Studies of Two-Phase Xenon Detector Response with the PIXeY Experiment

Transcription

1 Studies of Two-Phase Xenon Detector Response with the PIXeY Experiment Ethan Bernard, UC Berkeley This work was performed at Yale University February 19 th, 2016 UCLA Dark MaDer 2016

2 Design MoNvaNon and Overview PIXeY was designed to study study the response of a liquid xenon detector to both electronic and nuclear (NR) recoils over a wide range of electric fields. This avoids the difficulnes of comparing responses from different detectors.* Data collected from a single detector is especially useful in construcnng response parameterizanons such as NEST. Data acquired at 100 V/cm, 200 V/cm, 700 V/cm, 1 kv/cm and 2 kv/cm. 83m Kr and 37 Ar mono-energenc calibranon sources used to flat-field and monitor detector response. Electron recoil populanon acquired using a tagged 22 Na source. Nuclear recoils produced using a DD neutron generator, untagged * We are not alone in doing this. See results by Kaixuan Ni s group, Phys. Rev. D 92, (2015)

3 The PIXeY Detector Dimensions: 5.1 cm verncal drig length 9.2 cm side length hexagon Short and wide Teflon-clad hexagon: High fields with modest voltages OpNmal light collecnon Liquid Surface, set by weir height 2 x 7 arrays of R8778 PMTS Anode Gate Cathode Xenon is condensed by boiling liquid nitrogen to maintain a constant pressure of 2 bar, +/- 10 mbar Liquid xenon is connnuously circulated outside of the detector, cleaned by a hot metal geder and returned. The circulanon loop includes charcoal traps that can introduce both 83m Kr and 37 Ar into the xenon flow.

4 Dimensions: 5.1 cm verncal drig length 9.2 cm side length hexagon The PIXeY Detector 2 x 7 arrays of R8778 PMTS

5 Cryogenically CompaNble Wire Grids Monel wires are wound under 250 g tension and soldered to monel frames with 4% Ag / 96% Sn solder. Wires are 80 µm diameter, with 1 mm spacing (cathode, gate, anode) or 3 mm spacing (PMT shields)

6 Basic Two-Phase Xenon TPC OperaNon Electroluminescence Field Voltage S1 Drig Field S2 S1 Liquid surface Liquid xenon Gate, 0V Anode, +8 kv Cathode, -10 kv S2 Time (µs)

7 37 Ar CalibraNon Source 40 Ca + n à 37 Ar + α 37 Ar + e - à 37 Cl + ν e (35 day half-life) 2.82 kev cascade from K shell capture 270 ev cascade from L shell capture ObservaNon of 2.82 kev capture cascade in LXe: D.Yu. Akimov, et al., JINST, 9, 1104 (2014) ObservaNon of 2.82 kev and 0.27 kev cascades in LAr: S. Sangiorgio, et al., Nucl. Inst. Meth A, 728, 69 (2013)

8 37 Ar CalibraNon Source ObservaNon of 2.82 kev capture cascade in LXe: D.Yu. Akimov, et al., JINST, 9, 1104 (2014) ObservaNon of 2.82 kev and 0.27 kev cascades in LAr: S. Sangiorgio, et al., Nucl. Inst. Meth A, 728, 69 (2013)

9 37 Ar CalibraNon Source

10 FiducializaNon and PMT WeighNng OpNmizaNon OpNmizaNon procedure: 1) Approximate PMT weights found by single photoelectron response. 2) Center of mass weighnng of S2 signal cuts a central volume. 3) PMT weights of S1 and S2 are separately refined to opnmize energy resolunon within the central volume. 4) The opnmal S1/S2 anncorrelanon angle for combining S1 and S2 is determined. 5) A smaller central volume of ~13 cm 3 is cut to give the highest energy resolunon

11 Energy ResoluNon at 1 kv/cm Drig Field 1274 kev PhotoabsorpNon Blue = Large opnmizanon volume Black = Small central measurement volume Red = Gaussian fit to black 1.05% σ/e

12 Energy ResoluNon at 1 kv/cm Drig Field Fit: E -1/2 scaling with 1.11% σ at 1 MeV Michigan- S. Stephenson et al., J. Inst. 10 (2015) P10040 Shanghai- Q. Lin et al., J. Inst. 9 (2013) P04014 Exo200- Auger, M. et al. J. Inst. 7 (2012) P05010 Preliminary XENON100- E. Aprile et al., Astropart. Phys. 35 (2012), Columbia- Kaixuan Ni thesis, secnon (2006)

