SLAC - Advanced Instrumentation Seminars

Transcription

1 Samuele Sangiorgio LLNL Advanced Detector Group SLAC - Advanced Instrumentation Seminars Feb 20, 2013 LLNL-PRES This work was performed under the auspices of the U.S. Department of Energy by under contract DE-AC52-07NA Lawrence Livermore National Security, LLC 1

2 Low-energy nuclear recoils: motivations and challenges The LLNL prototype and performances Inducing nuclear recoils in Ar with neutrons Conclusions 2

3 CNNS a neutral current process where an incoming neutrino elastically scatters on a nucleus ν + Ar ν + Ar ν Z 0 ν undisputed prediction of the Standard Model enhanced cross-section: d" d(cos#) $ G2 8% N 2 E 2 (1+ cos#) 3

4 CNNS a neutral current process where an incoming neutrino elastically scatters on a nucleus undisputed prediction of the Standard Model enhanced cross-section: d" d(cos#) $ G2 8% N 2 E 2 (1+ cos#) very low recoil energy E r = 716 ev (E ν/mev) 2 A CNNS interests for: - Test the SM - Supernovae - Reactor antineutrino monitoring - dnde 1eV from Pu ν + Ar ν + Ar ν Z 0 Spectra of reactor ν on Argon Pu-239 <E R > = 207 ev Hagmann and Bernstein, IEEE TNS, 152, Recoil Energy ev Need detector with to low energy threshold ν U-235 <E R > = 243 ev 4 dnde 1eV from U235

5 dn/denr counts/(kev kg day) Detection of WIMPs hinges on nuclear recoils Low threshold allows to probe light WIMPs candidates!* * Dark Matter Elastic Scatter on Xe!*!!* "!* # σ n = cm 2 m χ =10GeV m χ =20GeV m χ =50GeV! " # $ % & ' ( )!* "* #* $* %* Nuclear Recoil Energy [kev] σn [cm 2 ] 10!37 10!38 10!39 10!40 10!41 10! [GeV] Ar 10 kg-day 1.0 kevr threshold CDMS II, PRL (2011) XENON100, PRL (2011) XENON10, PRL (2011) CRESST, Astropart. Phys (2002) Plots from P. Sorensen, CNNS Workshop, LLNL (2012) Setting Dark Matter Mass Limits Need detector with to low energy threshold m χ 5

6 Bolometers CUORE PHONONS ~10 mev/ph Superheated liquids COUPP Scintillating bolometers CRESST Hybrid bolometers CDMS EDELWEISS Solid Scintillators DAMA Single-phase noble liquids DEAP CLEAN SCINTILLATION ~1 kev/γ Dual-phase noble liquids LUX XENON ZEPLIN DARKSIDE IONIZATION ~10 ev/e - Ionization detectors CoGeNT Dual-phase noble liquids 6

7 Well known technology, extensively used in Dark Matter experiments Good electron drift properties Large mass Low thresholds Scalability time Proportional Proportional (S2) pulse ~12 pulse!s (S2) width Gas S2 Photomultiplier 4x Hamamatsu tubes 8520 PMTs Anode E gain E extract Extraction Grid Liquid e - e - e - e - e - e - drift ~2 mm/!s Primary Primary pulse (S1) pulse (S1) ~4!s width S1 E drift 128 Light nm collected UV light converted to 400 nm from by TPB PMTs Cathode Incoming particle 7

8 The energy loss mechanism in noble liquids depends on particle type and energy Nuclear recoils are less effective than electron recoils in producing ionization nuclear ionization quench factor q(e r ) = N ion(e r, nucleus) N ion (E r, electron) No data at low energy in Ar Experimental data for LXe for nuclear recoils down to 4 kev. Ionization yield in LXe Lindhard theory LLNL in-house MonteCarlo based on atomic collision in Ar Manzur et al, Phys. Rev. C 81 (2010) M. Foxe, PhD thesis Need to measure the ionization yield of nuclear recoils at < kevr 8

