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Timing Counter analysis C.Voena - INFN Roma for the TC group MEG Review Meeting Feb 17 th 2010

Timing Counter analysis C.Voena - INFN Roma for the TC group MEG Review Meeting Feb 17 th 2010. TC before insertion in COBRA. TC configuration in 2009 run. Trigger thresholds lower than 2008: 20mV on single PMT, 70mV on sum of PMT(40/100mV in 2008)

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Timing Counter analysis C.Voena - INFN Roma for the TC group MEG Review Meeting Feb 17 th 2010

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  1. Timing Counter analysis C.Voena - INFN Roma for the TC group MEG Review Meeting Feb 17th 2010

  2. TC before insertion in COBRA

  3. TC configuration in 2009 run • Trigger thresholds lower than 2008: • 20mV on single PMT, 70mV on sum of PMT(40/100mV in 2008) • PMT gains re-equalized by adjusting HV • Waveform digitization: • - DRS3 for NIM pulse from Double Threshold Discriminator • (DTD) for time measurement (like 2008) • - DRS4 for PMT pulse • Double-Threshold Discriminator thresholds revisited • to optimize efficiency and time resolution • 2009: 25/600 mV 2008:25/800mV

  4. PMT gain equalization TC bar • Use mean of • log(QPMT1)/QPMT0) • in cosmic ray data • at “center” of the bar • Change HV to have • PMTs (inner vs outer) • and bar equalization • within 30% • (changed 10 PMT HV • with respect to 2008) PMT1 (outer) PMT0 (inner)

  5. DTD thresholds scan • Low threshold: as low as possible (first photoelectron) • => Can improve time resolution • Limited by noise • No improvement seen lowering this threshold (tried 10-17 mV) • => left at 25mV which was already optimal value! • High threshold: select good pulses (tracks producing enough p.e., Landau peak) • - Lowered to 600mV (was 800mV) • to have more acceptance on • positron with lower pulses 800-25 400-25 250-25 Eloss (a.u.)

  6. TC time measurement e+ PMT0 PMT1 z L amplitude of PMT signal effective velocity t0,1= extracted with waveform template fits to NIM pulses from Double Threshold Discriminator for PMT0,1 T : time of positron at the impact point on first hit bar (connected to the positron track from DCH) z : impact point along bar length

  7. TC calibrations

  8. Time Walk calibration As in 2008 TW corrections from triple-bars events in Michel Data On events with three adjacent hit bars (triples) minimize the differences (for all the bars) of: e+ bar # TC TA 1st bar TB |z| • no TW • with TW Control sample: double-bars events TA TB TA-TB (ns)

  9. TC Time Resolution • from double-bars events: upper limit on: • TC intrinsic resolution + DRS resolution (~10ps) • Upper limit on time • resolution () in • 70-100 ps range • in 2009 (except • bar 21) • Slightly worse than • 2008: under study. • Still adequate for • MEG performances 2009 resolution 2008 resolution

  10. z-offset calibration Difference of PMTs electronic offsets - Needed for z measurement and to combine time measurement of adjacent hits - Use Michel matched positrons instead of previously used cosmic rays Obtained by aligning mean of ztrack-zTC ztrack= z predicted extrapolating track at TC zTC = z measured by TC The procedure assumes φ-symmetry

  11. TC hit-map with z-offset calibration Good alignment of bars as can be seen from hit-map trigger “MEG” data before calibration trigger “MEG” data after calibration

  12. z-scale:effective velocity Temporary calibration - Michel matched positrons Use ztrack as estimate of z at TC - Eventually use fibers for z mesurement veff = 14.8 cm/ns ztrack –zcenter (cm) t0-t1(ns)

  13. Inter-bar time offset calibration Tj Double-bar events in Michel data LIB Ti LIB = Inter-Bar path, taken from MC LIB/c ~200ps Offsets for DS bars Offsets for US bars After that, Downstream bars are aligned with bar #0 and Upstream bars are aligned with bar#15 (there are not double-bar events which connect US and DS)

  14. The Boron sample Boron events two photons: 4.4MeV (XEC) and 11.7MeV(TC) Cuts for cosmic ray rejection before calibration RMS of residual offsets (after calibration) is~70ps after calibration Mean of Tγγ (ns) Systematic effect of assumption on LIB/c (path between two bars) under study TC bar #

  15. Monitoring TC stability Single bar time resolution - different colors correspond to different weeks Mean of Tγγ (ns) • Inter-bar time offset • - Boron sample • different colors correspond • to Oct/Nov/Dec Stability over time TC bar #

  16. Absolute XEC-TC time offsets • Dalitz 0 events • Same topology as signal • Worse resolution due to LH2 target Do not look at time resolution! Center of blinding window (for pre-selection) μ=24.9ns Teγ for reference bar - Dalitz data suffer from hardware problem on DCH side (DRS) that may affect resolution Teγ (ns)

  17. TC-DCH match and Te+ algorithm • DCH-TC match • Extrapolated track at bar surface • Reject bars with multiple hits • Reject pairs TC-DCH with • bad ztrack-zTC , rtrack-rTC and bad χ2 • of match (multiple turns taken into • account) • Positron time : • - If more than 1 TC hit in matched cluster: combine • time measurement taking into account track length between bars • Correct ad-hoc for Te+ correlation with ztrack-zTC Plans: do systematic studies of the algorithms (Monte Carlo and Dalitz sample)

  18. Check on radiative decay peak Clearly see radiative decay peak in Eγ sideband Inter-bar calibration working well - Pre-selection window not well centered at this stage Temporary track and photon selection, kinematic cut (m2νν>0) Example : radiative peak for bar 19 Position of radiative decay peak vs TC bar# Mean of Teγ (ns) TC bar # Teγ (ns)

  19. Summary • TC bars very stable during 2009 run • - Ready for the incoming long data-taking • Calibration strategy applied successfully to 2009 • data • TC intrinsic time resolution < 70-100ps • (a little worse than 2008, investigating) • - one of the best Timing Counter detector • Calibration methods and analysis algorithm • constantly improving

  20. Backup

  21. Possible causes of worse resolution Electronic We checked the electronic contribution to the resolution by splitting PMT signal in two different electronic channels =>Same as 2008 Noise Same noise level as 2008 at DRS input for PMT signal (not sure of situation at DTD input) tin-tout PMT#

  22. Possible causes of worse resolution • Other possible causes: • deterioration of PMT-bar coupling? • Less scintillation light? • 1) (relative) width of Landau peak: done but • not conclusive, dominated by Eloss fluctuation • 2) change of Λeff. Underway but may be not • conclusive since we do not have precise • measurement of veff • 3) Tests in labs foreseen

  23. Width of CR landau distr. 2008 2009

  24. Applying z-calibration to doubles before calibration z-offset calibration from Michel data z-offset calibration from CR data z1 Mean of DZ=z2-z1 in double bar events (cm) z2 Second hit bar number

  25. Boron: High energy photon High energy photon in XEC Low energy photon in XEC

  26. CR backgound in Boron Sample Tγγ (ns) Black: boron data Red: CR data taken with same Boron trg

  27. Resolution in Boron Sample Tγγ resolution (ns) vs TC bar: 2009, 2008 (July processing) Tγγ resolution vs Time

  28. Multiple hits of TC bars Positron track TC hit position: dz = |z2|-|z1| Bar 1 * Bar 2 * 1st bar with multiple hit |z| dz>0 * * |z| dz< 0

  29. Teγ vs ztrack-zTC on Dalitz • No constraint for the track to come from muon target TC US Correlation is visible Correction of 20ps/cm (DZCorrection) Same as in 2008

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