ismd 2005, kromeriz czech republic aug.9-15 1 measurement of identified particle production at rhic...
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ISMD 2005, Kromeriz Czech Republic Aug.9-15 ISMD 2005, Kromeriz Czech Republic Aug.9-15 1
Measurement of identified Measurement of identified particle production at RHICparticle production at RHIC
An TaiUniversity of California at Los Angeles
For the STAR CollaborationFor the STAR Collaboration
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ISMD 2005, Kromeriz Czech Republic Aug.9-15 ISMD 2005, Kromeriz Czech Republic Aug.9-15 2
Outline
• Introduction
• Results from in 200 GeV Au+Au collisions at RHIC new
mechanism for hadronization
• Results from in 200 GeV dAu collisions at RHIC an
important reference
• Heavy flavor production
• Summary
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A Pictorial View of Micro-Bangs at RHIC
Thin PancakesLorentz =100
Nuclei pass thru each other
< 1 fm/c
Huge StretchTransverse ExpansionHigh Temperature (?!)
The Last Epoch:Final Freezeout--
Large Volume
What are properties of matter formed at RHIC ?
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ISMD 2005, Kromeriz Czech Republic Aug.9-15 ISMD 2005, Kromeriz Czech Republic Aug.9-15 4
J/D
K*
K
p
d, HBT
vv22
saturatessaturates
TT
saturatessaturates
Q2
time
Identified particles probing the matter properties
PID in STAR:TPC: tracking p,K,π ….BEMC electron …
*ToF patch p,K,π, electron.
Δφ π/30, -1 < η < 0
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STAR Particle Identification
Electron identification: TOFr |1/ß-1| < 0.03 TPC dE/dx electrons!!!
electrons
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Examples of mass plots
|y|<1
0.4 <pt< 6.0
|y|<1
0.4 <pt< 6.0|y|<1
0.6 <pt< 5.0
K0s, , : topology
cuts, like decay length,
DCA of V0-primV.
: event mixing
technique
|y|<0.5
0.4 <pt< 1.3
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Identified Spectra in Simpler Systems
• Theoretical understanding of p+p reference not completely under control• NLO calculations fail, especially for baryons: poorly constrained
fragmentation functions? Other hadronization schemes ?
fragmentation functions from e+e- data, hep-ph/0010289
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/K0s in Au+Au and pp –baryon
abnormally
(1) Baryon is enhanced at intermediate pt region with respective to meson in AA
(2) At higher pt, the ratios seem to approach that in pp
(3) Recombination/coalescence models at intermediate pt vs fragmentation at higher pt
Central0-5%
Peripheral60-80%
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How recombination/coalescence works
Efficient way to produce baryons at intermediate pt when parton density is high
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Study of nuclear effects
dydpdN
dydpdN
N
NpR
Tperipheral
Tcentralcentralcoll
peripheralcoll
TCP /
/)(
Number of Participants
Impact Parameter
Npart – No of participant nucleonsNcoll – No of binary nucleon-nucleon collisions
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Nuclear effects in AA
Nuclear suppression Nuclear suppression seen for both baryon seen for both baryon and mesonand meson
The suppression is The suppression is stronger for mesons stronger for mesons than for baryonsthan for baryons
The effect is grouped The effect is grouped by particle type by particle type (baryon vs meson), (baryon vs meson), supporting supporting recombination/coalescrecombination/coalescence pictureence picture
STAR Preliminary
Au+Au
Energy Loss: Partonic or hadronic interaction ?
Suppression:
Initial state or final state effect ?
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Φ production probing early state
mΦ~1019 MeV/c2 ; mΛ~1116 MeV/c2; mKs~498 MeV/c2
May determine whether the particle dependence of the nuclear modification factor is grouped by the particle mass or particle typePossible production mechanism:
(1) ggg -> (2) s sbar -> (3) K+K- -> Small cross section for scattering with hadronic medium
sensitive to source properties of early time.
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Φ production dynamics
N()/K- independent of collision centralities.
