PandaX detector calibration and response 报告人 : 肖梦姣 Shanghai Jiao Tong University (On behalf of the Panda-X Collaboration) 1
Outline 1. Detector running conditions 2. LED calibration Setup of the optical system PMTs gain and SPE resolution calibration 3. Radioactive source calibration Geometry of the source position Detector response and position reconstructed Gamma calibration (light yield, electron lifetime, resolution) Electron recoil band 4. Summary 2
1. Detector running conditions Inner Pressure: ~1.05 barg, Outer Vacuum: <1.0E-3 Pa; Cathode HV: -10 kv (drift field ~390 V/cm); Grid HV: -4.2 kv (extraction field ~7 kv/cm); Detected both scintillation (S1) and proportional (S2) light. 3
2. LED calibration The optical system: 1). Setup the LEDs outside the detector to void to induce the EMI; 2). Install 2 teflon balls as the diffusers on the top PMTs array; 3). LEDs and diffusers are coupled to the optical fibers and feedthroughs. 4
Calibration: Gain and SPE resolution Top pmt Gain were balanced ~2E6 Bottom pmt 5
3. Radioactive source calibration 1). Geometry of the source position SS tube PE tube 6
2). Detector response and position reconstructed 7
2). Detector response and position reconstructed Double scatter event 8
3). Gamma calibration: light yield at zero field Light yield at zero field: ~6.0 pe/kev for 662 kev (~6.42 pe/kev for122 kev) (Xenon100: 3.8 pe/kevee for 122 kevee) 9
3). Gamma calibration: light yield at field Light Yield at field (drift field ~390 V/cm and extraction field ~7 kv/cm): ~2.8 pe/kev Co60 Cs137 10
3). Gamma calibration: electron lifetime N=N0*exp(-dt/τ). N: number of electron drifting to gas/liquid interface; N0: number of initial free electrons; dt: the drift time; τ: electron lifetime, strongly dependent of impurity level. Average electron drift velocity ~2 mm/μs 165μs~33cm (maximum drfit length TPC is 15cm.) 11
3). Gamma calibration: resolution Resolution with only light (S1) or charge signal S2 Resolution with S1_only: 10.20% at Cs137 peak (662 kev) Resolution with S2_only: 7.36% at Cs137 peak (662 kev) 12
3). Gamma calibration: resolution Resolution with combined energy (S1+S2): ~3.5% Combine the energy through the anti-correlation of S2 and S1 Correlation of S1 and S2 Spectrum of combined energy 13
4.) Electron recoil band Discrimination between electron and nuclear recoils with S2/S1: S1: electrons recombination signal (scintillation) S2: ionized electrons escaped from recombination (ionization) 14
4.) Electron recoil band 15
Summary The detector of PandaX is working stable now and we are learning more and more about the detector. We carried out the LED calibration and the pmts and DAQ are working well. Many gamma calibration runs were taken and gave us much information about the detector, such as light/charge yield, electron lifetime, energy resolution and so on. We roughly got the electron recoil band now. The uniformity and neutron calibration will be carried on soon for the further study. 16
Thank you! 17