Demitri Muna

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Demitri Muna

Track Reconstructionin DRIFT-IIDemitri MunaUniversity of Sheffield, UKon behalf of the DRIFT CollaborationIDM 2006 / 14 September 2006


DRIFTIIDRIFT-II Overview1m 3 low pressure negativeion time projectionchamber (TPC)Directionally sensitive1 mLocated in Boulby Mine, UK8 TB of data collected(>10 kg-days)Currently in operation1 m


DRIFTIIcentral cathode(40 KV potential)DRIFT-II GeometryMultiwireProportionalChambers(MWPC)512 wires512 wiresVetowiresDrift direction512 wiresanodereadout 1Every 8th channel grouped:8 anode readouts, 8 grid readouts2 mm pitch


DRIFTIIWIMP–Nucleus InteractionElastic nuclear recoilproduces ionisationElectric fieldDrift directionzyCS2 iselectronegative —free e – are easilycaptured by gasIonisationtrackxNegative CS2 ionsdrift in field toMWPC endcapsCharge is depositedon the anode wiresand induced on thegrid wires


DRIFTIIMotivation forTrack ReconstructionTracks parameters provide background discriminationDirectionality (of course)Parameters measured:track length (neutrons typically 2-6 mm, alphas 300 mm or more)voltage weighted timetotal energy deposited on anodes and grid readoutsdz (length of track in time)no. of wires crossed


DRIFTII“Perfect” Alpha Event in DRIFT-IIbgrid-anode veto (GV-AV)anode veto (AV)grid veto (GV)anode sum (AS)grid sum (GS)}8 anode readouts(A1 - A8)}8 grid readouts(G1 - G8)DAQ triggers ongrid sum


DRIFTIIWire MultiplicityAnode ReadoutsA8α track


DRIFTII2D ReconstructionCollect all pulses on the anodes, order by voltageweighted timeStart from the first pulse and look for any pulse within500 µs of itContinue until no pulse is found within 500 µs of the lastReject any track that has gaps (missing wires)


DRIFTII2D Reconstructiondz (drift direction, measured from time & drift velocity)dz total time of track • vDRIFTvDRIFT = 46 m/strack time measured from start of FWHM of first pulse to endof FWHM of last pulse – 10 µs (shaping time)dx, track length in x direction (anodes)dx (no. of wires crossed – 1) • 2 mmR2, length of 2D projection on dx/dz planeR2 √(dx 2 + dz 2 )


DRIFTIIAlpha Track in 2D (x-z)Alpha Track in 2D Projection (x-z)X Hits / Anode Data (mm)-80 -60 -40 -20 02 mm wire spacingvoltage weightedmean time1 sample/microsecR2 = 337.8 mmdz = 289.5 mmNo. wires hit: 880 1000 2000 3000 4000 5000Time (microsec)


DRIFTIIAlpha Track in 2D (x-z)Alpha Track in 2D Projection (x-z), Point Size Proportional To Maximum Pulse HeightX Hits / Anode Data (mm)-80 -60 -40 -20 0voltage weightedmean time0 1000 2000 3000 4000 5000Time (microsec)


DRIFTII2D Reconstruction (y-z)GridsSample10 µs–10–18-19–15-9-1+4-3(scale exaggeratedfor illustration)To get the third dimension, the gridreadouts are analysedA time window is chosen, e.g. 10 µsPoints are averaged across eachwireThe greatest charge deposited isdetermined by circular statistics (toaccount for wire multiplicity)y = “wire” 2.85z = midpoint of time bin


DRIFTIIx-z & y-z 2D ProjectionsAlpha Track in 2D Projection (y-z)Y Hits / Grid Data (mm)0 5 50 10 100 15 20 150 25 200 30Grid Information (y)Preliminary00 5 50 10 100 15 20 150 25 200 30Time (microsec)Alpha Track in 2D Projection (x-z), ResampledX Hits / Anode Data (mm)0 -150 50 -100 150 -50 200 0Anode Information, Resampled (x)0 -150 50 -100 100 150 -50 200 0Time (microsec)~/DRIFT_data


DRIFTII3D Reconstructed Track3D Reconstruction of an Alpha TrackPreliminaryR3 = 410.6 mm


DRIFTIIAnimationPreliminary


DRIFTIIFuture WorkApply reconstruction to neutron calibration eventsSee if track sense can be determinedFine tune grid informationpulses have positive pulsessimulate how charges travel from anode to gridsUse R3 information for discrimination

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