calibra'on*and*modeling*of*nuclear*and* electron*recoils...
TRANSCRIPT
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
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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
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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
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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(