HotQuarks 2006 conference

“How important are next-to-leading order models in predicting strange particle spectra in p+p collisions at STAR ?”

Mark Heinz (for the STAR collaboration)Yale University

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 2

Outline

Status of Models STAR vs Leading Order (PYTHIA) STAR vs Next-to-Leading Order (NLO)

Quark vs Gluon fragmentation Strange Baryon production in

perturbative QCD (pQCD)

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 3

Leading-order vs Next-to-Leading pQCD

2-2 processes only Leading-Log approx-

imation of higher order processes: Initial and final state radiation, Multiple scattering

Lund Symmetric String fragmentation

LO (PYTHIA)c

chbbaa

abcdba

T

hpp

zDcdab

tddQxfQxfdxdxK

pdydd

0

/222 )(ˆ),(),(

NLO (several theorists)

2-2 and 2-3 processes Parametrized Parton

Distribution function using Deep inelastic Scattering (e+p) data

Parameterized flavor separated Fragmentation Functions from e+e- data

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 4

Intro PYTHIA: Leading order pQCD Parton showers based on Lund String Model Universal fragmentation function for all collision systems Strangeness and Di-Quark production is suppressed by model parameter

z = fractional long. momentum of hadron/parton a, b = tunable parameter

Strange suppression: P(s)/P(u) = 0.3Diquark suppression: P(qq)/P(q) = 0.1Strange Diquark suppression:

[P(us)/P(ud)]/[P(s)/P(d)] = 0.4

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 5

pT-spectra for strange particles PYTHIA Version 6.326 used

Incorporates parameter tunes from CDF (tune A) New multiple scattering and shower algorithms

Tune: MSEL=1 (inelastic collisions) K-Factor = 3 (higher order corrections)

Is a Flavour dependant K-factor necessary ?

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What about other particles ?Non-strange mesons and baryons

Strange Resonances

K=1K=3

K=1K=3

K=1K=3

All this is published or submitted STAR data !Pi/proton to 6.5 GeV: submitted PLB, nucl-ex/0601033Phi/K* : PLB 612 (2005), PRC 71(2005)Sigma*(1385): submitted PRL, nucl-ex/0604019

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 7

K-factor in LO pQCD 2 Definitions:

Kobs= exp / LO Kth= NLO / LO

In PYTHIA K-factor changes relative x-section of underlying parton processes

STAR

Eskola et al Nucl. Phys A 713 (2003)

PYTHIA 500’000 p+p events

q+q

K-factor=3 has been observed previously for charged hadrons at s=200 GeV

No events

q+g g+g

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 8

NLO for non-strange particles Inclusive charged hadrons have been well described for the last 10

years by Fragmentation functions (FF) from Kretzer, KKP and others.

Van Leeuwen, nucl-ex/0412023

Albino, Kramer and Kniehl (AKK) use latest OPAL data to calculate light flavor (u,d,s) separated fragmentation functions for the first time.

Baryons show a large improvement with AKK FF. EPOS achieves good agreement with data

Nucl-ex/0601033

Largest uncertainty comes from flavor dependance of FF

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 9

NLO for strange particles First NLO calculations K0s and Lambda at 200 GeV were obtained

privately from W.Vogelsang (BNL) In 2005 calculations at NLO by Albino, Kniehl & Kramer (AKK) for K0s

and Lambda produced better agreement by constraining gluon FF.

Largest uncertainty comes from Gluon FF important contribution in p+p

Normalization of Gluon Fragmentation function is constrained using STAR data

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 10

Quark vs Gluon fragmentation FF: Collider data available from 3-jet events from

ALEPH and OPAL PDF: DIS data from ie. ZEUS and H1 In both cases the gluon processes are least known

ALEPH (52 GeV)

AKK, Nucl.Phys.B725(2005)

Gluon Fragmentation func.Recent 3-jet data from OPAL and ALEPH

Gluon Distribution func.Evolution of parameterizations From CTEQ5M CTEQ6M

CTEQ6CTEQ5

OPAL (52 GeV)

How can we experimentally help constrain the Gluon FF ?

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 11

mT scaling of identified particles

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.

PYTHIA 6.3Preliminary DATA

Arbitrarily scaled mT-spectra data and PYTHIA simulation agree well

Quark jetGluon jet

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 12

Baryon-meson “anomalies” 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 underpredicts the Baryon/meson ratio for higher energies at UA1, s= 630 GeV

Gluon Jets will produce a larger Baryon/Meson ratio than quark-jets in the region of interest

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 13

Summary

Baryon enhancement Strange baryon to meson ratio at intermediate pT cannot be

reproduced with PYTHIA and K-factor tune. The Diquark suppression parameter in the Lund fragmentation

function needs to be adjusted to achieve agreement with data.

Mt-Scaling Scaled mT–spectra of mesons and baryons exhibit different shapes

observed in p+p data and PYTHIA model calculation. This behavior is consistent with dominant particle production from

gluon jets with respect to quark jets.

NLO calculations Recent calculations by Albino et al. (AKK) using new flavor separated

fragmentations functions reproduce STAR strangeness data nicely STAR Lambda data constrains gluon fragmentation function

STAR data vs PYTHIA PYTHIA version 6.3 describes STAR data for strange particles and

resonances well if a K-factor =3 is used Pions and protons agree best with K=1

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 14

Backup

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 15

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 16

Charged multiplicity distribution

Pythia + Simulated Trigger and detector acceptance. Probability of high multiplicity events is very sensitive to NLO corrections

STAR Preliminary

STAR data

PYTHIA 6.3PYTHIA 6.3, K=3

STAR data

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 17

PYTHIA <pT> vs Nch

More sensitive observable to implementation of multiple scattering algorithm This phenomenology has also been previously attributed to mini-jets

Higher K-factor, more NLO contributions, are required to account for increase of <pT> with charged multiplicity

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 18

Ratios vs pT (gluon vs quark jet)

Gluons have equal probability of fragmenting into particles or antiparticles, Quarks fragment predominantly into particles

At higher pT (higher z) we are probing the quark-jet dominated region.

STAR (Phys Lett. B submitted)

p+pSTAR preliminary

d+Au

mark.heinz@yale.edu Hotquarks 2006, Sardinia, Italy 19

Consistency with data at 630 GeV

How well does the constrained fragmentation function extrapolate to other energies?

K0s

NLO Lines are for μ=2*pT, pT, pT/2

UA1 (630GeV)

STAR (200GeV)

UA1 (630GeV)

STAR (200GeV)

Albino,Kniehl,Kramer et al. ,hep-ph/0510173