identified baryon and meson spectra at intermediate and high p t in 200 gev au+au collisions

22
03/14/2006 WWND2006 at La Jolla 1 Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions Outline: Motivation Intermediate p T particle production mechanism at mid-rapidity High p T charged & p spectra up to 12 GeV/c from STAR R CP , particle ratios Summary and Outlook Lijuan Ruan (for the STAR Collaboration) (Lawrence Berkeley National Laboratory)

Upload: curry

Post on 13-Jan-2016

48 views

Category:

Documents


0 download

DESCRIPTION

Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions. L ijuan Ruan (for the STAR Collaboration) ( Lawrence Berkeley National Laboratory ). Outline: Motivation Intermediate p T  particle production mechanism at mid-rapidity High p T - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 1

Identified baryon and meson spectra at intermediate and high pT in 200 GeV Au+Au Collisions

Outline:• Motivation• Intermediate pT

particle production mechanism at mid-rapidity

• High pT charged & p spectra up to 12 GeV/c from STAR

RCP, particle ratios

• Summary and Outlook

Lijuan Ruan (for the STAR Collaboration)(Lawrence Berkeley National Laboratory)

Page 2: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 2

Particle production at pT>2 GeV/c in p+p collisions

Convolution of PDFpQCDFF

PDF (parton distribution function): derived from e-h deep inelastic scattering.

pQCD (parton-parton interaction cross section from pQCD calculation)

FF (fragmentation function): derived from e+e- collisions.

Page 3: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 3

p+p collisions and pQCD (AKK)

NLO pQCD calculations withAKK FF are consistent with pion data at high pT (> 2 GeV/c)

NLO pQCD calculations onlywith AKK FF (Nucl.Phys.B725:181-206,2005)consistent with the p+pbar data

AKK differ from KKP, in the way the light flavor FF are

obtainedOPAL Collaboration : Eur. Phys. J. C 17

(2000) 207STAR Collaboration, nucl-ex/0601033

Page 4: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 4

from p+p Au+Au collisions

Soft particle production region: pT<2 GeV/c

Hard particle production region: pT>2 GeV/c, which can be described by NLO pQCD calculations.

pQCD approach p/ ratio <<1 due to D(q->p)/D(q->)<<1.

At low energy, pbar/p (pbar/) ratio< 0.1, consistent with very low anti-baryon production from quark jets.

Hot, dense, strongly interacting matter created

p(pbar)/>=1 at pT=2 GeV/c, which cannot be reproduced by pQCD approach.

Intrigue a lot of study for particle production mechanism: hydrodynamic, recombination/coalescence, gluon junction

The medium pushes the soft particle production region up to higher pT.

p + p collisions Au + Au collisions

Page 5: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 5

hydro+jet: Interplay between Soft and Hard

NSOFT~NHARD

ppTT

(1/

(1/ ppTT)

()(dNdN

// dpdpTT))

HydrodynamicHydrodynamicafterburnerafterburner

JetJetquenchingquenching

Interesting regionIntermediate pT

(2<pT<3.5 GeV/c)Pion hard, Proton soft

T.Hirano & Y.Nara(’03), PRC69(2004)034908

Crossing pCrossing pTT moves movestoward high ptoward high pTT

softhard

Au+Au at b=2 fm

PT, cross~ 1.8 GeV/c for

2.7 GeV/c for K3.7 GeV/c for p

Page 6: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 6

Consequence from hadron species dependent pT,cross

Hydro+JetT.Hirano & Y.Nara(’03), PRC69(2004)034908

Page 7: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 7

Recombination models

Recombination models predict that a scale according to the number of constituent quarks in a hadron seems to govern the particle production at intermediate pT.

R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003).R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004).V. Greco, et al., Phys. Rev. C 68, 034904(2003).

Recombination models:

Page 8: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 8

Centrality Dependence: Rcp in Au+Au

Baryons (p, ) increase faster than mesons (, Ks, K) from peripheral to central collisions. consistent with the coalescence of constituent quarks at hadronization from a collective partonic system.

STAR: Phys. Rev. Lett. 92 (2004) 052302PHENIX: Phys. Rev. Lett. 91 (2003) 172301

Page 9: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 9

Centrality Dependence: Rcp in Au+Au

Two groups (2<pT<6GeV/c):

- , Ks, K, K*, Φ mesons

- p, Λ, Ξ, Ω baryons

STAR: Nucl. Phys. A 757 (2005) 102

X. Cai QM05, STAR Preliminary

Page 10: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 10

From intermediate pT high pT region

• The interplay between soft and hard plays an important role for particle production at intermediate pT.

• The RCP shows baryon/meson difference.

