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Identified Particle Ratios at large p T in Au+Au collisions at s NN = 200 GeV. Matthew A. C. Lamont for the STAR Collaboration. - Talk Outline - Physics Motivation Current Models Identified Particle Spectra B/B and B/M ratios Strange Particle Correlations. - PowerPoint PPT Presentation
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Identified Particle Ratios at large pT in Au+Au collisions at sNN = 200 GeV
Matthew A. C. Lamont
for the STAR Collaboration
- Talk Outline -
Physics Motivation
Current Models
Identified Particle Spectra
B/B and B/M ratios
Strange Particle Correlations
13/01/04 Matthew A. C. Lamont - QM2004 2
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Motivation : Particle production vs pT
pT
pQCDHydro
2-3 GeV/c 6-7 GeV/c ?
SoftFragmentation and quenching
of jets
0
What do we think we know ?
• pT independence of p/p ratio.
• p/ ratio increases with pT to ~ 1 at pT ~ 3-4 GeV/c in central collisions.
• Suppression factors of p, different to that of , K0
s in the intermediate pT region.
What has the data already shown us at intermediate pT ?
What are the mechanism(s) atintermediate pT?
13/01/04 Matthew A. C. Lamont - QM2004 3
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Current theoretical models• Soft + Quench Model
– Two component model, soft production (hydro) at low pT, quenching of pQCD jets via gluon radiation at higher pT.
• Baryon junctions incorporated to explain large baryon yield at intermediate pT.
• Recombination– Model assumes the recombination of two and three low pT partons to form
hadrons from an exponential parton pT spectrum. High pT spectrum described by fragmentation once parton pT spectrum can be described by a power law.
• Requires a high phase space density of partons for method to work.
• Coalescence– Same as the recombination picture with the added assumption that thermal
‘QGP’ partons can coalesce with co-moving ‘pQCD’ partons from a mini-jet.
M. Gyulassy et. al., Phys. Rev. Lett. 86 (2001) 2537
R. J. Fries et. al., Phys. Rev. C 68 (2003) 044902
V. Greco et. al., Phys. Rev. C 68 (2003) 034904
13/01/04 Matthew A. C. Lamont - QM2004 4
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture. Identified particle spectra : p, p, K-,+, -,+, K0
s and
13/01/04 Matthew A. C. Lamont - QM2004 5
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.B/B ratios vs Transverse Momentum (pT)
Soft+Quench (130 GeV) : Nucl. Phys. A715 779-782 (2003)
Recombination (200 GeV) : Phys. Rev. C68 044902 (2003)
Note the different trend in the p/p ratio from that reported in Nantes. Experimental effects have been better modelled (mainly space charge distortions).
This pQCD calculation fails : uncertainties in PDFs and fragmentation functions ?
Both the ‘Soft+Quench’ and recombination model predictions are consistent with the data.
13/01/04 Matthew A. C. Lamont - QM2004 6
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Hydro: Phys. Rev. C67, 044903 (2003) S+Q: 200 GeV data - private communication S+Q: 130 GeV data - Phys. Rev. C65, 041902
p/ ratios, data and theory
Note that p data is not corrected for feed-down from weak decays p/ ratio will decrease.
Reco : Phys. Rev. C68 044902 (2003) Coal : Phys. Rev. C68 034904 (2003)
• S+Q : magnitude
low pT
• Hydro : magnitude
low pT
• Reco : magnitude low pT
• Coal : magnitude
low pT
13/01/04 Matthew A. C. Lamont - QM2004 7
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/K0s ratios vs collision centrality
• /K0s ratio increases with
increasing centrality– peaks in the intermediate pT
region.
– turns over and appears to tend to the same value for all centralities for pT ~ 5-6 GeV/c.
– Therefore pT range of baryon excess is limited to < 5-6
GeV/c. – Not yet down to level in pp
data not corrected for feed-down from weak decays - estimated to be a 10% effect and ~ independent of pT.
For p+p data, refer to poster by M. Heinz and J. Adams
13/01/04 Matthew A. C. Lamont - QM2004 8
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/K0s - comparison with models
S+Q : 200 GeV data - private communication S+Q : 130 GeV data - Phys. Rev. C65, 041902
Reco : Phys. Rev. C68 044902 (2003) Coal : Phys. Rev. C68 034904 (2003)
• Reco : magnitude turnover low pT
• Coal : magnitude turnover low pT
• S+Q : magnitude turnover
centrality
Require centrality dependent prediction from Recombination and Coalescence models.
13/01/04 Matthew A. C. Lamont - QM2004 9
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Another view of the same effect? …. Rcp
• Suppression of mesons different to baryons - not mass dependent effect.
• Rcp of baryons and mesons separate at pT ~ 2 GeV/c and come together at pT ~ 5-6 GeV/c.
