Barrel Time-Of-Flight
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Barrel Time-Of-Flight In Run10. Xin Dong. Many thanks to the TOF group. TOF Close-out Review. Reviewed on Aug 10-11, 2009 at BNL. Report can be found here:. Construction stage -> Operation stage.

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Barrel Time-Of-Flight In Run10

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Barrel time of flight in run10

Barrel Time-Of-Flight

In Run10

Xin Dong

Many thanks to the TOF group

Tof close out review

TOF Close-out Review

Reviewed on Aug 10-11, 2009 at BNL. Report can be found here:

Construction stage -> Operation stage

Run 10 summary

Run 10 “Summary”

  • 120 full barrel trays installed

  • 119 trays were active in Run 10 (one out due to the HV cable issue)

    - only 1 dead channel out of ~23000

  • Start detector (upVPD or VPD) hasn’t changed since last year

  • VPD coincidence (and vertex selection)

    • widely used as the MB condition at high energy collisions

    • A much cleaner trigger in low energy collisions

  • TOF multiplicity trigger

    • Central trigger

    • UPC trigger

  • VPD/TOF operation in Run10 went very well.

  • Preliminary calibrations (based on fast offline) are done, and in db.

Barrel tof geometry

Barrel TOF Geometry

One Module

local Y


local Z

“+” ―To TPC center

One Tray

η~ 0

η~ 0.9


Tray alignment calibration

Tray Alignment Calibration

Use the low luminosity data taken on day 074

Do local (x,y,z) alignment in one loop.

Tray alignment calibration constants were uploaded soon during 62 GeV run.

Reflected in the fast offline data.

Open: from fit to all

Solid: from fit to modules 1-6 only

Conventional timing calibration

Conventional Timing Calibration

  • Calibration for the start detectors - VPDs

  • Calculate the start time

  • Calibration for the BTOF trays

    - Need TPC tracking

but enhanced by  at high p limit

200 gev and 62 gev prel calibration

200 GeV and 62 GeV (prel.) calibration

200 GeV

62 GeV



Bingchu Huang

Difference comes from the start side

When going down energy

When Going Down Energy

The conventional VPD-start calibration method has some issues:

The small VPD acceptance causes to start losing significant amount of events, even central events.

2) Outliers from slow particles increase dramatically, which will dilute the start time resolution significantly.


Non-Vpd-Start (BTOF self) calibration algorithm implemented

Introduce a truncation algorithm in calculating the start time from VPD to suppress the outliers from slow particles

Triggers at 7 7 and 11 5 gev

BBC Minimum bias trigger: efficient but with large background

VPD trigger: much cleaner but inefficient (missing central/peripheral)

VPD trigger used as our luminosity monitor

Triggers at 7.7 and 11.5 GeV

“Good” events are identified via offline analysis by requiring a valid vertex within |Vz|<75 cm and |Vxy|<2 cm

~ a few % minbias triggered events are “good” events

1/3 of VPD trigger triggered events are “good” events

~2/3 of “good” minibias events are labeled as VPD triggers

AuAu 7.7 GeV

VPD trigger rate ~ 2*collision rates within |Vz|<75cm

39 gev truncation calib in vpd

39 GeV - Truncation Calib. in VPD

VPD Timing not symmetric in low energy collisions

- single particle hit in each channel

- slow particles lead to larger timings

Tdiff = Ti - <Tj>(j!=i)

Use truncated mean in calculating the averaged timing. Remove hits with top 20% high timing - coming from slow particles

39 gev calibration

39 GeV Calibration

Rafael, Bill

Resolution = 86ps

With improved start side

Calibration w o vpd

Calibration w/o VPD

Calibration completely w/o VPD

62 GeV test

Very promising timing resolution!

