1. Cronin Effect of  K p from d+Au Collisions at 200 GeV
Lijuan Ruan
USTC/BNL
Outline:
Introduction and Motivation
Physics Results and Discussions
Summary and Outlook
Thanks: STAR Collaboration
4/12/2019
CCAST Workshop, 2004

2. Cronin Data at Lower Energy
J.W. Cronin et al., PRD 11, 3105 (1975);
Enhancement of hadron production in proton-nucleus collisions.
R>1 at high pT.
Explained by initial multiple scattering.
What’s the Cronin Effect? 30 years ago, the enhancement of hadron production in proton-nucleus collisions was observed at higher pT.
If we use this equation to represent the Cronin Effect ratio R_A/B, that’s the differential cross section in pA collisions by comparison through the differential cross section in p+B collisions, scaled by atomic number. If there is no nuclear effect, R will be 1. However, the experimental results shows the enhancement for higher pT and suppression for small pT. As shown in left plot. This plot shows the power alpha dependence of the invariant cross section for pi, K, p. We can see at pT 2~3 GeV, alpha is larger than 1. Means the enhancement of the hadron production. Another important feature is that Cronin effect larger for protons compared to pions. This enhancement is explained by initial multiple scattering. We can see the alpha of pi is smaller than that of K and the alpha of K smaller than that of p.
Cronin effect larger for protons compared to pions
4/12/2019
CCAST Workshop, 2004

3. Cronin Effect at Lower Energy
P.B. Straub et al., PRL 68, 452 (1992)
Cronin effect decrease with energy
Also the lower energy shows the cronin effect R_w/Be decrease with energy at a certain pT.
4/12/2019
CCAST Workshop, 2004

4. Some Definitions
Initial-state effect: The effect happens before the hard scattering.
Final-state effect: The effect happens after or at the hard scattering.
4/12/2019
CCAST Workshop, 2004

5. Model Prediction:Initial Multiple Parton Scattering
X.N. Wang, nucl-th/
A. Accardi, hep-ph/
Px~1 GeV/c
1 <RM<2 , 2.5<PM<4.5 GeV/c
The natural question is that what’s the Cronin Effect for higher energy, such as RHIC energy. Many models gave their own predictions. One of the models is the pQCD model based on initial parton multiple scattering.
The predictions will give the feature like that in the right plot. When the pT~1 GeV, the R will be larger than 1 and reach the maximum value 1 to 2 at pT~2.5 to 4.5 GeV. However, it can’t tell the difference of the cronin effect between proton and pions.
Initial multiple parton scattering can reproduce Cronin Effect of the charge hadron.
IMPS+jet quenching can reproduce the suppression of the charge hadron in Au+Au collisions.
4/12/2019
CCAST Workshop, 2004

6. Centrality Dependence: Rcp in Au+Au
nucl-ex/ , STAR Collaboration
At intermediate pT, the Cronin Effect was observed while in 200 GeV AuAu collisions, the suppression for meson was observed.
Here shows the R_cp. Rcp is …
The left plot shows the Ks,lambda, K, Rcp for Ks, K is less than 1 while Rcp for Lambda is ~1. The right plots shows pion0 suppressed while the proton follow N_bin scaling. From the data, we can see Baryons (p, ) increase faster than mesons (, Ks, K) from peripheral to central collisions. So in central AA collisions, the yield of proton may be larger than that of pion or equal to pion. In order to deeply understand mechanism for the particle production at intermediate pT in AuAu collisions, the Cronin effect study for this energy becomes necessary.
IMPS+jet quenching will result in the same suppression of baryon/meson in Au+Au collisions.
Baryons () increase faster than mesons (Ks, K) from peripheral to central collisions; Baryon:~ Nbin scaling
4/12/2019
CCAST Workshop, 2004

7. Centrality Dependence: Rcp in Au+Au
R.J. Fries, et al., nucl-th/
Recombination models: q q
proton q q Ks
qbar
Recombination models predict that a scale according to the number of constituent quarks in a hadron seems to govern the particle production at intermediate pT.
4/12/2019
CCAST Workshop, 2004

