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MTD Calibration for Cosmic Ray Triggered Data in RUN 10 at STAR

MTD Calibration for Cosmic Ray Triggered Data in RUN 10 at STAR. Lijuan Ruan (BNL), ChengMing Du(IMP) 04/ 13 /201 2. Outline. Motivation Data Set Method Matching Results Summary. Motivation.

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MTD Calibration for Cosmic Ray Triggered Data in RUN 10 at STAR

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  1. MTD Calibration for Cosmic Ray Triggered Data in RUN 10 at STAR Lijuan Ruan (BNL), ChengMing Du(IMP) 04/13/2012 MTD workshop,Tsinghua,Beijing April 11-13,2012

  2. Outline • Motivation • Data Set • Method • Matching • Results • Summary MTD workshop,Tsinghua,Beijing April 11-13,2012

  3. Motivation • In run10 STAR implemented a cosmic ray trigger to study the performance of its several subsystems, including TPC, MTD, TOF etc. • Because the cosmic rays are primarily muons, we were able to get rid of the hadron background from material interactions in the MTD analysis, as seen in previous studies with data from physical collisions. • Also the cosmic ray data offers us significant amount of muon tracks with pt > 2 GeV/c, and these high momentum particles have less interaction with the material than the lower momentum particles therefore we can calculate the tracking information more precisely. MTD workshop,Tsinghua,Beijing April 11-13,2012

  4. Data Set • RUN 10 Au+Au 11 GeV fastoffline production of st_mtd data stream for Reversed Full Field • Selected cosmic ray tiggered events with “cosmic” offline Tigger ID 310803 • Global tracks were used MTD workshop,Tsinghua,Beijing April 11-13,2012 4

  5. QA Plots MTD workshop,Tsinghua,Beijing April 11-13,2012 5

  6. Method tMTD is calculated by averaging the times from two ends of an MTD strip so that it does not depend on the hit position on the strip. tTOF1 and tTOF2 are calibrated times associated with TOF hits due to the cosmic ray muons. tTPC is the calculated time of flight between two TOF trays 1 and 2 with the pathlength and momentum information from TPC. tSteel is the time of flight from MTD to TOF, also calculated with TPC information Zhangbu Xu The time difference between TOF+MTD measured time and TPC measured time is deltaT = (tTOF2 – tTPC + tTOF1)/2 – tMTD - tSteel MTD workshop,Tsinghua,Beijing April 11-13,2012 6

  7. Matching • The matching between 2 halves of a muon track in TPC requires nHitsFit>14, |eta|<1.5 and p>1 GeV/c for each half and |p1-p2|/p1<0.27, where p1 and p2 are the momenta for the two halves. • The next step is raw matching for the TPC tracks. The requirements are nFitPoints >= 25, Pt >= 2.0 GeV/c, TpcZ < 100 cm && TpcZ > (- mrpcLength - 100 cm), TpcPhi > 0.419 && TpcPhi < 0.628, where Z is the position along the beam pipe and an MTD strip, TpcZ and TpcPhi are extroplated Z and Phi values for a track from TPC. • Finally we do the matching between the TPC tracks and the MTD hits, requiring |TpcZ-MtdZ| < 6 cm and |TpcPhi-MtdPhi| < 0.2. MtdZ is from the timing difference between 2 ends of a strip and MtdPhi is from the center of the fired MTD strip. MTD workshop,Tsinghua,Beijing April 11-13,2012

  8. Position Resolutions deltaPhi Sigma = 0.006 rad deltaZ (cm) Sigma = 2.6 cm MTD workshop,Tsinghua,Beijing April 11-13,2012 8

  9. Spatial resolution A multiple-scattering effect driven formula is used to obtain the intrinsic resolution of MTD,which is 1.3 cm and 0.0027 rad(0.0027*400=1.1 cm). MTD workshop,Tsinghua,Beijing April 11-13,2012

  10. TOF Timing Resolution DeltaT0 = tTOF2- tTOF1 – tTPC TOF timing resolution ~118ps/sqrt(2) ~ 83 ps. MTD workshop,Tsinghua,Beijing April 11-13,2012 10

  11. The First T0 Offset Correction First, we did a T0 offset correction for each strip. Basically we fitted the deltaT histograms with a Gaussian function and subtracted the obtained mean value from tMtd. 11 MTD workshop,Tsinghua,Beijing April 11-13,2012

  12. After The First T0 Offset Correction MTD workshop,Tsinghua,Beijing April 11-13,2012 12

  13. TOF+MTD Timing Resolution Before Calibration MTD timing Resolution~201ps MTD workshop,Tsinghua,Beijing April 11-13,2012 13

  14. The Slewing Correction Secondly, we combined all channels and plotted deltaT versus averageTOT.The slewing correction curve is obtained by a 5th order polynomial function fitting the Gaussian mean deltaTs for all averageTOT bins. Then the slewing correction is done by subracting the function value from tMtd according to its averageTOT value. The slewing correction is done for only 10ns &TOT<22 ns . 14 MTD workshop,Tsinghua,Beijing April 11-13,2012

  15. The Second T0 Offset Correction A second T0 correction is done thereafter due to the observed T0 shift after the slewing correction MTD workshop,Tsinghua,Beijing April 11-13,2012 15

  16. Final TOF+MTD Timing Resolution MTD+TOF timing resolution: 118ps.Timing resolution from TOF: 59ps . multiple scattering effect for 6 GeV/c muons:25 ps. MTD timing resolution: ~99ps. MTD workshop,Tsinghua,Beijing April 11-13,2012 16

  17. Summary • ~118 ps timing resolution for MTD+TOF is achieved, giving ~99 ps for MTD alone. • 1 cm spatial resolution. Thanks! MTD workshop,Tsinghua,Beijing April 11-13,2012 17

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