mark heinz (for the star collaboration) yale university
DESCRIPTION
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. Outline. Status of Models STAR vs Leading Order (PYTHIA) STAR vs Next-to-Leading Order (NLO) - PowerPoint PPT PresentationTRANSCRIPT
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
[email protected] 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)
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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
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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
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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
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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
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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
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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
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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 ?
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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
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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
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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
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Backup
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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
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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
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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
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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