RHIC Strangeness Physics at RHIC Strangeness Physics at intermediate and high pt intermediate and high pt

R. Bellwied (Wayne State University)

Is strangeness production in medium different than production in vacuum ?

Strangeness Workshop, BNL, Feb.16-17,2006

Thanks to: Thanks to:

Helen Caines, Richard Witt,

Matt Lamont, Jana Bielcikova,

Mark Heinz, Ying Guo,

Camelia Mironov, Jeff Speltz,

Sevil Salur,

Wolf Holzmann (PHENIX)

The main topics The main topics

Strangeness production through fragmentation in pp

Nuclear suppression at high pT in AA

Canonical Suppression at high pT from pp to AA

Medium modification of fragmentation in AA

Jets through strange two-particle correlations

Do we understand strangeness productionin elementary collisions ?

Parton distribution functions (hep-ex/0305109)

RHIC

pp at RHICadron formation in QCDNLO for heavy masses requires quark separation in fragmentation function ?

zz

In AA: is the fragmentation function modification due to the partonicmedium universal ?

pp at RHICStrangeness formation in QCD(more on this tomorrow by Heinz, Strands and Werner)

Strangeness production not described by leading order calculation (contrary to pion production).It needs multiple parton scattering (e.g. EPOS) or NLO corrections todescribe strangeness production.Part of it is a mass effect (plus a baryon-meson effect) but in addition there is a strangeness ‘penalty’ factor (e.g. the proton fragmentation function does not describe production). s is not just another light quark

Baryon production mechanism through strange particles correlations

…

Test phenomenological fragmentation models

OPAL ALEPH and DELPHI measurements:Yields and cos distribution between correlated pairs distinguishes between isotropic cluster (HERWIG) and non-isotropic string decay (JETSET) for production mechanism.

Clustering favors baryon productionJETSET is clearly favored by the data.

Correlated bar pairs are produced predominantly in the same jet, i.e. short range compensation of quantum numbers.

jetsqqZee 0

Effects due to softer g-PDF and color factor

No evidence for pQCDdrop yet.

Are extensions of string models applicable in AA @ RHIC:

e.g. EPOS++ (K.Werner, see talk tomorrow)

Flavor dependence of fragmentation in vacuum & medium

Quark jets vs. gluon jets

Leading particle asymmetries

Baryon vs. meson asymmetries

Particle vs anti-particle asymmetries

Clustering

Why measure these effects with K and instead of and p ?

Particle identification benefits from fact that the topological reconstruction method has no intrinsic momentum cut-off compared to dE/dx.

…but the use of rdE/dx might change that at least for inclusive measurements

Identified Particle RCP

• strange RCP well behaved

• all particles have same RCP for pT>~5 GeV: dominance of fragmentation?

• no flavor dependence in fragmentation region ?

Nuclear Modification Factor Rcp

0-5%

40-60%

0-5%

60-80%

Y-4 K0s

√sNN=200 GeV

Baryon and meson suppression sets in at the same quark pT .

√sNN=200 GeV

Strange RCP signals range ofrecombination model relevance

Recombination scaling can be appliedto RCP as well as v2

RCP double ratios independent of collision energy ! Recombination at SPS ?

Strangeness Production @ 62 GeV

Increased baryon density, less energy density at 62 GeV:more in talk by Jeff Speltz

RAA of strange baryonsA remarkable differencebetween RAA and RCP

that seems unique tostrange baryons.Ordering with strangenesscontent.‘Canonical suppression’is unique to strange hadrons

This effect must occur ‘between’ pp and peripheral AA collisions

Flavor independence of RAA ?

u,d dominated c,b dominated

no flavor dependence in energy loss ??

Strange enhancement vs. charm suppression ?

But is it a flavor effect ?Kaon behaves like D-meson,we need a charmed baryon

RAA - A mocked upstring picture does well

(see V.Topor-Pop talk)

Topor Pop et al. hep-ph/0505210

HIJING/BBar + KT ~ 1 GeVStrong Color Field qualitatively describes RAA.

SCF - long range coherent fields

SCF behavior mimicked by doubling the effective string tension

SCF only produced in nucleus-nucleus collisions RAA≠ RCP

Flavor dependence of yield scaling

• participant scaling for light quark hadrons• binary scaling for heavy flavor quark hadrons

PHENIX D-meson measurement

Strangeness yields from pp to AA

Production not well modeled by Npart (correlation volume)

Canonical suppression increases with increasing

strangeness

and are not flat

s-quarks are formed primordial Scaling according

to quark content?

u, d – scale with Npart

s,c,b – scale with Nbin

p – Npart

K0s – 1/2*Npart + 1/2*Nbin

– 2/3*Npart + 1/3*Nbin

– 1/3*Npart + 2/3*Nbin

– Nbin

– Nbin

D – Nbin

Does strangeness “see” a different

correlation volume ?

Is a different phase space density

required for strangeness production ?

