# Presentation: 936206

## Simple measurements with GREAT impact  :  Nuclear Modification Factors

- Camelia Mironov
- Kent State University

## Slide 2

## Is A+A just a ‘bunch’ of ‘p+p’?

**Initial**

**Final**

**p+p**

**A+A**

## pQCD particle production: p+p (pT>2GeV/c)

**a**

**b**

**c**

**d**

**Initial**

**Final**

**p**

**p**

## pQCD particle production: Au+Au (pT>2GeV/c)

**Initial**

**Final**

**leading particle suppressed**

## Au+Au  vs.  p+p

**Au+Au **: initial +final state effects                                            **pp **      : ‘simple’

-  We NEED ALSO A collision system *to disentangle* the initial-final states effects
-             p (d) + Au – ‘no final state effects’

## pQCD particle production: d+Au (pT>2GeV/c)

**Initial**

**Final**

**Parton Distribution Functions**

**Intrinsic kT**

**PDF Modification ****(shadowing)**

**Fragmentation Function**

## Quantify deviations of A+A from p+p ?

- !!! Simplest: divide AA spectra to pp spectra!!!!  
**NUCLEAR MODIFICATION FACTORS**

## Quantify deviations of A+A from p+p

**NUCLEAR MODIFICATION FACTORS**

- ASSUMPTION:  both ratios exhibit the same behavior because of the same underlying physics

## 	Information via RXX

-                  R ~1 -- no nuclear effects:A+B = C * (p+p)
-  deviation from 1 indicate presence of nuclear effects:
-                  R>1 enhancement (usual explanation: soft scatters before hard collision)
-                 R<1 suppression (energy loss in dense medium)

## Nuclear modification factors for           h+-

## RAA/RCP: h±

*Charged Hadrons:*
-  Au + Au : RCP and RAA ~ suppression
-  d + Au   : RCP and RdA ~ enhancement (Cronin effect – experimental observation and not the explanation)  initial effects ‘not responsible’ for AuAu suppression

**R****AA ****& R****dA**

**R****CP**

**dAu**

**dAu**

**AuAu**

**AuAu**

## Theory: RAA for h+-

- STAR, nucl-ex/0305015

- pQCD + Shadowing + Cronin

- pQCD + Shadowing + Cronin + Energy Loss

- factor ~5
- suppression

- pQCD + initial state effects

- pQCD + initial+final state effects

- Theory: RAA for h+-

-  pQCD+final (energy loss) + initial (Cronin+shadowing) describes data  dense medium created in central AuAu !!!!!

## Final state hadronic rescattering?

-  Final hadrons with moderate pT could be fully established inside the late stage of the hadronic fireball  interaction with the bulk hadronic matter suppression

- NOT (entirely)!

## Conclusions from h+- 

-  RAA, RdA and RCP give same information
-  Au+Au suppression can NOT be explained entirely by ..:
-                      hadronic rescattering
-                      initial state effects

## Identified hadrons ...

- (dss) 1321 (MeV/c2)

- Λ(uds) 1116  (MeV/c2)

- (sss)  1673(MeV/c2)

- K(us) 494(MeV/c2)

- K0s(ds) 498(MeV/c2)

- (ss) 1020(MeV/c2)

- p + p     d + Au    Au + Au

- Do all these particles have  anything extra to add to what
- unidentified charged hadrons revealed already?

## Nuclear Modification Factors for K, Φ, π, Λ, Ξ, p ...

## RCP: identified hadrons

***Baryons ****suppressed****  *****~ 2.5GeV/c**
***Mesons*****  ***suppressed  ***~ 1.5GeV/c**

## Au + Au: Theory explain RCP...

- Topor-Pop, Gyulassy, Barrette, Gale, Wang, Xu   nucl-th/0407095

**HIJING/BBv2.0**: HIJING + jet quenching + shadowing +
-                                  baryon junction + strong color field effects

-  additional production mechanism for baryons (junctions)

## RCP Theory

***Reco***** for ****K0s**** and ****Λ****+****Λ****bar**** **
**Central(b=3fm) / Peripheral (b=12fm)**

## RAuAu: identified hadrons

- Mesons *suppressed*
- Baryons *enhanced*
-                                       AND
**           ****maxR****AA****p(uud)****<maxR****AA****Λ****(uds)****<maxR****AA****Ξ****(dss)**

## RAuAuTheory ...

- Topor-Pop (private comunication and nucl-th/0407095)

-  Experimental pattern reproduced

## d+Au: identified hadrons

** ****both ratio present enhancement compared to binary scaling**
** ****similar to AA, there seem to be a  difference between ****mesons and baryons **
** ****also R****dA**** (baryons) > R****CP ****(baryons) (error bars)**

**R****CP**

## To explain... 

- _1. Kopeliovich, Nemchik, Schafer, Tarasov – Phys. Rev. Lett. 88(2002) 232303_
- _2. Vitev, Gyulassy – Phys. Rev. Lett. 89 (2002) 252301_
- _3. X.N. Wang – Phys. Rev. C 61(2000) 064910_
- _4. Accardi, Trelani –Phys. Rev. D 64(2001) 116004_
- _5. Zhang, Fai, Papp, Bernafoldi, Levai – Phys. Rev. C 65(2002) 034903_

- Rescatterings (projectile hadron or its partons) PRIOR to the hard collision cause a broadening of the pT  spectrum

- 1.Hwa, Yang  nucl-th/0404066 ***Recombination model (Oregon)***

- FINAL STATE recombination of partons determine the enhancement of the nuclear modification factor

## RdA/RCP(d+Au): theory and experiment

##  Do we understand the baseline anyway?

-  2 different hadronization describe data
-  RCP suppression BUT when ratio to p+p (RAA) enhancement for strange baryons
-  DO WE UNDERSTAND THE BASELINE (p+p)?

## Conclusions from identified hadrons

- RAB/RCP HAS TO BE TREATED SEPARATELLY (at least until an explanation/scaling for the RAB strangeness ordering is found)
- Au+Au, d+Au:  difference between mesons and baryons in the intermediate pT region
-  models assuming different hadronization scenarios, qualitatively describe data  need other probes

## Other probes to answer the questions

- Looking at near side - hadronization mechanisms
- Looking at the away side  medium properties.
-  And the scene is set for the next (experimental) talks!

- DO JET ANALYSIS with identified particles
-  in p+p, d+A and A+A
-  trigger on mesons and baryons
-  trigger on strange and non-strange baryons and meson

## Just_in_Case plots

## Hadronization ReCo(Oregon)...

*********Mesons (qq)*** :

- Recombination function known from recombination model
-  Hwa, Phys. Rev. D (1980).

## To explain...