STAR

Strangeness production in jets from p+p 200 GeV collisions

Anthony Timmins for the STAR Collaboration

Motivation Analysis Results Summary

STAR

2/14

MotivationStrangeness 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

STAR

3/14

MotivationMedium modification of jet chemistry…

STAR preliminary

pT (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

STAR

4/14

AnalysisThe 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 Ejet > 8 GeV

x = 1 x 1 ~ 8 million events

STAR

5/14

AnalysisJet 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

pT > 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)

K0S

h+

STAR Preliminary

STAR

6/14

AnalysisMagnitude 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

STAR

7/14

AnalysisMagnitude of future corrections…

Taking ratios of FFs (reco/MC) shows corrections will be significant…

Largest corrections at low …

Appear approximately jet pT independent…

STAR Preliminary

STAR

8/14

AnalysisStrangeness PID…

, and K0S identified via decay

products….

Place topological cuts – Reduce combinatoric background– Not completely removed

pT > 1 GeV/c

STAR Preliminary

STAR

9/14

ResultsUncorrected h± FFs…

Helen Caines QM2009

STAR

10/14

ResultsUncorrected strange hadron FFs…

Measured data not corrected for tracking efficiency/jet energy uncertainties Errors statistic + systematic (different jet finders) V0 pT > 1 GeV/c

Pythia 6.4 ran through STAR reconstruction chain– Describes K0

S OK, some deviations for strange baryons

STAR Preliminary

pT cut pT cutpT cut

STAR

11/14

STAR Preliminary

ResultsStrange particle ratios in jets…

Strange baryon asymmetry observed in jets…

Jet like process give larger baryon/meson ratios than all processes

Jet /K0S ratio appears consistent with inclusive spectra at higher pT…

QuickTime™ and a decompressor

are needed to see this picture.

Phys. Rev. C 75 (2007) 064901STAR Preliminary

STAR

12/14

ResultsPeak position of …

In MLLA, peak position of in parton shower given by:

0 = Y + √Yc - c

Y = log(Ejet sin / Qeff)

Assuming Local Parton Hadron Duality (LPHD)

Qeff M0 (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:0804.2021v1STAR Preliminary

STAR

13/14

ResultsNon-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…

pT cut pT cutpT cut

STAR Preliminary

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 /K0S 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