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22 nd Winter Workshop on Nuclear Dynamics “Can STAR p+p data help constrain fragmentation functions for strange hadrons” Mark Heinz (for the STAR collaboration)

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Presentation on theme: "22 nd Winter Workshop on Nuclear Dynamics “Can STAR p+p data help constrain fragmentation functions for strange hadrons” Mark Heinz (for the STAR collaboration)"— Presentation transcript:

1 22 nd Winter Workshop on Nuclear Dynamics “Can STAR p+p data help constrain fragmentation functions for strange hadrons” Mark Heinz (for the STAR collaboration) Yale University

2 mark.heinz@yale.edu WW San Diego, March 2006 2 Outline Perturbative QCD Methods Factorization Fragmentation functions Next-to-Leading order calculations (NLO) Calculations by KKP, Kretzer, AKK, Vogelsang Leading order MC (Pythia) P T -spectra systematics Gluon vs Quark jets

3 mark.heinz@yale.edu WW San Diego, March 2006 3 Factorization Ansatz LO parton processes NLO parton processes Fragmentation Function (non-pert.) BKK, Phys Rev D (1995) Pions Parton Distribution Function (non-pert.) RHIC K-Factor

4 mark.heinz@yale.edu WW San Diego, March 2006 4 Universality of Fragmentation func. Suggested by Paper by Kniehl,Kramer & Poetter (2001) Experimental data from different collisions systems have been fit with the same fragmentation function KKP, Nucl.Phys.B597(2001) Fragmentation function for inclusive hadrons KKP, Nucl.Phys.B582(2000)  s=91.2 GeV OPAL,ALEPH uds-quark c-quark b-quark all

5 mark.heinz@yale.edu WW San Diego, March 2006 5 The gluon FF Collider data available from 3-jet events from ALEPH and OPAL Statistics still very limited Dotted: Delphi Dashed: BKK Full: KKP (new) M f =52 + 80 GeV AKK, Nucl.Phys.B725(2005) Curves scaled by 1/100

6 mark.heinz@yale.edu WW San Diego, March 2006 6 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. Baryons have been notoriously difficult to fit, due to limited knowledge of FF. Albino, Kramer and Kniehl (AKK) use latest OPAL data to calculate light flavor (u,d,s) separated fragmentation functions for the first time. Van Leeuwen, nucl-ex/0412023 STAR Preliminary STAR 200 GeV p+p data for identified non-strange mesons and baryons agrees well with NLO calculation by AKK.

7 mark.heinz@yale.edu WW San Diego, March 2006 7 NLO for strange particles First NLO predictions for RHIC energies K0s and Lambda were obtained by W.Vogelsang (RIKEN) In 2005 calculations at NLO by Albino, Kniehl & Kramer (AKK) for K0s and Lambda produced better agreement. Shape of Gluon  Lambda FF was constrained by Gluon  Proton FF Magnitude was constrained by STAR data

8 mark.heinz@yale.edu WW San Diego, March 2006 8 Consistency with data at 630 GeV How well does the constrained fragmentation function extrapolate to other energies? K0sK0s  NLO Lines are for μ=2*p T, p T, p T /2 UA1 (630GeV) STAR (200GeV) UA1 (630GeV) STAR (200GeV) Albino,Kniehl,Kramer et al.,hep-ph/0510173

9 mark.heinz@yale.edu WW San Diego, March 2006 9 Leading order pQCD (PYTHIA) Parton showers based on Lund String Model JETSET was used to successfully describe e+e- collisions Flavor dependence introduced by strange quark suppression factor Baryon production governed mainly by di-quark probabilities K-Factor accounts for NLO perturbative processes “Lund Symmetric fragmentation function” z = fractional momentum of parton/hadron a, b = tunable parameter

10 mark.heinz@yale.edu WW San Diego, March 2006 10 p T -spectra for strange particles PYTHIA Version 6.3 used (January 2005) Incorporates parameter tunes from CDF New multiple scattering and shower algorithms Necessary tune: K-Factor, which accounts for NLO processes in hard cross-section

