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Strangeness in Collisions Workshop “Strangeness in p+p: Data vs Models”

This workshop explores the phenomenon of strangeness in collisions, specifically focusing on the comparison of data and models in p+p collisions. Topics include the introduction of models, comparison of yields and pT-spectra, baryon vs meson production, dependance of <Nch> on <pT>, fragmenting gluon vs quark jets, and more. The workshop also acknowledges the collaboration of other researchers.

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Strangeness in Collisions Workshop “Strangeness in p+p: Data vs Models”

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  1. Strangeness in Collisions Workshop“Strangeness in p+p: Data vs Models” Mark T. Heinz Yale University Strangeness in Collisions, BNL, February 2006

  2. Acknowledgements • Includes work by other STAR collaborators: • Richard Witt • Sevil Salur • Jana Bielcikova • Pawan Nekrakanti • Zhangbu Xu 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 Strangeness in Collisions, BNL, February 2006

  4. Parton Distribution Function (non-pert.) Fragmentation Function (non-pert.) LO parton processes Pions NLO parton processes RHIC BKK, Phys Rev D (1995) K-Factor Factorization Ansatz Strangeness in Collisions, BNL, February 2006

  5. 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 Strangeness in Collisions, BNL, February 2006

  6. 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 Strangeness in Collisions, BNL, February 2006

  7. What about non-strange particles ? • Comparison to published STAR TOF data shows good agreement for pions and protons. Strangeness in Collisions, BNL, February 2006

  8. 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 Strangeness in Collisions, BNL, February 2006

  9. Charged multiplicity distribution • Pythia + Simulated Trigger and detector acceptance. PYTHIA 6.3 PYTHIA 6.3, K=3 STAR Preliminary Strangeness in Collisions, BNL, February 2006

  10. 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 K-factor in LO pQCD Eskola et al Nucl. Phys A 713 (2003) Strangeness in Collisions, BNL, February 2006

  11. <pT> dNch/d 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> Njet=2 Nch XN.Wang et al (Phys Rev D45, 1992) Strangeness in Collisions, BNL, February 2006

  12. PYTHIA <pT> vs Nch • More sensitive observable to implementation of multiple scattering algorithm -> mini-jets. • K-factor is required to account for increase of <pT> with charged multiplicity STAR Preliminary STAR Preliminary STAR Preliminary STAR Preliminary Strangeness in Collisions, BNL, February 2006

  13. 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 Strangeness in Collisions, BNL, February 2006

  14. p+p d+Au 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 p+p STAR preliminary STAR (Phys Lett. B submitted) Strangeness in Collisions, BNL, February 2006

  15. PYTHIA 6.3 Baryon-meson “anomalies” • Baryon production is interesting at intermediate pT • Strange baryon/meson ratio is under-predicted by PYTHIA at 200 and 630 GeV UA1(blue) STAR preliminary(red) Strangeness in Collisions, BNL, February 2006

  16. PYTHIA 6.3 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) Strangeness in Collisions, BNL, February 2006

  17. 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 Strangeness in Collisions, BNL, February 2006

  18. 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. Strangeness in Collisions, BNL, February 2006

  19. d+Au 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… -h -h -h K0s-h STAR Au+Au preliminary data (QM 2005) Strangeness in Collisions, BNL, February 2006

  20. Van Leeuwen, nucl-ex/0412023 STAR Preliminary 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 Strangeness in Collisions, BNL, February 2006

  21. 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  Strangeness in Collisions, BNL, February 2006

  22. 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) NLO Lines are for μ=2*pT, pT, pT/2 K0s UA1 (630GeV) UA1 (630GeV) STAR (200GeV) STAR (200GeV) OPAL (1999) Gluon -> Lambda FF was fixed with respect to proton FF (factor 3) Albino et al. ,hep-ph/0502188+ 0510173 Strangeness in Collisions, BNL, February 2006

  23. 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  - Strangeness in Collisions, BNL, February 2006

  24. STAR vs THERMUS p+p Statistical models in p+p Becattini/Heinz (1997) • 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 Strangeness in Collisions, BNL, February 2006

  25. 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 Strangeness in Collisions, BNL, February 2006

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