Calibra'on*and*Modeling*of*Nuclear*and* Electron*Recoils*in*Liquid*Argon* Workshop(on(Calibra/on(of( Low(Energy(Par/cle(Detectors( Samuele(Sangiorgio( Rare(Event(Detec/on(Group.(LLNL( Chicago, Sep 24, 2015 LLNL-PRES-677393 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC LLNL’s*Noble*Liquid*R&D*Program* Physics(Mo/va/ons( Liquid(Xenon(and(Argon(Detectors( • Two(small(dualIphase( detectors( • Dark(MaRer( • Coherent(Elas/c( NeutrinoINucleus( ScaRering( • Measure(electron(and( nuclear(recoils(<(few( keV( • Understand(and(( control(lowIenergy( backgrounds( • HV(stability(in(noble( liquids( Dedicate(lowIenergy(neutron(beam( • OnIsite(at(LLNL( • QuasiImonoenerge/c( filtered(neutron( beam( LLNL-PRES-677393 S.(Sangiorgio( 2( LLNL*Dual?Phase*LAr*Detector* • Ac/ve(volume:(~(100(g(Lar( • TPB(as(wavelength(shiYer( • HomeIbuilt(HV(feedIthroughs( • Very(good(LAr(purity( 4x Hamamatsu R8520 1” PMTs (1 atm @ 87K) Up to 11kV/cm liquid Ar Up to 3kV/cm Egain 3.5 cm gas Ar 2.5 cm liquid level Edrift liquid level field rings 5 cm rings support HV feedthroughs LLNL-PRES-677393 S.(Sangiorgio( 3( High*Gain*Detec'on*of*Ioniza'on*Signal* • Interest(in(the(lowest(energy( possible( • Emphasis(on(detec/on(of( ioniza/on(by(means(of(S2(only( • Operate(close(to(electron( mul/plica/on(in(gas( Monteiro et al, IEEE Trans. Nucl. Sci., 48 (2001) ~10 kV/cm ~2-4 kV/cm ~11 kV/cm at 1atm at 87K LLNL-PRES-677393 S.(Sangiorgio( 4( Ar?37*as*a*Diffuse*Low?E*Calibra'on*Source* natAr Decay(scheme( 100%(electron(capture( t1/2(=(35.04(d( ( Decay(radia/on( isotopes Mass number Natural Abundance 40 99.6% 36 0.34% 38 0.06% KI(capture(2.82*keV*(90.2%)( LI(capture(0.27*keV*(8.9%)( MI(capture(0.02(keV((0.9%)( ( Isotope(produc/on( Produced(by(neutron(irradia/on( of(natAr(at(a(nuclear(reactor( Aalseth,(C.(E.(et#al.(NIM#A652,(58–61((2011).( Barsanov,(V.(I.(et#al.(Phys.#Atomic#Nucl#70((2007).( LLNL-PRES-677393 S.(Sangiorgio( 5( Sub?keV*Calibra'on*for*Electron*Recoils* S2 LLNL-PRES-677393 S.(Sangiorgio( 6( Single*Electrons* 100 single ioniz electrons µ = 8.2 ± 0.1 p.e. ! = 3.4 ± 0.1 p.e. EventWidthT [µs] Counts • Typical(S.E.(event(as(seen(on(the( scope( 80 • Experimental(spectrum(of(single(and( double(ioniza/on(electrons( 25 h2 Entries Mean RMS !2 / ndf Prob µ " SE amp 2E amp 20 15 10 60 5 2807 10.52 5.398 115.4 / 94 0.06611 8.2 ± 0.1 3.418 ± 0.128 67.25 ± 2.25 12.72 ± 1.38 45 40 35 30 25 20 15 10 5 40 0 0 5 10 15 20 25 30 35 40 0 Integral [p.e.] • Provides(absolute(calibra/on(of(the( number(of(detected(electrons( 20 0 0 LLNL-PRES-677393 S.(Sangiorgio( 5 10 15 20 25 30 35 40 Collected Light [p.e.] 7( 37Ar*Electron*Recoils*vs*Electric*Field* 2.82 keV – electron recoil • Electric(field(reduces(recombina/on(of(electron(with(ions( • Measurements(of(the(0.27(keV(peak(vs(E(field(are(ongoing( • Need(to(deal(with(lowIenergy(background( LLNL-PRES-677393 S.