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Mark Heinz (for the STAR collaboration) Yale University

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)

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Mark Heinz (for the STAR collaboration) Yale University

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  1. 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

  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) Hotquarks 2006, Sardinia, Italy

  3. 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 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) 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) = 0.3 Diquark suppression: P(qq)/P(q) = 0.1 Strange Diquark suppression: [P(us)/P(ud)]/[P(s)/P(d)] = 0.4 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 ? Hotquarks 2006, Sardinia, Italy

  6. What about other particles ? Non-strange mesons and baryons Strange Resonances All this is published or submitted STAR data ! Pi/proton to 6.5 GeV: submitted PLB, nucl-ex/0601033 Phi/K* : PLB 612 (2005), PRC 71(2005) Sigma*(1385): submitted PRL, nucl-ex/0604019 K=1 K=3 K=1 K=3 K=1 K=3 Hotquarks 2006, Sardinia, Italy

  7. 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) K-factor in LO pQCD PYTHIA 500’000 p+p events No events • K-factor=3 has been observed previously for charged hadrons at s=200 GeV q+q q+g g+g Hotquarks 2006, Sardinia, Italy

  8. Nucl-ex/0601033 Van Leeuwen, nucl-ex/0412023 NLO for non-strange particles • 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 • Inclusive charged hadrons have been well described for the last 10 years by Fragmentation functions (FF) from Kretzer, KKP and others. Largest uncertainty comes from flavor dependance of FF 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. • Normalization of Gluon Fragmentation function is constrained using STAR data Largest uncertainty comes from Gluon FF  important contribution in p+p Hotquarks 2006, Sardinia, Italy

  10. CTEQ6 CTEQ5 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 Gluon Fragmentation func. Recent 3-jet data from OPAL and ALEPH Gluon Distribution func. Evolution of parameterizations From CTEQ5M  CTEQ6M ALEPH (52 GeV) OPAL (52 GeV) AKK, Nucl.Phys.B725(2005) How can we experimentally help constrain the Gluon FF ? Hotquarks 2006, Sardinia, Italy

  11. Preliminary DATA Gluon jet Quark jet PYTHIA 6.3 mT scaling of identified particles Arbitrarily scaled mT-spectra data and PYTHIA simulation agree well • 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. Hotquarks 2006, Sardinia, Italy

  12. Baryon-meson “anomalies” • PYTHIA also underpredicts the Baryon/meson ratio for higher energies at UA1, s= 630 GeV • PYTHIA cannot describe Baryon/Meson ratio at intermediate pT even with tuned K-factors. In addition di-quark probabilities need to be tuned. • Gluon Jets will produce a larger Baryon/Meson ratio than quark-jets in the region of interest Hotquarks 2006, Sardinia, Italy

  13. Summary • 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 • 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. • 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 • 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. Hotquarks 2006, Sardinia, Italy

  14. Backup Hotquarks 2006, Sardinia, Italy

  15. Hotquarks 2006, Sardinia, Italy

  16. STAR data PYTHIA 6.3, K=3 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 6.3 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 Hotquarks 2006, Sardinia, Italy

  18. d+Au Ratios vs pT (gluon vs quark jet) STAR (Phys Lett. B submitted) • 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 preliminary p+p Hotquarks 2006, Sardinia, Italy

  19. Consistency with data at 630 GeV • How well does the constrained fragmentation function extrapolate to other energies? K0s UA1 (630GeV) UA1 (630GeV) STAR (200GeV) STAR (200GeV) Albino,Kniehl,Kramer et al. ,hep-ph/0510173 NLO Lines are for μ=2*pT, pT, pT/2 Hotquarks 2006, Sardinia, Italy

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