TOF CALIBRATION and ALIGNMENT DATABASE ALICE Offline Week

TOF CALIBRATION and ALIGNMENT DATABASE ALICE Offline Week, Feb 22 nd 2005 TOF, Chiara Zampolli

TOF CALIB and ALIGN DB Ø TOF alignment DB Øsupermodules Østrips Ø TOF calibration DB Øtime slewing ØTDCs’ channels equalization Ø TOF calib and align DB: summary ALICE Offline Week, Feb 22 nd 2005 2 TOF, Chiara Zampolli

TOF ALIGNMENT DB ALICE Offline Week, Feb 22 nd 2005 TOF, Chiara Zampolli

ALIGNMENT DB - SUPERMODULES Ø Positioning of the 18 SUPERMODULES inside the frame: (x, y, z) Ø three spatial coordinates (x, y, z) for four precise reference points for each supermodule 3 × 4 × 18 = 216 y z ALICE Offline Week, Feb 22 nd 2005 4 x TOF, Chiara Zampolli

ALIGNMENT DB - STRIPS external mod intermediate mod central mod h q Ø Positioning of the STRIPS inside the modules: Ø 2 external mod. : 2 × 19 strips Ø 2 interm. mod. : 2 × 19 strips Ø central mod. : 15 strips (4 × 19 + 15) × 2 × 18 = 3276 Ø two coordinates (h, q) for each strip ALICE Offline Week, Feb 22 nd 2005 5 TOF, Chiara Zampolli

TOF CALIBRATION DB ALICE Offline Week, Feb 22 nd 2005 TOF, Chiara Zampolli

CALIBRATION DB – TIME SLEWING Ø Time slewing is caused by the finite amount of charge necessary to trigger the discriminator. Ø Charge fluctuations generate a time walk. NB: TOT ALICE Offline Week, Feb 22 nd 2005 7 Signal Charge TOF, Chiara Zampolli

CALIBRATION for TIME SLEWING Ø In order to unfold the time spread due to the momentum spectrum, calibration for time slewing effects can exploit the reconstructed tracks. Ø Since Ntr ~ 1000 tracks/pad are necessary, the number of required events is: ØNtr = # tracks/pad ~ 1000 Øk = reco tracks “occupancy” = Ø /160000 = O(103), central Pb-Pb collisions Nev ~ O (105) ( ) the effective time to accumulate sufficient statistics will depend on the data taking rate Ø In p-p the # of necessary events will depend on the type of trigger (MB, jets. . . ) ALICE Offline Week, Feb 22 nd 2005 8 TOF, Chiara Zampolli

TIME SLEWING CONSTANTS Ø The number of costants estimated for calibration for time slewing effects depends on the detailed shape of the signal in the HPTDC O(10) per TDC channel ALICE Offline Week, Feb 22 nd 2005 9 TOF, Chiara Zampolli

CALIBRATION DB – TDCs EQUALIZATION Ø After slewing corrections, an equalization of the channels of the TDCs is necessary because of the delays introduced by the electronics (mainly cable lengths and pulse line lengths). Ø In order to equalize the TDCs’ channels, an algorithm based on the comparison between the times of the reconstructed tracks (from track length and momentum measurements) and the measured times is in progress. ALICE Offline Week, Feb 22 nd 2005 10 TOF, Chiara Zampolli

CALIBRATION DB – RECO TRACKS ALGO Ø The chosen parameter is the mean of the gaussian fit of the distribution of (texp- t. TOF): Mean Sigma -0. 00197± 0. 00029 0. 09136± 0. 00023 NB: optimistic case!! no contamination from incorrect mass assignment Ø With the events already used for the time slewing correction an uncertainty on the calibration constants of ~ O(10) ps is expected. ALICE Offline Week, Feb 22 nd 2005 11 TOF, Chiara Zampolli

CALIBRATION UNCERTAINTY Ø The estimate of the uncertainty on the additive calibration constants depends on the number of events used in the analysis: Ø σcal = uncertainty on the calibration constants Ø σTexp-TOF = width of the distribution, ~ 100 ps assumed Ø k = reco tracks “occupancy” = /160000 ~ O (103) Ø central Pb-Pb collisions Nev ~ O (105) σcal ~ O(10)ps assuming the same statistics as that used for time slewing correction ALICE Offline Week, Feb 22 nd 2005 12 TOF, Chiara Zampolli

CALIBRATION CONSTANTS Ø Each TDC channel is independent from the others Øone additive constant per pad 18 × 91 × 96 ~ 160000 # supermodules ALICE Offline Week, Feb 22 nd 2005 # pads in a strip # strips in a supermodule 13 TOF, Chiara Zampolli

CALIB and ALIGN DB: SUMMARY TYPE of CONSTANTS NUMBER of CONSTANTS UPDATE FREQUENCY supermodules’ alignment in frame 216 every alignment cycle strips’ positioning in supermodules 3276 once for all time slewing correction O(106) TDCs’ channels equalization ~ 160000 once per month( ) same frequency as time slewing correction ( ) at the start-up, the calibration update will be likely to be more frequent, because of adjustment of parameters such as thresholds, operating voltages. . . Calibration and alignment constants will all be single precision numbers four byte each DB size ~ 7 MB ALICE Offline Week, Feb 22 nd 2005 14 TOF, Chiara Zampolli

FURTHER COMMENTS (from workshop) Ø Access frequency: Øcalib DB once/run Øalign DB once/run Ø Relationship with other DBs will be soon provided! ALICE Offline Week, Feb 22 nd 2005 15 TOF, Chiara Zampolli