(Sangiorgio( 8( Recombina'on*in*LAr* Consider(electron(recoils(first( For(electron(recoils(the(amount(of(ini/al( ioniza/on(Ni(is(calculable:( • Nex(/(Ni(=(0.21( • E(=(2.82(keV(for(37Ar(KIshell( • W(=(19.5(eV( • q(E)(=(1( S2 ∝ ne = rNi Ni + Nex E · q(E) = W ThomasIImel(parameteriza/on(of( recombina/on( r = ln(1 + ξ)/ξ Introduce( phenomenological( scaling(for(field( dependence:( 2.82 keV – electron recoil ξ = CNi · E −b Extract(field(dependence( parameter(C,(b(from(fit( Cfr.(Sorensen,(P.(and(Dahl,(C.(E.,(Phys.#Rev.#D.#83*(2011)( LLNL-PRES-677393 S.(Sangiorgio( 9( Modeling*recombina'on*in*Liquid*Argon* At(low(energy,(empirical(ThomasIImel(box(model(seems(successful(but( I Empirical(field(dependence( I All(electronIion(pairs(recombine(for(zero(electric(field( I LiRle(insight(on(physical(processes(involved( M.#Foxe,#C.#Hagmann,#et#al,#NIM#A#771#(2015)# Simula'on*Approach* 1. Ini/al(interac/on( • Simulate(ini/al(emission(of(photoelectrons(and/or(auger(electrons(( 2. Follow(electrons(using(electron(transport(algorithm( • • • based(on(prior(work(by(Wojcik(et(al(for(thermal(electrons( Solves(equa/on(of(mo/on(for(electrons(under(external(fields(and(ions(field( Posi/ons(and(velocity(of(electrons(are(forward(propagated( 3. Compute(interac/ons(as(electrons(slow(down( • electronsIinduced((excita/on,(ioniza/on(and(elas/c( scaRering( • secondary(electron(generated(and(followed(as(well( • Thermal(model(validated(against(measurements( (driY(velocity,(escape(probability,…)( Elas/c(energy( transfer( Momentum( transfer( ioniza/on( excita/on( 4. Recombina/on(criteria:( • • Electron(energy(<(1(eV( ElectronIion(distance(<(1.3(nm( No tunable parameter! LLNL-PRES-677393 S.(Sangiorgio( 10( M.#Foxe,#C.#Hagmann,#et#al,#NIM#A#771#(2015)# Modeling*37Ar*Decays* Average(ioniza/on(track( length(<<(electron( thermaliza/on(length( (2.6(µm)( Compare with 0.21 from Doke from 217Bi conversion electrons 5.9(keV((55Fe)(( 2.8(keV((37Ar(K)(( DATA:(2.8(keV((37Ar(K)(( 1.0(keV(eI(( Model(limita/ons:( • Ioniza/on(crossIsec/on( uses(binding(energies(of( gas( 0.27(keV((37Ar(L)(( LLNL-PRES-677393 S.(Sangiorgio( 11( Nuclear Recoil Neutron?induced*Nuclear*Recoils*in*LAr* ! Elas/c(neutron(scaRering( Neutron rvable signal than electron recoi ! Two(complementary(approaches:( NARRLI SCENE Neutron Argon Recoils Resulting in Liquid Ionization SCintillation (and ionization) Efficiency Noble Elements • Recoils from tagged neutron scatter • Energy 11 – 57 keV " DarkMatter • Scintillation & Ionization LLNL-PRES-677393 S.(Sangiorgio( • End-point measurement • Low energy < 10 keV " CENNS • Ionization signal only 12( T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)# Crea'ng*a*low?E*neutron*beam* 7Li(p,n)7Be NearIthreshold(kinema/cs(of( 7Li(p,n)(allow(control(of(maximum( neutron(energy( Lab Neutron Energy (keV) Proton Energy Countours for a Thick Lithium Target from Lee and Zhou NIMB 152 (1999) 45º - 1.93MeV Requirements: - Continuous p beam - No ToF in detector (no S1) Lab Neutron Emission Angle (degrees) LLNL-PRES-677393 S.(Sangiorgio( 13( T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)# The*Li*target* Same total Li content Ep = 1.93 MeV Li metal target LLNL-PRES-677393 Li2O target LiF target S.