Laser Calibration of a Liquid Argon TPC G. Sinnis J. Danielson W. Sondheim

dE/dx in units of MIP Energy Measurement in LAr TPC Recombination and loss of charge during transport Recombination factor parameterized by Birk’s Law Drift speed at 500 V/cm is 1.6mm/μs 2.3m drift distance is 1.4 ms drift time τ=1 ms 24% of charge survives 2% energy calibration 1% uncertainty in τ Need to measure  in situ 2

Electric Field Distortions Surface detector has high muon rate (~1 muon/drift time/APA) Ion velocity ~8mm/s or ~5 min from APA to CPA – Space charge effects will distort applied field Space charge field ~-17 to 8 V/cm in X and -5 to 12 V/cm in Y Changes drift velocity (~3% of drift field) Will “compress” track – distort measured dQ/dx (4% effect) 3-D models from Bo Yu (BNL) 9 V/cm -17 V/cm APA CPA 3

Time Variability 4

5 The muon rate at ground level depends on the density profile of the atmosphere and solar activity Expect to see ~2% diurnal variations Solar events (Forbush decreases) ~20% affects possible Impulsive events (Ground-level events) hours

Photon Detection System On surface PDS must disentangle multiple events in drift time window. Must understand optical model of TPC In situ calibration of timing and pulse height of PDS system can use laser calibration system Working with PDS group to understand what measurements are needed Can we use Rayleigh scattered light? 6

Laser Ionization of Liquid Argon Sun et al NIM – LAr binding energy eV – Quad. Nd-YAG (4.66 eV/photon) – 3 photon process (13.98 eV) Ionization ∝ (laser intensity) 2 Recent work by U. Bern (Rossi et al.) 7

Understand laser ionization of liquid Argon Develop a laser ionization system for a small TPC to study ionization and recombination (laser power, impurities, electric field) Perform R&D for LBNE system to: – Measure drift field – Measure electron lifetime in-situ – Develop calibration for photon system Goal – install and test laser system in LANL TPC Goals for Far Detector LDRD Work 8

Laser System Status Quantel “Brilliant B” Nd-YAG laser Laser system now at LANL IWD approved – system checked Design of mirror control system begun TPC interface finalized 9

LANL TPC Design 4 optical ports -2 set 15cm from anode -2 set 15 cm from cathode 10

Schedule Procurement complete Testing (ex-situ) beginning June installation in small LANL TPC October installation in large LANL TPC We welcome external involvement 11

Preliminary Design for LBNE 10 kT 12

Preliminary Design Optical penetration of cryostat -inject light below the liquid surface -minimize path length -maximize flexibility (arbitrary beam paths) -ease of maintenance (no entry to cryostat) -minimize thermal impact (evacuated pipe) ~25% of laser light survives to far corners (with periscope in center) ~15% if periscope placed at edge Develop requirements 13

Very Preliminary Design ~10 cm aperture (perhaps smaller if needed) ~2.6m long (penetrate insulation, ullage, inactive LAr volume) passive mirror independent of periscope AR coated hemisphere evacuated pipe mirror on rotation stage zenith control open pipe AR coated optic feedthrough vacuum flange 14

Summary Laser calibration needed for measure of: – Drift field in presence of cosmic ray muons – Electron lifetime throughout detector volume – Optical model of TPC for photon detection system – Calibration of photon detection system Concept is now supported by the LBNE project LANL TPC will be used to perform R&D for LBNE calibration system – Collaboration interest from ANL, Indiana, LSU Collaboration welcome – laser ionization, photon system calibration and testing Preliminary LBNE laser system design in progress 15