Performance and Radioactivity Measurements of the PMTs for the LUX - PowerPoint PPT Presentation

Performance and Radioactivity Measurements of the PMTs for the LUX and LZ Dark Matter Experiments Carlos Hernandez Faham Brown University Carlos Faham Brown University Particle Astrophysics Group TIPP 2011, June 11

The LUX Detector

VIDEO The Large Underground Xenon Experiment Video by Harvard-Smithsonian Center for Astrophysics and Learner 3

VIDEO Video by Harvard-Smithsonian Center for Astrophysics and Learner 4

S1 e - e - e - e - e - e - e - e - e - Carlos Faham, Brown University 11 5 TIPP 2011

top hit pattern: x-y localization e - e - e - e - e - e - e - e - e - S2 Δ t : z localization Δ t x Carlos Faham, Brown University 12 6 TIPP 2011

Photo by C. Faham 7

Dark Matter

Dark Matter: Direct Detection �� 10 m � =100 GeV, � � �� =1.0 � 10 �� 7 cm 2 ����� r ������������ r ����������� �� 10 ��� 10 Xe A=131 Ge A= 73 Ar A= 40 ��� 10 0 20 40 60 80 100 120 Recoil Energy, E r [keVr] Carlos Faham, Brown University 9 TIPP 2011

The LUX Hamamatsu R8778 PMTs

Photo by C. Faham Hamamatsu R8778 11

Hamamatsu R8778: High Expectations Developed by Hamamatsu Photonics, in collaboration with XMASS, specifically for liquid xenon operation Desired Characteristic Value Operational at LXe temperatures -110 C min. temperature High QE at 175 nm (UV) ~33% High CE 90% ~35% sphe sigma/mu Single-photon sensitive, good single phe resolution (ENF ~1.15) High peak anode current linearity 2% at 14 mA (~100 keV ee S2) Low afterpulsing < 5% (charge) for new PMTs Carlos Faham, Brown University 12 TIPP 2011

Hamamatsu R8778 Single-phe (Sphe) Spectrum BA0339 Sphe Spectrum 2000 1800 Gain = 3.9e+06 1600 σ / µ = 0.384 ENF = 1.15 1400 1200 Counts 1000 800 600 400 200 0 10 20 30 40 50 Sphe Area [mVns] Carlos Faham, Brown University 13 TIPP 2011

Hamamatsu R8778 QE in LUX Distribution of QE of 59 LUX R8778 PMTs Mean 33.3% 14 STD = 2.3% 12 10 Counts 8 6 4 2 25 30 35 40 QE at 175 nm [%] Carlos Faham, Brown University 14 TIPP 2011

Healthy R8778 PMT Afterpulsing Spectrum Carlos Faham, Brown University 15 TIPP 2011

R8778 exposed to He, and having a small air leak Afterpulsing Spectrum for BA0214 0 10 H+ He+ N+,O+ Normalized height � 1 10 � 2 10 Main Pulse � 3 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 t [ µ s] Carlos Faham, Brown University 16 TIPP 2011

Carlos Faham, Brown University 17 TIPP 2011

Hamamatsu R8778 Output Linearity BA0404 Nonlinearity Plot 20 -100 C 10 2% Linearity 0 % nonlinearity 2% nonlinearity 2% Hamamatsu Spec � 10 at 14 mA � 20 � 30 � 40 0 5 10 15 20 Peak Anode Current (mA) 20100506 CHF QUPID 2% nonlinearity ~1 mA Carlos Faham, Brown University 18 TIPP 2011

LUX 20 PMT Commissioning Photo by C. Faham Partial PMT deployment due to pressure testing of vessel All 122 PMTs scheduled to be deployed in July, 2011 Carlos Faham, Brown University 19 TIPP 2011

Radioactivity

Faking a WIMP 1) Electron Recoil Leakage 2) Single-scatter neutrons 3) Other non-gaussian rare events Carlos Faham, Brown University 21 TIPP 2011

Radioactivity Comparison 10 kBq 10 Bq 10 mBq 40 K, 14 C 238 U, 232 Th, 40 K, 60 Co 40 K Carlos Faham, Brown University 22 TIPP 2011

LUX’s R8778 Measured Radioactivity 1 10 R8778 Background Counts / keV / kg / day 0 10 �� 10 �� 10 10 2 10 3 Energy [keV] SOLO counting facility Carlos Faham, Brown University 23 TIPP 2011

LUX Component Radioactivity Comparison D. Malling These PMTs are not ultra-low background. Levels have improved much since then (see R11410 MOD radioactivity levels coming up...) Carlos Faham, Brown University 24 TIPP 2011

Implications for LUX Carlos Faham, Brown University 25 TIPP 2011

The LZS and LZD Experiments

LUX-ZEPLIN (LZ) Carlos Faham, Brown University 27 TIPP 2011

LZD 1000 3’’ PMTs LUX Carlos Faham, Brown University 28 TIPP 2011

The Hamamatsu R11410 MOD An ultra-low background PMT

R11410 MOD T wice the photocathode area of the R8778 QE, gain, etc. equivalent to R8778 ~x2 better anode linearity See Yoshizawa’s presentation Carlos Faham, Brown University 30 TIPP 2011

