TOF, Status of the Code

1
TOF, Status of the Code
F. Pierella, Bologna University and INFN TOF
Offline Group ALICE Offline Week, June 2002
2
For participants in virtual rooms

• URL for this presentation
• Explorer
• http//www.bo.infn.it/alice/pierella/Doc/June02E.h
  tml
• Netscape
• http//www.bo.infn.it/alice/pierella/Doc/June02.ht
  ml

3
Contents

• Activity during the past 2 month
• Geometry
• SDigitization
• Merging/Digitization
• CPU time estimation for Sdigitization and Merging
• Reconstruction/PID QA and test macros
• Probabilities for PID
• Propagation from TPC to TOF using Kalman
• AliTOFV2
• AliTOFV3
• Conclusions outlook on 'time zero'

4
Geometry

• Review on TOF geometry
• Some volume overlaps has been fixed
• review on materials.
• Cooling tubes and FE card has been introduced in
  the GEANT description of the TOF detector

5
Geometry (2)

• Proof

6
Sdigitization (1)

• UML diagram ClassDef(AliTOFSDigitizer,2)

7
Sdigitization (2)

• Summary
• Class AliTOFSDigitizer
• Inherits from TTask
• Output TClonesArray of AliTOFSDigit
• The AliTOF fSDigits data member is transient
• QA and test macros
• AliTOFhits2SDigits.C
• AliTOFanalyzeSDigitsV2.C
• AliTOFanalyzeSDigits.C (to be used if fSDigits is
  persistent)

8
Sdigitization (3)

• TDC distribution (1 TDC bin 50ps) as an example
  (25 central HIJING events in the theta range
  45-135)

9
Merging/Digitization (1)

• Algorithm description
• Sdigits from different files (e.g. for BKG and
  SGN) are merged (i.e. 'summed' if necessary,
  using the AliTOFHitMap) and collected in a tmp
  array
• from this array they are converted into TOF
  digits.
• No noise added (for the time being) due to the
  negligeable expected noise level of 1Hz/pad
• taking into account a readout window of 500ns
  (and the total number of readout channels) the
  expected noise value is 0.08

10
Merging/Digitization (2)

• Summary
• Class AliTOFDigitizer
• Inherits from AliDigitizer
• Output TClonesArray of AliTOFdigit
• QA and test macros
• AliTOFSDigits2Digits.C (only digitization, no
  merging)
• AliTOFanalyzeDigits.C

11
Merging/Digitization (3)

• UML diagram

12
CPU time estimation for sdigitization and merging

• Sdigitization
• 3s/ event
• LEGENDA eventcentral Hijing event in theta
  range 45,135

• Digitization only
• 1s/event

13
Reconstruction/PID QA and test macros

• Reconstruction
• Class AliTOFReconstructioner
• Inherits from TTask
• Output TNtuple object (assignment of time of
  flight to tracks)
• QA and test macros
• AliTOFtestRecon.C
• AliTOFanalyzeMatching.C

• PID ('last step' efficiency data added)
• Class AliTOFPID
• Inherits from TTask
• Output TH1F objects
• QA and test macros
• AliTOFtestPID

14
Probabilities for PID (1)

• Definition of probability from TOF-PID (Hijing)

15
Probabilities for PID (2)

• the same but for Shaker (different 'model' -gt
  different amplitudes) (how to avoid model
  dependency in defining probability?)

16
Probabilities for PID (3) (Sigmas comparison in
Shaker Hijing)

• Hijing
• Unit MeV/cc
• Pions s(m)90
• Kaons s(m)56
• Protonss(m)33

• Shaker
• Unit MeV/cc
• Pions s(m)90
• Kaons s(m)53
• Protonss(m)32

17
Probability to be pion

• 1.5GeV/cltplt2.GeV/c (Pb-Pb Hijing)

18
Probability to be pion (2)

• 1.5GeV/cltplt2.GeV/c (pp, PYTHIA)

19
Probability to be kaon

• 1.5GeV/cltplt2.GeV/c (Pb-Pb) (fit problem)

20
Probability to be kaon (2)

• 1.5GeV/cltplt2.GeV/c (pp)

21
Probability to be proton

• 1.5GeV/cltplt2.GeV/c (fit problem)

22
Probabilities for PID (2)

• ... in different momentum range

23
Propagation from TPC to TOF using Kalman

• This exercise started before the TRD tracking was
  ready
• We plan to use the backpropagation from TRD to
  TOF detector (very short distance compared to the
  previous TPC-gtTOF)
• Preliminary results for the area spread by the
  track propagation (it results less than the
  statistical method -see TOF TDR Addendum Chapter
  5, Section 5.5-)

24
Propagation from TPC to TOF using Kalman (2)

• From TPC reconstructed tracks (and back
  propagated in TPC!)
• I step propagation through the outer wall of
  the TPC (radiation length from TPC TDR)
• II step propagation in air (for the time being,
  applied to events with no TRD)
• III step propagation through the outer wall of
  the TOF
• IV step derive the area spread by the track
• Area3?(y)3?(z)

25
Back Propagation in TPC

• Area after back propagation in TPC

26
Propagation from TPC to TOF using Kalman (4)

• Area after propagation to TOF(4 TOF pads)

27
AliTOFT0V2 (1)

• Algorithm description
• Combinatorial method as described in TOF TDR
  Addendum (Chapter 5, Section 5.7)
• BUT, now applied to reconstructed tracks (i.e.
  including also the tracks with a wrong time of
  flight assignment) - with pgt1GeV/c, to have the
  larger matching efficiency -
• In any case (preliminary!) a better resolution
  than 50ps can be reached
• And, (no surprise!) by using the library (not an
  interpreted code as in the past) the computing
  time is reduced by a factor 10.

28
AliTOFT0V2 (2)

• Preliminary result for time zero (B0.4T)

29
AliTOFT0V2 (3)

• Same as previous slide but at B0.2T

30
AliTOFT0V3 (1)

• Implementation of the following idea "Assume
  for all (high statistics) reconstructed tracks
  the pion mass and derive the time zero by meaning
  the zero time of all tracks"
• Preliminary result the zero time mean
  distribution is narrow (60ps) BUT it is not
  centered around zero (as it as to be in MC) due
  to the systematic wrong mass assumption (need for
  truncated mean analysis).

31
AliTOFT0V3 (2)

• Preliminary result for 100 HIJING events

32
AliTOFT0V3 (3)

• Preliminary result for 100 SHAKER events

33
Conclusions Outlook on 'time zero'

• Several ideas for 'time zero' determination are
  under investigation
• the most interesting and fascinating one is the
  following
• Take the earliest signals on TOF (they are mainly
  due to electrons from prompt gamma conversion in
  the TOF volume - to be verified and how to tag
  them?-gt may be using TOF signals not matched with
  the TRD reconstructed tracks-)
• Use a straight line approximation, assume as
  velocity the speed of the light -as in the gamma
  case - and derive the 'time zero'
• No reconstruction needed at all