Baryon/Meson Baryon/Meson Ratios for Ratios for

Intermediate pIntermediate pTT

Eun-Joo KimEun-Joo Kim

University of Kansas University of Kansas

For the BRAHMS For the BRAHMS collaborationcollaboration

October 27-30 APS/DNP 2004 Eun-Joo Kim

In pQCD approach, p/ ratios at high pT are determined by the fragmentation of energetic partons, independent of the initial colliding systems. However… The clear increase in p/ ratios from peripheral to central collisions is observed. Rcp for p, pbar is close to 1 below 4GeV/c, while it is about 0.3 for pions.

MotivationMotivationPRC69(2004)034909

At pT > 1.5GeV/c, ratios are from p/0

Baryon Anomaly at RHIC

(0-10%)/(60-92%)

October 27-30 APS/DNP 2004 Eun-Joo Kim

Theoretical ModelsTheoretical Models

V. Greco et al. (TAMU) PRL90(2003)202302, PRC68(2003)034904 added assumption that soft partons in QGP can coalesce with comoving hard partons from a mini-jet.

R. Hwa et al. (Oregon)PRC70(2004)024904, PRC67(2003)034902

replaces fragmentation functions by a scenario where mini-jet partons develop a shower which subsequently recombines, i.e. recombination of soft partons with shower partons.

Parton CoalescenceParton Coalescence

PHENIX p/ ratio (0-10% central)

R.J. Fries et al. (Duke)PRL90(2003)202303, PRC68(2003) 044902- recombination dominates over fragmentation for an exponentially falling parton spectrum, but the fragmentation wins out, when the spectrum takes the form of a power law.- strictly separates soft and hard physics, allowing only the soft partons to recombine and only the hard partons to fragment.

ReCombinationReCombination

October 27-30 APS/DNP 2004 Eun-Joo Kim

New for Run IV

AuAu sNN=200GeV MRS 90o, 40o, 45o

20% data only processed!

October 27-30 APS/DNP 2004 Eun-Joo Kim

C4 performanceC4 performance

October 27-30 APS/DNP 2004 Eun-Joo Kim

C4 EfficiencyC4 Efficiency

October 27-30 APS/DNP 2004 Eun-Joo Kim

PID at TFW2PID at TFW2

October 27-30 APS/DNP 2004 Eun-Joo Kim

ppTT Spectra : Spectra : BRAHMS Preliminary

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We are still working on…

October 27-30 APS/DNP 2004 Eun-Joo Kim

ppTT Spectra : p, pbar Spectra : p, pbarBRAHMS Preliminary

We are still working on…

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October 27-30 APS/DNP 2004 Eun-Joo Kim

--//++, pbar/p ratios, pbar/p ratios

No significant pT dependence up to 3GeV/c Similar behavior at y~0 and y~1

BRAHMS Preliminary

October 27-30 APS/DNP 2004 Eun-Joo Kim

p/p/ ratios ratios

Greco et.al.,PRL90(2003)202302

Hwa et.al, PRC70(2004)024905

p/ ratios increase with pT up to 3GeV/c. feed down correction applied.

BRAHMS Preliminary

October 27-30 APS/DNP 2004 Eun-Joo Kim

Summary Summary && Outlook Outlook The new BRAHMS Cherenkov detector functions well at

high pT, and we are currently working on the efficiency and background estimates.

With upgraded Cherenkov and Time-of-Flight detectors, BRAHMS has measured the identified hadron transverse momentum spectra and particle ratios up to 4GeV/c.

With our complete data (a factor 5 increase), BRAHMS can extend the pT coverages up to 5-6 GeV/c at y~0.

p/ ratios increase with pT up to 3GeV/c. Striking similarity between y~0 and y~1. The recombination and parton coalescence models seem

to give reasonable explanation of the data at intermediate pT.