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Mark T. Heinz Yale University

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

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

3 Strangeness in Collisions, BNL, February 2006
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 Mark Heinz Strangeness in Collisions, BNL, February 2006

4 Strangeness in Collisions, BNL, February 2006
Factorization Ansatz K-Factor Parton Distribution Function (non-pert.) RHIC Fragmentation Function (non-pert.) BKK, Phys Rev D (1995) Pions LO parton processes NLO parton processes Mark Heinz 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” The last formula implies harder fragmentation functions for heavier hadrons. z = fractional momentum of parton/hadron a, b = universal parameter Mark Heinz 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 Mark Heinz 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. Mark Heinz 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 Mark Heinz 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 Mark Heinz Strangeness in Collisions, BNL, February 2006

10 Strangeness in Collisions, BNL, February 2006
K-factor in LO pQCD STAR What is a reasonable K-factor ? Flavor dependence of K-factor ? Decreases for collision energy Contribution of NLO processes is smaller at higher energies Eskola et al Nucl. Phys A 713 (2003) Mark Heinz Strangeness in Collisions, BNL, February 2006

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

13 Strangeness in Collisions, BNL, February 2006
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 Mark Heinz Strangeness in Collisions, BNL, February 2006

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

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

16 Baryon-meson “anomalies” (2)
Baryon/meson enhancement also seen in proton to pion ratio PYTHIA underpredicts this observable by factor ~2 PYTHIA 6.3 STAR (submitted to Phys Lett B) Mark Heinz Strangeness in Collisions, BNL, February 2006

17 Strangeness in Collisions, BNL, February 2006
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 Mark Heinz Strangeness in Collisions, BNL, February 2006

18 Strangeness in Collisions, BNL, February 2006
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. Mark Heinz Strangeness in Collisions, BNL, February 2006

19 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 d+Au STAR Au+Au preliminary data (QM 2005) Mark Heinz Strangeness in Collisions, BNL, February 2006

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

23 Strangeness in Collisions, BNL, February 2006
EPOS pT-spectra K.Werner et al. hep/ph This model incorporates: Parton splitting ladders (pomerons) Energy conserving mult. scattering approach Off-shell remnants Also describes d+Au data nicely h+/- K0s - Mark Heinz Strangeness in Collisions, BNL, February 2006

24 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 STAR vs THERMUS p+p Becattini UA5 p+p STAR p+p T (MeV) 175±15 177±9 s 0.54±0.07 0.5 ±0.04 Mark Heinz Strangeness in Collisions, BNL, February 2006

25 Strangeness in Collisions, BNL, February 2006
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 Mark Heinz Strangeness in Collisions, BNL, February 2006

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