(Sangiorgio( Li2CO3 target 14( T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)# P.#Barbeau#et#al,#NIM#A#(2007)# Neutron*Filtering* • Take advantage of nuclear physics to selectively transmit neutrons through interference dips in scattering x-sections 40 Ar, 56Fe, and 48Ti (n,el) cross-sections 1 82 keV 10-2 73 keV 24 keV Cross Section (barns) 102 56 Fe Ar 48 Ti 40 10-4 20 40 60 80 100 Incident Energy (keV) LLNL-PRES-677393 S.(Sangiorgio( 15( T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)# Pb( LAr( detector( Fe(filter( Li(target( 106 neutrons/250eV/sr/mC Crea'ng*a*low?E*neutron*beam* Ideal 45º collimation p( Backgrounds: - gammas from 7Li(p,p’) - neutron-capture gammas in shield - 24 keV neutrons through the filter " LLNL-PRES-677393 Measure at different collimation angle, normalize and subtract 106 neutrons/250eV/sr/mC Ideal 55º collimation S.(Sangiorgio( 16( Expected*Recoil*Spectrum*in*LAr* detectors MCNP calculation of neutron transport and interaction using detailed geometry Lead n LAr detector Fe filter Li target BPoly All scatters in active volume (x0.5) - 45 deg Counts (counts/keV/ѥC) 3 2.4 keVr p Single scatters fiducial volume - 45 deg Single scatters fiducial volume - 55 deg 2.5 Background subtracted signal - model input 2 6.7 keVr 1.5 Endpoint Measurement 4mM MAX En TAr = (m + M )2 1 6.7 keV endpoint 0.5 0 Multiple scatter Scatters from 24 keV neutrons 0 2 4 6 Deposited energy (keV) 8 10 Endpoint measurement at 6.7 keV nuclear recoils LLNL-PRES-677393 S.(Sangiorgio( 17( LLNL’s*on?site*dedicated*neutron*beam* 1.7 MeV Tandem accelerator at LLNL’s CAMS The collimator setup 7mm dia Li 1µm thick Proton beam Unique neutron facility for detector calibration to low-energy neutrons (< 150 keV) LLNL-PRES-677393 S.(Sangiorgio( Protons on target Beam on target 18( T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)# Ioniza'on*Yield*at*6.7*keVr* Fit(using(the(MCNP(spectrum(convolved(with(measured(detector(resolu/on(and( three(free(parameters:( +0.1 +0.7 − Q = 4.9 (stat) (syst) e /keV • fixed(ioniza/on(yield,(( y −0.2 −0.9 • rate(normaliza/on,(( at 640V/cm 19( S.(Sangiorgio( • fano(factor(((( LLNL-PRES-677393 T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)# Uncertainty*Es'ma'on* LLNL-PRES-677393 S.(Sangiorgio( 20( T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)# Nuclear recoils at 6.7 keVr at varying electric field Counts (counts/electron/ѥC) Electric*Field*Dependence*of*Ioniza'on*Yield* = ܦ640 V/cm ѯ2/ndf = 8.1/10 = ܦ240 V/cm ѯ2/ndf = 3.4/8 0.12 0.10 Signal - all cuts Background - all cuts Background subtracted Best fit of model 0.08 0.06 0.04 0.02 0.00 20 30 40 50 1600 V/cm = ܦElectrons Detected 2 ѯ /ndf = 12.6/9 60 10 20 30 40 50 Detected Electrons = ܦ2130 V/cm 2 ѯ /ndf = 11.2/10 60 20 30 40 Detected Electrons 60 10 20 30 40 Detected Electrons 60 counts/electron/µC ܦ ѯ 10 60 10 LLNL-PRES-677393 S.