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2012/7/231 Cosmic Ray at STAR Shuai Yang Center of Particle Physics and Technology University of Science and Technology of China STAR Regional Meeting.

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Presentation on theme: "2012/7/231 Cosmic Ray at STAR Shuai Yang Center of Particle Physics and Technology University of Science and Technology of China STAR Regional Meeting."— Presentation transcript:

1 2012/7/231 Cosmic Ray at STAR Shuai Yang Center of Particle Physics and Technology University of Science and Technology of China STAR Regional Meeting Weihai, China, July 23 th – 25 th, 2012

2 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 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

3 2012/7/23 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

4 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 4 Cosmic ray at STAR Advantage: Precisely measure muon momentum upto several hundred GeV/c Large acceptance to measure muon bundles x y

5 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 5 Event selection Cosmic triggers Laser run All Events Reversed Full Field tra ck s> =2 & & ru nI d cu ts Full Field Global tracks >=2 Reject bad runIds Cosmic trigger Ids & no laser trigger Id Event Candidates

6 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 6 Track selection 700>Track_flag>0 nHitsFit>=15 P > 3 GeV/c Muon Track Candidates

7 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 7 x y Match muon tracks  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.

8 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 8 2D cuts to further suppress random combinatorial background 2D correlation for muon matching

9 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 9 Improve momentum resolution Refit_1

10 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 10 Refit_2 ： makes a direct helix refit to all the hit points from the paired tracks(still ongoing, not finish yet) By Prof. Shao

11 2012/7/23 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)

12 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 12 Gamma conversion 3-10GeV/c 200-1000GeV/c The charge sign is redefined from the refit after rejecting the gamma conversion events according the deflection direction

13 2012/7/23 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

14 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 14 Ratio vs. Momentum FF

15 2012/7/23 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)

16 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 16 MuonpairMult. - the most reliable multiplicity definition RFF FF Decrease with multiplicity? Reconstructed Muonpair Multiplicity is too small

17 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 17 MatchMult. RFF FF

18 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 18 SingleMuonMult. RFF FF

19 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 19 GlobalMult. From the ratio vs. four different multiplicity definitions: Ratio decreases with increasing multiplicity. Physics reason? Detector reason? RFF FF

20 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 20 TofMult. Most of the tof hits are not associated with global track.

21 2012/7/23 Shuai Yang, STAR Regional Meeting, Weihai 21 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.

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