Normalized to central data

Quark Scaled RAA of Strange Particles

s-quarks scaled with NBin

u&d-quarks scaled with Npart

scaled with N part

Description of correlation functions

p+p/d+Au

A+A

flow+bkg

near-side away-side

• trigger/associated particles: charged particle or V0 (Λ, Λ, K0

S)

• correlation function (need to subtract elliptic flow in Au+Au)

))cos(2v2v(1 B )2σ

π)(Δ(- expA)

2σ

Δexp(-A )C(Δ Δ

2assoc2trig2π

2

π20

2

0

correlation functions before elliptic flow subtraction

correlation functions after elliptic flow subtraction

Correlation functions for strange particle triggers in Au+Au at 200 GeV

Selection criteria:• 3.0 GeV/c<pT

trigger<3.5 GeV/c • 1 GeV/c<pT

associated<2 GeV/c• ||<1

Corrections applied:•reconstruction efficiency of charged particles •TPC sector boundariesSTAR preliminarySTAR preliminary

STAR preliminarySTAR preliminarySTAR preliminarySTAR preliminary

STAR preliminarySTAR preliminary

trigger: baryon/meson particle/antiparticletrigger: baryon/meson particle/antiparticle

Near side yield dependence on system size

Although within statistical errors all trigger particle species behave similarly, yield for “meson” triggered correlations appears to be systematically lower than for “baryon” triggers

Why is yield increasing with Npart ?

statistical errors only

STAR STAR preliminarypreliminary

Large AA/pp ratio of near sideassociated yield

STAR preliminarySTAR preliminary

What does a parton recombination model predict?

• the ratio of near-side associated yield in central/peripheral Au+Au collisions is ~ 3 at pT

associated = 1 GeV/c and decreases slowly with increasing pT

associated

• data are in a good agreement with predictions from a parton recombination model: In Au+Au the thermal-shower recombination dominates

R. Hwa, Z.Tan: nucl-th/0503060

Au+AuAu+Au

d+Aud+Au

Au+Au @ 200 GeVAu+Au @ 200 GeV3GeV/c<p3GeV/c<pTT

triggertrigger<6GeV/c<6GeV/c

Recombination contribution is quark content dependent (R.Hwa, nucl-th/0602024)

Alternate (?) or additional (?) explanation: long range correlations in AuAu

Jet-like correlation are on top of an additional flat long range correlation background in : cannot differentiate between the two correlations : additional

correlation

gets grouped into

subtracted

background

d+Au, 40-100%

Au+Au, 0-5%

STAR preliminary

3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig)

Big ridge effect within our acceptancein pT and

Most of the yield is due to the ridge. Preliminary result: after ridge subtraction: assoc. yield (pp) = assoc. yield (AA), no PID dep.

MesonMeson vs. vs.BaryonBaryon trigger trigger(for fixed (for fixed MesonMesonpartner)partner)

Distribution of partner mesons per trigger-particle depends on trigger particle Distribution of partner mesons per trigger-particle depends on trigger particle species in this pspecies in this pTT range. range.

Less energy available on same-side leads to smaller associated meson yield ?Less energy available on same-side leads to smaller associated meson yield ?

Distribution of partner mesons per trigger-particle depends on trigger particle Distribution of partner mesons per trigger-particle depends on trigger particle species in this pspecies in this pTT range. range.

Less energy available on same-side leads to smaller associated meson yield ?Less energy available on same-side leads to smaller associated meson yield ?

Particle species dependent correlations according to

PHENIX

MesonMeson vs. vs.BaryonBaryon partner partner(for fixed (for fixed MesonMesontrigger)trigger)

Away-side partner baryon to meson ratio ~2.5 times larger than near-sideAway-side partner baryon to meson ratio ~2.5 times larger than near-sidepartner baryon to meson ratio for meson triggered correlationspartner baryon to meson ratio for meson triggered correlations

More energy available on the away-side leads to baryon production ?More energy available on the away-side leads to baryon production ?

Away-side partner baryon to meson ratio ~2.5 times larger than near-sideAway-side partner baryon to meson ratio ~2.5 times larger than near-sidepartner baryon to meson ratio for meson triggered correlationspartner baryon to meson ratio for meson triggered correlations

More energy available on the away-side leads to baryon production ?More energy available on the away-side leads to baryon production ?

Particle species dependent correlations according to

PHENIX

Near side yield as f(pt(assoc))

Slope parameters in agreement with PHENIX For baryon/meson triggered associate yields

440+-7 MeV403+-15 MeV407+-16 MeV460+-23 MeV

instead of z = pThadron/pTparton

use zT = pTassociated/pTtrigger

(X.N.Wang: PLB 495 (2004))

Summary Strange baryon production in pp requires multiple scattering (EPOS or NLO pQCD)

High pt strange baryon production in AA enhanced instead of suppressed compared to pp . Is this due to simple canonical suppression ?

Strange baryon does not scale with either Nbin or Npart. Do primordial strange quarks recombine with thermal light quarks and thus have a different correlation volume ? No strong flavor effects in high pt two particle correlations. Surprising absence of pQCD effects (gluon vs. quark contributions)

Large associated particle yield in AA compared to pp. Might be due recombination or a long range correlation or both. There might be a baryon/meson trend in agreement with recombination, but it is a small effect. Predictions for and need to be tested.

VERY RICH PHYSICS IN THE STRANGENESS SECTOR @ RHIC