d. caffarri – university and infn padova a. alici – p. antonioli infn bologna

D. Caffarri – University and INFN PadovaA. Alici – P. Antonioli INFN BolognaF. Noferini – CNAF e INFN Bologna

CERN, 24/03/10 TOF meeting– T0 Analysis. D. Caffarri 1

Time-zero evaluation using TOF, T0 and vertex detectors

Outline

CERN, 24/03/10 TOF meeting – T0 Analysis. D. Caffarri 2

- 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 3

Introduction

- 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

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)

CERN, 24/03/10 TOF meeting – T0 analysis. D. Caffarri 4

T0A T0C

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

T0 position


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.


Data sample and cutsThis 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 vertexIf ncontributors < 3 z coordinate of the inner pixel detector vertex (vertexer Z has higer efficiency at low multplicity)


Primary vtx – T0 correlations: corrections

Offset in T0C different mean but almost the same sigma than track vtx.

T0A*

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.


Using sample of events where we have both T0A* and T0C* (corrected by vertex) it is possible to estimate T0det resolution using:

(T0A*-T0C*)/2This quantity filters jitter introduced by the beam and its width is

direct estimate of T0det resolution.

Estimate of T0det resolution

T0det resolution = 63 ps


The time-zero estimated by T0det is: (T0A+T0C)/2The width of this distribution contains the jitter introduced by the

beam

Estimate of the jitter due to the beam

T 0and T 0and det2 Jitter

2

T 0and det 63psT 0and 161ps

Jitter 148ps

Consistent with the estimate of the vertex


The T0or is defined when or only one T0A or T0C or both give a signal. All the distributions are corrected for the vertex.

Estimate on the resolution on the T0or

T 0or T 0or det2 Jitter

2

Jitter 148psT 0or 167ps

T 0or det 77ps

CERN, 24/03/10 TOF meeting– T0 Analysis. D. Caffarri 11

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.


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%)


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.

Low number of eventsPRELIMINARY

TOF PID using T0best


p (GeV/c)


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%

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!


BACK UP SLIDE


Standard track cuts

Cuts on the tracks matched with TOF:

Minimum number of cluster of the TPC = 50Maximum χ2 per cluster of the TPC = 3.5 Require kTPCrefitMaximum DCA to the vertex Z = 3.0 cmMaximum number of sigma to vertex = 4

T0det after VTX corrections

CERN, 22/03/10 PWG1 – T0 Analysis. D. Caffarri 18

d. caffarri – university and infn padova a. alici – p. antonioli infn bologna

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