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T0 Detector Overview and Run2 Plans

This document provides an overview of the T0 detector, its capabilities and the plans for Run2. It includes information on the detector arrays, trigger functions, event reconstruction, and T0 calibration. The document also discusses the use of the T0 detector in online and offline data analysis.

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T0 Detector Overview and Run2 Plans

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  1. T0: status and plans for Run2 A.Maevskaya for T0 team ALICE offline week 26 March 2013

  2. T0 detector overview 2 arrays of Cherenkov counters located at +370 cm ( T0A) and −70 cm (T0C) along the beam-line. Each counter: quartz radiator/PMT/readout • Precise start signal for TOF (time resolution of below 40 ps) • Trigger functions (on-line): • Coarse vertex position position resolution (along the beam direction) 1 cm; • Coarse multiplicity • “wake-up” signal to TRD • Luminosity using T0 • Online background estimation 2 2

  3. T0 reconstruction • Event reconstruction • read raw: time and amplitude for all channels ; • apply slewing correction (from OCDB) to time according amplitude channel by channel; • subtract mean time from OCDB (calculated online or during CPass0) to have time centered around zero (channel by channel); • choose min (1st) time for A and C side ( T0A and T0C); • calculate interaction time (T0A+T0C)/2 which is not depend on vertex; • correct T0A and T0C with primary vertex position; • shift T0A, T0C and (T0A+T0C)/2 with global time offsetfrom OCDB calculated in CPass1 to have them centered around zero. (T0A+T0C)/2, T0A, T0C are ready to be used by TOF as timeZero

  4. T0 reconstruction output What T0 detector writes in ESD: • interaction time – T0A, T0C, (T0A+T0C)/2 - with accuracy ~25ps for PbPb and ~40 for pp; • Z vertex position; • T0 trigger signals ( even if they were not used in trigger); • Signals from OrA, OrC, TVDC (0TVX) modules, 5 hits for pile-up detection; • 5 hits of time signal from each PMT without time-amplitude correction to be used for vertex of 5 pile-up events; • pileup, background and satellite flags .

  5. T0 calibration: slewing correction each channel For pp LaserDAbefore start of the period a set of laser runs ( 1 run per amplitude) are taken. Results are written in alien OCDB and in OCDB snapshot on DA machine entryOCDB/T0/Calib/SlewingWalk :24 TGraphs: amplitude in channel vs amplitude in MIPs;24 TGraphs: time – amplitude dependence. For PbPb runs manual time-amplitude correction based on RAW physics data was used. At least 1 Meventsshould be accumulated for proper fit of high amplitude tails.

  6. T0 calibration during RUN2 time-amplitude correction each channel Calibration should be done once on 1st runs of RUN2 data taking and after each electronics repairment. Not clear now will we have laser calibration system or not. We are ready to make all time-amplitude correction based on 1st Mevents pp and 1st Mevents PbPb. LHC11h :Time walk vs amplitude, channel width=24.4ps

  7. T0 calibration:global time offset for T0A, T0C, T0AC Now: Get from ESD (T0A+T0C)/2 ,T0A, T0C. Global time offsets (TimeAdjust) are calculated during CPass1 based on CPass0's TimeDelays RUN2: Online Simple reconstruction based on mean time value for each PMT with slewing correction for 1st 5000 events; • subtract mean time to have time centered around zero (channel by channel) • choose min (1st) time for A and C side ( T0A and T0C); • calculate interaction time (T0A+T0C)/2 which is not dependent on vertex; • correct T0A and T0C with primary vertex position (from HLT?); • fill histograms with T0A, T0C, (T0A+T0C)/2 • write in OCDB mean position of these histograms to be used in reconstruction to align T0s around zero ONLY EVENTS WITH 0TVX TRIGGER ON COULD BE USED FOR CALIBRATION

  8. To be done now • MC: • To include in simulation realistic electronics response; • Match MC and data amplitude measurements and efficiency. • Calibration: • For re-reconstruction • Test and upload to OCDB slewing correction for LHC11h based on all triggered events . Existing reconstruction done with MB trigger and slewing correction does not fit to central events • Prepare slewing correction for LHC10h based on RAW data – needs RAW staged

  9. Before RUN2 • Slewing correction : • New code should be developed: • Fill histograms over amount of runs; • Fit with piece-wise polynomial function; • Make TGraphs from fit function • Write to OCDB • Time offsets • existing DA should be adapted to new calibration scheme and with T0 based event selection and calculation global time offsets Could be done for 2013 pA data but we did not want to tauch working thing

  10. Before RUN3 It is no decided which T0 will be after LS2 . But it will be calibrated online.

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