9 For A = 2N, E!=5 MeV Ar Xe Atomic number Boiling point [K] Liquid phase density [g/cm 3 ] Radioactive isotopes 39 Ar 136 Xe? Recoil Energy ev Argon Assumes A=2N, En=5MeV 1.0 x x x x x10 40 Cross section cm 2 Price [$/ft 3 ] $ $$$ Scintillation light [nm] Fraction of recoils Simulated ionization spectrum from reactor neutrinos on Ar ~ 30% Fraction of recoils x Neutron number N Simulated ionization spectrum from reactor neutrinos on Xe ~ 6% Number of primary electrons Number of primary electrons 9

10 Cryocooler Cold head Purifier Gas Ar Electronics rack Movable table 10

11 In-situ production of LAr w/ cryocooler Automated cooldown and liquefaction in ~14h cryocooler condenser Temperature stability ± 0.05 K Total ~1 liter of Argon can be circulated 3-4 times per day Temperature (K) Condenser Temperature Dewar Temperature Liquid Level Meter Capacitance (pf) inner vacuum jacket Ar Injection Elapsed Time (hours) 5.5 dewar 11

12 Active volume: ~ 100 g LAr Materials selected for low outgassing TPB as wavelength shifter Home-built HV feedthroughs 4x Hamamatsu R PMTs liquid level gas Ar (1 87K) Up to 11kV/cm liquid Ar Up to 3kV/cm 3.5 cm 2.5 cm E gain E drift liquid level field rings 5 cm rings support HV feedthroughs 12

13 Emphasis on detection of ionization by means of S2 only Operate close to electron multiplication in gas z-axis [cm] Electric field magnitude for a simplified model of the detector -21 kv grounded anode ~9.2 kv/cm ~6 kv/cm extraction grid Liquid level Monteiro et al, IEEE Trans. Nucl. Sci., 48 (2001) ~2.5 kv/cm -30 kv cathode ~11 kv/cm at 1atm at 87K x-axis [cm] 13

14 Hamamatsu R PMTs for cryogenic operation 14

15 Sample event from a 60 kev photoelectric interaction in the detector as seen by the 4-PMT array S1 S2 241 Am raw spectrum Time between S1 and S2 gives depth of the interaction 15

16 Position of extraction grid Electron lifetime τ = 95±7 µs = 30±2 cm Bottom of active volume Plot of S2 amplitude in 241 Am photopeak as a function of depth extracted from S1-S2 time Electron lifetime during cooldown Recirculation needed only after ~6.5 days recirculation 16

17 Schematic top view PMT1 PMT2 PMT1 PMT2 241 Am vertically collimated slab PMT3 PMT4 dewar Active region area PMT3 PMT4 241 Am spectrum with fiducialization Raw data Square box cut size Am peak fiducial plot (PMT1+PMT2) / (PMT3+PMT4) (PMT1+PMT3) / (PMT2+PMT4) 60 kev photopeak 17

18 Spectrum of 55 Fe X-ray source Electroplated ~100Bq 55 Fe on a movable arm Resolution: 9.2% at 1σ 55 Fe Mn Kα1 Kα kev 55 Fe Mn Kβ1 Kβ kev 5 mm Under study: Mapping of fiducialization parameter space Position systematics 55 Fe in the center 55 Fe on one side [a.u] [a.u] 18

19 Provides low-energy uniform calibration throughout the whole detector volume nat Ar isotopes Isotope production Produced by neutron irradiation of nat Ar at a nuclear reactor Decay scheme 100% electron capture t 1/2 = d Q(gs) = kev Decay radiation K- capture 2.82 kev (90.2%) L- capture 0.27 kev (8.9%) M- capture 0.02 kev (0.9%) Mass number Natural Abundance % % % Barsanov, V. I. et al. Phys. Atomic Nucl 70 (2007). Aalseth, C. E. et al. NIM A652, (2011). 19

20 Provides low-energy uniform calibration throughout the whole detector volume Isotope production Produced by neutron irradiation of nat Ar at a nuclear reactor Decay scheme 100% electron capture t 1/2 = d Q(gs) = kev Counts! Counts Fe Fe & Ar Decay radiation K- capture 2.82 kev (90.2%) L- capture 0.27 kev (8.9%) M- capture 0.02 kev (0.9%) Collected light [p.e.] Collected Light [p.e.]! 20

