12-17 February 2007 Winter Workshop on Nuclear Dynamics STAR identified particle measurements at large transverse momenta in Cu+Cu collisions at RHIC Richard Hollis for the STAR collaboration

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics outline previous results and motivation data analysis data, comparison and interpretation high-p T and low-p T phenomena across energy and system-size summary

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics previous results and motivation

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics two effects: relative to p+p collisions spectral suppression B/M enhancement in Au+Au effect are turned on and off dependent on centrality how can one understand these effects? system size dependence energy* dependence * discussed in the previous talk by Bedanga Phys.Rev.Lett. 91 (2003) Phys.Rev.Lett. 97 (2006) Phys.Lett. B637 (2006) 161 previous results: inclusive spectra & B/M ratio

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics motivation: 1. why high-p T ? why do we look at high-p T ? cartoon showing the relative effects of N part and N coll scaling calculable by pQCD

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics motivation: 2. why identified particles? why do we look at identified particles? at high-p T affords insight into gluon and quark jet production gluon jets produce more baryons than quark jets a probe relative energy loss for quark and gluon jets expected, but not seen Phys.Lett. B606 (2005) 303

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics motivation: 3. why Cu+Cu? smaller system-size is Central Cu+Cu ~ Central Au+Au? or Central Cu+Cu ~ Peripheral Au+Au? observe path length effects of energy loss with Cu+Cu can explore the turn on of the suppression Phys.Lett. B639 (2006) 38 p T >6GeV/c

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data analysis

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: analysis analysis summary low-p T (0.2<p T <1.2) energy loss in TPC clear particle separation low- to intermediate-p T (0.2<p T <3.0) TOF clear particle separation high-p T (p T >2.5) relativistic rise of energy loss in TPC statistical separation

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: low-p T analysis summary direct identification from separated bands at low-p T 4-gaus fits determine the yield  -, e -, K -,pbar data are then corrected for feed-down track efficiency Negative Particles

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: high-p T analysis summary use the relativistic rise of energy loss at high-p T estimate K contribution from bin-counting 3-gaus fits (with K fixed) data are then corrected for feed-down track efficiency variety of methods for the kaon contribution are used: bin counting, K 0 data and TOF data

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics preliminary results

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: preliminary results spectra 1<p T <2 GeV/c gap will be filled by TOF - analysis underway in STAR  spectra proton spectra

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: preliminary results anti-particle to particle ratios     and pbar/p ratios: no centrality dependence similar p T dependence as found in Au+Au collisions pbar/p consistent with Vitev model Phys.Rev.C 71 (2005)

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: preliminary results nuclear modification factor systematic differences in R AA between  and p data  data are flatter with p T (at high-p T ) p data have a weak centrality dependence

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: preliminary results proton/pion ratios baryon/meson enhancement intermediate-p T enhancement in baryon production is observed maximal enhancement at p T ~2GeV/c centrality independent for p T >5GeV/c Phys.Lett. B37 (2006) 161

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data interpretation how do the new data compare to existing data?

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics Cu+Cu data: questions: how do Cu+Cu and Au+Au compare? fractional cross-section number of collisions/participant number of particles produced (N ch at mid-rapidity) i.e. Cu+Cu (0-20%) =? Au+Au (0-20%) or Cu+Cu (N part ) =? Au+Au (N part )* or Cu+Cu (N ch ) =? Au+Au (N ch ) * Note that from a Glauber Model calculation, the functional form of N coll is the same for Au+Au and Cu+Cu collisions

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison nuclear modification factor Cross-sectionN part similar dependence for same N part Phys.Rev.Lett. 97 (2006) Phys.Lett. B37 (2006) 161

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison baryon/meson enhancement Cross-sectionN part similar dependence for same N part Phys.Lett. B37 (2006) 161 Phys.Rev.Lett. 97 (2006)

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison path length effects centrality dependence probes different jet propagation lengths system-size dependence adds additional new dimension Phys.Lett. B37 (2006) 161 Phys.Rev.Lett. 97 (2006)

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison path length effects enhancement of baryons gluon jets are more easily propagated? more gluon jets initially produced or induced for more central data? need further differential analysis to investigate this versus reaction plane? current statistics too limited for this analysis Phys.Lett. B37 (2006) 161 Phys.Rev.Lett. 97 (2006)

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison observed scaling properties at low-p T Mean-p T Kinetic Freeze-out temperature for same energy: scaling observed for same N part energy dependence: scaling observed with N ch A.Iordanova, QM2006 poster

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics data: comparison high-p T similar scaling trends? scaling with N ch (at mid-rapidity) for high-p T data data from B.Mohanty, QM2006 STAR Preliminary STAR Preliminary Au+Au 200GeV Au+Au 62.4GeV Au+Au 200GeV Au+Au 62.4GeV ++-++- ++-++-

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics summary we have a systematic data sample of identified  and p(p) measured at RHIC systematic effects are observed versus the system size of the collision  suppression at large transverse momenta (R AA ) for larger system sizes (i.e. more central data) enhanced p/  ratio at intermediate p T N ch scaling for low- and high-p T particles further differential measurements are needed to help determine the precise nature of the collision dynamics

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics auxiliary slides

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics why more baryons in gluon jets? e + +e - collisions gluon jets result in: softer fragmentation function higher multiplicities softer → energy must go into particle production more particles heavier particles

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics why more mesons in quark jets? in fragmentation: much more likely to produce a than

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics recombination and fragmentation competing processes: recombination fragmentation high-p T dominated by fragmentation? intermediate-p T dominated by recombination? Figs from B. Muller: nucl-th/ , R. Fries: QM 2004, PRL (2003) DATA and FITS Thermal Exponential pQCD power-law

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics recombination and fragmentation Figs from B. Muller: nucl-th/ , R. Fries: QM 2004, PRL (2003) fragmenting parton: p h = z p, z<1 recombining partons: p 1 +p 2 =p h fragmentation: lessens B/M recombination: enhances B/M

STAR February 2007 Richard Hollis University of Illinois at Chicago Winter Workshop on Nuclear Dynamics comparison of data comparison of PHENIX low- to intermediate-p T to STAR high-p T data note: PHENIX: 0-10% Central STAR: 0-20% Central