1 Energy and system size dependence of strangeness production, from SPS to RHIC Jun Takahashi & Marcelo Munhoz for the STAR collaboration

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 2/34 Motivation In A+A, With a QGP scenario strangeness production is expected to be enhanced. Strangeness enhancement has been observed from various data from SPS and RHIC. In p+p, Strangeness production may be limited due to canonical suppression. This suppression should scale with the strange quark content of the particles. Energy dependence of the yields: Can we see any dramatic variation in the excitation function of different parameters? Chemical Equilibrium: Is strangeness equilibrated? Baryon to Meson enhancement and R CP behavior in the intermediate p T region.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 3/34 The STAR experiment STAR is a large acceptance collider detector. We have accumulated a large amount of data that allows a systematic study of the strangeness production, both as a function of energy and as a function of system size. Strange particles are identified through various analysis methods, such as: V0 and Cascade reconstruction, event mixing and dE/dx. In this presentation, I will mainly concentrate on the weak decaying strange particles: K 0 s, Λ, Ξ, Ω.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 4/34 Data RHIC data: STAR p+p  200 GeV d+Au  200 GeV Au+Au  200 GeV  130 GeV  62.4 GeV  19.6 GeV Cu+Cu  200 GeV  62.4 GeV (some very preliminary results) SPS data: NA57 & NA49 Pb+Pb

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 5/34 System Size: Event centrality classes are defined based on the measured charge particle multiplicities. The equivalent number of particles that participate in the reaction N part is calculated using Glauber Model, that also provides the equivalent number of binary collisions N Coll or N Bin. Phys. Rev.C 70, (2004)

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 6/34 System Size: Au+AuCu+Cu CentN part N Bin CentN part N Bin ± ± ± ± ± ± ± ± ± ± ± 5.82 ± ± ± ± ± ± ± ± ± ± ± 3.9

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 7/34 CuCu200 spectra: K 0 s and Λ´s 55M min-bias events analyzed. High statistic data, with spectra extended to high p T coverage. Fully corrected spectra, with feed-down corrections. From A. Timmins

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 8/34 CuCu200 spectra: Ξ´s and Ω´s STAR Preliminary Statistics is high enough to separate even the Ω spectra in different event centrality classes. After efficiency, acceptance and feed-down correction, total yield is obtained from a fit using a Boltzmann function. STAR Preliminary

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 9/34 Λ Spectra Comparison between Au+Au and Cu+Cu From A. Timmins Talk on sunday Λ spectra measured from Cu+Cu(0-10%) has same shape as spectra measured in Au+Au(20-40%), with equivalent N part. Shows deviation from Maxwell-Boltzmann behavior at high p T. STAR Preliminary

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 10/34 Ξ spectra shows same shape and slope parameter for Cu+Cu(0-10%) and Au+Au (20-40%). Ξ error bars are larger but, similar trend as seen in the Lambda spectra can be observed with a deviation from exponential at the high pt region. STAR Preliminary Ξ Spectra Comparison between Au+Au and Cu+Cu

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 11/34 Mean Transverse momentum of Ξs and Ωs. Spectra measured from Au+Au seems to be harder than p+p. For Au+Au collisions, does not seem to vary with N part, in the measured range. Ω spectra shows higher than Ξ´s. New Cu+Cu data seems to be consistent with Au+Au values. STAR Preliminary

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 12/34 CuCu200 & AuAu200 Yields: K 0 s, and Λ´s Au+Au: particle yields increase with system size. Cu+Cu: On a first look, data seems to be consistent with Au+Au yields. Central Λ yields from Cu+Cu data seems to be slightly higher than the equivalent centrality region in Au+Au. Red symbols are for Au+Au 200GeV Black symbols are for Cu+Cu 200 GeV Solid symbols are for the particles Open symbols are for anti-particles.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 13/34 Clear enhancement of hyperon production in Au+Au compared to pp. Strangeness enhancement over p+p data is already observed at most peripheral Au+Au bin. Difference between baryon and Anti-baryon is expected due to non-zero net baryon number. Clear increase of strangeness enhancement with strange quark content, indicating enhancement hierarchy that is in accordance to GC Thermal production. Strangeness enhancement show dependence with volume (N part ) which disagrees with GC thermal production. STAR Preliminary Strangeness Enhancement: Au+Au 200 GeV nucl-ex/ A. Tounsi, A. Mischke and K. Redlich, Nucl. Phys. A 715, 565 (2003).

