Overview of Strangeness Production for the STAR Experiment… Anthony Timmins for the STAR Collaboration

Contents Bulk Strangeness Production… Thermal Model Comparisons… Mid-pT Particle Spectra… v2 Measurements… Low Energy Scan… Fragmentations Functions in p+p… Summary…

Bulk Strangeness Production What did we learn at the SPS?    J. Phys. G 32 (2006) 427-441 Canonical formalism (Phys. Lett. B 486 (2000) 61) reproduces various features… Thermal model for hadron gas Insists strangeness conservation strictly met Strangeness production more suppressed in smaller system Assumes system volume  Npart Observed strangeness enhancement not unique to QGP formation… What can the data at RHIC tell us? 1)One of the major findinngs in the SPS progrmams Led to statement…. 2) Enhancement factor = yields/Npart divided by yields/Npart PP at 17.3 GeV Lagre deviations observed from pp Factor of 20 for Omega, 3) Finish on 3rd point…. CERN Press statement: "The combined data coming from the seven experiments on CERN's Heavy Ion programme… We now have evidence of a new state of matter where quarks and gluons are not confined. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and later to CERN's Large Hadron Collider." CERN Press statement: "The combined data coming from the seven experiments on CERN's Heavy Ion programme… We now have evidence of a new state of matter where quarks and gluons are not confined. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and later to CERN's Large Hadron Collider." CERN Press statement: "The combined data coming from the seven experiments on CERN's Heavy Ion programme… We now have evidence of a new state of matter where quarks and gluons are not confined. There is still an entirely new territory to be explored concerning the physical properties of quark-gluon matter. The challenge now passes to the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and later to CERN's Large Hadron Collider."

Bulk Strangeness Production Cu+Cu and Au+Au 200 GeV… Enhancement in strangeness production has been established for Au+Au at 200 GeV Canonical formalism again reproduces various features… AGS and SPS showed strangeness systematics don’t scale with Npart in light and heavy systems Does this apply to Cu+Cu and Au+Au at 200 GeV? Higher yields in (mid) central Cu+Cu at given Npart Inconsistent with Canonical formalism… Also applies to non strange sector… 3) Will see this later…. arXiv:0809.0823v1 [nucl-ex]

Bulk Strangeness Production Cu+Cu and Au+Au 62 GeV… STAR Preliminary Marcelo Gameiro Munhoz, SQM 2008 What about Cu+Cu and Au+Au 62.GeV?  and K0S exhibit similar patterns as 200 GeV.. Same applies to multi-strange sector…

Bulk Strangeness Production The  particle… STAR Preliminary  particle shows above unity enhancement for Cu+Cu and Au+Au 200 GeV Contrary to naive interpretation of the Canonical model… Enhancement=1 for particles with closed strangeness…  enhancement sits between  and  Dynamical effect boosting  yield? Core/Corona effect? arXiv:0805.0098v2 Differences between Cu+Cu Au+Au not observed within errors for 62 and 200 GeV… J. Phys. G. Nucl. Part. Phys. 35 (2008) 044031

Bulk Strangeness Production EPOS and AMPT comparisons… STAR Preliminary EPOS (Phys. Rev. Lett. 98 (2007) 152301) Core hadron production Aims to mimic QGP High density region follows statistical emission… Upon hadronization, strangeness oversaturated with s>1 Corona hadron production Superposition of p+p collisions Strangeness under-saturated with s<1 Strangeness conservation precisely met… AMPT (Phys.Rev. C72 (2005) 064901): HIJING based model Soft hadron production is from by nucleon excitation and string breaking.. Hard hadron production from (mini) jets Mini-jet partons and newly produced hadrons allowed to rescatter… arXiv:0810.0017v1 [nucl-ex]

Bulk Strangeness Production EPOS and AMPT comparisons… STAR Preliminary arXiv:0810.0017v1 [nucl-ex] Model Comparisons Both models reproduce key qualitative features for , anti- and K0S Rising per participant yields for a given system Higher yields at given Npart for Cu+Cu EPOS does better for strange baryons… Multi-strange predictions?

