# Presentation: 000321

## Identified particle spectra from pp, dA and AA collisions

- Julia Velkovska

- Quark Matter 2004
- January 15

## Outline

**This talk focuses on:**
**Identified particles**
**Mid-rapidity**
**Intermediate p****T**
**Results not covered in this talk:**
**PHOBOS: Important measurement at very low m****T ****from AuAu + broad momentum range ********K,p dAu spectra**
**Talk by G.Veres**
**BRAHMS – broad momentum range ********K,p**** spectra measured vs rapidity (AuAu and dAu)**
**Talks by D. Ourdane, Z. Yin **

## Motivation: the baryon “anomaly”

**Peripheral: consistent **
**with standard fragmentation**
**Central: a factor ~ 3 higher than peripheral, e****+****e****- ****and ISR pp data**

**Pions**** are ****suppressed**** at high pT in central Au+Au collisions**
**No apparent proton suppression**** for 2-4 GeV/c **
**different production mechanism ?**

- _[Phys. Rev. ](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000017172301000001&idtype=cvips&gifs=yes)__[Lett](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000017172301000001&idtype=cvips&gifs=yes)__[ 91, 172301](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000017172301000001&idtype=cvips&gifs=yes)__[ ](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000017172301000001&idtype=cvips&gifs=yes)__[(2003)](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000017172301000001&idtype=cvips&gifs=yes)_*.** *

## Start “simple”: pions in p+p collisions

**pp @200 GeV**

**hard scattering:**
**power-law “tail”**

- soft production:
- exponential

- preliminary

**Charged pion data:**
**Poster M.Harvey**

## pQCD description in pp

**pQCD calculations work**
**Note: **
**fragmentation function**
**input from experiment**
** **

**Soft to hard transition in**  **p/********ratio**

- _[Phys. Rev. ](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000024241803000001&idtype=cvips&gifs=Yes&jsessionid=1102141073512399685)__[Lett](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000024241803000001&idtype=cvips&gifs=Yes&jsessionid=1102141073512399685)__[. 91, 241803 (2003) ](http://ojps.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000091000024241803000001&idtype=cvips&gifs=Yes&jsessionid=1102141073512399685)_*.*** **

## Nuclear modifications: Soft physics

**Collective radial flow described by hydrodynamics from 20AGeV PbPb**
**to top RHIC energy**

**NA49**

**NA57**

- STAR

## Nuclear modifications to hard scattering

**Large Cronin**
**effect at SPS**
**and ****ISR**
**Suppression at RHIC**

**Is the suppression due to the medium?**
**(initial or final state effect?)**

## The null result on the cover of PRL: dAu

**The suppression**
**of hadrons at **
**mid-rapidity is due to the medium**
**produced in the **
**collisions.**
**(final state)**

## But what happens to the protons ?

**Can Cronin effect produce the enhanced p/******** ratio in AuAu ?**
**What is Cronin effect? Theorists seem to agree: **
**“****Initial state multiple scattering leading to pt broadening.”**
**Why is it different for protons and pions ?**
**“****Nobody really knows.”**

- P.B.Straub et al., Phys.Rev.Lett., **68**,452(1992)

- P.B. Straub et al., PRL 68 (1992)
- FNAL experiments measuring R (W / Be)
- for identified particles at sqrt(s) of 27.4 and 51.3 GeV.

## Cronin effect for protons and pions

**Protons exhibit stronger Cronin enhancement**
**Not enough to account for**
** ****factor of 3 increase**
**of p/********in central AuAu**

## Does strangeness “matter” ?

**Does Cronin enhancement depend on strangeness content ? Compare p and ******

**Talk: D. Kotchetkov: Friday,Parallel 2**
**Poster: A. Taranenko**

## Cronin effect for pions at high pt

**The effect disappears at high pt**

**Poster by J.Jia**

## Centrality dependence of Cronin effect

**Similar centrality dependence for all particle species**
**Enhancement grows with Ncoll and tends to saturate **
**See Talk by Felix Mathatias : Parallel 1,Thursday**

## Cronin effect summary

**Mass dependence: **
****** ****< p ~ ******
**or is it baryon/meson ?**
**Flavor depdendence:**
**Does not depend on strangeness content: p ~ ******
**Centrality dependence: **
**Increases with Ncoll**
**Tends to saturate**
**Pt depdendence:**
**Limited to pt <8 GeV/c**
**Seems insufficient to explain the mid-pt baryon enhancement in AuAu **