Hamamatsu R11410 MOD Carlos Faham, Brown University 31 TIPP 2011

Hamamatsu R11410 MOD Sphe Spectrum ZK4991 Sphe Spectrum 1000 900 Gain = 1.4e+07 800 σ / µ = 0.351 ENF = 1.12 700 600 Counts 500 400 300 200 100 0 50 100 150 200 Sphe Area [mVns] Carlos Faham, Brown University 32 TIPP 2011

Hamamatsu R11410 MOD Measured Radioactivity 1 10 R8778 R11410 MOD Counts / keV / kg / day Background 0 10 �� 10 �� 10 10 2 10 3 Energy [keV] Carlos Faham, Brown University 33 TIPP 2011

Hamamatsu R11410 MOD Radioactivity Results mBq/PMT Decay chain <0.4 238 U <0.3 232 Th <8.3 40 K 2 ± 0.2 60 Co 90% CL for upper limits, 1-sigma error bars • 60 Co will be further reduced in new Hamamatsu production units by replacing Kovar metal enclosure • Further, 60 Co always decays with correlated gammas, making the single-scatter probability lower • 40 K only has a 10% BR to EC + gamma decay mode Carlos Faham, Brown University 34 TIPP 2011

Conclusions • LUX employs 122 Hamamatsu R8778 for signal detection. These PMTs fulfill all performance benchmarks for physics requirements. • They are the dominant source of radioactivity in LUX. • However, measured radioactivity levels yield <1 WIMP-like event in 300 days. • New ultra-low background Hamamatsu R11410 MOD PMTs have been measured to have < 1 mBq/PMT combined U/Th. • Co remains at 2.0 ± 0.2 mBq, but will be removed by Hamamatsu in future productions by changing Kovar enclosure • K, at 10% gamma decay BR, has negligible effects in backgrounds • Performance of R11410 MOD is identical to the thoroughly tested R8778 PMTs. The LZS and LZD experiments will greatly benefit from using these PMTs. • This new technology is the best available in PMTs, and has equivalent radioactivity levels to those of QUPIDs. • Background reduction in photodetectors beyond current limits will not result in further gains for dark matter experiments, as coherent atmospheric neutrino scattering will remain the limiting background signal. Carlos Faham, Brown University 35 TIPP 2011

Thank you

Extra Slides

LUX 0.1 Event (Summed across all channels) 150 S2 4543 phe phe/sample 100 S1 50 52.8 phe 0 0 5 10 15 20 µ s S1 S2 10 60 phe/sample 40 5 20 0 0 � 0.5 0 0.5 17 18 19 µ s µ s J. Chapman 01 � Oct � 2009 Brown Particle Astrophysics Carlos Faham, Brown University 38 TIPP 2011

Photo by J. Chapman Carlos Faham, Brown University 39 TIPP 2011

SOLO Soudan Low-Background Counting Facility • 0.6 kg HPGe detector, 0.15 cm copper shield • Located at the Soudan Underground Laboratory (2000 mwe) • >30 cm lead shielding • The inner 5 cm lining of the chamber is comprised of ancient lead, with 210 Pb activity measured below 50 mBq/kg • A mylar shell and 2.5 slpm nitrogen gas purge are used to eliminate gaseous radon from the chamber Carlos Faham, Brown University 40 TIPP 2011

Co-60 and K-40 Decay Chains ) 3 M + ( 2 5.2714 y E ) 5+ 2 0 7 E Q 3 ( 2 + 60 . 3 D 7 5 ) 27 Co 3 9 2 0 5 7 E . 5 . 6 1 6 8 ( 2 0 1 4 5 . 3 1 1 6 -6 Q =2823.9 6 2 2 0 0 3 6 8 5 1 7 7 . 1 2 9 0 1 6 3 0 . 0 1 7 9 3 . . 4+ 0 0 2 9 0 99.925% 7.5 1 2505.766 0 0 1.1 ps . . 2+ 0 0 6 >12.9 2 2158.64 <0.022% 5 0.59 ps 8 9 . 9 2+ 9 0.057% 15.0 2 1332.518 0.713 ps 1.277 10 9 y 0+ 4 – 0 0 11 1460.830 E2 stable 60 40 28 Ni 19 K Q EC =1504.9 10.72% 2+ 11.6 1 1460.859 10.67% 1.12 ps 0+ 0 21.0 3 0.048% stable 40 18 Ar Carlos Faham, Brown University 41 TIPP 2011

LUX, LZS and LZD Sensitivities Carlos Faham, Brown University 42 TIPP 2011

Afterpulsing Delay - Ion Identification Afterpulsing Delay vs. Bias Voltage, BA0217, Main Pulse ~100 pC (Anode) 1.5 AP1 Charge/Mass Ratio: AP2 AP1 = 1.1 ± 0.6 AP3 AP2 = 4.00 AP3 = 15.2 ± 0.1 N + , O + Afterpulsing Delay τ [ µs ] AP3 1 He + Measured by He exposure AP2 0.5 H + AP1 0 0.025 0.026 0.027 0.028 0.029 0.03 0.031 0.032 � 1/ ( bias ) [V] Carlos Faham, Brown University 43 TIPP 2011

Carlos Faham, Brown University 44 TIPP 2011