Bulk Strangeness Production Mid-rapidity s+s rates… STAR Preliminary Approximate total strangeness production at y~0 at 200 GeV Add yields from single and multi-strange particles AMPT shows… If main s+s production is from string fragmentation in initial collisions Mechanism sufficient in producing s+s yield for Cu+Cu and Au+Au… EPOS shows… Hadronization of s+s quarks may require core+corona mechanism Gives better description of strange baryon yields compared to AMPT mod arXiv:0810.0017v1 [nucl-ex]

Thermal Model Comparisons Chemical freeze out… STAR Preliminary STAR Preliminary Jun Takahashi SQM 2008 Thermus package (hep-ph/0407174) used to extract statistical parameters from particle ratios … Canonical and Grand Canonical implementations compared to data Chemical freeze-out temperature constant of over all systems and centralities…

Thermal Model Comparisons Strangeness saturation… STAR Preliminary arXiv:0806.0286v1 [nucl-ex] Jun Takahashi SQM 2008 STAR Preliminary S indicates deviation for strangeness production from equilibrium expectations Despite higher strangeness production for Cu+Cu at given <Npart> Cu+Cu and Au+Au lie on the same trend… S controlled by K/ ratio? Also lies on same trend for Cu+Cu and Au+Au…

Mid-pT Spectra RCP in Cu+Cu 200 GeV… RCP contrasts production per binary collision in central and peripheral collisions Systematic differences found for mid-pT baryons and mesons in Au+Au 200 GeV Interpretation: Production from coalescence more favorable for baryons Such differences apply to Cu+Cu collisions… RCP < 1 at pT >~ 5 GeV: Jet quenching occurs in central Cu+Cu… STAR Preliminary J. Phys. G. Nucl. Part. Phys. 35 (2008) 104074

Mid-pT Spectra RCP in Cu+Cu 62 GeV… J. Phys. G: Nucl. Part. Phys. 35 (2008) 044062 STAR Preliminary 2) Animate the 200 GeV particles in after 62….. Marcelo Gameiro Munhoz, SQM 2008 How Does RCP change with energy for Cu+Cu 62 and 200 GeV collisions?  and K0S lie on the same curve Same pattern observed for Pb+Pb 17.4 GeV, Au+Au 62.4 GeV 200 GeV Coalescence in all systems?

Mid-pT Spectra Particle ratios… Cu+Cu@200GeV Au+Au@200GeV STAR preliminary J. Phys. G. Nucl. Part. Phys. 35 (2008) 104074 Previous Au+Au data shows / ratio consistent with coalescence predictions Applies to Cu+Cu… Anti-Baryon/Baryon ratios constant for all pT in central Cu+Cu collisions / and / ratios lie on the same trend May have some relevance in the coalescence framework (nucl-th/0801.2265)

v2 Measurements Probe of initial conditions… Nature 448 (19 July 2007) 302 Hiroshi Masui, SQM 2008 Characterizes the conversion from initial spatial anisotropy to momentum anisotropy… Initial hydrodynamic predictions appeared to describe mass and pT dependence for Au+Au 200 GeV collisions What is observed for Cu+Cu?

v2 Measurements Quark scaling… Phys. Rev. C 75 (2007) 54906 Hiroshi Masui, SQM 2008 Quark v2 (v2/nq) vs Quark Kinetic Energy (mT - mass)/nq Scaling expected in coalescence framework where kinetic energy is conserved (Phys. Rev. C 75 (2007) 03190) Au+Au 200 GeV results showed this scaling applied across full pT for minbias collisions… Cu+Cu 200 GeV collisions show.. Particles lie on same curve for 0-60% Also applies to 0-20% and 20-60%…. 1) Indrioduce plot after first after first point

v2 Measurements Hydro-limit not reached at RHIC? Yuting Bai, SQM 2008 is 1 when K=0 Right panel: Transport model fits v2 to data; division of v2/epsilon-hydro tells you how far the system Transport theory Gives v2/ as a function of system density… Finite Knudsen number K indicates deviation from ideal hydro K=0 Ideal hydro, K > 0 Non-ideal hydro Curve shows decreasing K with increasing system density… Hydro limit not reached for Cu+Cu and Au+Au strange particle v2?

