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STAR Strangeness production in jets from p+p 200 GeV collisions Anthony Timmins for the STAR Collaboration  Motivation  Analysis  Results  Summary.

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Presentation on theme: "STAR Strangeness production in jets from p+p 200 GeV collisions Anthony Timmins for the STAR Collaboration  Motivation  Analysis  Results  Summary."— Presentation transcript:

1 STAR Strangeness production in jets from p+p 200 GeV collisions Anthony Timmins for the STAR Collaboration  Motivation  Analysis  Results  Summary

2 STAR 2/14 Motivation Strangeness fragmentation functions… Strange particle fragmentation functions (FFs) for p+p at RHIC energies lacking… Understand the species dependance of fragmentation  Compare to PYTHIA, MLLA etc… Understand trends behind p+p inclusive spectrum measurements  Soft vs hard production…. Eur. Phys. J. C55 (2008) 293  Modified Leading Log (MLLA) FF variable

3 STAR 3/14 Motivation Medium modification of jet chemistry… STAR preliminary p T (GeV/c) Modification in HI jet chemistry observed in inclusive measurements and predicted… p+p FFs essential baseline for HI jet-finding studies Eur. Phys. J. C55 (2008) 293

4 STAR 4/14 Analysis The experiment… p+p 200 GeV data taken in 2006…  Full installation of calorimeter TPC -> charged particles Calorimeters -> neutrals Calorimeter based jet patch trigger used..  Neutral E jet > 8 GeV  x  = 1 x 1  ~ 8 million events

5 STAR 5/14 Analysis Jet finding… 3 jet finders used to measure FFs  FastJet, (Cacciari, Soyez, arXiv:0704.0292)  Seedless Cone SIS  KT  Anti-kt Jets cuts  Recoil WRT trigger  Resolution parameter (~radius) = 0.4  |  | < 0.6  Charged track, Tower Energy  p T > 200 MeV/c Corrections applied  Double counting Corrections we’re working on…  Energy resolution  Missing jet energy…. Triggered online jet Recoil jet (used for FFs)  K0SK0S h+h+ STAR Preliminary

6 STAR 6/14 Analysis Magnitude of future corrections… Current charged hadron FFs not corrected for.. –Jet energy BEMC acceptance/inefficiencies Missing neutral energy TPC acceptance/inefficiencies –Fragment yields TPC acceptance/inefficiencies Compare PYTHIA particle (reco) and simulation (MC) levels –FFs clearly different… STAR Preliminary

7 STAR 7/14 Analysis Magnitude of future corrections… Taking ratios of FFs (reco/MC) shows corrections will be significant… Largest corrections at low  … Appear approximately jet p T independent… STAR Preliminary

8 STAR 8/14 Analysis Strangeness PID… ,  and K 0 S identified via decay products…. Place topological cuts –Reduce combinatoric background –Not completely removed p T > 1 GeV/c STAR Preliminary

9 STAR 9/14 Results Uncorrected h ± FFs… Helen Caines QM2009

10 STAR 10/14 Results Uncorrected strange hadron FFs… Measured data not corrected for tracking efficiency/jet energy uncertainties  Errors statistic + systematic (different jet finders)  V0 p T > 1 GeV/c Pythia 6.4 ran through STAR reconstruction chain –Describes K 0 S OK, some deviations for strange baryons STAR Preliminary p T cut

11 STAR 11/14 STAR Preliminary Results Strange particle ratios in jets… Strange baryon asymmetry observed in jets… Jet like process give larger baryon/meson ratios than all processes Jet  /K 0 S ratio appears consistent with inclusive spectra at higher p T … Phys. Rev. C 75 (2007) 064901 STAR Preliminary

12 STAR 12/14 Results Peak position of  … In MLLA, peak position of  in parton shower given by:  0 = Y + √Yc - c Y = log(E jet sin  / Q eff ) Assuming Local Parton Hadron Duality (LPHD) Q eff  M 0 (hadron mass) First relation implies scaling behaviour…  0 increases with jet energy  0 decreases with hadron mass Correct meausred FF for tracking efficiency –Fit Gaussian in peak region to extract  0 e + e - CM energy F Anulli, arXiv:0804.2021v1 STAR Preliminary

13 STAR 13/14 Results Non-leading h ± FFs for various leading hadrons… Eur. Phys. J. C13 (2000) 573 Do strange particle tagging baryon/meson select on quark/gluon jets?  Gluon jets have ~2x more hadrons than quark jets Measurements show non-leading h ± FF invariant upon strange particle tagging…  Similar amount of hadrons in each case… p T cut STAR Preliminary

14 STAR 14/14 Summary Pythia describes charged hadron fragmentation functions  OK for strange mesons, deviations for strange baryons Baryon asymmetries observed in  ~0 p+p jets Jet-like processes give  /K 0 S ratios ~0.5-0.6 Predicted MLLA mass ordering observed to first order Jets with leading baryon and mesons  Have the same number of non-leading charged hadrons


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