Understanding the response of LXe to electronic and nuclear recoils at low energies

Transcription

1 Understanding the response of LXe to electronic and nuclear recoils at low energies Christopher W. Geis Johannes-Gutenberg Universität Mainz 2015/01/ / 16

2 Response from Electronic Recoils in LXe PRD _2013 JINST 6 p10002 (2011) 2 / 16

3 Response from Nuclear Recoils in LXe PRD _2013 Need to improve understanding of LXe response (Leff, Qy) at low recoil energies for electronic and nuclear recoils 3 / 16

4 Pulse Shapes in LXe LXe has 2 decay components (singlet, triplet state of Xe2*) - different scintillation pulse decay shape in liquid noble gases further possibility for particle discrimination - works well in LAr - challenging in LXe NIM A612 (2010) Time between components is short (ns) Pulse shape is electric field dependent Phys. Rev. B 27, Need to improve understanding of ER/NR pulse shapes in LXe at different energy/electric fields 4 / 16

5 Mainz TPC Requirement Specs Electronic Recoils: Re and QY focus: low energies (1-10 kev) what is new compared to former measurements: simultaneous measurement of R and Q e Y improved measurement of recoil energies (using a HPGe-detector) in the Compton scatter experiment 3D-position reconstruction ( 1.3mm) allows fiducialization and detection of multiple scatters Nuclear Recoils: Leff and QY as for electronic recoils measurement of nuclear recoils requires a suitable neutron source (neutron scatter experiment) neutron detector to measure energy deposit in LXe (scatter angle / TOF) Scintillation pulse shape (S1): Nuclear and electronic recoils measure pulse shape systematically for different drift fields and recoil energies with fast digitizers use fast fadcs to account for small decay time differences (5GS/s) Test of calibration techniques 37Ar, 83mKr 5 / 16

6 Mainz TPC Design 2 PMT x/y-position-resolution using 8 large area APDs x/y-resolution 1.3 mm d = 52 mm 50 mm high transparency meshes pitch: 268 µm wire-diameter: 14 µm Transparency: more uniform field less field leakage in detector volume 0.2 kv/cm 3 kv/cm 2 PMT 6 / 16

7 Cryogenics with Compton Setup TPC inside cryostat pulse tube refigerator + LN2 emergency cooling Ge-detector collimator for γ-source (137Cs, 60Co) 7 / 16

8 Cryogenics with Compton Setup TPC inside cryostat pulse tube refigerator + LN2 emergency cooling Ge-detector collimator for γ-source (137Cs, 60Co) 8 / 16

9 October 2014 Δt 20µs First runs successfully done! can apply drift and extraction field (Oct 2014) data run with all sensors (PMTs, APDs, Ge) (Nov 2014) first Compton scatter spectrum taken (Dec 2014) To Do: minor improvements more sophisticated data analysis systematic studies of electronic recoils 9 / 16

10 - Driftfield: 0.4 kv/cm - Extraction field: 4 kv/cm 10 / 16

11 Compton Scatter Experiment S1 spectra: 137Cs Source (662keV) RY A N I LIM IS E R P LYS A N A RY A N I LIM PRE ALYSIS AN all scattering angles Ge detector at 30 ~ 90 kev energy deposit Upcoming: take more data at different scatter angles (energies) charge calibration of PMTs (SPE) 11 / 16

12 Compton Scatter Experiment Corresponding Ge spectrum of the scattered gammas: Ge 30 ~90keV ARY N I M LI PRE ALYSIS AN Example: RY A N I LIM PRE ALYSIS AN preamplified event in Ge-detector 12 / 16

13 Test of Calibration Techniques Ampulla of 37Ar produced at Mainz neutron reactor TRIGA: - ~ 2cm3-6 hours exposure ~200 kbq - electrons with E = 2.38 kev - 35d half life - nice to calibrate our TPC Test setup with 1 PMT gas out Also plan to test: - 83mKr PTFE 13 / 16

14 Neutron Scatter Setup Scattering Target = MainzTPC Source mn vn mn vn neutron source requirements: within reach (Europe, ideally in Germany) neutron energies that allow to study ΔETPC of 1 kev to 50 kev neutron rates of 2kHz or less Neutron Detector neutron detector requirements: position resolution (1 cm) time resolution (500 ps) energy threshold: (500keV) design/technology: plastic scintillator + fibre-grid suggestions? 14 / 16

15 Summary & Outlook Mainz TPC goals: understand the response of liquid xenon to electronic and nuclear recoils (scintillation yield, pulse shape and ionization yield) first comissioning runs done upcoming: more measurements of electronic recoils in the compton scatter experiment Mainz TPC with Neutron Scatter Setup simulations ongoing to study feasability upcoming: design, study and construction of a suitable neutron detector 15 / 16

16 Thanks to the XENON Mainz group U. Oberlack, C. Grignon, R. Othegraven B. Beskers, P. Sissol, M. Scheibelhut, Ch. Hils E.S. Kjartansson, T. Jennewein, M. Morbitzer, D. Wenz 16 / 16

17 Backup NEST 17 / 16

18 APD: QE measurement APD rotatable disc with αsource and optical fibre QE at xenon scintillation (178nm): solid angle: Ω gen energy of α-particles E => # photons generated N α ph test pulse: scale MCA spectra to charge => calculate # photons detected: Nphdet with the previously measured gain, we can calculate the quantum efficiency 18

19 gain vs. bias voltage different APDs colors: 6 APDs from wafer black: 1 APD from wafer T=176.3 K ± 0.3 K ΔT < 0.1K for each APD 19