11 mark.heinz@yale.edu WW San Diego, March 2006 11 What about non-strange particles ? Comparison to published STAR data Good agreement for pions with K=1 and proton with K>1 However only lower p T region measured

12 mark.heinz@yale.edu WW San Diego, March 2006 12 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 PYTHIA 6.3 PYTHIA 6.3,K=3

13 mark.heinz@yale.edu WW San Diego, March 2006 13 K-factor in LO pQCD How is the K-factor defined? 2 Definitions: K obs =  exp /  LO K th =  NLO /  LO Flavor dependence of K- factor, ie. NLO contributions ? For h - it decreases for collision energy, ie. contribution of NLO processes is smaller at higher energies STAR Eskola et al Nucl. Phys A 713 (2003)

14 mark.heinz@yale.edu WW San Diego, March 2006 14 systematics in p+p Perturbative QCD models are ideal to look at Mini-jet phenomenology High multiplicity p+p events  more mini-jets  Higher p T final states  higher of hadrons XN.Wang et al (Phys Rev D45, 1992) N ch N jet =2 dN ch /d 

15 mark.heinz@yale.edu WW San Diego, March 2006 15 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 PYTHIA 6.3, K=3 STAR data

16 mark.heinz@yale.edu WW San Diego, March 2006 16 PYTHIA vs N ch 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 with charged multiplicity

17 mark.heinz@yale.edu WW San Diego, March 2006 17 Gluon vs Quark jets Extensive studies of jet properties have been done in e+e- data Gluon jets produce higher particle multiplicity Quark jets fragment produce a harder pT-spectrum The ratio of anti-particle to particle production should be sensitive to quark- vs-gluon jet

18 mark.heinz@yale.edu WW San Diego, March 2006 18 Ratios vs p T (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+p STAR preliminary d+Au

19 mark.heinz@yale.edu WW San Diego, March 2006 19 m T - scaling m T -scaling first studied with ISR data. In the Color Glass Condensate (CGC) picture m T -scaling would be indicative of evidence of gluon saturation. No absolute scaling. Species are scaled with arbitrary prefactors to overlap in low pt region STAR data reveals an interesting feature of baryon vs meson splitting above 2 GeV in m T STAR preliminary

20 mark.heinz@yale.edu WW San Diego, March 2006 20 m T scaling in PYTHIA Gluon jets produce meson vs baryon “splitting”, Quark jets produce mass splitting in m T. This confirms that our p+p events are gluon jet dominated. PYTHIA Preliminary DATA Arbitrarily scaled m T -spectra data and PYTHIA simulation agree well Gluon jet Quark jet

21 mark.heinz@yale.edu WW San Diego, March 2006 21 Baryon-meson “anomalies” Baryon production at intermediate p T is interesting since fragmentation by itself cannot describe data Strange baryon/meson ratio is under-predicted by PYTHIA at 200 and 630 GeV Magnitude of UA1 ratio is similar to central Au+Au in STAR. PYTHIA 6.3

22 mark.heinz@yale.edu WW San Diego, March 2006 22 Summary Most recent NLO calculations by AKK using constrained fragmentation functions reproduce STAR and UA1 strangeness data nicely Latest version of the PYTHIA model (6.3) describes strange particle and resonance data well if a LO K-factor=3 is used Increase of of strange hadrons with N ch due to mini-jets & multiple scattering is successfully modeled in PYTHIA 6.3 with K- factor 3 In p+p collisions the anti-baryon/baryon ratio vs p T does not yet show any clear quark vs gluon jet signature due to limited statistics. In d+Au however a significant drop of the ratio is observed. Perturbative QCD models are unable to reproduce the large baryon/meson ratio at intermediate p T m T scaling of identified particles may be a useful tool for investigating quark vs gluon jets phenomena

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