21 Counts! Ar L-shell EC! 0.27 kev! µ = 86 p.e.!! = 22%! 37 Ar K-shell EC! 2.82 kev! µ = 530 p.e.!! = 11%!! 2 / ndf = / 115 Prob ExpCoeff ± 8.6 ExpOffset ± Fe Mn K#1 K#2! 5.89 kev! µ = 768 p.e.!! = 12%! ExpConst ± 6.3 p.e./kev - Fe ± 0.5 FeCoeff 84.5 ± 2.3 FeWidth ± 3.32 p.e./kev - ArK ± 0.9 ArKCoeff ± 2.74 ArKWidth ± 2.19 p.e./kev - ArL 328 ± 12.3 ArLCoeff 27.9 ± 4.8 ArLWidth ± 3.49 Exp2Coeff ± Fe Mn K"1 K"3! 6.49 kev! Exp2Coeff ± 0.17 Exp2Coeff ± Collected Light [p.e.], et al. arxiv: Collected Light [p.e.]! 21

22 Peak Raw data After cuts and fiducialization Peak Tail Tail Events in the tail mostly due to lower geometric light collection efficiency 22

23 DS56026 File 1 Trace 1864 Reconstructed event: Event Width: 6.98 µs Total light: 8.14 spe Typical S.E. event as seen on the scope Full trace is 100µs long and has no s.p.e. other than those shown Experimental spectrum of single and double ionization electrons Not compatible with primary scintillation signal (S1) because: Event width of 5-8 µs is too long Light distribution not compatible with LAr S1 characteristics Dependence on gain field Counts single ioniz electrons µ = 8.2 ± 0.1 p.e.! = 3.4 ± 0.1 p.e. EventWidthT [µs] h2 Entries 2807 Mean RMS 5.398! 2 / ndf / 94 Prob µ 8.2 ± 0.1 " ± SE amp ± E amp ± Integral [p.e.] Collected Light [p.e.]

24 S.E.s appearance has been seen in the aftermath of electrical discharges from the HV system, with rate decreasing with time Different from observations in Xe by RED collaboration Light content per PMT in S.E. events Indications of S.E. production from a specific point in the detector from the light content per PMT Single Electrons: Absolute detector calibration Source of background Need to understand origin Controlled production? 24

25 Initial ionization from energy partitioning between ionization and excitation: N i = E er w q 1 (1 + N ex /N i ) Assume Thomas-Imel box model of recombination: n e N i = 1 ξ ξ = ln(1 + ξ) N iα 4a 2 ue constant single fit parameter n e Detected ionization Ionization [electrons/kev]! Cfr. Sorensen, P. and Dahl, C. E., Phys. Rev. D. 83 (2011) 50! 2 / ndf / 2! 2 / ndf!!0.041 / 2! Prob "/(4a 2 µe) ± ! 2 45 " /(4a µe) ± w q 19.5 ± Ar L-capture Nex/Ni E = kv/cm! ± Ar K-capture, et al. arxiv: Electron recoil energy [kev] Electron recoil energy [kev]! W q = 19.5 ev Nex/Ni = Fe X-rays E er Can this be extended to nuclear recoils? - See NEST [M. Szydagis, arxiv:

26 LLNL prototype Novel calibration approach with 37Ar Sub-keV spectroscopy Single electron sensitivity Inducing nuclear recoils with neutrons Electron Recoil Demonstrated low-energy threshold in LAr Nuclear Recoil Electromagnetic Radiation Neutron uclear recoils result in less observable signal than electron reco 26

27 Elastic scattering of neutrons on argon End-point measurement T MAX Ar = 4mM (m + M) 2 E n 7 Li(p,n) 7 Be Using near-threshold kinematics we can control maximum neutron energy Proton Energy Countours for a Thick Lithium Target from Lee and Zhou NIMB 152 (1999) Lab Neutron Energy (kev) 45º MeV Lab Neutron Emission Angle (degrees) 27