Low Energy Scan Motivation… NSAC 2007 Long-range Plan Various lattice QCD calculations prediction a thermodynamic critical point QGP  hadron gas phase transition becomes first order at the higher values of B RHIC has the capability to provide heavy-ion collisions with sNN ~ 5  50 GeV Large acceptance detector (AKA STAR) best placed to investigate… Proposed scan aims to cover all predicted critical points with respect to B Very much the future of RHIC program… Lokhesh Kumar, SQM 2008

Low Energy Scan Multiplicity distributions… Lokhesh Kumar, SQM 2008 3000 Au+Au 9.4 GeV collisions recorded early 2008 in 4 hours Measured multiplicity distribution well reproduced by simulation: Monte Carlo Glauber + Kharzeev-Nardi

Low Energy Scan K/ ratios… STAR Preliminary Lokhesh Kumar, SQM 2008 STAR’s K+/+ and K-/- and ratios sit on world trend Same applies to K-/K+, -/+ and p-/p+ ratios Year 1’s Au+Au 19 GeV results also consistent.. STAR detector very much ready to take more data…

Fragmentation Functions in p+p Charged hadron and strange meson and baryon… Mh ~ 200-300 MeV M ~ 1000 MeV MK ~ 500 MeV  Full jet reconstruction in p+p 200 GeV allows for measurement of fragmentation functions Number density of given hadron with given pT per jet with energy Ejet Expressed in terms of  Charged hadron fragmentation functions compare well with PYTHIA… True for all jet energies.. What happens for strangeness? QCD models predict mass ordering of  Phys. Lett. B 273 (1991) 319 Not reproduced by data! Errors still under study… 20< Ejet< 50 GeV This is somethinh a little, but in my view this reasserts the importantance of strangeness production in our understanding of QCD…. Logarithmic measure of momentum… 2) arXiv:0809.3769v1

Fragmentation Functions in p+p /K0S as a function of  and pT… arXiv:0809.3769v1 10< Ejet< 15 GeV Phys. Rev. C 75 (2007) 64901 What about the /K0S ratio in jets? Approaches one at mid-pT from high-pT .. <Ncharge> dependence observed for inclusive mid-pT ratio Higher <Ncharge> in p+p event, higher probability of hard parton scatter…

Summary Bulk Strangeness Production in Heavy-ion Collisions Yields do not scale with <Npart> in Cu+Cu and Au+Au: reproduced by AMPT and EPOS at 200 GeV Processes in initial collisions appear sufficient in producing bulk strangeness, core-corona needed to get better agreement for strange baryon yields Tch and S lie on same trend for Cu+Cu and Au+Au as a function of <Npart> Mid-pT Spectra Baryon-meson RCP differences apply to Cu+Cu collisions Cu+Cu / ratios described by coalescence predictions v2 Measurements Quark scaling holds for strange meson and baryon v2 vs pT in Cu+Cu Transport theory indicates hydro limit may not be reached in heavy-ion collisions Low Energy Scan STAR has collected first data Global consistency already achieved with other experiments Fragmentation Functions in p+p Observed mass ordering of 0 contrary to QCD expectations /K0S ~1 at pT 2-3 GeV/c for jets

Summary  Yuting Bai  K Thermal production of particles at RHIC Jun Takahashi Strange and multi-strange hadron production in Cu+Cu collisions at 62.4 GeV at RHIC Marcelo Gameiro Munhoz System size, energy and centrality dependence of strange hadron elliptic flow at STAR Hiroshi Masui Anisotropic flow: indications for incomplete thermalization Yuting Bai First results from Au+Au collisions at 9.2 GeV in STAR Lokesh Kumar   K