100 neV-scale energies and be captured by magnetic fields or material bottles.
• Can store the neutrons within the superfluid helium; neutrons cannot absorb on He-4.
• Detection based on scintillation light.
DanMcKinsey,LBNLDarkMa/er
Superfluidhelium-4asadetectormaterial• Search for the neutron electric dipole
moment: R. Golub and S.K. Lamoreaux, Phys. Rep. 237, 1-62 (1994).
DanMcKinsey,LBNLDarkMa/er
Measurement of neutron lifetime: P.R. Huffman et al, Nature 403, 62-64 (2000).
Superfluidhelium-4asadetectormaterial
Proposed for measurement of pp solar neutrino flux using roton detection (HERON): R.E. Lanou, H.J. Maris, and G.M. Seidel, Phys. Rev. Lett. 58, 2498 (1987).
Two signal channels, heat and light. Both measured with a bolometer array.
DanMcKinsey,LBNLDarkMa/er
WhySuperfluidHeliumforLow-massDarkMa/erDetecOon?
• KinemaOcmatchingwithlightdarkma/ercandidates.– PulltheenergydeposiOonsupinenergy,toabovethreshold.– GainaccesstomoreoftheWIMPvelocitydistribuOon,foragivenenergy
threshold.– New:accesstoextremelylowmassdarkma/erthroughmulO-excitaOon
producOon,back-to-backjets(seeK.Zurektalk,arXiv:1604.08206).• SuperfluidheliumoffersmulOplesignalstochoosefrom,andtoseparate
darkma/ersignalfrombackgrounds(bothelectronrecoilsanddetectorbackgrounds).– Promptlight– Delayedtripletexcimers– Charge– Heat(rotonandphotonquasiparOcles)
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WhySuperfluidHelium?• Liquiddownto0K,allowing10-100mK-scaleTESreadout.
– TakeadvantageofthegreatadvancesinTEStechnology– Takeadvantageofpossible~100%detecOonefficiencyforphotons,tripletexcimers– Takeadvantageoftheextremelylowvaporpressureofsuperfluidheliumatlow
temperatures,enablingquantumevaporaOon-basedheatsignalamplificaOon.
• HeliumisexpectedtohaverobustelectronicexcitaOonproducOonefficiency,withaforgivingLindhardfactor(highLeff),sonuclearrecoilscinOllaOonsignalsshouldberelaOvelylarge.
• Negligibletargetcost• LowvibraOonsensiOvity:Asasuperfluid,smallvelociOesdon’tgenerate
excitaOons.• LargeionizaOongap->lesssignalquantaperkeVthaninsuper-,
semiconductors.ButnoERbackgroundbelow14eV.• ImpuriOeseasilyremoved,andwillfalloutofthesuperfluid.
D.McKinseyCPADWorkshop4/29/16
TheimportanceofdiscriminaOonItishighlyadvantageoustohaveatleast2signalchannelswithdifferentERandNRresponse.Thisistoallownuclearrecoil/electronrecoildiscriminaOon,bothtorejectERbackgrounds,butalsotohaveaseparatehandleonNRsignalinthefaceofunexpectedbackgrounds.Inrealexperiments,discriminaOoniscrucial,asyoucanseefromthehistoryofthefield.ER/NRdiscriminaOonisalsocriOcalfordiscoveryofdarkma/erinteracOons.TheconceptspresentedhereallusemulOplesignalchannelstoallowER/NRdiscriminaOon,whilemaintainingexcellentsignalstrength.
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Helium-4Nuclei:ANaturalMatchforLightDarkMa/erDetecOon
LoseoverallrecoilrateasA2,butgainrateabovesomeenergythreshold
S.Hertel
4/29/16 D.McKinseyCPADWorkshop
Helium-4Nuclei:ANaturalMatchforLightDarkMa/erDetecOon
Anotherview:maximumrecoilenergyforvarioustargets,asafuncOonofWIMPmass.
Light WIMP Detector Concept #1: Two-Phase Helium Energies down to ~ 1 keV
D.McKinseyCPADWorkshop4/29/16
Alpha data: A.N. Gerritsen, Physica 14, 407 (1948)..
A two-phase helium detector; salient properties
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Liquidhelium-4predictedresponse(GuoandMcKinsey,arXiv:1302.0534,Phys.Rev.D87,115001(2013).)LiquidheliumhaslowerelectronscinOllaOonyieldforelectronrecoils(19photons/keVee)But,extremelyhighLeff,goodcharge/lightdiscriminaOonandlownuclearmassforexcellentpredictedlightWIMPsensiOvity
Measurementsinliterature!
Calculatednuclearrecoilsignals
D.McKinseyCPADWorkshop4/29/16
for He decreases to about 0.4 at low energies, due to Lindhard effect, but is not equal to the Lindhard factor !
PredictednuclearrecoildiscriminaOonandsignalstrengthsinliquidhelium
D.McKinseyCPADWorkshop4/29/16
Howtodetecttripletheliummolecules?
DetectwithTESarrayimmersedinsuperfluid,andletthemoleculestravelballisOcallytobedetected(v~1-10m/s)
– <1eVresoluOonquitepossible– Eachmoleculehas~18eVofinternalenergy,whichwillmostlybe
releasedasheat,electronicexcitaOoninTES.– Notethatthesamebolometerarraycoulddetectbothlightand
tripletexcimers!– Nowhasbeendemonstratedexperimentally(seeS.Herteltalk).
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Concept#2
Signalchannels:1)ScinOllaOon2)BallisOcTripletExcimers3)Phonons/Rotons
Nodrisfield,andnoS2signal• noworryoffew-electronbackground• PosiOonreconstrucOonviasignalhit
pa/erns• (Thoughcouldapplydrisfieldtodetect
singleelectronsviaroton/phononproducOon.)
Bestforenergiesdownto300eV.DiscriminaOonusingsignalraOosPosiOonreconstrucOonusingsignalhitpa/erns
4/29/16 D.McKinseyCPADWorkshop
Concept#3
Signalchannels:PhononsRotons
Energiesdownto~fewmeV!!DiscriminaOonusingroton/phononsignalraOoslikely.Electronrecoils,detectoreffects,nuclearrecoilslikelycreatedifferentroton/phonondistribuOons.PosiOonreconstrucOonusingsignalhitpa/erns