An APD Readout for EL Detectors Thorsten Lux IFAE, Barcelona, Spain

Introduction R&D started years ago Funded mainly by Consolider CUP Motivation: alternative to SiPMs in the NEXT detector APDs known to give similar energy resolution as PMTs in EL detectors (1 sensor chambers) What can one achieve with Multi-APD readouts? 14/12/201025th TPC Symposium, Paris, France

Previous Measurements 14/12/201035th TPC Symposium, Paris, France Large set of studies performed at University of Coimbra Excellent energy resolution of < 5% at 22 keV achieved (4-6 bar) Only one APD (16 mm diameter) Similar performance under identical conditions and similar coverage for APDs and PMTs What one could achieve with a multi-APD readout?

Setup Kapton coated Copper as cathode 15 mm drift 7 mm EL gap Completely built at IFAE hot getter ~20 cm 14/12/201045th TPC Symposium, Paris, France

APDs Modified standard APDs from Hamamatsu Deliverable in large quantities Size 5x5, 10x10 mm 2 High sensitivity directly to 175 nm Measurements: 70+/-16 % ( in collaboration with Coimbra and presented at EXRS conference) Chamber was equipped with 5 APDs Size 5x5 mm 2, pitch  10 mm All APDs were connected to the same HV channel Each APD was read out independently 14/12/201055th TPC Symposium, Paris, France

Electronics One APD measurements could be performed with commercial electronics Not feasible for more APDs Low cost readout (preamp/shaper) was designed and built at IFAE Capable to process signals of several  s Followed by a 8 channel digitizer from CAEN (V1724) DAQ system based on Midas 14/12/201065th TPC Symposium, Paris, France

Data Taking Triggering only on central APD 1000 signal events, 10 pedestal events Converted to root format and analyzed with scripts Scans of large set of parameters (APD bias voltage, EL field, drift field) for several pressures One long run for each pressure 14/12/201075th TPC Symposium, Paris, France

Common Noise Pedestals highly correlated (  70%) Coming from ground and bias voltage common lines. Pedestals are Gaussians 14/12/201085th TPC Symposium, Paris, France

Intercalibration 14/12/201095th TPC Symposium, Paris, France Plotting charge in the center versus the asymmetry in the side APDs allows intercalibration If charge in APD 0 maximal, there should be no asymmentry Additional intercalibration from the spectra Central APD: Minimum when varying E=E 0 +  E out Depends on APD voltage ( currently calibration of 400 V applied to all data ) (E1-E3)/(E1+E3) E0

Position Determination 14/12/ th TPC Symposium, Paris, France Center-of-Gravity method APD plane seem to be shifted in one direction/collimator opening deformed? We will use in the future a collimator with displaced hole to test this further Monte Carlo predicts resolutions better than 1 mm Y (mm) X (mm)

Energy Resolution Method 14/12/ th TPC Symposium, Paris, France Various methods to measure the spectra were tested Best results with: Determining the position of the minimum in the central APD Integrating +/-200 time bins from this position for all APDs Dividing by number of time bins Substracting the pedestal for each APD Correct for the left-right (up-down) asymmetry ΣEΣE (E1-E3)/(E1+E3)

Energy Resolution 14/12/ th TPC Symposium, Paris, France Position +/- 5mm in respect of the center Fitting 2 Gaussians (width and position fixed for 25 keV peak wrt 22 keV) Additional peak at 8 keV -> x-ray fluoroscence of copper Best result until now:  9.7% keV (not optimal settings) Ratio of the two Gaussians in agreement with literature MC predicts  7% from pure ionization and photon fluctuations 9.7% FWHM => MeV 1.65 bar APD: 410 V EL: 4 kV/cm/bar Drift: 200 V/cm/bar Calibration for 400 V

Threshold 14/12/ th TPC Symposium, Paris, France Applying the same procedure to pedestal (except the minimum/maximum requirment) Low noise when adding all APDs Threshold of 2-3 keV seems to be possible Still improvable -> common noise problem, temperature reduction, etc.

2 Extreme Cases 14/12/ th TPC Symposium, Paris, France Energy resolution only for central APD and only for outer APDs No calibration or corrections Position: +/- 5 mm from the center Central APD: 17.5 % FWHM Sum of outer APDs: 12.4% FWHM (conversion happens within the empty space) 17.5% 12.4%

Spatial Energy Distribution 14/12/ th TPC Symposium, Paris, France Conversion in the EL region Cd peaks Cu peak Cosmics Pedestals

Drift Field Scan 14/12/ th TPC Symposium, Paris, France 1.6 bar 1. bar V/cm/bar Preliminary results APD bias 405 V EL Field 3.5 kV/cm/bar

EL Field Scan 14/12/ th TPC Symposium, Paris, France Preliminary results APD bias 405 V Drift Field 200 V/cm/bar Pressure 1.6 bar V/cm/bar

APD Bias Voltage Scan 14/12/ th TPC Symposium, Paris, France Preliminary results Drift Field 200 V/cm/bar EL Field 3.5 kV/cm/bar Pressure 1.6 bar

Tracking Chamber 14/12/ th TPC Symposium, Paris, France In collaboration with CIEMAT, Madrid Setup for about 30 APDs and 2 PMTs Active volume: diameter 20 cm, length 12 cm Aim: evaluating the tracking capabilities + effect of longer drift distances Design finished and production started

Summary and Outlook 14/12/ th TPC Symposium, Paris, France An EL setup with 5 APDs was succesfully designed and operated Suitable for EL applications in which moderate position information and good energy resolutions are required Good performance of the Hamamatsu APDs observed For the case of a DB experiment based on xenon <=1% energy resolution at 2.5 MeV seems to be achievable Room for improvements: reduction of noise, larger APDs, higher pressure, better calibration, temperature corrections, etc. A chamber with  30 APDs and 2 PMTs is currently constructed to study tracking and longer drift distances Tests with Argon planned in the future

Space for Improvements 14/12/ th TPC Symposium, Paris, France Very new results Calibration for 410 V Same run as before 8.8 % 22 keV =>  MeV