# Presentation: 000304

## Variations on a Theme:Identified Particle production in Au+Au, d+Au and p+p collisions 

-  Felix Matathias

-        Columbia University

**Andy Warhol, *****Marilyn Monroe*****, 1967**

**the PHENIX experiment, *****R******AuAu****** and R******dAu *****, 2005**

***21******st****** Winter Workshop ***
***on Nuclear Dynamics*****,**
**Breckenridge, Colorado   **
**5-12 February, 2005**

## Motivation:     

**Motivation:     **

- Strong suppression of 0 yields above pT ~ 2 GeV/c at 200 GeV central Au+Au collisions at RHIC, but no suppression for proton and antiproton at intermediate          pT  ~ (2-5 GeV/c):                **“Baryon anomaly at RHIC”**

- “Anomalous” proton to pion ratio at 200 GeV central Au+Au collisions at RHIC.

**Variation:     **

- PHENIX: PRL 91, 172301 (2003), PRC 69, 034909 (2004)
- Au+Au collisions at sNN = 200 GeV

- Measurement of identified particle  production in p+p collisions at the same energy, establishes the elementary hadronic reference that spectra are compared to. From RCP to RAuAu

- = 200 GeV Au+Au

- Measurement of identified particle production in d+Au collisions at the same energy establishes the size of initial state nuclear matter effects. Detailed study of the Cronin effect for pions, kaons and protons.

- Measurement of identified particle production in Au+Au collisions at lower energies, 62.4 GeV, absence or presence of the baryon anomaly ? What is the magnitude at lower energies ?

## BBC start/DCH track/TOF stop

- Acceptance:
-  = /4
- |n|< 0.35
- Method: PID based on particle mass
- Calculated by:
- BBC: start time
- DCH, PC: tracking, momentum
- Track Model: path length
- TOF: Time of Flight
- TOF = 100-130 ps
- p/p= 0.7% + 1.1%p (GeV/c)
- Pion identification   : pT~2.5-3.0GeV/c
- Kaon identification  : pT~2.0 GeV/c
- Proton identification: pT~ 3.5-4.0 GeV/c

## High Resolution TOF                                        Solid performance, year after year

## The Baseline: p+p and d+Au

**PRELIMINARY**

- p+p and d+Au data from RHIC RUN 03 at √sNN=200 GeV
- p+p and d+Au data have been corrected for feed-down corrections
- 42M d+Au Events
- Minimum Bias trigger accepts 88.5+/-4% of all d+Au collisions
- 25M p+p Events
- Minimum Bias trigger accepts 51.6+/-9.8% of total inelastic p+p cross section at      √sNN=200 GeV
- Au+Au at √sNN=62.4 GeV from RHIC RUN 04: 37M Au+Au Events

## Nuclear Modification Factorsin Minimum Bias d+Au

- No suppression at intermediate and high pT at midrapidity
- Protons have a significant enhancement, traditionally called “the Cronin effect”
- On the order of 40%
- Pions show smaller enhancement, Kaons seem  to scale with Ncoll
- Notice: Phenix measures directly differential invariant p+p differential cross section, with no assumptions made

- Systematic errors are always shown in boxes:           Overall normalization and point-to-point

## Energy Dependence of the Cronin Effect

- Antreasyan, Cronin, et. al demonstrated that the p+A cross sections (A=D2, Be, Ti, W) can be parameterized as:
- The alpha-factors are momentum dependent and species dependent and have been tabulated for √sNN=27.4 GeV
- We can make a conversion from the a-factors to nuclear modification factors with modest assumptions:
- pD = 2xpp
- dAu ~ 2xpAu

- lines: √sNN=27.4 GeV

## Centrality Dependence ofthe Cronin effect

**PRELIMINARY**

- Phys. Lett. **B **586, 244 (2004)

- Centrality selection in d+Au using BBC south, assume that BBC signal on Au-going side is proportional to number of participating nucleons in Au nucleus.
- Number of collisions for centrality bins calculated with a Glauber Model.
- Initial Glauber-Eikonal multiple scattering model by Accardi and Gyulassy describes the data very well
- ..

- Very little room for additional dynamical shadowing.

- CGC: Kharzeev, Levin, McLerran
- Phys. Lett. B 561, 93 (2003)

## Recombination model for Fragmentation: the Hwa-Yang programme

- A hard parton with high virtuality initiates a parton shower through gluon radiation and pair creation.
- Non perturbative process.
- The fragmentation function (FF) can be written in terms of the shower parton distributions (SPD) and the recombination function (RF).
- Use the measured FFs.
- Solve the equation for the SPDs.
- Use the SPDs in different environments (d+Au, Au+Au).

## Recombination of Shower Partons in A+A and p+A Collisions:  Thermal and Shower components

- First application of SPD outside the realm of parton fragmentation.
- Start with the meson production.
- Fix all the parameters, involves fitting at low momentum.
- Predictive power of the model is at moderate to high pt through the TS and TT  term.
- Proton term will have: TTT+TTS+TSS+SSS+...

## Recombination in d+Au as the Origin of the Cronin effect

**Recombination in d+Au as the Origin of the Cronin effect**

- This radical interpretation of he Cronin effect introduces a reinterpretation of particle production with far reaching consequences
- Separation of partons into two non-interacting components, soft and hard, is perhaps an oversimplification ?
- The same framework can successfully account for the baryon anomaly observed at central Au+Au collisions.

**PROTON PRODUCTION IN D+AU COLLISIONS                                              AND THE CRONIN EFFECT.****Phys.Rev.C70:037901,2004** , e-Print Archive: **nucl-th/0404066**

## Identified Nuclear Modification Factors in Au+Au

- The measurement of identified particle production in p+p establishes the elementary hadronic reference.
- We do not have to use anymore the peripheral Au+Au centrality, with its large uncertainties, as the reference for nuclear modification factors.
- Central Au+Au collisions show a large suppression for pions, less for Kaons, and a small enhancement for protons.
- Peripheral Au+Au collisions are consistent with point-like scaling.