(Sangiorgio( 50 50 21( T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)# For nuclear recoils S2 ∝ ne = rNi Ni + Nex E · q(E) = W Use modified Thomas-Imel to account for recombination using parameters obtained from 2.82 keV electron recoils Detected number of electrons Field*Dependence* 70 2.82 keV – electron recoil 60 50 40 6.7 keV – nuclear recoil 30 20 Fit with Ni as only free parameter LLNL-PRES-677393 1000 1500 2000 2500 3000 Drift Field (V/cm) Same phenomenological model of recombination holds in both cases " For nuclear recoils the amount of initial ionization Ni is unknown: • Nex / Ni = ?? • E = 6.7 keV • W = 19.5 eV • q(E) = ?? 500 Similarities in spatial distributions of ions and electrons S.(Sangiorgio( 22( Comparison*with*SCENE*Measurements* • Different(energies(and(electric(field(range.(Very(complementary(but(hard( to(crossIcheck(directly( • Agreement(on(recombina/on:(same(fit(result(for(the(electric(field( parameter(‘b’(in(the(modified(ThomasIImel((b(=(0.61)( • Combined(ioniza/on(yield(data:( 7" 6" 5" 4" 16.9"keVr"SCENE" 3" 25.4"keVr"SCENE" 2" 57.3"keVr"SCENE" 36.1"keVr"SCENE" 1" 6.7"keVr"LLNL" Ionization Yield [e-/keV] Ionization Yield [e-/keV] 8" 0" 30" LLNL-PRES-677393 300" 5" 4.5" 4" 3.5" 3" 2.5" 2" 1.5" 1" 0.5" 0" At 240 V/cm field SCENE((interpolated)( LLNL( 0" 3000" Electric Field [V/cm] 20" 40" 60" 80" Nuclear Recoil Energy [keVr] S.(Sangiorgio( 23( Modeling*Low?E*Nuclear*Recoils*in*Liquid*Argon* ArIAr(Inelas/c(Cross(Sec/ons( TRIMIbased(binary(collision(Monte(Carlo(Model( • Elas/c(Coulomb(collisions( • Inelas/c(collisions(producing(excita/on( and(ioniza/on( Ar + Ar " Ar* + Ar Ar + Ar " Ar+ + Ar + e- Recoiling Ar Ar+IAr(Inelas/c(Cross(Sec/ons( Ar+ + Ar " Ar + Ar+ Ar+ + Ar " Ar + Ar+ Ar+ + Ar " Ar* Notes:( • Ioniza/on(energy(spectrum(is(not(well(known(and( depends(on(collision(energy("(use(3(and(10(eV( • ThreeIbody(collisions(are(neglected( • BiIexcitonic(quenching(mechanism(not(included( M.#Foxe,#C.#Hagmann,#et#al,#AstroparOcle#Physics#69#(2015)# LLNL-PRES-677393 S.(Sangiorgio( 24( M.#Foxe,#C.#Hagmann,#et#al,#AstroparOcle#Physics#69#(2015)# Modeling*Results* Track(Length(( Electron(thermaliza/on(length( Electron(recoil( Ioniza/on(Yield(vs(E(Field( Ar(recoil( Ioniza/on(Yield(at(1(kV/cm( LLNL-PRES-677393 S.(Sangiorgio( 25( Conclusions*and*outlook* • Demonstrated use of 37Ar to calibrate down to sub-keV energies • Measured the ionization yield at 6.7 keVr in liquid argon as a function of electric field • Developed atomic collision simulation for low-energy (< 10 keV) interactions in liquid argon • Appreciably good agreement • Would be interesting to extend it to xenon • Nuclear recoil measurements: • Refurbishment of Li target for higher neutron efficiency • Access lower recoil energy using different filters • Xe target • Things to consider: • Liquid Argon vs Liquid Xenon • Few-electrons backgrounds • Single electron calibration LLNL-PRES-677393 S.(Sangiorgio( 26( Acknowledgements ** ! A.(Bernstein,(C.(Hagmann,(K.(Kazkaz,((( V.(Mozin,(S.(Pereverzev,(F.(Rebassoo,( S.(Sangiorgio( ! T.(Joshi( ! P.(Sorensen( ! I.(Jovanovic( ! M.(Foxe( LLNL-PRES-677393 S.(Sangiorgio( 27(
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