## Strange baryon/meson ratios

**The mid-pT anomaly not unique to p/******
******K****0****s********has a peak at ~ 3GeV/c**
**Height depends on centrality**
**Peripheral – above pp**
**data **

## The proton “bump” in the h/ ratios

- The proton “bump” in the h/ ratios

- Expectation (pp, e+e-): **h/******** ******** 1.6**
- Above 5 GeV/c
- and in peripheral
- collisions: recover standard fragmentation

- Au+Au @ 200AGeV

- nucl-ex/0310005

**Talk: C.Klein-Boesing**

## Hydro + Jet Model

**Hydro + Jet Model**

- Hirano, Nara nucl-th/0307015

** **Hydrodynamics can describe the spectra up to ~ 2 GeV/c.
-  **Jet contributions > 2 GeV/c.**
-  Needed detailed comparison with data (e.g. centrality dependence) .
**Proton enhancement (with respect to the pions) is a mass effect.**

## Coalescence/recombination models

**Coalescence/recombination models**

- Fries et al: Phys.Rev. C68 (2003) 044902

- Greco, Ko, Levai: Phys.Rev.Lett. 90 (2003) 202302

- describe particle ratios and spectra:
**p****T****(baryons)**** ****>p****T****(mesons)>p****T****(quarks)****  **

- Hwa & Yang
- nucl-th/0401001

## Another non-perturbative mechanism: Baryon junctions

- Vitev, Gyulassy
- PRC 65, 041902, 2002

**Baryon Junction**

**Predicted centrality **
**dependence of p/********ratio**
**and anti-baryon/baryon**
**ratio**

**Notes:**
BJ: it invokes a topological gluon configuration with jet quenching. 
gluon junctions produce copious baryons at intermediate pT (pion is suppressed by jet quenching). 
Parton recombination : the competition between recombination and fragmentation of partons. 

## Centrality scaling of mesons and baryons:

**N****coll ****errors**
**correlated**

- 12% syst. error
- uncorrelated

**Line at 0.62**
**fit to ********data**

- Difference between RCP of p+p and 
- beyond the systematic  error

## Compare  scaling across experiments

**Remarkable agreement between PHENIX and STAR**

## The meson: high-pt comparison with 

**Adding ******** into the mix: agrees with ************ within errors**

**Phenix preliminary AuAu @200GeV**

**poster S.Mioduszewski : High pT 8**

## Centrality scaling of mesons and baryons :

**Compilation of R****cp ****results from STAR**
**follows baryon/meson distinction (independent of mass)**** **

**Talk byM.Lamont**
**Tuesday, Parallel 1**

**Baryons and mesons are different **

**Do soft and hard partons recombine, or is it just soft+soft ?**
**Explore correlations with leading**
**baryons and mesons **

## Do mid-pT baryons have jet-like correlations ?

**Do mid-p****T ****baryons have jet-like correlations ?**

** ****jet partner equally likely for trigger baryons & mesons **
** ****no significant decrease with centrality! **

**See talk by Anne**
**Sickles: Friday Parallel 1**

## Conclusions

**Intermediate p****T ****with distinct baryon dynamics from AuAu data**
**Cronin effect shows (weak) mass dependence: **
**Is it enough to explain the large p/******** ratio in AuAu ?**
**Need better theoretical understanding**
**The suppression/non-suppression at mid-p****T**** follows baryon/meson lines (not mass effect)**
**Mid-p****T ****leading baryons show jet-like correlations**
**Soft-soft recombination models excluded**
**Need to recombine hard-soft **

## Experimental Outlook

**The RHIC experiments are taking AuAu data (as I speak)**
**High statistics run: **
**Expect much smaller error bars on the singles measurements**
**Expand  (with enough statistics) v2 and correlation mesurements **
**Provide data that will help in understanding the hadronization process**

**EXTRA**

## System size dependence of p/ ratio

**Peripheral AuAu and dAu agree**
**pp data ~ 25% lower :**
**different Cronin enhancement for protons and pions**

**Caveat: (anti)proton data not feed-down corrected**
** **

## RAA for 0 and charged hadron

**PHENIX AuAu 200 GeV**
- 0 data: PRL 91 072301 (2003), nucl-ex/0304022.
- charged hadron (preliminary) : NPA715, 769c (2003).

## p/p ratio vs. pT

**Minimum bias**

**Baryon **
**Junction**

**pQCD**

- Constant within the experimental errors

- Vitev, Gyulassy
- NPA 715, 779c (2003)