STAR

The Centrality Dependence of Strange Baryon and Meson

Production in Cu+Cu and Au+Auwith √sNN = 200 GeV

Anthony Timmins for the STAR Collaboration

24th June 2007

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Contents

Motivation The Cu+Cu Dataset Spectra Comparisons Spectra Comparisons K0

Short Spectra Comparisons Integrated Yields vs. <Npart> The /K0

Short Ratio Summary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

MotivationStrangeness Enhancement

For Au+Au 200 GeV, integrated strange particle Yields per Participant, increase with increasing system size.

Can be explained in terms of a phase space/volume effect:– Canonical Suppression…– Curves assume volume <Npart>

With its differing geometry, recently produced Cu+Cu data should help us understand more about this volume dependency…

M. Lamont, SQM 2006

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

MotivationStrange Baryon/Meson Differences

For Au+Au collisions, increasing mid-pT /K0

Short ratios are observed with increasing centrality

Competing particle production mechanisms at mid pT;

– Thermal processes more prominent for

– Fragmentation for K0Short

Again, Cu+Cu data may help with the understanding of the system size dependency… M. Lamont, SQM 2006

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Cu+Cu sNN = 200 GeV Data Set

Large amount of data taken in 2005:– 55 million events for this analysis particles reach pT of 8 GeV/c,

K0Short 9 GeV/c

The neutral strange particles are identified via their decay daughters in the STAR TPC

As seen with Au+Au data, the yields appear to have exponential behaviour up to 5-6 GeV, the K0

Short

yields up to ~2-3 GeV

STAR Preliminary

STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Spectra Comparisons

Thermal component pushes out further in Cu+Cu for similar <Npart>

Fit Range

Fit RangeSTAR Preliminary

STAR Preliminary

Although Au+Au has slightly larger <Npart>, thermal component more prominent in Cu+Cu at high pT Despite much bigger Au+Au system, thermal/fragmentation components comparable at high pT

Cu+Cu and Au+Au spectra are fit with a Maxwell-Boltzmann at low pT

– Au+Au spectra from Phys. Rev. Lett. 98 (2007) 06230 and nucl-ex/0601042

Each spectra are then divided by the respective fit function

– Aim is to access the relative thermal and fragmentation contributions for each system…

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Thermal component pushes out further in Cu+Cu for similar <Npart> Although Au+Au has slightly larger <Npart>, thermal component more prominent in Cu+Cu at high pT Again, despite much bigger Au+Au system, thermal/fragmentation components comparable at high pT

Spectra Comparisons

Fit Range

Fit RangeSTAR Preliminary

STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

K0Short Spectra Comparisons

Thermal/fragmentation contributions appear similar for both systems...

Fit Range

Fit Range

STAR Preliminary

STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Integrated Yields vs. <Npart>

All species show an enhanced production in Cu+Cu…

– <Npart> appears not to provide satisfactory scaling for both systems

STAR Preliminary STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Cu+Cu 200 GeV STAR Preliminary

/K0Short Ratio

Common low pT and high pT values for all systems and centralities

Mid pT ratios don’t scale with <Npart> for the different systems

Cu+Cu <Npart> = 98.3 Au+Au <Npart> = 141.4 Cu+Cu <Npart> = 46.2 Au+Au <Npart> = 61.8 Cu+Cu <Npart> = 21.2 Au+Au <Npart> = 20.5

STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

/K0Short Ratio

Central /K0Short ratio can be divided

by peripheral to give RCP()/RCP(K0

Short):

– Measure of relative strange baryon/meson difference

– Remarkable consistency for different energies.

Add in Cu+Cu with similar C and P:

– Consistency extends to the lighter system…

– Central <Npart>/Peripheral <Npart> ~ 5 for Cu+Cu and Au+Au at 200 GeV

STAR Preliminary

Low and high pT ratios ~ 1

M. Lamont, SQM 2006

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

Summary

Enhanced production via thermal processes of strangeness in Cu+Cu– Thermal component of and spectra pushes out further in pT

, and K0Short integrated yields per participant are higher

Higher mid-pT / K0Short ratios in Cu+Cu for similar <Npart>

– Suggests that increasing peak is mediated by increasing thermal production

RCP()/RCP(K0Short) shows remarkable consistency for heavy systems

across different energies– This is extended to the Cu+Cu for similar definitions of C and P

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √sNN = 200 GeV Anthony Timmins, 24th June 2007

STAR

AcknowledgementsĎAKUJEM STAR….

University of Illinois at Chicago - Argonne National Laboratory Institute of High Energy Physics - University of Birmingham - Brookhaven National Laboratory - California Institute of Technology - University of California, Berkeley - University of California, Davis - University of California, Los Angeles - Carnegie Mellon University - Creighton University – Nuclear Physics Inst., Academy of Sciences - Laboratory of High Energy Physics - Particle Physics Laboratory - University of Frankfurt - Institute of Physics, Bhubaneswar - Indian Institute of Technology, Mumbai - Indiana University Cyclotron Facility - Institut de Recherches Subatomiques de Strasbourg - University of Jammu - Kent State University - Institute of Modern Physics - Lawrence Berkeley National Laboratory - Massachusetts Institute of Technology - Max-Planck-Institut fuer Physics - Michigan State University - Moscow Engineering Physics Institute - City College of New York - NIKHEF and Utrecht University - Ohio State University - Panjab University - Pennsylvania State University - Institute of High Energy Physics - Purdue University – Pusan National University - University of Rajasthan - Rice University - Instituto de Fisica da Universidade de Sao Paulo - University of Science and Technology of China - Shanghai Institue of Applied Physics - SUBATECH - Texas A&M University - University of Texas, Austin - Tsinghua University - UNICAMP - Valparaiso University – Variable Energy Cyclotron Centre, Kolkata - Warsaw University of Technology - University of Washington - Wayne State University - Institute of Particle

Physics - Yale University - University of Zagreb