# Presentation: 183530

## STAR identified particle measurements at high transverse momentum in p+p at sNN = 200 GeV

**Mark Heinz**
**Yale University**
-  *for the STAR Collaboration*

-  Motivation
-  STAR experiment
-  Results
-  PT-Spectra compared to NLO results
-  Quark vs Gluon jets
-  Particle ratios vs PYTHIA
- Conclusions

- DIS 2007, Munich

- mark.heinz@yale.edu

## Perturbative QCD Ansatz

- DIS 2007, Munich

- mark.heinz@yale.edu

## Universality of Fragmentation functions

- Suggested by Kniehl, Kramer & Poetter : _*Nucl.Phys.B597(2001) *_
- Experimental data from different collisions systems have been fit with the same fragmentation function (FF)
- Nevertheless the constraint on Gluon FF is much worse than for light quarks, and similar to heavy quark FF.

- Fragmentation function for Quarks

_***KKP, Nucl.Phys.B582(2000)***__* *_

**OPAL ********s=91.2 GeV**

**uds-quark**

**c-quark**

**b-quark**

**all**

- Fragmentation function for Gluons

***Large uncertainties remain for the gluon distributions & fragmentation functions ***

- Parton Dist function for Gluons

- DIS 2007, Munich

- mark.heinz@yale.edu

## STAR experiment - Detectors

- Time-Of-Flight (–1.0 < < 0
- and/30 in )

- Time projection Chamber (TPC)
- (||<1.8, full  and 4.2 m long)

- DIS 2007, Munich

- mark.heinz@yale.edu

## Particle Identification

- Weak decay vertices (strange particles):
- Charged daughters identified by dE/dx
- Relativistic Rise dE/dx:
- Identify high pt ,k, p for momenta of: 3 < p < 10 GeV/c

- K0S  - + +

- Ξ-  - + Λ

- Λ   p  +  -

- Ω-  K-+ Λ

- Separation: p (K,p) separation: 2s

- DIS 2007, Munich

- mark.heinz@yale.edu

## Transverse Momentum Spectra

_*STAR, PLB 637 (2006) 161*_

- pT spectra for protons and pions up to 10 GeV/c and strange particles up to 5 GeV/c

- Momentum pT (GeV/c)

- _STAR (nucl-ex/0607033) accepted by Phys Rev C_

- Fitted curves to data are Levy-functions

- DIS 2007, Munich

- mark.heinz@yale.edu

## Understanding the p+p collisions

***NLO pQCD*** calculations with ***Kretzer ***FF **inconsistent** with data at midrapidity

_**S. Kretzer, Phys. Rev. D 62 (2000) 054001**_

_**STAR, PLB 637 (2006) 161**_

- Sensitivity to choice of fragmentation function (FF)

- _SPIN2006,hep-ex/0612004 _

- 0

- DIS 2007, Munich

- mark.heinz@yale.edu

## Sensitivity to gluon contribution of FF

**NLO pQCD calculations by W. Vogelsang**

***NLO pQCD*** calculations with ***KKP FF*** are **consistent** with pion data  at **high p****T**** (> 2 GeV/c)**
- They are **inconsistent** with the **proton+anti-proton** data

- KKP : B. A. Kniehl, G. Kraner and B. Potter,
-  Nucl. Phys. B  597 (2001) 337

- Difference between KKP and Kretzer FF is the way g
- g fragmentation is more in KKP

_**STAR, Phys Lett B, 637 (2006) 161**_

- (KKP-Kretzer)/Kretzer

- Gluons
- Light quarks

- DIS 2007, Munich

- mark.heinz@yale.edu

## Uncertainties in FF

- Recent compilation and error analysis of available fragmentation functions by (KKP,Kretzer, AKK) by Hirai et al. (_hep-ph/0702250_)

- Pions

- Protons

- DIS 2007, Munich

- mark.heinz@yale.edu

## Light flavor separated FF

***NLO pQCD*** calculations with
***AKK FF***  are **consistent** with pion data at **high p****T**** (> 2 GeV/c)**

- NLO pQCD calculations with ***AKK FF  *****compares relatively better than *****KKP  ***for the **p+********p data**
****** ****AKK **differ from ***KKP*****,** in the way the **light flavor FF** are obtained
- from the light flavor separated measurements in e+e- collisions by OPAL

- _AKK : S. Albino, B. A. Kniehl, and B. Potter,_
- _ __Nucl. Phys. B  725 (2005) 181_

- _OPAL: Eur. Phys. J. C 16 (2000) 407_

- DIS 2007, Munich

- mark.heinz@yale.edu

## What about strange particles ?

**NLO pQCD** calculations with **AKK FF*****  *****compares relatively better than *****KKP  ***for the strange particle data
- Lambda **gluon FF** was constrained using STAR data

**Calculations by W.Vogelsang (BNL)**
**AKK : S. Albino, B. A. Kniehl, and B. Potter,**
** ****Nucl. Phys. B  725 (2005) 181**

**STAR (nucl-ex/0607033) accepted for **
**Publication in Phys Rev C**

- DIS 2007, Munich

- mark.heinz@yale.edu

## 0 production at forward rapidity 

- Inclusive forward p0 production in p+p collisions at 200 GeV consistent with NLO pQCD calculations
- At small h, data consistent with KKP, as h increases data approaches cal. with Kretzer  set of FF

_*STAR, Phys.Rev.Lett.97,152302 (2006)*_

**probing the initial gluon densities**

- DIS 2007, Munich

- mark.heinz@yale.edu

## Gluon Jets Vs. Quark Jets

- Gluon jet contribution to protons is significantly larger than to pions at high pT in p+p collisions at RHIC.