13 Detector Response S1 light collecnon 9.1 ± 0.2(stat)% - calculated from Doke plot method using 83m Kr data at different fields*. Normalized to the center of the detector. Single electron response measured separately for every dataset - typically 34 ± 1.5(sys) phe. CorrecNons applied for depth-dependent correcnons (electron lifenme and S1 light collecnon). CorrecNons not required for xy posinon dependent response within the inner 1/3 of the detector volume. S1/E = n γ /(n γ + n e ) g1/w [Phd/keV] Preliminary Kr 83m data (41.5 kev) Ar 37 data (2.8 kev) Best fit => g1 = g2 = S2/E = n e /(n γ + n e ) g2/w [Phd/keV] * W = 13.7 ev from C. E. Dahl thesis, Princeton, (2009)

14 ExtracNon Efficiency Measurements To anode -> Gas 5.55 mm gas gap to anode Drig field constant at 700 V/cm Increasing anode steps gas field from 4.3 kv/cm to 12 kv / cm <- From cathode Liquid Liquid surface Gate grid 1 mm pitch 1.85 mm from gate to surface

15 Electron ExtracNon Efficiency Measurements Extraction efficiency 1 PIXeY (Kr-83m) PIXeY (Ar-37) Gushchin LUX Run03 XENON Preliminary LUX: D. Akerib et al. PRL 112, (2013). arxiv: Electric field (liquid), kv/cm Gushchin: E.M. Gushchin et al. Sov. Phys. JETP 49(5), May 1979 XENON100: E. Aprile et al. J Phys, G: Nucl. Part. Phys (2014)

16 Single electron area, detected phe Electroluminescence Light Yield Measurements PIXeY Fonseca yield Aprile yield PIXeY fit Preliminary Fonseca: A.C. Fonseca et al., 2004 IEEE Nucl. Sci. Symp. Conference Record (2005). Electric field (gas), kv/cm Aprile: E. Aprile et al., IEEE Trans. Nucl. Sci. 51 (2004) 1986; IEEE Nucl. Sci. Symp., November 2003, SeaDle, USA. Monteiro: C. M. B. Monteiro et al., J. Inst 2, P05001 (2007)

17 Electron Recoil Photon Yield Photon yield is calculated by correcnng the S1 signal for depth-dependent light collecnon and factoring out S1 light collecnon. Photon yield decreases with increasing electric field as recombinanon decreases. 37 Ar kev Preliminary 17

18 Electron Recoil Charge Yield 37 Ar ev 37 Ar kev Preliminary

19 Electron recoil recombinanon RecombinaNon fracnon measured as a funcnon of energy for different fields. IniNal rano of excitanons to ionizanons (α) assumed as 0.2. As expected, recombinanon fracnon decreases with increasing field and energy. 37 Ar kev α = 0.2 assumed Preliminary

20 Conclusion PIXeY has measured responses to low energy electronic and nuclear recoils over a wide range of electric fields. PIXeY has measured the 37 Ar 270 ev capture cascade and shown its suitability as a low-energy internal calibranon source for noble liquid dark mader detectors. PIXeY has shown ~ 1% σ/e energy resolunon in response to high energy gammas. Yale University (many now at UC Berkeley) Ethan Bernard, Elizabeth Boulton, Alessandro Curioni, Blair Edwards, ScoD Hertel, Markus Horn, Nicole Larsen, James Nikkel, Brian Tennyson and Daniel McKinsey University of ConnecNcut Nicholas Destefano and Moshe Gai Funding Thank you! NSF grant PHY , DHS grant 2011-DN-007-ARI056, DOE grants DE-SC and DE-FG02-94ER40870 R8778 PMT

21 Backup Slides

22 The PIXeY Detector

23 Energy ResoluNon at 1 kv/cm Drig Field 511 kev PhotoabsorpNon Blue = Large opnmizanon volume Black = Small central measurement volume Red = Gaussian fit to black 1.67% σ/e

24 Energy ResoluNon at 1 kv/cm Drig Field 662 kev PhotoabsorpNon Blue = Large opnmizanon volume Black = Small central measurement volume Red = Gaussian fit to black 1.17% σ/e

25 Energy ResoluNon at 1 kv/cm Drig Field 1274 kev PhotoabsorpNon Blue = Large opnmizanon volume Black = Small central measurement volume Red = Gaussian fit to black 1.05% σ/e

26 Energy ResoluNon at 1 kv/cm Drig Field 2614 kev PhotoabsorpNon Blue = Large opnmizanon volume Black = Small central measurement volume Red = Gaussian fit to black 0.86% σ/e

27 Anode IsolaNon Single piece of teflon to hold anode grid Teflon lip separates gate and anode grids Top shield grid hangs from above (no connecnons to anode) Up to 14 kv/cm in gas between surface and anode Anode PTFE lip and liquid surface Gate Up to 2 kv/cm drig field in liquid Up to 68 photoelectrons produced in gas per electron driged in liquid

28 High Voltage Feedthroughs Ethan Bernard, LIDIE 2015 Feedthroughs are epoxy-encapsulated cable terminanons Miniature versions of LUX cathode feedthrough.