Post on 22-Dec-2015
12-17 February 2007
Winter Workshop on Nuclear Dynamics
STARSTAR identified particle measurements at large transverse momenta in Cu+Cu collisions at RHIC
Richard Hollis
for the STAR collaboration
212-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
outline
previous results and motivation
data analysis
data, comparison and interpretation
high-pT and low-pT phenomena across energy and system-size
summary
312-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
previous results and motivation
412-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
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) 072304
Phys.Rev.Lett. 97 (2006) 152301
Phys.Lett. B637 (2006) 161previous results:
inclusive spectra & B/M ratio
512-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR motivation:
1. why high-pT?
why do we look at high-pT? cartoon showing the
relative effects of Npart and Ncoll scaling
calculable by pQCD
612-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR motivation:
2. why identified particles? why do we look at identified
particles? at high-pT 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
712-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR 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
pT>6GeV/c
812-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
data analysis
912-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: analysis
analysis summary
low-pT (0.2<pT<1.2) energy loss in TPC clear particle separation
low- to intermediate-pT (0.2<pT<3.0) TOF clear particle separation
high-pT (pT>2.5) relativistic rise of energy loss in TPC statistical separation
1012-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: analysis @ low-pT
analysis summary direct identification from
separated bands at low-pT
4-gaus fits determine the yield
• -, e-, K-,pbar
data are then corrected for feed-down track efficiency
Negative Particles
1112-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: analysis @ high-pT
analysis summary use the relativistic rise of
energy loss at high-pT
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, K0 data and TOF data
1212-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
preliminary results
1312-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: preliminary results
spectra
1<pT<2 GeV/c gap will be filled by TOF - analysis underway in STAR
spectra proton spectra
1412-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: preliminary results
anti-particle to particle ratios
and pbar/p ratios: no centrality
dependence similar pT dependence
as found in Au+Au collisions
pbar/p consistent with Vitev model
Phys.Rev.C 71 (2005) 041901
1512-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: preliminary results
nuclear modification factor
systematic differences in RAA between and p data data are flatter with pT (at high-pT) p data have a weak centrality dependence
1612-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: preliminary results
proton/pion ratios
baryon/meson enhancement
intermediate-pT enhancement in baryon production is observed maximal enhancement at
pT~2GeV/c
centrality independent for pT>5GeV/c
Phys.Lett. B37 (2006) 161
1712-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
data interpretation
how do the new data compare to existing data?
1812-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR Cu+Cu data:
questions:
how do Cu+Cu and Au+Au compare? fractional cross-section number of collisions/participant number of particles produced (Nch at mid-rapidity)
i.e. Cu+Cu (0-20%) =? Au+Au (0-20%) or Cu+Cu (Npart) =? Au+Au (Npart)* or Cu+Cu (Nch) =? Au+Au (Nch)
* Note that from a Glauber
Model calculation, the
functional form of Ncoll is the
same for Au+Au and Cu+Cu
collisions
1912-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: comparison
nuclear modification factor
Cross-section Npart
similar dependence for same Npart
Phys.Rev.Lett. 97 (2006) 152301
Phys.Lett. B37 (2006) 161
2012-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: comparison
baryon/meson enhancement
Cross-section Npart
similar dependence for same Npart
Phys.Lett. B37 (2006) 161
Phys.Rev.Lett. 97 (2006) 152301
2112-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR 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) 152301
2212-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR 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) 152301
2312-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: comparison
observed scaling properties at low-pT
Mean-pT Kinetic Freeze-out temperature
for same energy: scaling observed for same Npart
energy dependence: scaling observed with Nch
A.Iordanova, QM2006 poster
2412-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR data: comparison
high-pT
similar scaling trends? scaling with Nch (at mid-rapidity) for high-pT data
data from B.Mohanty, QM2006
STAR
Preliminary
STAR
Preliminary
Au+Au 200GeV
Au+Au 62.4GeVAu+Au 200GeV
Au+Au 62.4GeV
++- ++-
2512-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
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 (RAA) for larger system sizes(i.e. more central data)
enhanced p/ ratio at intermediate pT
Nch scaling for low- and high-pT particles
further differential measurements are needed to help determine the precise nature of the collision dynamics
2612-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
auxiliary slides
2712-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
why more baryons in gluon jets?
e++e- collisionsgluon jets result in:
• softer fragmentation function• higher multiplicities
softer → energy must go into particle productionmore particlesheavier particles
2812-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
why more mesons in quark jets?
in fragmentation: much more likely to produce a than qq qqqq
uddu uu
uddddu uu
2912-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
recombination and fragmentation
competing processes: recombination fragmentation
high-pT
dominated by fragmentation?
intermediate-pT
dominated by recombination?
Figs from B. Muller: nucl-th/0404015, R. Fries: QM 2004, PRL 90 202303 (2003)
DATA and FITS
Thermal Exponential
pQCD power-law
3012-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
recombination and fragmentation
Figs from B. Muller: nucl-th/0404015, R. Fries: QM 2004, PRL 90 202303 (2003)
fragmenting parton:ph = z p, z<1
recombining partons:p1+p2=ph
fragmentation: lessens B/M
recombination: enhances B/M
3112-17 February 2007
Richard HollisUniversity of Illinois at Chicago
Winter Workshop onNuclear Dynamics
STARSTAR
comparison of data
comparison of PHENIX low- to intermediate-pT to STAR high-pT data
note: PHENIX: 0-10%
Central STAR: 0-20%
Central