Timing Counter Status Timing Counter 2008 configuration Monitoring

Timing Counter Status Timing Counter 2008 configuration Monitoring and Calibrations Timing resolution (TC and MEG) G. Cavoto INFN Roma Feb 18 th 2009 G. Cavoto 1

Timing Counter (TC) Two sectors, Down. Stream and Up. Stream, each with – 15 scintillator bars readout by PMTs (TICP) » Trigger » Measure time, and z – 256 Scint. Fibers readout by APDs (TICZ) » (Meant for) geometrical trigger selection » Measure z G. Cavoto 2

Hardware upgrades New EVAL bag for N 2 Reduced APD noise Very tight! He concentration at few times atm. bkg level Light tight Tedlar foil added Some maintenance work (fix connectors, cables…) Both US and DS TC remounted in late spring G. Cavoto 3

TICZ readout tests After installation, test with ‘pass-thru’ cosmics • All analog channels (8 APD in one ch. ) show good signals! • US TICZ digital readout working! • DS TICZ worsened by higher environmental noise US TICZ fiber # • 3 (out of 8) DS TICZ readout sections failed during the 2008 run • “on-board” hardware problems: fixing deferred to 2009 G. Cavoto 4

Laser system – Additional timing calibration device » Providing 532 and 266 nm light at 50 Hz » Optical fibers distribution to TC bars (and XEC) – Problems in operation: » environment temperature became too high cavity unstable drift in the feedback signal electronic saturation, damages of optical components and electronics. 256 nm 50 Hz @ 532 nm 50 Hz 2 stages pulse amplifier Acustic-optical pulse selectors -For 2009 run: - Proper box with actively stabilized temperature - Retuning of cavity - New feedback electronics 3 m cavity 48 MHz, Diode pumped Nd: YVO 1064 nm G. Cavoto 5

• Change HV to have same average charge for PMTs of the same bar After • Select Michel positron hitting bar center (magnetic field ON) Before PMT gain equalization G. Cavoto 6

TC measurements e+ PMT 0 PMT 1 h L amplitude of PMT signal effective velocity T : time of positron at the impact point on first hit bar (connected to the positron track from DCH) h : impact point along bar length (z direction) DRS 3 digitization for Double Threshold Discriminator NIM pulses t 0 and t 1 extracted with waveform template fit to NIM pulses. Checked with cross-correlation method (optimal filtering). G. Cavoto 7

TC calibrations Timing with DTD NIM signals Time walk correction for each PMT Michel nmult=3 Time offset between PMT of the same bar (z offset calibration) Cosmics Relative time offset between bars Boron Effective velocity for each bar (z measurement) Pass-thru cosmics Absolute time offset between positron and gamma _ G. Cavoto Dalitz 0 8

bar # ‘Double’ and ‘triple’ hit events e+ On events with three adjacent hit bars (triples) minimize the differences (for all the bars) TC TA TB 1 st bar |z| On sample of two hit adjacent bars (‘doubles’) test time walk correction (c 0 and c 1) G. Cavoto ns 9

TC time resolution Estimate of single bar time resolution Assuming the two bars to have the same intrinsic time resolution Upper limit on average time resolution ( ) in 60 -90 ps range Includes effect of DRS digitization (~10 ps) (estimated sending same signal to two DTD inputs) G. Cavoto 10

TC time resolution stability Runs 24 xxx Runs 25 xxx Runs 26 xxx Runs 27 xxx Runs 29 xxx Runs 30 xxx Runs 31 xxx G. Cavoto • Same TW calibration constants • Stable over time no need of different sets of constants 11

Inter-PMT offsets Dedicated cosmics runs taken in different down-time periods – Select event with 1 or 2 hit bar Assume symmetric distribution along the bars Most of the bars have this flat distribution t 1 - t 0 [ns] Data taken in different periods very consistent (TICP very stable!!!) G. Cavoto 12

MEG physics runs TC hitmap After Before US DS t 1 -t 0 [ns] Distribution nicely “justifies” Need veff to have the correct z scale G. Cavoto 13

Effective velocity with TICZ Pass-thru cosmics, 2 hit fibers (clusters) expected Single-cluster inefficiency: 27% due to cosmics geometrical inefficiency + dead/hot fibers (5%) Using veff (cm/ns) Bar 16 Syst err. 1. 5% zbar-zfiber (cm) G. Cavoto 14

Inter-bar offset extraction Boron events 4. 4 Me. V (XEC) and 11. 7 Me. V(TC) Bar 14 -signal -bkg (rescaled) Bar 17 -signal -bkg (rescaled) T [ns] • Gaussian fits. – Cosmic background evaluated in runs with no-beam and same trigger requirements (TC & XEC) • Syst error on calibration constants at 50 ps level G. Cavoto 15

Inter-bar offsets monitoring Bar 15: change in DRS board time T mean [ns] relative to bar 17 Sep 08/10 13/10 20/10 25/10 10/11 24/11 01/12 Weekly monitoring (periodic DB updates) bar# - No clear trend vs time - Relative offsets stable G. Cavoto 16

DCH-TC match hitmap Extrapolate tracks from DCH to TC bars [cm] Given a track and a TC bar hit matching efficiency is 91% Some data/MC discrepancy G. Cavoto 17

MEG absolute time offset Dalitz 0 events – Same topology as signal ! – Gamma/positron energy range (can be chosen) same as for signal – Worse resolution due to LH 2 target Comparison with signal is not exact Centre of signal window Bar 17 μ = 26. 06± 0. 01 ns = 267± 10 ps Control sample (flight length correction) MC validation ns G. Cavoto 18

T (e)- T (e)(bar 17) [ns] T (e) [ns] Timing systematics check Boron (E =4. 4 Me. V) Dalitz (E >45 Me. V) bar# Residual time walk effect on XEC timing Dalitz before calibration Dalitz after calibration with Boron Relative to bar 17 bar# Residual inter-bar differences (different target for 0 Dalitz) G. Cavoto 19

Summary • TICP very stable over the 2008 run. • TICZ: 13 out of 16 sectors working. • Calibration strategy developed and successfully applied to data. • Data monitored during data-taking. • Some fine-tuning still needed – Residual bar differences – Detailed data-MC comparison G. Cavoto 20

Outlook for 2009 – Detector activity • New APD electronics – Shorter shaping time to fit trigger timing – Currently prototyping new el. boards • LASER • Upgrade of TC slow control – On track for a 2009 data-taking period – Data analysis • Calibrated TC data and TC simulation available for MEG analysis • MEG timing measurements well underway G. Cavoto 21

Back up G. Cavoto 22

New APD electronics To insert APD into trigger • Requirements: – – - fast signal ( 3 -5 times faster) 15 ns achievable. better EMI immunity Implement redundant schemes for the command transmission (I 2 C) Improve over all settings capability ( on board test /calibration signal, …) Bread-boarding is started, final design of the prototype board will be sent for the production by Dec 08. Test pulse response G. Cavoto Move Amplifier to the APD board and/or differential input 23