K+K- Φ is not a dominant channel
Φ does not pick up as much as transverse flow as proton
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Rcp of Φ meson in AA
Au+Au
STAR preliminary
Species dependence Species dependence at intermediate pt at intermediate pt region is verifiedregion is verified
The suppression can The suppression can not be due to later not be due to later hadronic processeshadronic processes
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K0s, , : 0.4 – 6 GeV/c; : 0.6 – 5 GeV/c. Statistical errors only.
Double exponential fit function
d+Au as a reference
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Rcp in dAu
• ‘Cronin effect’ is seen in dAu system
•Same baryon/meson separation in dAu as in AuAu collisions Recombination/coalescence modes work in d+Au ?
•Rcp in AA is lower than that in dAu the suppression is due to final state effect
dAu 200 GeV
STAR Preliminary
AuAu 200 GeV
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Heavy flavor measurements
D0 K (B.R=3.8%)
D*± D0π (B.R=68% 3.8% (D0 K ) = 2.6% )
D*±
2.4<pt<3.5 GeV/c
Semileptonic Channels:D0 e+ + anything (B.R=6.87%) D e + anything (B.R= 17.2%)B e + anything (B.R=10.2%)
single “non-photonic” electron continuum
“Photonic” Single Electron Background:
Mainly from Photon conversion and π0 Dalitz decays
D0
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Charm cross section at RHIC
(1) NLO pQCD calculations tuned for low energy points under-predict the ccbar production cross section at RHIC(2) The Pythia prediction with the Peterson fragmentation function is softer than the measured electron spectrum
Phys. Rev. Lett. 94 (2005) 062301
π+A 350 GeV/c
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Heavy Flavor RAA ---Challenge to radiative picture?
Suppression is approximately the same as for hadrons
Where is b contribution ?
M. Djordjevic, et. al. nucl-th/0507019
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Summary
• STAR has a vigorous program which is pushing our measured probes more and more sensitive to the early stage of the formed medium
• Nuclear effects at intermediate pt show particle type dependence, supporting recombination/coalescence as dominant processes for hadronization
• Strong suppression of high pt hadron production is observed for both light and heavy quarks, which demonstrates the formation of strongly-interacting dense medium at RHIC.
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Dead cone effect---Radiative Energy Loss of Heavy
Quarks
See also Armesto et al, Phys. Rev. D71 (2005) 054027
• Coupling of heavy quarks to the medium reduced due to mass
• Expectation: even for high medium density, higher RAA for single electrons from heavy flavor than for light hadrons
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/2K0s in d+Au
Close to Au+Au most peripheral ratio (60-80%)
No significant centrality dependence in d+Au
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Electron ID in STAR – EMC
1. TPC for p and dE/dx● e/h ~ 500 (pT dependent)
2. Tower E p/E● e/h ~ 100 (pT dependent)
3. Shower Max Detector (SMD) shape to reject hadrons
● e/h ~ 20
4. e/h discrimination power ~ 105
Works for pT > 1.5 GeV/c
electrons
hadrons
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Inclusive Single Electrons p+p/d+Au
•Inclusive non-photonic spectra : How to assess the background?
•PHENIX 1: cocktail method
•PHENIX 2: converter method
•STAR: measurement of main background sources (TPC !!!)