See poster by P. Sorensen
13/01/04 Matthew A. C. Lamont - QM2004 10
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• Q) Can we measure particle correlations with identified particles ?
• A) Yes - though measurements are limited by statistics.
∆ (radians)
dashed line is random backgrounddashed line is random background
1/N
1/N
Tri
gger
Tri
ggerd
N/d
dN
/d((
))
Identified Particle Correlations• We have seen previously the
disappearance of back-to-back jet correlations in central Au+Au, with charged particles.
1/N
1/N
Tri
gger
Tri
ggerd
N/d
dN
/d((
))
Same SideSame SideBack Back sideside
Back Back sideside
∆ (radians)See poster by Y. Guo
(trigger pT > 2.5 GeV/, associated pT > 2.5 GeV/c & less than trigger pT)
Back to back jet disappearance for charged trigger particles (Phys. Rev. Lett. 91 072304 (2003))
• Measuring correlations with identified particles could give us insight on possible different production mechanisms for baryons and mesons.
• Correlation appears stronger for compared to , though in both cases, there is an absence of a ‘back-to-back’ partner correlation.
trig: , assoc : charged hadron
trig: , assoc : charged hadron
13/01/04 Matthew A. C. Lamont - QM2004 11
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Back sideBack side
dash lines indicate dash lines indicate estimated flow contributionestimated flow contribution
Trigger PT
Quantifying the Correlation Strength
• Correlation difference defined as : Nsame - Nback
See poster by Y. Guo
trigger
pairsback
N
NN ∑ >
=)49.2(
trigger
pairssame
N
NN ∑ ≤
=)65.0(
Trigger PT
Same sideSame side
Trigger PTrigger PTT
NNs
am
es
am
e -
N -
Nb
ac
kb
ac
k
trig: , assoc : charged hadrontrig: , assoc : charged hadron
• Suppression of as a function of pT is slightly different from the , K0
s and primaries. • Under investigation whether this is an experimental effect or whether there is indeed sensitivity to quenching or production mechanism effects
NNs
am
es
am
e -
N -
Nb
ac
kb
ac
k
Trigger PTrigger PTT
trig: , assoc : charged hadrontrig and assoc : charged hadrontrig: K0
s, assoc : charged hadron
13/01/04 Matthew A. C. Lamont - QM2004 12
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– pQCD calculation fails : uncertainties in PDFs and fragmentation functions ?
• p/ ratio increases with pT up to 3 GeV/c.• /K0
s ratio increases smoothly with centrality, turns over at pT ~ 3 GeV/c.– baryon excess over mesons is limited in pT to < 5-6 GeV/c.– A+A value still above p+p value.
• The Rcp measurement exhibits differences between baryons and mesons - not just a mass effect.
• Strange correlations hint at a flavour dependence.– correlations with triggers possibly enhanced over those with
and K0s triggers.
13/01/04 Matthew A. C. Lamont - QM2004 13
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Backup Slides
13/01/04 Matthew A. C. Lamont - QM2004 14
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STAR pp vs UA1 pp• Ratio very different in two
systems
• Different production mechanisms or just differences in experiments ?
STAR UA1
Ratio Plotted /K0
s +/2K0s
Colliding System p+p p+p
Energy 200 GeV 630 GeV
Coverage |y| < 1 || < 2.5
13/01/04 Matthew A. C. Lamont - QM2004 15
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STAR RICH Geometry
||<0.3 and 20
~235cm
1) Charged particle through radiator2) MIP and photons detection
13/01/04 Matthew A. C. Lamont - QM2004 16
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Integral method and Fitting
Cherenkov angle distribution in momentum bins
pions
kaonsprotons
13/01/04 Matthew A. C. Lamont - QM2004 17
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Comparison of Spectra with PHENIX
13/01/04 Matthew A. C. Lamont - QM2004 18
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Current theoretical models• Coalescence
– Same as the recombination picture with the added assumption that thermal ‘QGP’ partons can coalesce with co-moving ‘pQCD’ partons from a mini-jet.
M. Gyulassy et. al., Phys. Rev. Lett. 86 (2001) 2537R. J. Fries et. al., Phys. Rev. C 68 (2003) 044902V. Greco et. al., Phys. Rev. C 68 (2003) 034904
• Recombination– Recombination of two and three low pT partons form hadrons from an
exponential parton pT spectrum. High pT spectrum described by fragmentation due to power-law parton pT spectrum.
• Requires a high phase space density of partons for method to work.
• Soft + Quench Model– Two component model, soft production (hydro) at low pT, quenching of
pQCD jets via gluon radiation at higher pT.
• Baryon junctions incorporated to explain large baryon yield at intermediate pT.