**PRELIMINARY**

## The gap has been bridged in d+Au

- With the identified spectra from p+p, d+Au and Au+Au at the same energy we can make quantitative statements about the baryon anomaly in central Au+Au collisions
- d+Au collisions can not account for the huge gap between protons and pions in central Au+Au collisions.

**PRELIMINARY**

**PRELIMINARY**

## Comparing RdAu and RAuAu: same species

- Striking effect for protons and antiprotons, unique behavior.
- The remarkable scaling of the protons and antiprotons, now expressed in an absolute scale by using the p+p reference.

**PRELIMINARY**

## Antimatter/Matter: flat in pT and collision species independent

**PRELIMINARY**

- No centrality dependence in d+Au either.

## Proton to pion ratio:baseline measurement is different 

- Peripheral Au+Au and Minimum Bias d+Au have the same behavior
- Smaller ratio in p+p due to larger Cronin effect for protons than pions in d+Au
- Central Au+Au show a large effect that can not be accounted for by the baseline systems

- Protons and antiprotons feed-down corrected in all systems

**PRELIMINARY**

- Closer look at baseline: p+p and d+Au

## √sNN=62.4 GeV Au+Au: spectra 

- Three centrality bins defined at the moment
- Large proton content at intermediate pT
- The familiar 200 GeV picture reemerges
- Antiprotons though are not as copiously produced as in the higher energy case

**0-10%**

**10-30%**

**30-60%**

## Proton to Pion ratio at 62.4 GeV

**Proton to Pion ratio at 62.4 GeV**

- Significantly enhanced proton to pion ratio > 1
- Notice: protons and antiprotons are not     feed-down corrected
- Smaller antiproton to   pion ratio ~0.7    compared to the 200 GeV data
- Indicates more baryon transport at 62.4 GeV   and less p-pbar pair creation
- Weaker centrality dependence for both  ratios compared to the higher collision energy

## Antimatter/Matter at 62.4 GeV

**Antimatter/Matter at 62.4 GeV**

- Flat pT dependence for all ratios
- Same picture as in 200 GeV data
- Smaller antiproton/proton ratio

_**Particle ratios (Central 0-10%) **_**PHENIX Preliminary**
- -/+ = 1.097  0.022 (stat.)  0.063 (sys.)
- K-/K+ = 0.816  0.027 (stat.)  0.046 (sys.)
- pbar/p = 0.495 0.012 (stat.)  0.029 (sys.)

**√****s****NN****=200 GeV**

## Centrality dependence of particle ratios

**Centrality dependence of particle ratios**

- Antimatter/Matter ratios are flat with centrality.
- K/ increases as a function of centrality.
- p/+ small increase.
- pbar/- independent of centrality.

_**Ratios (Central 0-10%): **_**PHENIX Preliminary**
- K+/+ = 0.199  0.003 (stat.)  0.010 (sys.)
- K-/- = 0.148  0.005 (stat.)  0.008 (sys.)
- p/ = 0.156  0.002 (stat.)  0.008 (sys.)
- pbar/ = 0.070 0.002 (stat.)  0.004 (sys.)

## Antibaryon/ baryon ratios vs. √sNN at mid-rapidity

- Smooth excitation function from SPS to RHIC
- Consistent with bar/ (STAR preliminary) at 62.4 GeV

***Experimental Data:***** **
**AGS:**
-  E802, 2650 PRL 83, (1998)
**SPS:**
-  NA44: PRC 66, 044907 (2002)
-  NA49: J. of Phys. G 30, S357 (2004)
**RHIC:**
-  PHENIX
- 62 GeV (preliminary, no feed-down)
- PRL 88, 242301 (2002), PRC 69, 034909 (2003), PRL 89 092302 (2002).
-  STAR
- 62 GeV (Preliminary, HQ2004); 130 GeV PRL  89, 092301 (2002).

## Summary and Conclusions

- Variations on a theme: Identified particle production in Relativistic Heavy Ion Collisions at RHIC.
- p+p and d+Au data at the same energy as the “discovery energy” at RHIC, √sNN = 200 GeV.
- Establish the baseline spectra.
- Sizeable Cronin effect for the protons and antiprotons in d+Au, in lesser degree for pions and Ncoll scaling for kaons.
- No suppression observed at intermediate pT.
- Recombination in d+Au or initial multiple scattering ?
- Baryon anomaly is clearly a final state effect.
- Identified nuclear modification factors in Au+Au.
- Remarkable scaling of protons and antiprotons.
- Au+Au at √sNN=62.4 GeV.
- Large proton contribution persists.
- Antiproton production is reduced compared to the 200 GeV data.
- Smooth transition from SPS to RHIC of baryon production.

## Backup slides

## -/+ and K-/K+ vs. pT at 200 GeV Au+Au 

- For each of these particle species and centralities, the particle ratios are constant within the experimental errors over the measured pT range.

## Particle Ratio vs. Npart at 200 GeV Au+Au 

-  Ratios for equal mass particle are  independent of Npart.
-  K/ : increase rapidly for peripheral and then saturate (or rise slowly to central).
-  p/ : similar to these of K/.

## Centrality determination in d+Au

- Centrality determination in d+Au is done with the South BBC (Au-side).
- Assumption: BBC signal is proportional to participating Au nucleons.
- Glauber Model calculation and BBC simulation response, map the BBCS signal to impact parameter distributions.
- Corresponding Ncoll distributions in d+Au are then used to define the nuclear modification factors.

## Recombination in d+Au and Au+Au

- Au+Au