“Hard” & “Soft” Interactions in Proton + Proton Collisions @ 200GeV

1. “Hard” & “Soft” Interactions in Proton + Proton Collisions @ 200GeV Huang Shengli (USTC) Outline: • 1. How to defined and tell “hard” & “soft” interactions? • 2. Motivations • 3. Analysis results • 4. Conclusions 黄胜利(USTC)

2. How to tell “hard” & “soft” Interactions • Theory: “Hard” interaction (Qs>2GeV/c) • Experiment: Jet can be used to select event containing “hard” interactions Jet Definition in TPC: 1.At least two charged tracks in one cone Rcone=sqrt(∆φ2+∆η2) =0.7 2.Seed track Pt>=1.0GeV/c,the other Pt>=0.2GeV/c CDF PRD65(2002)072005 The definition of “soft” events & “hard” events Soft Event : Without defined jet, dominated by soft interactions HardEvent: At least one defined jet, dominated by hard interactions By studying the difference of “soft” & “hard” events to study the properties difference of “soft” & “hard” interactions ! 黄胜利(USTC)

3. 0 10 20 30 40 charge multiplicity 0 10 20 30 40 charge multiplicity “Hard” & “soft” events @ Tevetron minijets CDF PRD 65 (2002) 072005 pp Et>1.1GeV At Tevetron energies:630GeV,1.8TGeV • Soft: only depends on multiplicity (“sqrt”) • Hard: energies, multiplicity (“linear”) How about RHIC sqrt(s)=200GeV? 黄胜利(USTC)

4. ET~ few GeV Mini-jet? Mini-jet in pp & AuAu Dominate particle production pp collisions dNch/d = nsoft+nhjet/in AA collisions dNch/d = 0.5Npartns+nhNbinjet/in • Soft process: • 1)Coherent process, number of strings • proportional to number of participants • 2)Fritiof string phenomenology • Hard process: • 1)Incoherent process, proportional to • number of binary collisions • 2)Use PYTHIA for simulation of pQCD 黄胜利(USTC)

5. Motivations Previous experimental and phenomenal results show: • “Soft” physics: “Soft” event results from Tevetron need to be further checked at RHIC energy! • “Hard” physics: Mini-jet property need to be studied! 1. The mini-jet effect on <PT> of hadron 2. The mini-jet effect on the strangeness and baryon production (fragmentation) 3. Give a good reference for the Au + Au collisions 黄胜利(USTC)

6. Data Set • Analyzed data:          ppMini.Bias at sqrt(s)=200GeV • Production:                    P02ge+P02gf • Nch definitions:        # of good primary track with the cuts:         #of fit pts > 15, | dca | < 3.0, | | < 0.5 1)Charged hadron: 0.4<PT<2.0GeV/c, |VertexZ| <25cm 2) PID analysis: 0.2<PT<2.0GeV/c, |VertexZ| <30cm • Cut conditions: Good primarytrack cut 1)Charged hadron: ||<0.5, PT>0.4GeV/c, |VertexZ| <25cm 2)PID analysis: |y|<0.2, PT>0.2GeV/c, |VertexZ| <30cm The input data set was ~13M events, after the cuts it reduced to ~2.4M events for charged hadron analysis and ~3.6M for PID. 黄胜利(USTC)

7. Inclusive charged hadron in “minimum bias” event • Inclusive charged hadron invariant yield distribution • with PT in each Nch bin • Fake vertex, background and • Efficiency are corrected • 3. Power-Law function is fitted 黄胜利(USTC)

8. Inclusive charged hadron invariant yield distribution with PT in “soft” and “hard” event 黄胜利(USTC)

9. <PT> vs. Multiplicity 1.<PT> is gotten from power-law function from (0.4GeV/c,) 2. In “soft” event, the <PT> just depends on the multiplicity while not energy from RHIC energy to Tevetron 3. In “soft” event, the <PT> increase with Nch even in smaller Nch 黄胜利(USTC)

10. PID by dE/dx Distribution • 1.Identifing particle by dE/dx • Z=log(dE/dx/<dE/dx>) • 2.Four Gaussian functions fit • 3.Electron yield is gotten from • TOFr and embedding simulation • in cross section PT bin 黄胜利(USTC)

11. Inclusive  invariant yield distribution with PT Fit Functions: 1.Bose-Einstein Distribution 2. mT exponential Distribution 3. PT exponential Distribution 黄胜利(USTC)

12. Result 6:Inclusive K invariant yield distribution with PT Fit Functions: 1.Bose-Einstein distribution 2.mT exponential distribution 3.Maxwell-Boltzmann distribution 黄胜利(USTC)

13. InclusivePinvariant yield distribution with PT Fit Functions: 1.Gaussian distribution 2.mT exponential distribution 3.Maxwell-Boltzmann distribution 黄胜利(USTC)

14. <PT> dependence on Nch of ,K,P 1. The <PT> is extracted from mT exponential function 2. The error bars are statistical errors only. The systematic errors of  are about 3%, K,P are about 3%~7% in mini-bias events, 4% in soft and 5%~9% in hard 3. <PT> of  is almost flat in “soft”, “mini-bias” and hard events 4. <PT> of K,P increase with Nch even in “soft” events 黄胜利(USTC)

15. K/ & P/ with Nch 1.The K/,P / yield ratios in mid-rapidity (|y|<0.2). Yields are gotten by mT exponential distribution 2. In “hard” event, K/,P / yield ratios is higher than “soft” event 3.HIJING and PYTHIA models both reproduce this results but can’t describe its relation with Nch well 4. Au-Au collision results do not show difference with “soft” and “hard” event in error bar. More accurate measurement required! 黄胜利(USTC)

16. Conclusion • 1.Mini-jet exists in high energy p-p collision and plays an important role in particle production • 2.In RHIC energy, analysis further verify the properties of “soft” event do not depend on collision energy from RHIC to Tevetron which is model unexpected. It manifests more work need to do on “soft” physics in future • 3. Analysis shows “hard” interactions will produce more strangeness and baryon compared with “soft” interactions from K/,P/ratio, it will help us further understand mini-jet fragmentation process and give a good reference on the study of Au-Au collision and phenomenal models 黄胜利(USTC)

17. Thanks! 黄胜利(USTC)

18. Backup1:Two-particle azimuthal correlation • Low PT jet (mini-jet) • exists in p-p collision • Using jet cone can • select out events which • contain mini-jet a) Trigger PT:0.5~1.0GeV/c b) Trigger PT:1.0~2.0GeV/c c) Trigger PT:2.0~3.0GeV/c d) Trigger PT:3.0~4.0GeV/c  Associated track pT 0.2 黄胜利(USTC)