ToF + TPC: 0.3 GeV/c < pT < 3 GeV/c
TPC only: 2 < pT < 3.5 GeV/c
EMC + TPC:pT > 1.5 GeV/c
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Photonic Single Electron Background Subtraction in pp and dAuMethod:
1. Select an primary electron/positron (tag it)
2. Loop over opposite sign tracks anywhere in TPC
3. Reject tagged track when m < mcut ~ 0.1 – 0.15 MeV/c2
4. Cross-check with like-sign
Rejection Efficiency: • Simulation/Embedding
• background flat in pT
• weight with measured 0 spectra (PHENIX)
conversion and 0 Dalitz decay reconstruction efficiency ~60%
• Relative contributions of remaining sources: PYTHIA/HIJING + detector simulations
Invariant Mass Square
Rejected
Signal
Opening Angle
conversion and 0 Dalitz decay reconstruction efficiency :~60% at pT>1.0 GeV/c
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Photonic Single Electron Background Subtraction
pT dependent hadron contamination (10-30%) subtracted
Excess overbackground
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Non-Photonic Single Electron Spectra in p+p and d+Au
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Nuclear Effects RdAu ?•Nuclear Modification Factor: inel
ppdAubindAu
TppdAu
TdAudAu NT
ddpdT
ddpNdR
/ where;/
/2
2
•Within errors compatible with RdAu = 1 … •… but also with RdAu(h)
•NOTE: RdAu for a given pT comes from heavy mesons from a wide pT range p(D) > p(e) (~ 2-3) makes interpretation difficult
hadrons
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D0 Mesons in d+Au
•Mass and Width consistent •with PDG values considering •detector effects:• mass=1.867±0.006 GeV/c2;• mass(PDG)=1.8645±0.005 GeV/c2
• mass(MC)=1.865 GeV/c2
• width=13.7±6.8 MeV• width(MC)=14.5 MeV
cp
dy
dN
T
y
Aud
D
/GeV 08.032.1
008.0004.0028.00
0
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Obtaining the Charm Cross-Section cc
•D0 Mesons– Requires fit to data points for extrapolation
• functional form?• error on extrapolation
– Requires the knowledge of ND0/Ncc
•Non-Photonic Single Electrons– What functional form ?
• PYTHIA does not describe data – tweaking it is not satisfactory
• NLO/FONLL not reliable for pT < F = R = mc pTD
•STAR Combine both measurements– Fraction of covered ?
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Obtaining the Charm Cross-Section cc• Combined fit:
– Assume D0 spectrum follows a power law function– Generate electron spectrum using particle composition from PDG
• ND0/Ncc ~ 0.540.05• Decay via routines from PYTHIA
– Assume that only normalization scale different between the various D meson pT spectra is different (D0, D*, D, …)
• From D0 mesons alone:– ND0/Ncc ~ 0.540.05– Fit function from exponential fit to mT spectra
• In both cases for d+Au p+p: pp
inel = 42 mb– Nbin = 7.5 0.4 (Glauber) – |y|<0.5 to 4: f = 4.70.7 (simulations)– RdAu = 1.3 0.3 0.3
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Obtaining the Charm Cross-Section cc
•pp Charm Cross-Section
•From D0 alone:cc = 1.3 0.2 0.4 mb
•From combined fit:cc = 1.4 0.2 0.4 mb
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Discrepancy between STAR and PHENIX ?STAR from d+Au: cc = 1.4 0.2 0.4 mb (PRL94,062301)
PHENIX from p+p (preliminary): cc = 0.709 0.085 + (+0.332,0.281) mbPHENIX from min. bias Au+Au: cc = 0.622 0.057 0.160 mb (PRL94,082301)
Reality check: 1.4 0.447 mb and 0.71 0.343 mb are not so bad given thecurrently available statistics (soon be more!)
pp p
SPS, FNAL (fixed target) and ISR (collider) experiments
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Discrepancy between STAR and PHENIX ?
90%
15%
Combined fit of STAR D0 and PHENIX electrons:No discrepancy: cc=1.1 0.1 0.3 mb
STAR: PRL 94, 062301 (2005)PHENIX p+p (QM04): S. Kelly et al. JPG30(2004) S1189
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Consequences of High Cross-Section: J/ Recombination Statistical model (e.g. A. Andronic et. al. PLB 571,36(2003)) :
Largecc yield in one heavy ion collision J/ production through recombination possible J/ enhancement
Statistical model
In stat models: cc typically from pQCD calculations Consequence of STAR cc (from d+Au) much larger enhancement (~3-
10) for J/ production in central Au+Au collisions PHENIX’s upper limit would invalidate the expectation from large cc ?!