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 14/34 Still see clear hyperon enhancement in Cu+Cu data. On a first look, Cu+Cu data seems to be consistent with enhancement observed at Au+Au. Λ enhancement from most central Cu+Cu data seems to be higher than equivalent Au+Au data, should try different scaling. STAR Preliminary Strangeness Enhancement: AuAu200 & CuCu200

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 15/34 Statistical Thermal Model: Cu+Cu 200 GeV Statistical Thermal Model (THERMUS) * was used fitting T ch, μ B, μ S, and γ S (strangeness saturation factor). Particles used in the fit: π, K, p, Λ, Ξ, Ω. Particles were corrected for weak decays. Measured particle ratios are reasonably well fit with statistical thermal model. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 16/34 Statistical Thermal Model: Au+Au 200 GeV Statistical Thermal Model (THERMUS) * was used fitting T ch, μ B, μ S, and γ S (strangeness saturation factor). Particles used in the fit: π, K, p, Λ, Ξ, Ω. Particles were corrected for weak decays. Measured particle ratios are reasonably well fit with statistical thermal model. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 17/34 Statistical Thermal Model: Au+Au 62.4 GeV Statistical Thermal Model (THERMUS) * was used fitting T ch, μ B, μ S, and γ S (strangeness saturation factor). Particles used in the fit: π, K, p, Λ, Ξ, Ω. Particles were corrected for weak decays. Measured particle ratios are reasonably well fit with statistical thermal model. Ratio K 0 /π was excluded to improve chi2. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 18/34 Statistical Thermal Model: Fit parameters vs. system size Baryon chemical potential μ B is small for Au+Au 200 GeV. Small variation with system size. μ S is consistent with zero. Au+Au 62 GeV data shows higher value of baryon chemical potential. Au+Au 62 GeV shows larger variation with system size when compared to Au+Au 200 GeV. Cu+Cu 200 GeV baryon chemical potential seems to be in good agreement with Au+Au 200 GeV. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/ Cu+Cu 200 GeV

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 19/34 Statistical Thermal Model: Fit parameters vs. system size Temperature seems constant with system size for Au+Au 200 GeV. Au+Au 62 GeV data shows same temperature values of Au+Au 200 GeV and also no system size dependence can be observed within error bars. Cu+Cu 200 GeV temperature shows a smaller value then compared to Au+Au data, but is in agreement within error bars. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/ Cu+Cu 200 GeV

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 20/34 Statistical Thermal Model: Fit parameters vs. system size Strangeness saturation constant, shows an increase with system size, reaching saturation around N part ~150. Au+Au 62 GeV data shows same values and behavior of Au+Au 200 GeV. Cu+Cu 200 GeV data fits seems to yield a strangeness saturation constant consistent with 1. * Thermus, A thermal Model Package for Root S. Wheaton & Cleymans, hep-ph/ Cu+Cu 200 GeV

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 21/34 Statistical Thermal Model: Excitation function

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 22/34 Particle ratios SPS data from NA49 AGS data from E896 & E802 STAR preliminary Smooth rise of ratio with energy from SPS to RHIC, indicating an evolution from baryon transport regime to pair production dominated regime. Ratio approaching baryon free environment at RHIC energies. The higher the strangeness content, ratio is closer to unity. New Cu+Cu data seems to follow systematic. Ratio seems to be the same, independent of the system size.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 23/34 Baryon Excitation function Above AGS energies baryon yield is relatively constant with energy. Λ yield variation with energy seems to follow proton dependence. For LHC: Λ ~ Ξ ~ 3-6 Ω ~ STAR Preliminary

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 24/34 Anti-Baryon Excitation function Anti-baryon yield increase continuously and smoothly with energy, indicating smooth increase of pair- production. STAR Preliminary

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 25/34 Baryon to Meson ratio: Au+Au 62 GeV & Au+Au 200 GeV Baryon enhancement in the intermediate p T region observed in p/π ratio, consistent with recombination model. Λ/K 0 S ratio shows that strange baryon production is also enhanced over strange meson production in the intermediate p T region. Strange baryon enhancement is higher than enhancement observed with p/π ratio. Au+Au 62 GeV also shows baryon to meson enhancement at intermediate p T. Values seems to be higher than Au+Au 200 GeV data. Lambdas are not feed-down corrected

