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

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

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LLNL’s*Noble*Liquid*R&D*Program*

Physics(Mo/va/ons( Liquid(Xenon(and(Argon(Detectors(

Dedicate(lowIenergy(neutron(beam(

•  Two(small(dualIphase(

detectors(

•  Measure(electron(and(

nuclear(recoils(<(few(

keV(

•  Understand(and((

control(lowIenergy(

backgrounds(

•  HV(stability(in(noble(

liquids(

•  OnIsite(at(LLNL(

•  QuasiImonoenerge/c(

filtered(neutron(

beam(

•  Dark(MaRer(

•  Coherent(Elas/c(

NeutrinoINucleus(

ScaRering(

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LLNL*Dual?Phase*LAr*Detector*

•  Ac/ve(volume:(~(100(g(Lar(

•  TPB(as(wavelength(shiYer(

•  HomeIbuilt(HV(feedIthroughs(

•  Very(good(LAr(purity(

5 cm

gas Ar (1 atm @ 87K)

3.5

cm

2

.5 cm

Up to 3kV/cm

liquid Ar

Up to 11kV/cm

4x Hamamatsu R8520 1” PMTs

field rings

rings support

liquid level

HV feed-throughs

liquid level

Edrift

Egain

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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)

~11 kV/cm at 1atm at 87K

~2-4 kV/cm

~10 kV/cm

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Ar?37*as*a*Diffuse*Low?E*Calibra'on*Source*

Aalseth,(C.(E.(et#al.(NIM#A652,(58–61((2011).(

Barsanov,(V.(I.(et#al.(Phys.#Atomic#Nucl#70((2007).(

Decay(scheme(

100%(electron(capture(

t1/2(=(35.04(d(

(

Decay(radia/on(

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(

Mass

number

Natural

Abundance

40 99.6%

36 0.34%

38 0.06%

natAr isotopes

LLNL-PRES-677393

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Sub?keV*Calibra'on*for*Electron*Recoils*

S2

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Single*Electrons*

•  Typical(S.E.(event(as(seen(on(the(

scope(

h2Entries 2807

Mean 10.52

RMS 5.398 / ndf 2! 115.4 / 94

Prob 0.06611 µ 0.1± 8.2 " 0.128± 3.418

SE amp 2.25± 67.25 2E amp 1.38± 12.72

Collected Light [p.e.]0 5 10 15 20 25 30 35 40

Co

un

ts

0

20

40

60

80

100h2

Entries 2807

Mean 10.52

RMS 5.398 / ndf 2! 115.4 / 94

Prob 0.06611 µ 0.1± 8.2 " 0.128± 3.418

SE amp 2.25± 67.25 2E amp 1.38± 12.72

Integral [p.e.]

0 5 10 15 20 25 30 35 40

s]

µE

ve

ntW

idth

T [

0

5

10

15

20

25

0

5

10

15

20

25

30

35

40

45

single ioniz electrons µ = 8.2 ± 0.1 p.e.

! = 3.4 ± 0.1 p.e.

•  Experimental(spectrum(of(single(and(

double(ioniza/on(electrons(

•  Provides(absolute(calibra/on(of(the(

number(of(detected(electrons(

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37Ar*Electron*Recoils*vs*Electric*Field*

•  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(

2.82 keV – electron recoil

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Recombina'on*in*LAr*

S2 ∝ ne = rNi

r = ln(1 + ξ)/ξ

ThomasIImel(parameteriza/on(of(

recombina/on(

Consider(electron(recoils(first(

Introduce(

phenomenological(

scaling(for(field(

dependence:(

Ni +Nex =E

W· q(E)

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(

Extract(field(dependence(

parameter(C,(b(from(fit(

ξ = CNi · E−b

Cfr.(Sorensen,(P.(and(Dahl,(C.(E.,(Phys.#Rev.#D.#83*(2011)(

2.82 keV – electron recoil

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Elas/c(energy(

transfer( ioniza/on(

Momentum(

transfer(

excita/on(

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(

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(

M.#Foxe,#C.#Hagmann,#et#al,#NIM#A#771#(2015)#

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,…)(

4. Recombina/on(criteria:(•  Electron(energy(<(1(eV(

•  ElectronIion(distance(<(1.3(nm(

No tunable parameter!