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NLO/FONLL•Recent calculations in NLO (e.g. R. Vogt et al. hep-ph/0502203)
– Since m≠0 heavy quark production is a hard process– Calculations depend on:
• quark mass mc
• factorization scale F (typically F = m or 2m)
• renormalization scale R (typically R = F)
• parton density functions (PDF)
– Total cross-section depends only on mc, not kinematic quantities
– Hard to obtain large with R = F (which is used in PDF fits)
– For pT spectra m(for calculations m
• pT integrateddirect calculated
•Fixed-Order plus Next-to-Leading-Log (FONLL)– designed to cure large logs for pT >> mc where mass is not relevant
– FONLL higher over most pT than NLO (also tot)
•K factor (NLO NNLO) ?
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NLO/FONLL
b
bb
FONLLbb
NLOcc
FONLLcc
99.067.0
381134
400146
87.1
244 ;256
from hep-ph/0502203
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Charm Total Cross SectionCan we confirm or rule out Cosmic Ray experiments? (Pamir, Muon, Tian Shan) under similar conditions?NPB (Proc. Suppl.) 122 (2003) 353Nuovo Ciment. 24C (2001) 557
X. Dong USTC
– NLO calculations under-predict current cc at RHIC
– More precise data is needed high statistics D mesons in pp
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Comparison: Non-Photonic Electrons with NLO
•FONLL calculations:•Charm:•scaled by STAR/FONLL
•Bottom:•derived from fit of sum to data
•Errors used: data + FONLL uncertainty bands
Plenty of room for bottom !!!
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Can We Disentangle Charm from Bottom ?
•Method I: Finding the Secondary Vertex – Requires excellent resolution of vertex tracker (< 50 m)– Survival probability P(x) depends on M/c
• D ~ 15 MeV/m• B ~ 11 MeV/m (B lives long but is heavy)
– Works only at high p but bb is dominated by pTe < 4 GeV/c
•Method II: Identifying the Ks from the semileptonic decay– If a K is present within certain kinematical region around the e the ratio of opposite/same sign pairs
(K+e- + K-e+)/(K-e- + K+e+) is– charm (ce K anything): ~ 55:1 (PYTHIA) – bottom (be K anything): ~ 1:6 (PYTHIA) – works only in pp and requires large acceptance + high pT PID
•Method III: Subtracting e evaluated from measured D spectra– Requires knowledge of D spectra out to very high pT
• Need D spectra out to 11 GeV/c to describe electrons at pT ~ 5 GeV/c
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High-pT D0-Meson Spectra in d+Au•How is it done ?
– Assumptions:• pT spectra of D0, D*, D
• same shape
– D0 K defines low pT points
– D0 K defines one high-pT point
– Combined allow power law fit– functional form allows to move
D* and D spectra into place– cross-check with known ratios
OK– Problem: D*/D0 and D/ D0 not
well known (pT, s dependent ?)Note: spectrum depends onone point: D0 K
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High-pT D-Meson Spectra in d+Au•Headache: Spectra very hard (too hard)
– Fragmentation function function (Peterson FF needs c = b) ?
– Yield at 10 GeV/c only factor 3 below CDF (LO/NLO ~ 10) ?
Intensive systematic studies of D0 K of many people over many month …
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High-pT D-Meson Spectra in d+Au•Until we found the problem …
– very, very, subtle effect – Downside: combined low to high-pT D0 spectra is gone
• ratios not well enough known• cannot normalize D*, D to D0 appropriately any more
Upper limits from D0 K (90% CL)Note: D* itself is still valid!!! Now a “standalone” spectra. Doesn’t affect possibility of studying RAA in Au+Au
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Thermalization of heavy quarks ?
v2 of non-photonic electrons in
Au+Au
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Strong Elliptic Flow at RHIC
•Strong elliptic flow at RHIC (consistent with hydro limit ?)– scaling with Number of Constituent Quarks (NCQ)
• partonic degrees of freedom !?
