S

DanMcKinsey,Sco/HertelUCBerkeley,LBNL

SuperfluidHeliumforLightDarkMa7erDetec9on

DarkSectorsWorkshopSLAC

April29,2016

OutlineThistalk:•  Somehistory,context•  Someadvantagesofsuperfluidhelium•  Signalsinsuperfluidhelium•  EnergyparOOoning•  SomedetectorconceptsNexttalk(Sco/Hertel)•  SomerecentTESmeasurementswithsuperfluidhelium•  Phonon/rotonreflecOonanddetecOon•  Light/heatbasedERvsNRdiscriminaOon•  Darkcounts

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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.

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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

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Helium-4Nuclei:ANaturalMatchforLightDarkMa/erDetecOon

Anotherview:maximumrecoilenergyforvarioustargets,asafuncOonofWIMPmass.

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Light WIMP Detector Concept #1: Two-Phase Helium Energies down to ~ 1 keV

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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

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for He decreases to about 0.4 at low energies, due to Lindhard effect, but is not equal to the Lindhard factor !

PredictednuclearrecoildiscriminaOonandsignalstrengthsinliquidhelium

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Howtodetecttripletheliummolecules?

DetectwithTESarrayimmersedinsuperfluid,andletthemoleculestravelballisOcallytobedetected(v~1-10m/s)

–  <1eVresoluOonquitepossible–  Eachmoleculehas~18eVofinternalenergy,whichwillmostlybe

releasedasheat,electronicexcitaOoninTES.–  Notethatthesamebolometerarraycoulddetectbothlightand

tripletexcimers!–  Nowhasbeendemonstratedexperimentally(seeS.Herteltalk).

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SignalparOOoning–electronsrecoils

GeorgeSeidel

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SignalparOOoning–nuclearrecoils

GeorgeSeidel

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AthermalEvaporaOon–DemonstratedbyHERONR&D

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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

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Concept#3

Signalchannels:PhononsRotons

Energiesdownto~fewmeV!!DiscriminaOonusingroton/phononsignalraOoslikely.Electronrecoils,detectoreffects,nuclearrecoilslikelycreatedifferentroton/phonondistribuOons.PosiOonreconstrucOonusingsignalhitpa/erns

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Summary

Highestenergies:Usechargeandlight?Mediumenergies:Lightandheatlooksverypromising.Lowenergies:Usephononsandrotons,likelysOllhavediscriminaOon.MulOpleadvantages,thislookslikeanidealtechnologyforlow-massdarkma/erdetecOon.