8. Motivation
Initial multiple parton scattering can reproduce Cronin Effect of the charge hadron.
IMPS+independent Fragmentation will result in the same Cronin Effect of pion and proton.
IMPS predict that the Cronin effect on deuteron side is larger than that on Au side at forward rapidity.
X.N. Wang, nucl-th/
Recombination models can produce the Rcp of baryon/meson at intermediate pT in AuAu collisions
Measure the Cronin effect of pion/proton.
Compare with recombination model
How about the eta asymmetry of Cronin effect?
Cronin effect is initial state or final state effect?
4/12/2019
CCAST Workshop, 2004

9. MRPC-TOFr PID plot Hadron PID proton:3GeV/c kaon: 1.6GeV/c
nucl-ex/
4/12/2019
CCAST Workshop, 2004

10. Spectra from 200GeV d+Au, p+p
STAR Collaboration, nucl-ex/
d+Au MinBias: 95%3% of total nuclear cross section
p+p NSD : 30.0 3.5 mb, spectra correction <5% to inelastic
4/12/2019
CCAST Workshop, 2004

11. Spectra in 3 centrality bin
peripheral
The spectra in d+Au collisions are harder than those in p+p collisions
4/12/2019
CCAST Workshop, 2004

12. Cronin Effect:  K p RdAu
Low pT, RdAu <1
High pT, RdAu >1
Px~=1 GeV/c
RdAu(p)> RdAu(,K)
RdAu of protons rises
faster than those of
pions and kaons.
Proton spectra at
intermediate pT : no
binary scaling
STAR Collaboration, nucl-ex/
Characteristic Cronin Effect
4/12/2019
CCAST Workshop, 2004

13. The Ratios between p+pbar and h
STAR Collaboration, nucl-ex/
d+Au: (pbar+p)/h=0.240.01 0.01 (2<PT<3 GeV/c)
p+p: (pbar+p)/h=0.210.02 0.01 (2<PT<3 GeV/c)
p-=0.041 0.01 0.006 (1.2<PT<3 GeV/c),
lower energy sqrt(s)~30 GeV/c, p-= 0.004
(pbar+p)/h=0.24, A factor of 2 smaller than that in Au+Au  AuAu baryon excess due to Final State Effect.
4/12/2019
CCAST Workshop, 2004

14. Model Comparison: recombination
Recombination model can reproduce the  spectra in d+Au collisions.
Great Thanks to C.B. Yang (CCNU)!
R.C. Hwa et al., nucl-th/ ; R.C. Hwa et al., nucl-th/
4/12/2019
CCAST Workshop, 2004

15. Model Comparison: recombination
Recombination model can reproduce the p spectra in d+Au collisions.
Great Thanks to C.B. Yang (CCNU)!
R.C. Hwa et al., nucl-th/ ; R.C. Hwa et al., nucl-th/
4/12/2019
CCAST Workshop, 2004

16. Integral Yield RdAu Integral yield RdAu is smaller than 1:
- Shadowing effect ?
- Mass dependent ?
The integral yield RdAu is bigger for proton than for pion.
4/12/2019
CCAST Workshop, 2004

17. Cronin Effect  Asymmetry
This model, initial multiple parton scattering alone, can’t reproduce the eta asymmetry of Cronin effect. Hwa et al. claims they can do it.
X.N. Wang, nucl-th/
4/12/2019
CCAST Workshop, 2004

18. Conclusions
RdAu of protons rises faster than those of pions and kaons at 200 GeV d+Au collisions, Characteristic Cronin Effect.
The mass dependence of Cronin effect at RHIC energy is much smaller than that at lower energy.
Recombination model can reproduce the Cronin Effect of , p  Final State Effect.
Baryon enhanced p/h (dAu/pp)=1.19 0.05 0.03. In Au+Au, the ratio is about a factor of 2 higher  Final State Effect.
Initial multiple parton scattering can reproduce Cronin Effect of the charge hadron.
IMPS + independent fragmentation will result in the same Cronin Effect of pion and proton.
The model, based on initial multiple parton scattering, can’t reproduce the measured rapidity asymmetry.
Cronin Effect is not the initial-state effect only, the final-state effect plays an important role.
4/12/2019
CCAST Workshop, 2004

19. Outlook
Coherent multiple parton scattering: for a nucleus, if x<xc/A1/3~0.1/A1/3, the probe cannot tell which nucleon the parton comes from. 1 2 3
PT(GeV/c)
J.W. Qiu et al., hep-ph/ ; J.W. Qiu et al., hep-ph/
Coherent multiple parton scattering may shed light on the physics of Cronin effect.
4/12/2019
CCAST Workshop, 2004