– v2/n(pT/n) shows no mass and flavor dependence– Strong argument for partonic phase with thermalized quarks
•What’s about charm?– Naïve kinematical argument: need Mq/T ~ 7 times more collisions to thermalize – v2 of charm closely related to RAA
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Charm Elliptic Flow from the Langevin Model
– Diffusion coefficient in QGP: D = T/M momentum drag coefficient)
– Langevin model for evolution of heavy quark spectrum in hot matter
– Relates collisional energy loss and elliptic flow v2
– pQCD gives D(2T) 6(0.5/s)2
AMPT:(C.M. Ko)
← =10 mb
← =3 mb
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Charm Elliptic Flow through Resonance Effects
• Van Hees & Rapp, PRC 71, 034907 (2005) – Assumption: survival of resonances in the QGP– Introducing resonant-heavy-light quark interactions– heavy particle in heat bath of light particles (QGP) +
fireball evolutiontime-evolved c pT spectra in local rest frame
“Nearly” thermal: T ~ 290 MeV
Including scalar, pseudoscalar, vector, and axial vector D mesons gives:
σcq→cq(s1/2=mD)≈6 mb
Cross-section is isotropic the transport cross section is 6 mb, about 4 times larger than from pQCD t-channel diagrams
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How to Measure Charm v2
•Best: D mesons need large statistics, high background not now•Alternative: Measure v2 of electrons from semileptonic charm decays
– Emission angles are well preserved above p = 2 GeV/c– 2-3 GeV Electrons correspond to ≈3-5 GeV D-Mesons
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Measuring v2 of Non-Photonic Electrons
•Analysis– Same procedures as for single electrons (incl. background subtraction)– … but with much harder cuts (plenty of statistics)– special emphasis on anti-deuteron removal– reaction plane resolution ~ 30%Consistency check: PYTHIA + MEVSIM (flow generator) through analysis chain
● D0 (input)○ e±
● 0 ee (input)○ e±
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Phenix : Min. BiasStar: 0-80%STAR: stat. errors onlyCorrected for residual e± contaminations from π decays with v2
max=17%
Phenix:nucl-ex/0404014 (QM2004)nucl-ex/0502009 (submitted to PRC)Star:J. Phys. G 190776 (Hot Quarks 2004)J. Phys. G 194867 (SQM 2004)
v2 of Non-Photonic Electrons
Indication of strong non-photonic electron v2
consistent with v2(c) = v2(light quark)smoothly extending from PHENIX resultsTeany/Moor D (2T) = 1.5 expect substantial suppression RAA
Greco/Ko Coalescence model (shown above) appears to work well
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Argonne National Laboratory Institute of High Energy Physics - Beijing University of Bern 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 - Dubna Particle Physics Laboratory - Dubna 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. Lanzhou Lawrence Berkeley National Laboratory Massachusetts Institute of Technology Max-Planck-Institut fuer PhysicsMichigan State University Moscow Engineering Physics Institute
City College of New York NIKHEF Ohio State University
Panjab University Pennsylvania State University
Institute of High Energy Physics - Protvino Purdue UniversityPusan University
University of Rajasthan Rice University
Instituto de Fisica da Universidade de Sao Paulo
University of Science and Technology of China - USTC
Shanghai Institue of Applied Physics - SINAP 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
545 Collaborators from 51 Institutionsin 12 countries
STAR Collaboration
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Motivation II
the Cronin effect in pA, d+Au collisions
Nuclear Modification factor RAA or RCP
Should the Cronin effect be influenced by the final state particle Should the Cronin effect be influenced by the final state particle formation dynamics?formation dynamics? Recombination models! Recombination models!
p
q
h
A
traditional models :
Multiple parton/hardon scatterings in initial state
Recombination/Coalescence:
Final state effect
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STAR Detector at RHIC
Time Projection Chamber
Forward TPCs
• pion, kaon, proton and electron : identified using ionization energy loss technique.
• Other particles are reconstructed from them.
