TOF%20Tracking%20What%20have%20we%20learned%20-%20What%20do%20we%20need?

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TOF TrackingWhat have we learned - What do we
need?

• E. Johnson, N. Khan, W. Skulski, F. Wolfs
• PHOBOS Time-of-Flight Group
• University of Rochester
• Rochester, NY 14627

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Outline

• Straight-line tracking
• Correlation between SPECN track and TOF
  multiplicity.
• How well does it work?
• What have we learned?
• Curved tracking
• Correlation between SPECN track and TOF
  multiplicity.
• How do we make it work?
• How well does it work?
• What have we learned so far?
• TOF PID with curved tracks
• Does it work?
• What do we need to optimize TOF PID?

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Straight-line tracking

• Use Inkyu Parks code to create straight-line
  tracks.
• The number of hits on the TOF is about 2 - 3
  times the number of reconstructed tracks (vertex
  dependent).
• A clear correlation exists between the hits on
  the TOF and the straight-line tracks.

z lt 1 cm
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Straight-line Tracking

• Create straight-line tracks
• Use theta-track to extrapolate to TOF
• Use hits on last two planes to extrapolate to TOF
• Conclude that using the last two hits improves
  TOF - SPEC matching.

??TC 0.3 ??TB 0.2
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Impact of multiplicity on TOF trackingMust use
y position to improve Signal/Noise!!

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Using straight-line tracks for vertical position
calibration of the TOF

• The vertical position of the TOF scintillators
  can be determined using the vertical position
  information from the track.
• Due to vertical segmentation of last silicon
  planes, we need to use the azimuthal track angle.
• A clear correlation is observed between y(track)
  and y(TOF).
• Procedure works nicely for the central
  scintillators, but not for those near 32.5 and 90
  degrees.

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Curved Tracks and TOF Multiplicity

• The number of straight-line tracks in all layers
  of SPECN with field-off scales with the TOF
  multiplicity (the number of TOF hits is 2 - 3
  times the number of spectrometer tracks).
• The number of straight-line tracks in the first 6
  layers of SPECN with field-on also scales with
  the TOF multiplicity (the number of TOF hits is 2
  times the number of straight-line tracks).

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Curved Tracks and TOF Multiplicity

• The number of straight-line tracks in the first 6
  layers of SPECN with field-on scales with the TOF
  multiplicity.
• Number of curved tracks in SPECN peaks at 1,
  independent of TOF multiplicity.
• Only events with at least two tracks can be used
  for TOF-based particle identification.

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Curved Tracking
Simulation for pions

• Use Gunthers DSTs with curved tracks.
• Use last two hits in SPECN and do a linear
  extrapolation to the TOF.
• Expect a correlated angular shift as a function
  of momentum.

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B-, PID 9 Positive charges, bending backward
Correlated Hits.
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B-, PID 8Negative charges, bending forward
Correlated Hits.
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B, PID 9 Negative charges, bending backward
Correlated Hits.
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B, PID 8 Positive charges, bending forward
Correlated Hits.
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Track matchingFirst observations

• Signal to background ratio is poor 15 - 10 for
  central events.
• Width of the correlated peak is about 5 (FWHM).
• Corrections to be made
• Momentum dependence this reduces the width to
  about 2 (FWHM).
• Position/angle dependence expect that this will
  reduce the width to about 1 (FHWM).
• Corrections will improve signal to background
  ratio to 11 - 2.
• Using the vertical position information will
  further improve this ratio.

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TOF PID

• We like to use protons and Kaons to optimize
  individual slewing corrections for PMTs. Most
  background from secondaries have a shorter
  time-of-flight.
• Current limitations
• Very few tracks from last data run (728 protons
  and 606 Kaons). Only half of these are directed
  to the TOF.
• To understand procedures, low multiplicity data
  are crucial.

B- PID 9
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TOF PID
No T0 correction, no slew correction, and no
path- length correction yet.

• Observed correlation between TOF and P is
  consistent with expectations.
• What would we like to have?
• 100 protons per scintillator (minimum bias data)
  24000 total.
• Currently we have at most a few hundred protons
  total, mostly from central events.
• Achieve good calibration data set by
• Collecting more data (should be ok next run).
• Improving tracking efficiency (get more protons
  per event).

B- PID 9
MC
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Summary and To-Do List

• Capability to match SPECN tracks and TOF hits has
  been developed for both field-on and field-off
  data.
• Straight-line tracks useful for vertical position
  calibration.
• Finish vertical position calibration for
  scintillators located close to 32.5 degrees and
  90 degrees.
• Optimize slewing corrections by using separate
  rise times for each PMT channel (various
  procedures are under consideration).
• Correct TOF for path length variations for curved
  tracks.
• Use vertical position info to improve matching
  efficiency.