- DIS 2007, Munich

- mark.heinz@yale.edu

## mT-scaling

- STAR data shows baryon-meson splitting, hence supports dominance of gluon jets at RHIC

- In PYTHIA gluon jets produce baryon-meson splitting whereas quark jets produce mass splitting.

**Gluon jet                     Quark jet**

- _PYTHIA 6.3_

- DIS 2007, Munich

- mark.heinz@yale.edu

## xT-Scaling 

- n ~ 4 for basic scattering process
- n ~ 5-8 depending on evolution of structure function and fragmentation function (as seen in data)
-  Suggests transition from soft/hard processes ~pT=2GeV

- _STAR, Phys Lett B, 637 (2006) 161_

-  e+ e- collisions

-  p+p / p+p collisions

- 

- K

- p

- xT = 2pT/s

- _TPC, PRL 61(1988)_
- _ALEPH,ZPC66(1995)_
- _ARGUS,ZPC44(1989)_

- Cross-section are multiplied by (sNN )2 factor

** ****n~6.5**

- DIS 2007, Munich

- mark.heinz@yale.edu

## Particle Ratios – PYTHIA comparison

**PYTHIA***** ***
-  predicts a more prominent ***p******T*** dependence for**p/p** and a flat dependence at high pT for ****************
-  predicts an even stronger dependence forCurrent data does not allow to conclude, but is consistent with gluon jet dominated production.

_**STAR, Phys Lett B, 637 (2006) 161**_

- _STAR (nucl-ex/0607033)_

- DIS 2007, Munich

- mark.heinz@yale.edu

## Baryon-meson ratios

- Gluon Jets will produce a larger Baryon/Meson ratio than quark-jets in the region of interest
- PYTHIA cannot describe Baryon-Meson ratio at intermediate pT even with tuned K-factors. In addition di-quark probabilities need to be tuned.

- PYTHIA also under-predicts the Baryon-meson ratio other energies:
- /K0 UA1, s= 630 GeV
- p/ at ISR and FNAL: 19-53 GeV

_**STAR (nucl-ex/0607033)**_

_**STAR, Phys Lett B, 637 (2006) 161**_

******s=630 GeV**

******s=200 GeV**

- DIS 2007, Munich

- mark.heinz@yale.edu

## Conclusions

- NLO pQCD describes the proton and  pT spectrum for the _first time_ in p+p collisions
- Importance of the significant improvement of FF for baryons and strange particles from the light-flavor separated measurements in e+e- collisions (OPAL)
- Neutral pion pT spectra at forward rapidity provides unique data to study pQCD processes and understand the gluon vs. quark jet contributions
- mT-scaling together with xT scaling in p+p collisions shows that the dominance of hard process (related to PDF and FF) over soft process for minbias collisions starts at pT ~ 2 GeV/c
- Splitting of high baryon-meson mT spectra confirms gluon jet dominance at RHIC
- Anti-particle to particle ratio is show little dependence to pT for the studied pT range again indicating gluon jet dominance at RHIC for these processes
- Baryon-to-meson ratios not well reproduced by LO pQCD (PYTHIA), over a broad range of energies in p+p collisions

- DIS 2007, Munich

- mark.heinz@yale.edu

**U.S. Labs:****   ****	**
**	****Argonne,  Lawrence Berkeley,  and Brookhaven National Labs**
**U.S. Universities:****    **
**	****UC Berkeley, UC Davis,  UCLA,  Caltech, Carnegie Mellon, UIC,**
**	****Creighton,  Indiana, Kent State, MIT, MSU,  CCNY, Ohio State, Penn State,  Purdue,  Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale**
**Brazil:****	****    **
**	****Universidade de Sao Paulo**
**China:****	****    **
**	****IHEP - Beijing, IPP - Wuhan, USTC,**
**	****Tsinghua, SINAP, IMP Lanzhou**
**Croatia:****	****    **
**	**** ****Zagreb University**
**Czech Republic:****	****    **
**	**** ****Nuclear Physics Institute**

**England:**
**	****University of Birmingham**
**France:****     **
**	****Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes**
**Germany:****  **
**	****Max Planck Institute – Munich University of Frankfurt**
**India:**
**	****Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC****	**
**Netherlands:**
**	****NIKHEF/Utrecht**
**Poland:**
**	****Warsaw University of Technology**
**Russia:****  **
**	****MEPHI – Moscow,  LPP/LHE JINR – Dubna,  IHEP – Protvino**
**South Korea:**
**	****Pusan National University**** **

*STAR Collaboration*

- DIS 2007, Munich

- mark.heinz@yale.edu

## Backups

- DIS 2007, Munich

- mark.heinz@yale.edu

- DIS 2007, Munich

- mark.heinz@yale.edu