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Cosmic Ray at STAR

Cosmic Ray at STAR. STAR Regional Meeting Weihai, China, July 2 3 th – 25 th , 2012. Shuai Yang C enter of P article P hysics and T echnology U niversity of S cience and T echnology of C hina. Outline. Introduction Muon charge ratio from cosmic ray EAS Cosmic ray at STAR

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Cosmic Ray at STAR

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  1. Cosmic Ray at STAR STAR Regional Meeting Weihai, China, July 23th – 25th, 2012 Shuai Yang Center of Particle Physics and Technology University of Science and Technology of China

  2. Outline Introduction Muon charge ratio from cosmic ray EAS Cosmic ray at STAR Event and Track selection Event selection Track selection Match muon tracks Analysis results Improve of momentum resolution Reject of gamma conversion event μ+/μ- vs. Momentum μ+/μ- vs. Multiplicity Summary Shuai Yang, STAR Regional Meeting, Weihai

  3. Muon charge ratio from cosmic ray EAS Result of the MC simulation of iron and proton induced showers • EAS: Extensive Air Shower, A fixed target experiment beyond LHC energy Shuai Yang, STAR Regional Meeting, Weihai

  4. Cosmic ray at STAR y x • Advantage: • Precisely measure muon momentum upto several hundred GeV/c • Large acceptance to measure muon bundles Shuai Yang, STAR Regional Meeting, Weihai

  5. Global tracks >=2 • Reject bad runIds • Cosmic trigger Ids & no laser trigger Id tracks>=2 && runId cuts Reversed Full Field Cosmic triggers All Events Laser run Event Candidates Event selection Full Field Shuai Yang, STAR Regional Meeting, Weihai

  6. 700>Track_flag>0 • nHitsFit>=15 • P > 3 GeV/c Muon Track Candidates Track selection Shuai Yang, STAR Regional Meeting, Weihai

  7. Match muon tracks y x Project tracks onto R=220cm plane, pickup the upstream point For every two tracks with p>3 GeV/c Compare R*(pos_phi2-pos_phi1) Compare pos_z2 – pos_z1 Compare p_phi2-p_phi1 and p_theta2 – p_theta1 p = -p for the track with larger firstPoint_y For those qualified from above 2D cuts are considered as matched candidates. Shuai Yang, STAR Regional Meeting, Weihai

  8. 2D correlation for muon matching 2D cuts to further suppress random combinatorial background Shuai Yang, STAR Regional Meeting, Weihai

  9. Refit_1 Improve momentum resolution Shuai Yang, STAR Regional Meeting, Weihai

  10. By Prof. Shao Refit_2： makes a direct helix refit to all the hit points from the paired tracks(still ongoing, not finish yet) Shuai Yang, STAR Regional Meeting, Weihai

  11. “Neutral” track • The reason of "neutral" track: • Gamma conversion (low momentum) • The charge sign for one track is wrong(large momentum) Shuai Yang, STAR Regional Meeting, Weihai

  12. 200-1000GeV/c 200-1000GeV/c 3-10GeV/c 3-10GeV/c Gamma conversion The charge sign is redefined from the refit after rejecting the gamma conversion events according the deflection direction Shuai Yang, STAR Regional Meeting, Weihai

  13. Results μ+/μ- vs. Momentum μ+/μ- vs. Multiplicity • Proton induced showers: • low multiplicity • ratio > 1 (~1.3) • Iron induced showers: • high multiplicity • ratio ~ 1 Shuai Yang, STAR Regional Meeting, Weihai

  14. Ratio vs. Momentum FF FF FF FF Shuai Yang, STAR Regional Meeting, Weihai

  15. Different Multiplicity definition MuonpairMult: Selected Muonpair events MatchMult: flag of global track ∈(0,700) ; flag of match >0 SingleMuonMult: Selected Muon events GlobalMult：flag of global track ∈(0,700) ; nHitsFit>= 15 ; firstpoint.Z() && lastpoint.Z() ∈[-180,180] TofMult：BTofHit(BTofHit_mTray[i]<=120) Shuai Yang, STAR Regional Meeting, Weihai

  16. MuonpairMult.- the most reliable multiplicity definition RFF FF • Decrease with multiplicity? • Reconstructed Muonpair Multiplicity is too small Shuai Yang, STAR Regional Meeting, Weihai

  17. MatchMult. FF RFF Shuai Yang, STAR Regional Meeting, Weihai

  18. SingleMuonMult. FF RFF Shuai Yang, STAR Regional Meeting, Weihai

  19. GlobalMult. RFF FF • From the ratio vs. four different multiplicity definitions: • Ratio decreases with increasing multiplicity. • Physics reason? Detector reason? Shuai Yang, STAR Regional Meeting, Weihai

  20. TofMult. • Most of the tof hits are not associated with global track. Shuai Yang, STAR Regional Meeting, Weihai

  21. Thank You! Summary We can matched muon tracks with good s/b ratio and efficiency Combined two muon tracks can improve the momentum resolution Can get ratio with very good precision upto several hundred GeV/c Can observe ratio decrease with multiplicity, but need to check the reason. Shuai Yang, STAR Regional Meeting, Weihai

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