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 26/34 Baryon to meson ratio: Cu+Cu 200 GeV & Au+Au 200 GeV STAR preliminary Baryon to meson enhancement is also observed in Cu+Cu data, but seems to be higher then in Au+Au data when comparing equivalent centrality classes.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 27/34 Baryon to meson enhancement Higher enhancement of Λ to K 0 s in the intermediate p T region in Cu+Cu 200 GeV when comparing to Au+Au 200 GeV. These seems to be also a energy dependence of the baryon to meson enhancement.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 28/34 Nuclear Modification factor: Au+Au 200 GeV Baryon meson difference in the intermediate p T region is also observed in R cp and R AA plots for strange particles. R AA of protons seems to be different from the R AA of strange particles, where higher values of R AA are observed for strange particles. Maybe canonical suppression of strangeness production in p+p collisions observed in low pt region extends to the intermediate p T region causing the increase of R AA ratio, something that cannot be observed with R cp plots. This is different from Cronin effect. STAR preliminary nucl-ex/

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 29/34 R cp - Nuclear Modification factor: Cu+Cu 200 GeV & Au+Au 200 GeV Similar suppression observed in Cu+Cu at high p T for same centrality ratios. Similar baryon meson suppression difference seen in the intermediate p T region.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 30/34 R cp - Nuclear modification factor: Au+Au 62 GeV & Au+Au 200 GeV Similar suppression observed in Au+Au 62.4 GeV at high p T. Similar baryon meson suppression difference seen in the intermediate p T region.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 31/34 Difference between mesons & baryons R cp This ratio describes how different is the baryon R cp from the meson R cp in the intermediate p T region. Remarkable consistency is seen between different systems and different energies.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 32/34 Summary / Conclusions New Cu+Cu data was compared with Au+Au data scaled by N part to study system size dependence.  Overall yields and spectra shape seems to be consistent with the equivalent peripheral Au+Au collision.  Lambdas produced at most central event centrality classes seems to show higher yield compared to the equivalent Au+Au peripheral collision. Perhaps a higher thermalization degree is achieved for Cu+Cu central collisions?  Ξ and Ω are consistent within error with Au+Au data, but, error bars are large and may not be sensitive to an enhancement over Au+Au data.  We are currently analyzing Cu+Cu 62.4 GeV data that should enrich this systematic study.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 33/34 Summary / Conclusions Statistical Thermal model fits reasonably well the particle ratios measured in STAR, indicating that data is consistent with a thermalized system.  Au+Au 200 and 62 GeV: Centrality dependence of thermal fits show increase of the strangeness saturation parameter, and it reaches 1 only after N part ~150.  Cu+Cu200 GeV: yields the same temperature and baryon chemical potential values obtained from the fit to Au+Au data, but, the strangeness saturation parameter is already at 1, even in the peripheral events. Excitation functions of strange baryon production don’t show any surprises. At intermediate p t, baryon to meson enhancement is observed.  Λ/π ratio shows an enhancement higher than the enhancement observed with p/π.  The enhancement increases with centrality and are different for Au+Au 62 and 200 GeV and Cu+Cu 200 GeV data.  Nuclear modification factor R cp data also consistent with baryon to meson enhancement in the intermediate p T.  Even in a small system like Cu+Cu, we still see a suppression at high p T region and the baryon to meson difference in the intermediate p T region.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 34/34 The STAR Collaboration 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 - 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 -UNICAMP

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 35/34

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 36/34 p/π - Baryon to meson ratio (PHENIX) PHENIX Preliminary Cu+Cu D. Morrison, SQM2006 Au+Au 200 GeV M. Konno, JPS2007 Baryon to meson ratio show baryon enhancement in the intermediate pt region.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 37/34 R cp - Nuclear modification factor: AuAu62 & AuAu200

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 38/34 Scaling with charge particle production (dN ch /dy)

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 39/34 SPS NA57 data also shows clear enhancement behavior. Enhancement rate at RHIC seems to be lower than the enhancement observed at SPS data. Need to check if the enhancement reduction is in agreement with GC Thermal model predictions. NA57 data from nucl-ex/ Strangeness Enhancement: RHIC & SPS

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 40/34 Total Yield STAR Preliminary After efficiency, acceptance and feed-down correction, total yield is obtained from a fit using a Boltzmann function.

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 41/34 Scaling with N bin

Jun Takahashi for the STAR collaboration, Levoca, Slovakia 42/34 Lambda/K0s from SPS