Transcript Strangeness Production in Heavy

Strangeness production in jets
from p+p 200 GeV collisions
Anthony Timmins for the STAR Collaboration

Motivation
 Analysis
 Results
 Summary
STAR
2/14
Motivation
Strangeness fragmentation functions…
 Modified Leading Log (MLLA)

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
FF variable
STAR
3/14
Motivation
Medium modification of jet chemistry…
Eur. Phys. J. C55 (2008) 293
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
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 Ejet > 8 GeV
  x  = 1 x 1
 ~ 8 million events
STAR
5/14
Analysis
Recoil jet
(used for FFs)
Jet finding…

3 jet finders used to measure FFs
 FastJet, (Cacciari, Soyez, arXiv:0704.0292)
 Seedless Cone SIS
 KT
 Anti-kt
K0S

h+

Jets cuts
 Recoil WRT trigger
 Resolution parameter (~radius) = 0.4
 || < 0.6
 Charged track, Tower Energy
 pT > 200 MeV/c

Corrections applied
 Double counting
Triggered
online jet
STAR Preliminary

Corrections we’re working on…
 Energy resolution
 Missing jet energy….
STAR
6/14
Analysis
Magnitude of future corrections…
STAR Preliminary

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
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 pT independent…
STAR Preliminary
STAR
8/14
Analysis
STAR Preliminary
Strangeness PID…

,  and K0S identified via decay
products….

Place topological cuts
– Reduce combinatoric background
– Not completely removed
pT > 1 GeV/c
STAR
9/14
Results
Uncorrected h± FFs…
Helen Caines
QM2009
STAR
10/14
Results
Uncorrected strange hadron FFs…
STAR Preliminary
pT cut
pT cut
pT cut

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 K0S OK, some deviations for strange baryons
STAR
11/14
Results
Strange particle ratios in jets…
STAR Preliminary
STAR Preliminary
Phys. Rev. C 75 (2007) 064901
QuickTime™ and a
decompressor
are needed to see this picture.

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…
STAR
12/14
Results
Peak position of …

In MLLA, peak position of  in parton shower
given by:
STAR Preliminary
F Anulli, arXiv:0804.2021v1
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
e+e- CM energy

Correct meausred FF for tracking
efficiency
–
Fit Gaussian in peak region to extract 0
STAR
13/14
Results
Non-leading h± FFs for various leading hadrons…
STAR Preliminary
pT cut
pT cut
pT cut
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…
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
STAR