Mark Heinz Strangeness in Collisions, BNL, February 2006

1

Strangeness in Collisions Workshop

“Strangeness in p+p: Data vs Models”

Mark T. Heinz

Yale University

Mark Heinz Strangeness in Collisions, BNL, February 2006 2

Acknowledgements

Includes work by other STAR collaborators:Richard WittSevil SalurJana BielcikovaPawan NekrakantiZhangbu Xu

Mark Heinz Strangeness in Collisions, BNL, February 2006 3

Outline

Model introduction LO pQCD Models (PYTHIA)

Comparison of yields & pT-spectra Baryon vs Meson production <Nch> dependance of <pT> Fragmenting Gluon vs Quark jets Mt-scaling

NLO pQCD calculations EPOS model Statistical models

Mark Heinz Strangeness in Collisions, BNL, February 2006 4

Factorization Ansatz

c

chbbaa

abcdba

T

hpp

z

Dcdab

td

dQxfQxfdxdxK

pdyd

d

0

/222

)(ˆ

),(),( K-Factor

LO parton processes

NLO parton processes

Fragmentation Function (non-pert.)

BKK, Phys Rev D (1995)

Pions

Parton Distribution Function(non-pert.)

RHIC

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Leading order pQCD (PYTHIA)

Parton showers based on Lund String Model JETSET was used to successfully describe e+e- collisions Strings break into hadrons according to Lund symmetric FF Flavor dependence introduced by strange quark suppression

factor Baryon production governed by di-quark probabilities.

“Lund Symmetric fragmentation function”

z = fractional momentum of parton/hadron a, b = universal parameter

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pT-spectra comparison

First comparisons with PYTHIA version 6.2 (2004) Version 6.3 (January 2005)

New multiple scattering algorithm Tune K-Factor: accounts for NLO processes in hard cross-section

STAR Preliminary STAR Preliminary STAR Preliminary

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What about non-strange particles ?

Comparison to published STAR TOF data shows good agreement for pions and protons.

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What about strange resonances ?

Published STAR data for , K* Preliminary STAR data for * (baryon resonance) K-factor = 3 fits all resonances very nicely

STAR Preliminary

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Charged multiplicity distribution

Pythia + Simulated Trigger and detector acceptance.

PYTHIA 6.3 PYTHIA 6.3, K=3

STAR Preliminary

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K-factor in LO pQCD

What is a reasonable K-factor ?

Flavor dependence of K-factor ?

Decreases for collision energy Contribution of NLO

processes is smaller at higher energies

STAR

Eskola et al Nucl. Phys A 713 (2003)

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Mini-jet production in p+p

pQCD models are ideal to look at Mini-jet phenomenology High multiplicity p+p events “Harder” parton interaction - Mini-jets

Higher pT final states Higher <pT>

XN.Wang et al (Phys Rev D45, 1992)

Nch

Njet=2

dNch/d

<p

T>

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PYTHIA <pT> vs Nch

More sensitive observable to implementation of multiple scattering algorithm -> mini-jets.

STAR Preliminary

STAR Preliminary

K-factor is required to account for increase of <pT> with charged multiplicity

STAR PreliminarySTAR Preliminary

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Gluon vs Quark jets

Studies have been done in e+e- data and at higher energies

Quark-jets fragment harder than Gluon jets which produce more multiplicity

Look at anti-particle to particle ratios Accessing this through ID-particle

azimuthal correlations

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Ratios vs pT (gluon vs quark jet)

Baryon ratios vs pT vs PYTHIA Quarks fragment predominantly into particles, gluons do not favor

particles over antiparticles Not sufficient statistics at high pT in p+p collisions. But results from d+Au look promising

STAR (Phys Lett. B submitted)STAR preliminary

d+Au p+p p+p

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Baryon-meson “anomalies”

Baryon production is interesting at intermediate pT

Strange baryon/meson ratio is under-predicted by PYTHIA at 200 and 630 GeV

PYTHIA 6.3

STAR preliminary(red)

UA1(blue)

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Baryon-meson “anomalies” (2)

Baryon/meson enhancement also seen in proton to pion ratio PYTHIA underpredicts this observable by factor ~2

STAR (submitted to Phys Lett B) PYTHIA 6.3

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mT - scaling

mT-scaling first studied with ISR data.

In the Color Glass Condensate (CGC) picture mT-scaling would be indicative of evidence of gluon saturation.

No absolute scaling. Species are scaled with prefactors

STAR data reveals an interesting feature of baryon vs meson splitting above 2 GeV in mT

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mT scaling in PYTHIA

Gluon jets produce meson vs baryon “splitting” Quark jets produce mass splitting in mT This confirms that our p+p events are gluon jet dominated.

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Identified azimuthal correlations

Shape of correlations expected to be different for quark vs gluon jet.

Accessing this through ID-particle azimuthal correlations (ongoing studies in STAR)

Very statistics hungry…

K0s-h-h-h

STAR Au+Au preliminary data (QM 2005)

-h

d+Au

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NLO calculation (Intro)

Natural next step to enhance precision of model prediction Use parametrized PDF and FF to NLO FF are proposed to be “universal” (KKP) Good agreement with non-strange STAR hadron data

Van Leeuwen, nucl-ex/0412023STAR Preliminary

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NLO for strange particles

STAR data shown with calculations by Vogelsang FF by Kniehl,Kramer,Poetter (KKP) for K0s yields reasonable agreement Lambda NLO calculation is marginal.

K0s

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NLO strange particles (update)

Recent data from e+ e- collider (OPAL) now allow measurement of light flavor seperated FF calculated by Albino, Kramer,Kniehl (AKK)

OPAL (1999)

K0s

NLO Lines are for μ=2*pT, pT, pT/2

UA1 (630GeV)

STAR (200GeV)

UA1 (630GeV)

STAR (200GeV)

Gluon -> Lambda FF was fixed with respect to proton FF (factor 3)

Albino et al. ,hep-ph/0502188+ 0510173

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EPOS pT-spectra

K.Werner et al. hep/ph-0506232

This model incorporates:• Parton splitting ladders (pomerons)•Energy conserving mult. scattering approach•Off-shell remnants•Also describes d+Au data nicely h+/-

K0s -

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Statistical models in p+p

Statistical models have been proposed by Becattini et al for small systems (e+e-, p+p)

Canonical calculation How do we interpret the

model parameter T ? Codes are now available

publicly: SHARE, THERMUS

Becattini/Heinz (1997)

STAR vs THERMUSp+p

Becattini

UA5 p+p

STAR

p+p

T (MeV) 175±15 177±9

s 0.54±0.07 0.5 ±0.04

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Summary

New version of the PYTHIA model (6.3) describes strange particle and resonance data well when a K-factor of 3 is used. For mesons no K-factor is required.

Increase in <pT> with Nch due to mini-jets & multiple scattering is succesfully modeled in PYTHIA 6.3 with K-factor 3.

Further statistics needed to see drop of anti-baryon/baryon ratio vs pT as predicted from quark vs gluon jet phenomenology

Baryon/meson “anomalie” is not reproduced in pQCD models mT scaling also shows interesting baryon vs meson differences at

intermediate pT

AKK (Albino,Kniehl,Kramer) NLO calculations using constrained fragmentation functions reproduce STAR and UA1 strangeness data nicely

EPOS does a good job compared to our p+p d+Au data. Statistical models (THERMUS) can describe our particle yields in p+p

collisions with T~177 MeV