Time-zero evaluation using TOF, T0 and vertex detectors D. Caffarri – University and INFN Padova A. Alici – P. Antonioli INFN Bologna F. Noferini – CNAF e INFN Bologna CERN, 24/03/10 TOF meeting– T0 Analysis. D. Caffarri 1

Outline - Introduction and some definitions - Reference data sample used and cuts Use of vertex information for T0 correction T0 resolutions - Getting the right time-zero in different case of event. - Conclusions and outlook CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 2

Introduction Aim of this analysis: exploit combined ALICE detectors information to provide the best time-zero estimate to analyse TOF data (and in turn best PID from TOF) - The T0 detector is a small ALICE detector close to the beam pipe able to provide precise interaction time of each collision (used by TOF as a time-zero) T0 detector in ALICE has been built for Pb-Pb collisions. In p-p collisions, due to its low acceptance region, cannot always give the signal for the time-zero of the collisions Note TOF provided TDC and read-out electronics to T0 exactly to have the same hardware measuring time signals CERN, 24/03/10 TOF meeting – T0 analysis. D. Caffarri 3

T0A T0C T0 position T0A pseudorapidity acceptance : −5 < η < −4.5 - 350 cm from nominal interaction point T0C pseudorapidity acceptance : 2.9 < η < 3.3 - 70 cm from nominal interaction point CERN, 24/03/10 TOF meeting – T0 analysis. D. Caffarri 4

Some definitions T0. The detector T0, the hardware system. Made of two parts T0A, T0C one on each side of the experiment as shown. T0det. The interaction time (time-zero) as measured by the T0 detector T0TOF A time-zero estimate using tracks that reach the TOF. T0fill: the average time-zero estimated in the fill (used as “last resort” when other means are not available) T0Best.  What we want to obtain. Trying to find the best available time-zero for each event. This depends on: track multiplicity, T0A and T0C response, vertex measurement, number of tracks reaching the TOF. CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 5 5 5

Data sample and cuts This analysis was performed on the Run 104892 - pass 4 TOTAL EVENTS 109.752 “Physics” EVENTS 66.354 (we reject beam-gas, beam-empty events events with the wrong trigger configurations) Cuts on the tracks matched with TOF: standard collaboration cuts to consider only “good” tracks coming from the central tracker Vertex Z: To have the bigger efficiency on the vertex recostruction: If ncontributors >= 3  z coordinate of the tracks vertex If ncontributors < 3  z coordinate of the inner pixel detector vertex (vertexer Z has higer efficiency at low multplicity) CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 6

Primary vtx – T0 correlations: corrections T0A* Offset in T0C  different mean but almost the same sigma than track vtx. T0A and T0C individually depends on vertex position. We found corrections T0A*=T0A(vtx) T0C*=T0C(vtx) to clear this dependency. Vertex position measured by ITS. CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 7

Estimate of T0det resolution Using sample of events where we have both T0A* and T0C* (corrected by vertex) it is possible to estimate T0det resolution using: (T0A*-T0C*)/2 This quantity filters jitter introduced by the beam and its width is direct estimate of T0det resolution. T0det resolution = 63 ps CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 8

Estimate of the jitter due to the beam The time-zero estimated by T0det is: (T0A+T0C)/2 The width of this distribution contains the jitter introduced by the beam Consistent with the estimate of the vertex CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 9

Estimate on the resolution on the T0or The T0or is defined when or only one T0A or T0C or both give a signal. All the distributions are corrected for the vertex. CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 10

Getting the right time-zero Total events selected: 61840 (100%) Events with at least one T0 detector (“T0or”): 37264 ( 60 %) Events with both T0A and T0C (“T0and”): 9130 (14.4 %) These numbers are in very good agreement with MC given from T0 group. CERN, 24/03/10 TOF meeting– T0 Analysis. D. Caffarri 11

Getting the right time-zero for TOF - Request of at least 1 track matched to TOF (that is… when a time-zero is needed): 26709 events selected (43% of the total) - Within this sample: 18277 events with T0or (68%) 5355 events with T0and (20%) CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 12

Getting the right time-zero without T0 32% of events don’t have a time-zero from T0 detector. Before to use average time-zero fill as last resort, we can obtain a time-zero event-by-event from TOF data (bayesian fit iterating over tracks making PID hypothesis) We tested T0TOF algorithm using events when a time-zero from T0 detector (and) is available obtaining T0det-T0TOF distributions We didn’t use here the latest calibration from the TOF detector, but we are already working in that direction. PRELIMINARY Low number of events CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 13

TOF PID using T0best p (GeV/c) CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 14

TOTAL NUMBER OF EVENTS NUMBER of EVENTS WITH T0or NUMBER of EVENTS WITH A TRACK MATCHED WITH TOF 66354 37264 26709 100% 60% 43% NUMBER of EVENTS WITH A TRACK MATCHED WITH TOF NUMBER of EVENTS WITH a TRACK at TOF and T0or NUMBER of EVENTS WITH T0 WITH TOF (because there is no T0) NUMBER of EVENTS with T0 fill 26709 18277 2418 6143 100% 68% 10% 22% CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 14

Conclusions and outlook Combined analysis of T0, TOF and vertex detectors data to allow a precise time zero determination for TOF (and in turn PID) is well in progress. Improvements are expected on further analysis (no need of various ad-hoc offsets used here, improvements of TOF calibration, improved track-length estimates). - Propagation of this approach to on-going analysis (namely identified spectra) is already under way. Statistics and resolution improvements expected! CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 15

BACK UP SLIDE CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 16

Standard track cuts Cuts on the tracks matched with TOF: Minimum number of cluster of the TPC = 50 Maximum χ2 per cluster of the TPC = 3.5 Require kTPCrefit Maximum DCA to the vertex Z = 3.0 cm Maximum number of sigma to vertex = 4 CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 17

T0det after VTX corrections CERN, 22/03/10 PWG1 – T0 Analysis. D. Caffarri 18