STAR The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au with √s NN = 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 √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Contents  Motivation  The Cu+Cu Dataset   Spectra Comparisons  K 0 Short Spectra Comparisons  Integrated Yields vs.  The  /K 0 Short Ratio  Summary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Motivation Strangeness 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   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 √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Motivation Strange Baryon/Meson Differences  For Au+Au collisions, increasing mid-p T  /K 0 Short ratios are observed with increasing centrality  Competing particle production mechanisms at mid p T ; –Thermal processes more prominent for  –Fragmentation for K 0 Short  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 √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Cu+Cu  s NN = 200 GeV Data Set  Large amount of data taken in 2005: –55 million events for this analysis –  particles reach p T of 8 GeV/c, K 0 Short 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 K 0 Short yields up to ~2-3 GeV STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR  Spectra Comparisons  Thermal component pushes out further in Cu+Cu for similar Fit Range STAR Preliminary  Although Au+Au has slightly larger, thermal component more prominent in Cu+Cu at high p T  Despite much bigger Au+Au system, thermal/fragmentation components comparable at high p T  Cu+Cu and Au+Au spectra are fit with a Maxwell-Boltzmann at low p T –Au+Au spectra from Phys. Rev. Lett. 98 (2007) and nucl- ex/  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 √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR  Thermal component pushes out further in Cu+Cu for similar  Although Au+Au has slightly larger, thermal component more prominent in Cu+Cu at high p T  Again, despite much bigger Au+Au system, thermal/fragmentation components comparable at high p T  Spectra Comparisons Fit Range STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR K 0 Short Spectra Comparisons  Thermal/fragmentation contributions appear similar for both systems... Fit Range STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Integrated Yields vs.  All species show an enhanced production in Cu+Cu… – appears not to provide satisfactory scaling for both systems STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR Cu+Cu 200 GeV STAR Preliminary  /K 0 Short Ratio  Common low p T and high p T values for all systems and centralities  Mid p T ratios don’t scale with for the different systems Cu+Cu = 98.3 Au+Au = Cu+Cu = 46.2 Au+Au = 61.8 Cu+Cu = 21.2 Au+Au = 20.5 STAR Preliminary

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR  /K 0 Short Ratio  Central  /K 0 Short ratio can be divided by peripheral to give RCP(  )/RCP(K 0 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 /Peripheral ~ 5 for Cu+Cu and Au+Au at 200 GeV STAR Preliminary Low and high p T ratios ~ 1 M. Lamont, SQM 2006

The Centrality Dependence of Strange Baryon and Meson Production in Cu+Cu and Au+Au √s NN = 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 p T – ,  and K 0 Short integrated yields per participant are higher  Higher mid-p T  / K 0 Short ratios in Cu+Cu for similar –Suggests that increasing peak is mediated by increasing thermal  production  RCP(  )/RCP(K 0 Short ) 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 √s NN = 200 GeV Anthony Timmins, 24th June 2007 STAR 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