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Modeling*37Ar*Decays*

Average(ioniza/on(track(

length(<<(electron(

thermaliza/on(length(

(2.6(µm)(

Model(limita/ons:(

•  Ioniza/on(crossIsec/on(

uses(binding(energies(of(

gas(

Compare with 0.21 from Doke from 217Bi

conversion electrons

M.#Foxe,#C.#Hagmann,#et#al,#NIM#A#771#(2015)#

5.9(keV((55Fe)((

2.8(keV((37Ar(K)((

DATA:(2.8(keV((37Ar(K)((

1.0(keV(eI((

0.27(keV((37Ar(L)((

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Neutron?induced*Nuclear*Recoils*in*LAr*

!  Elas/c(neutron(scaRering(

!  Two(complementary(approaches:(

SCENE NARRLI

•  End-point measurement •  Low energy < 10 keV " CENNS

•  Ionization signal only

•  Recoils from tagged neutron scatter •  Energy 11 – 57 keV " DarkMatter

•  Scintillation & Ionization

Neutron Argon Recoils Resulting

in Liquid Ionization SCintillation (and ionization)

Efficiency Noble Elements

rvable signal than electron recoi

Nuclear Recoil

Neutron

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NearIthreshold(kinema/cs(of(7Li(p,n)(allow(control(of(maximum(

neutron(energy(

Crea'ng*a*low?E*neutron*beam*

Proton Energy Countours for a Thick Lithium Target

from Lee and Zhou NIMB 152 (1999)

La

b N

eu

tro

n E

ne

rgy

(ke

V)

Lab Neutron Emission Angle (degrees)

45º - 1.93MeV

7Li(p,n)7Be

T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)#

Requirements: -  Continuous p beam

-  No ToF in detector (no S1)

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The*Li*target*T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)#

Li metal target Li2CO3 target Li2O target LiF target

Ep = 1.93 MeV Same total Li content

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Neutron*Filtering*T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)#

P.#Barbeau#et#al,#NIM#A#(2007)#

•  Take advantage of nuclear physics to selectively transmit neutrons through interference dips in scattering x-sections

40Ar, 56Fe, and 48Ti (n,el) cross-sections

Incident Energy (keV)

Cro

ss S

ectio

n (

ba

rns)

20 40 60 80 10010-4

10-2

1

102

73

ke

V

82

ke

V

24

ke

V

56Fe40Ar

48Ti

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Crea'ng*a*low?E*neutron*beam*

Backgrounds: -  gammas from 7Li(p,p’)

-  neutron-capture gammas in shield -  24 keV neutrons through the filter

T.#Joshi,#S.#Sangiorgio,#et#al,#NIM#B#333#(2014)#

Ideal 45º collimation

10

6 n

eu

tro

ns/2

50

eV

/sr/

mC

1

06 n

eu

tro

ns/2

50

eV

/sr/

mC

Ideal 55º collimation

Measure at different collimation angle,

normalize and subtract

"

Li(target(

Fe(filter(

Pb( LAr(

detector(

p(

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Expected*Recoil*Spectrum*in*LAr*

MCNP calculation of neutron transport and interaction using detailed geometry

Deposited energy (keV)

Counts

(counts

/keV

/C

)

0

0.5

1

1.5

2

2.5

3

All scatters in active volume (x0.5) - 45 deg

Single scatters fiducial volume - 45 deg

Single scatters fiducial volume - 55 deg

Background subtracted signal - model input

102 64 80

6.7 keV endpoint

Scatters from

24 keV neutrons

2.4 keVr

6.7 keVr

Multiple scatter

Endpoint measurement at 6.7 keV nuclear recoils

TMAX

Ar =4mM

(m + M)2En

Li target BPoly

detectors

Lead

LAr detector

p

n

Fe filter

Endpoint Measurement

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LLNL’s*on?site*dedicated*neutron*beam*

1.7 MeV Tandem accelerator at LLNL’s CAMS

The collimator setup

Protons on target

Unique neutron facility for detector calibration to low-energy neutrons (< 150 keV)

7mm dia Li

1µm thick

Proton

beam

Beam on target

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Ioniza'on*Yield*at*6.7*keVr*T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)#

