Anthony Timmins for the STAR Collaboration 24th June 2007

1. 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

2. Contents • Motivation • The Cu+Cu Dataset •  Spectra Comparisons •  Spectra Comparisons • K0Short Spectra Comparisons • Integrated Yields vs. <Npart> • The /K0Short Ratio • Summary

3. 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

4. MotivationStrange Baryon/Meson Differences • For Au+Au collisions, increasing mid-pT /K0Short 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

5. 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 K0Short yields up to ~2-3 GeV STAR Preliminary STAR Preliminary

6. Fit Range Fit Range Spectra Comparisons • 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… • Thermal component pushes out further in Cu+Cu for similar <Npart> STAR 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

7. Fit Range Fit Range Spectra Comparisons • Thermal component pushes out further in Cu+Cu for similar <Npart> STAR Preliminary STAR Preliminary • Again, despite much bigger Au+Au system, thermal/fragmentation components comparable at high pT • Although Au+Au has slightly larger <Npart>, thermal component more prominent in Cu+Cu at high pT

8. Fit Range Fit Range K0Short Spectra Comparisons • Thermal/fragmentation contributions appear similar for both systems... STAR Preliminary STAR Preliminary

9. 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

10. STAR Preliminary Cu+Cu 200 GeV STAR Preliminary Cu+Cu <Npart> = 21.2 Au+Au <Npart> = 20.5 Cu+Cu <Npart> = 46.2 Au+Au <Npart> = 61.8 /K0Short Ratio Cu+Cu <Npart> = 98.3 Au+Au <Npart> = 141.4 • Common low pT and high pT values for all systems and centralities • Mid pT ratios don’t scale with <Npart> for the different systems

11. /K0Short Ratio M. Lamont, SQM 2006 STAR Preliminary • Central /K0Short ratio can be divided by peripheral to give RCP()/RCP(K0Short): • 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 Low and high pT ratios ~ 1

12. 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

13. Acknowledgements ĎAKUJEM 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