1. “Hard” & “Soft” Interactions in Proton + Proton Collisions @ 200GeV
2019/4/7
“Hard” & “Soft” Interactions in Proton + Proton 200GeV
Huang Shengli
(USTC)
Outline:
1. How to defined and tell “hard” & “soft” interactions?
2. Motivations
3. Analysis results
4. Conclusions
2019/4/7
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
Hard Event: 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 !
2019/4/7
黄胜利(USTC)

3. “Hard” & “soft” events @ Tevetron
charge multiplicity
minijets
CDF PRD 65 (2002)
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?
2019/4/7
黄胜利(USTC)

4. Mini-jet in pp & AuAu dNch/d = nsoft+nhjet/in
ET~ few GeV
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
2019/4/7
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
2019/4/7
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 primary track 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.
2019/4/7
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
2019/4/7
黄胜利(USTC)

8. Inclusive charged hadron invariant yield distribution with PT in “soft” and “hard” event
2019/4/7
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
2019/4/7
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
2019/4/7
黄胜利(USTC)

11. Inclusive  invariant yield distribution with PT
Fit Functions:
1.Bose-Einstein
Distribution
2. mT exponential
3. PT exponential
2019/4/7
黄胜利(USTC)

12. Result 6: Inclusive K invariant yield distribution with PT
Fit Functions:
1.Bose-Einstein
distribution
2.mT exponential
3.Maxwell-Boltzmann
2019/4/7
黄胜利(USTC)

13. InclusiveP invariant yield distribution with PT
Fit Functions:
1.Gaussian distribution
2.mT exponential
distribution
3.Maxwell-Boltzmann
2019/4/7
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
2019/4/7
黄胜利(USTC)

15. K/ & P/ with Nch 1.The K/,P / yield ratios
2019/4/7
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!
Without global systematic errors and model dependence
2019/4/7
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
2019/4/7
黄胜利(USTC)

17. Thanks!
2019/4/7
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
2019/4/7
黄胜利(USTC)