Fit(using(the(MCNP(spectrum(convolved(with(measured(detector(resolu/on(and(

three(free(parameters:(

•  fixed(ioniza/on(yield,((

•  rate(normaliza/on,((

•  fano(factor((((

Qy = 4.9+0.1−0.2 (stat)

+0.7−0.9 (syst) e

−/keVat 640V/cm

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Uncertainty*Es'ma'on*T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)#

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Nuclear recoils at 6.7 keVr at

varying electric field

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Counts

(counts

/ele

ctr

on/

C)

Detected Electrons10 20 30 40 50 60

Detected Electrons10 20 30 40 50 60

= 240 V/cm

2/ndf = 3.4/8 = 640 V/cm

2/ndf = 8.1/10

Signal - all cutsBackground - all cutsBackground subtractedBest fit of model

10

co

un

ts/e

lectr

on

/µC

60Detected Electrons

10 20 30 40 50 60

= 2130 V/cm

2/ndf = 11.2/10

Detected Electrons10 20 30 40 50 60

= 1600 V/cm

2/ndf = 12.6/9

Electric*Field*Dependence*of*Ioniza'on*Yield*T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)#

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Drift Field (V/cm)500 1000 1500 2000 2500 3000

De

tecte

d n

um

be

r o

f e

lectr

on

s

20

30

40

50

60

70

2.82 keV – electron recoil

6.7 keV – nuclear recoil

Field*Dependence*

S2 ∝ ne = rNi

Use modified Thomas-Imel to

account for recombination using

parameters obtained from 2.82

keV electron recoils

For nuclear recoils

Ni +Nex =E

W· q(E)

For nuclear recoils the amount of initial

ionization Ni is unknown:

•  Nex / Ni = ??

•  E = 6.7 keV

•  W = 19.5 eV

•  q(E) = ??

Fit with Ni as only free parameter

Same phenomenological model of recombination holds in both cases

Similarities in spatial distributions of

ions and electrons

"

T.#Joshi,#S.#Sangiorgio,#et#al,#PRL#112#(2014)#

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0"

0.5"

1"

1.5"

2"

2.5"

3"

3.5"

4"

4.5"

5"

0" 20" 40" 60" 80"

Comparison*with*SCENE*Measurements*

Nuclear Recoil Energy [keVr]

•  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:(

0"

1"

2"

3"

4"

5"

6"

7"

8"

30" 300" 3000"

16.9"keVr"SCENE"

25.4"keVr"SCENE"

57.3"keVr"SCENE"

36.1"keVr"SCENE"

6.7"keVr"LLNL"

Electric Field [V/cm]

Ion

iza

tio

n Y

ield

[e

-/ke

V]

Ion

iza

tio

n Y

ield

[e

-/ke

V]

LLNL(

SCENE((interpolated)(

At 240 V/cm field

LLNL-PRES-677393

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Modeling*Low?E*Nuclear*Recoils*in*Liquid*Argon*

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-

Ar+ + Ar " Ar + Ar+

Ar+ + Ar " Ar + Ar+

Ar+ + Ar " Ar*

ArIAr(Inelas/c(Cross(Sec/ons(

Ar+IAr(Inelas/c(Cross(Sec/ons(

M.#Foxe,#C.#Hagmann,#et#al,#AstroparOcle#Physics#69#(2015)#

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(

Recoiling Ar

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Modeling*Results*

Ioniza/on(Yield(vs(E(Field(

Ioniza/on(Yield(at(1(kV/cm(

Track(Length((

Electron(recoil(

Ar(recoil(

M.#Foxe,#C.#Hagmann,#et#al,#AstroparOcle#Physics#69#(2015)#

Electron(thermaliza/on(length(

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Conclusions*and*outlook*

•  Nuclear recoil measurements: •  Refurbishment of Li target for

higher neutron efficiency •  Access lower recoil energy using

different filters •  Xe target

•  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

•  Things to consider: •  Liquid Argon vs Liquid Xenon

•  Few-electrons backgrounds •  Single electron calibration

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Acknowledgements **

!  A.(Bernstein,(C.(Hagmann,(K.(Kazkaz,(((

V.(Mozin,(S.(Pereverzev,(F.(Rebassoo,(

S.(Sangiorgio(

!  T.(Joshi(

!  P.(Sorensen(

!  I.(Jovanovic(

! M.(Foxe(