1 / 25

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.

Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related