28 detectors Fe filter Lead n LAr detector Neutrons/cm 2 /100eV/s Spectrum of neutrons through the collimator protons 1uA 1.93MeV 45º collimation Li target BPoly p MNCPX simulations Backgrounds from - (p,p ) in Li à 478 kev γ kev γ from n capture in BPoly 28

29 detectors Lead 7 cm Fe cm Fe Ti filter n LAr detector Neutrons/cm 2 /100eV/s unfiltered protons 1uA 1.93MeV 45º collimation Li target BPoly filtered p 40 Ar, 56 Fe, and 48 Ti (n,el) cross-sections Take advantage of nuclear data to selectively transmit neutrons through interference dips in scattering x-sections [see P. Barbeau et al, NIM A (2007)] Quasi-monoenergetic beam ~73 kev match Ar(n,el) resonance Cross Section (barns) kev 73 kev 56 Fe 40 Ar 48 Ti 82 kev Incident Energy (kev) 29

30 detectors Simulated neutron spectrum in active region Lead n LAr detector Fe filter Li target BPoly p Expected energy depositions in the active volume Look for paper on the neutron beam design in the near future Due to multiple scatters, not yet suppressed 30

31 1.7 MeV Tandem accelerator at LLNL Center for Accelerator Mass Spectroscopy Collimating/filtering setup deployed at CAMS The collimator setup The move. Garage sale? 10 LLNL-PRES DRAFT 31

32 Ag Target Backing - proton sink Li target -8mm diameter -10µm thick Target holder Protons on Target - 3mm x 3mm square beam spot - halo extends out ~15 mm 32

33 Goals: - Integrate our setup with accelerator J - Verify accelerator performances J - Validate neutron signal and gamma background using He3 and NaI detectors L Problems: - Gamma shielding was found to be insufficient - Deficit of neutrons from the target Gamma Background (Measured) Neutron Spectrum (Simulated) cts/p.e./s Si detector Collected Light [p.e.] 33

34 Li target was produced in 2006 Li was evaporated on Ag puck Lower neutron yield due to diffusion of Ag in Li AgLi Approximate neutron yield deficite vs.liatom fractioninag -Li Alloy AgLi2 Ag4Li9 Ag3Li10 AgLi4 AgLi13 n -yield relativeto metal Li target Atom fractionofli Li 34

35 Thin (1µm) Lithium procured No low-energy neutrons Remove Ti filter Lower gamma background Optimized shielding Endpoint measurement with neutron beams at 73 kev and 24 kev Tag neutrons to access lower recoil energies Neutrons in forward solid angle (1/keV/source p/steradian) n-tag Neutron spectrum at 45º from 1.93 MeV protons on Li target Thick target (10µm) Energy (MeV) Thin target (1µm) 40 Ar, 56 Fe, and 48 Ti (n,el) cross-sections BPoly Pb Lar detector Cross Section (barns) kev 73 kev 82 kev 56 Fe 40 Ar 48 Ti beam Incident Energy (kev) 35

36 Nuclear Resonance Fluorescence ϒ fluoresced ϒ resonant 40 Ar P absorption! P total 40 Ar * Pemission Recoil energy E NR = 2(E r sin(θ/2)) 2 Mc 2 Resonance energy (for Ar: 4.8 MeV & 9.8 MeV) Angle of fluorescence Possible gamma source: HIγS Experimentally challenging Argon mass Could probe sub-kev recoils Argon Recoil Energy [evr] P absorption angular domain available for γ-tagging T. Joshi, NIM A 656 (2011) Fluorescence Angle [degree] 36

37 Detector has capabilities to observe nuclear recoils > 2keVr for reasonable quenching values ( > 0.1 ). Planned measurement at LLNL in the next few months. Detector improvements are being considered to extend sensitivity to even lower energies Improve understanding of detector response and backgrounds at low energy Complete detector simulation 37

38 LLNL LAr detector: Single electrons: achieved lowest detector sensitivity Demonstrated sub-kev spectroscopy with LAr Ready to measure low energy nuclear recoils in LAr determine ionization yield key parameter to assess feasibility of Coherent Neutrino-Nucleus Scatter and extend range of accessible Dark Matter WIMPs mass 38

39