Resolution (ns)

Ming Shao

# of pions

T - Texp (ns)

Resolution (ns)

# of pions

# of pions

TDIG board ID

Startless calibration strategy

Startless Calibration Strategy

Step 1:

Obtain the calibration constants (at expert level), two ways:

- with the standard VPD start calibration

conventional, but require more statistics due to VPD inefficiency

- with the new BTOF self calibration

Step 2:

Apply the calibration constants to data

- Algorithm with the new BTOF self calibration (maximize efficiency)

Applying with btof self calib algorithm

Applying with BTOF self calib. algorithm

7.7 fast offline data

Calibration constants obtained in 39 GeV with VPD-start calibration procedure.

- Demonstrates the tray stability across different collision systems.

Tof - Tofexp (ns)

Day 125 7.7 GeV

Day 125 7.7 GeV

Pid method i

PID method (I)

  • Particle flight time from TOF

  • Track length from TPC

  • Depend on masses of particles

  • Can be fitted with Gaussians

    default time resolution is 110 ps (Run9), may change with p for proton

Masayuki Wada

This is the default method in production!

Pid method ii m 2

PID method (II) - M2

Dylan TheinMasayuki Wada

  • Calculate m2 from

  • get the probability of being a particle

    Currently not in MuDst, people can calculate it by themselves if needed.

  • momentum and position resolution are essentially determined by the TPC

1-Sigma error bar

Pid combining tof and de dx

PID combining TOF and dE/dx

  • In progress

Masayuki Wada

Yuri Fisyak

Remarks on efficiency acceptance

Remarks on Efficiency & Acceptance


= (tracks with matchFlag>0)

/ (tracks that can be projected to TOF modules)

pp2pp Run9

Acceptance: eta -0.9 - 0.9 at Vz=0

phi averaged acceptance ~0.87 due to tray gaps

TOF Matching * Acceptance ~ 0.8 * 0.87 ~ 0.7 single track at plateau

- Run9 only 86 trays (out of 120), thus total TOF acceptance * efficiency ~ 0.5



  • 1) Run10 TOF operation went quite well.

  • 2) Preliminary calibrations have been done

  • - Promising performance in various collision energies

    • High energy datasets (200, 62.4 GeV)

  • - Wait for the final TPC calibration and complete the TOF

  • calibration for production

    • Low energy production are using the fast offline calibration

  • - Check the TOF calibration when doing your analysis

  • 3) TOF PidTraits is available in the MuDst for physics analysis

    • now developing an integrated PID algorithm combining TOF+dE/dx+(…)

Calibration status

Calibration Status

Preliminary 200 GeV and 62 GeV calibration were done, and constants were in db.

39 GeV calibration were finished, constants will be uploaded to db soon.

7.7 GeV calibration is underway (in accumulating enough statistics)

- based on fast offline (preliminary TPC calibration)

Important infrastructure updates:

1) Low energy runs: to suppress the outliers from slow particles, introducing

a truncation algorithm in calculating the start time from VPD.

2) Non-Vpd-Start (BTOF self) calibration algorithm is implemented in the calibration maker to allow the BTOF self calibration.

Fast offline QA - Ulisses Gulart, Rafael Derradi

Vpd-start calibration - Rafael Derradi, Bingchu Huang, Bill Llope

Non-vpd-start calibration - Ming Shao, Bill Llope

Applying with btof self calib algorithm1

Applying with BTOF self calib. algorithm

62 GeV:

Constants from the Vpd-Start calibration in data base

(alignment not updated when these constants were obtained)

62 GeV

How to load tof calibration

How to load TOF calibration




StChain *chain = new StChain("StChain");

StMuDstMaker *muDstMaker = new StMuDstMaker(0,0,"",fileList,"MuDst.root",nfiles);

St_db_Maker *dbMk = new St_db_Maker("db","MySQL:StarDb","$STAR/StarDb","StarDb");

StVpdCalibMaker *vpdCalib = new StVpdCalibMaker();


StBTofCalibMaker *btofCalib = new StBTofCalibMaker();


StMyMaker *myMaker = new StMyMaker();

Introduce xlocal

Introduce xLocal

Bingchu Huang

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