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Data Set and Cuts
STAR d+Au 200GeV Minimum Bias data
Event Selection:
|VertexZ| < 50cm, Primary vertex found, good run ~ 10M events after the cuts.
Centrality definition in STAR: 0-20%(Nch>=17), 20-40%(17>Nch>=10), 40-100%(Nch<10) Nch (Uncorrected # of charged
particles @ Forward TPC-Au
side, -3.8<<-2.8)
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Invariant mass plots
|y|<1
0.4 <pt< 6.0
|y|<1
0.4 <pt< 6.0
|y|<1
0.6 <pt< 5.0
K0s, , : topology
cuts, like decay length,
DCA of V0-primV.
: event mixing.
These particles can be
identified at much
higher pT ( up to 6 GeV/c
).
|y|<0.5
0.4 <pt< 1.3
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K0s, , : 0.4 – 6 GeV/c; : 0.6 – 5 GeV/c. Statistical errors only.
Double exponential fit function
better than the exponential function ( low pT )and the power-law ( high pT ).
mT Spectra and fits in d+Au
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Compare various fit functions
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The mean pTs are little
dependence of Number
of Charged Particles.
Themean pTs
increase with Number of
Charged Particles
<PT> vs. Number of Charged Particles
dAu Minbias
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/K0s in Au+Au and pp
Au+Au and pp @ 200 GeV
Au+Au most peripheral
Recombination models
Central0-5%
Peripheral60-80%
R.J.Fries et al. 2003 Phys. Rev. C 68 044902
V.Greco et al. 2003 Phys. Rev. C 68 2537
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/2K0s in d+Au
No significant centrality dependence in d+Au
Close to Au+Au most peripheral ratio (60-80%)
Soft+Hard Reco may work in d+Au
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Rcp in Au+Au 200 GeV
Suppression
Rcp’s are grouped into Mesons (K0
s, ) and Baryons (, ).
Particle-type dependence!
STAR Preliminary
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RAB charged hadrons in d+Au STAR
d+Au : Cronin enhancement
Au+Au : Suppression
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Rcp of KK00ss/// in d+Au STAR
Rcp’s are grouped into Mesons (K0
s, ) and Baryons (, ).
Particle-type dependence again!
Cronin effect
Final state formation dynamics (Recombination model ) Rcp difference between BM.
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Rcp of K//p in d+Au
D. Kotchetkov, QM2004PHENIX B-M dependence:
(, K) vs. (p, )
STAR TOF measurement
B-M dependence: (, K) vs. (p)
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RAA in low energy p+A collisions
s =27.4GeV
P.B Straub,PRL 68, 452(1992)Rw/Be in p+A collisions
W: tungsten Be: beryllium
s =38.8GeV
RRw/Bew/Be : : Mesons Mesons (2 quarks):(2 quarks):
kaon and pionkaon and pion ~ 1.5; ~ 1.5; Baryons Baryons (3 quarks):(3 quarks):
protonproton ~ 2.5 ~ 2.5
Particle-type Particle-type dependence ??dependence ??
~1.4
~1.5
~2.5
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Summary
• Measured productions for 4 identified particles(K0s, , ,
) in d+Au collisions at RHIC;
• /K0s ratio increases with multiplicity.
– dAu ratio is close to AuAu most peripheral (60-80%)– Recombination models are in qualitative agreement with the data.
• pA Nuclear modification factor, RAB, shows Cronin effect– Baryon–Meson(B-M) dependence?.
• Au+Au Nuclear modification factor, RCP, shows B-M difference and suppression.
– Consistent with parton recombination + jet quenching.
• d+Au Nuclear modification factor, also shows B-M difference and Cronin effect.
– PHENIX : (K/ vs. p/), STAR : (K0s/vs. )
– Cronin: Final state particle formation dynamics (recombination)
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<p<pTT> centrality > centrality dependencedependence
1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;
1) , K, p mean transverse momentum <pT> increase in more central collisions;2) Heavier mass particle <pT> increase faster than lighter ones as expected from hydro type collective flow;3) -meson seems flow differently.