• No precise measurements of identified baryon and meson spectra at high pT (pT>6 GeV/c).

The high pT PID spectra will be presented to address

• The transition between coalescence and jet fragmentation.

• Possible color charge dependence of energy loss (g/q)

Page 11: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 11

g/q jet contribution to particle production

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

Page 12: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 12

Color charge dependence of energy loss

X.N. Wang: PRC58(2321)1998.

PID spectra, centrality dependence of pbar/p and pbar/ ratios, address the color charge dependence of energy lossTo further understand how the gluon jet/quark jet interact with the medium created in Au+Au. collisions.

Page 13: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 13

STAR Detector: TPC & MRPC-TOF

A new technology ----Multi-gap Resistive Plate Chamber (MRPC)

adopted from CERN-Alice.

A prototype detector of time-of-flight (TOF) was installed in year4Intrinsic timing resolution: 85 ps in STAR.

• RHIC run4 (2004) 200 GeV Au+Au data

• ~14 M minbias events

after |z_vertex|<30cm

• ~7.8 M TOF matched events

Page 14: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 14

Spectra

STAR Preliminary

Page 15: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 15

Nuclear Modification Factors RCP

In central Au+Au collisions:

• At 4<pT<12 GeV/c, both and p are strongly suppressed in RCP.

• At 1.5<pT<7 GeV/c, RCP(p+pbar) > RCP() , RCP(p+pbar) shows obvious decreasing trend, not consistent with the binary scaling at intermediate pT.

I. Vitev, nucl-ex/0603010.

STAR Preliminary

Page 16: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 16

Anti-particle to particle ratios

1. -/+ are consistent with flat at unity in all pT, no significant centrality dependence.

2. pbar/p ratio: no significant centrality dependence, not consistent with the jet quenching prediction (X.N. Wang, PRC 58 (2321) 1998).

STAR Preliminary

Page 17: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 17

Proton over pion ratios

1. The p(pbar)/ ratios in Au+Au collisions show strong centrality dependence. 2. In central Au+Au collisions, the p(pbar)/ ratios reach maximum value at pT~2-

3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>5 GeV/c.

R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).

STAR Preliminary

Page 18: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 18

Discussion

• In Au+Au collisions, at pT>6 GeV/c: RCP(p+pbar) ~ RCP();

p(pbar)/ ~ p(pbar)/ (d+Au,p+p); pbar/p ~ pbar/p (d+Au). Indicate that partonic sources of p(pbar) and have similar energy loss.

• Gluon contribution to p(pbar) is significantly larger than to (p); Gluons lose twice as much energy as quarks; RCP(p+pbar)<RCP(); p(pbar)/ < p(pbar)/ (d+Au,p+p); pbar/p < pbar/p (d+Au).

• With the addition of collisional energy loss in the recent calculation, the gluon jet quenching is a factor of 3 higher than quark jet quenching (S. Wicks et al., nucl-ex/0512076).

• There is no model to readily explain these measurements. Direct comparisons to the measurements require proper fragmentation functions.

Page 19: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 19

Summary• The spectra of and p (pbar) from 200 GeV Au+Au collisions are

analyzed up to pT=12 GeV/c.

• At central Au+Au collisions, at intermediate pT, RCP(p+pbar) > RCP() , RCP(p+pbar) decreasing trend with pT, not consistent with binary scaling; the p(pbar)/ ratio~1 at pT 2~3 GeV/c.

• In central Au+Au collisions, at high pT, RCP(p+pbar) ~ RCP() the p(pbar)/ ratios approach the ratios in p+p and d+Au collisions. In Au+Au collisions, jet fragmentation mechanism region: pT>6 GeV/c.

• The -/ + and pbar/p ratios, no significant centrality or pT dependence.

Indicate that the partonic sources of protons and pions have similar

energy loss.

Page 20: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 20

Discussion: energy loss in QCD matter

• Color charge dependence: g vs q. experimentally, p and pbar at high pT.

In order to systematically study this effect measure p(pbar)/, pbar/p ratio in different energy by changing the g/q relative contribution to particle production.

• Flavor dependence: u, d quarks vs c, b quarks. go to charm.

• The partonic sources of , protons, and (D,B to) non-photonic electrons have similar energy loss.

S. Wicks et al., nucl-th/0512076

STAR Preliminary

Page 21: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 21

Outlook: A Heavy-Flavor Tracker for STAR

Page 22: Identified baryon and meson spectra at intermediate and high p T in 200 GeV Au+Au Collisions

03/14/2006 WWND2006 at La Jolla 22

Outlook: A Heavy-Flavor Tracker for STAR

The energy loss

of heavy flavor

will be measured

from open charm directly!!!