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