hadron spectra and yields experimental overview
DESCRIPTION
Hadron Spectra and Yields Experimental Overview. Julia Velkovska. INT/RHIC Winter Workshop, Dec 13-15, 2002. Outline. Spectra Radial flow Does every particle flow ? What are the freeze-out conditions ? Yields and Ratios Chemical properties of the system Is T ch > T fo ? - PowerPoint PPT PresentationTRANSCRIPT
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Hadron Spectra and YieldsExperimental Overview
Julia Velkovska
INT/RHIC Winter Workshop, Dec 13-15, 2002
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)2
Outline
Spectra Radial flow Does every particle flow ? What are the freeze-out conditions ?
Yields and Ratios Chemical properties of the system Is Tch > Tfo ?
How far in pT do soft processes dominate ?
Conclusions
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)3
Charged hadron spectra at 200 GeV
Exponential at low pT < 2 GeV/c
Power-low at high pT > 2 GeV/c
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)4
Spectral shape evolution with centrality
pT < 2 GeV/c
Inverse slope increases with centrality due to radial flow
Relatively little change from 0 – 50 % pT > 2 GeV/c
Suppression of high pT hadrons increasing with centrality
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)5
P spectra from Star
High quality data over 9 centrality selections
Shape described by
blast wave fit
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)6
Spectra with broad momentum range from PHENIX
0 – 5 % 5 -10 %10- 15 %15 – 20 %20 – 30 %30 – 40 %40 – 50 %50 – 60 %60 – 70 %70 – 80 %80 – 93 %
Au+Au at s = 200 GeV PHENIX preliminary
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)7
The general features
Peripheral : ~ equal slopes Pions dominate
over (anti)protons at all pT
Central low-pt slopes
increase with particle mass
proton and anti-proton yields equal the pion yield at
high pT
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INT/RHIC Winter Workshop 2002
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Comparison for 200 GeV central data from all RHIC experiments
Relatively good agreement on preliminary data
Low pT data from PHOBOS will help constrain extrapolations to pT = 0 GeV/c
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)9
Characterizing the expansion
Strong radial flow: Spectra are NOT
exponential in mT
Inverse slopes depend on fitted (measured) range
Curvature increases with particle mass
At high mT all spectra converge to the same slope
< pT > versus mass – better than Teff versus mass, but still depends on fit function – very low pT data helps
1/m
T d
N/d
mT
(a.u
.)mT-m
mass
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)10
<pT> versus mass
M. Kaneta/N. Xu (STAR)
<pT> prediction with Tth
and <> obtained from blastwave fit (green line)
<pT> prediction for Tch = 170 MeV and <>=0pp no rescattering, no flowno thermal equilibrium
STAR
preliminaryF. Wang
<pT> of and from exponential fits in mT
Do they flow ? Or is <pT> lower due to different fit function?
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)11
Fits to Omega mT spectra
M. van Leeuwen (NA49)
• At SPS and are now found to be consistent with common freeze-out• Maybe and are consistent with a blastwave fit at RHIC• Need to constrain further more data & much more for v2 of
C. Suire (STAR)
SPS/NA49
RHIC
STAR preliminary
T is not well constrained !
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INT/RHIC Winter Workshop 2002
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<pT> systematics: centrality and beam energy
open symbol : 130 GeV data
•Systematic error on 200 GeV data (10 %), K (15 %), p (14 %)
<p
T>
[G
eV
/c]
<p
T>
[G
eV
/c]
• Increase of <pT> as a function of Npart and tends to saturate < K < proton (pbar)• Consistent with radial flow increasing with beam energy and centrality• But also can come from initial state multiple scattering or gluon saturation.
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)13
Kinetic freeze out parameters
From hydrodynamics fit
Au+Au at sqrt(sNN) =200GeV
Top 5% centrality:
STAR:
Tfo ~ 100 MeV
T ~ 0.55c (130) & 0.6c (200)
PHENIX:
Tfo ~ 121MeV(130) &110 MeV(200)
T ~ 0.47c (200)
Full model calculations give similar results
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)14
BRAHMS, submitted to PRL12/07/02 nucl-ex/0207006
Becattini: T=170, s=1
PBM (PhysLettB518
(2000)41) predicts y=0
ratios almost exactly
K-/K+=
exp(2s/T)(pbar/p)1/3
K- /K+=(pbar/p)1/4 is
a fit to the data points
Thermal parameters from K-/K and pbar/p ratios
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INT/RHIC Winter Workshop 2002
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The chemistry of the collisions
Thermal models work well in describing particle ratios, even for the multi-strange particles : Tch
= 177 MeV – close to critical temperature
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Short-lived resonances : a measure for rescattering timescale
Chemical freeze-out
Kinetic freeze-out
K*
lost
K*
measured
K
K* K
K*
K*
K
K*
K K K*
measured
Consistent with sudden freeze-out
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)17
Is Tch > Tfo ?
Single freeze-out model: Broniowski,Florkowski hep-ph/0209286
2 thermal and 2 geometric (flow) parameters describe all central data including K*0 (892) How good is the
agreement really ? Plots of theory/experiment
on a linear scale ? Comparison to other
observables?
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INT/RHIC Winter Workshop 2002
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When does the flow start ?
P.Kolb and R. Rapphep-ph/0210222 Including pre-equilibrium
transverse flow field improves agreement with the data
centrality0-5%
20-30%40-50%
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And how far in pT does flow dominate?
Fit the soft part of , K,p
spectra using hydrodynamics expression
h+ + h - = , K, p
Compare to measured non-identified charged data
Significant soft component up to 2.5 – 3 GeV/c
130 GeV PHENIX
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Another approach: look for jet fragmentation ratios as seen in pp data
• Experimentally observed:
above pt=2 GeV/c particles are fragments of jets
• Characteristic particle
composition determined by
fragmentation function Soft to hard transition in p/
ratio
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INT/RHIC Winter Workshop 2002
Julia Velkovska (BNL)21
(anti)proton/pion ratio: Can we determine soft to hard transition?
Ratios steeply rising to pT ~ 2 GeV/c
Above pT = 2 GeV/c – flat ~ 1 for central Au+Au ~ 0.3 – 0.4 for peripheral Au+Au
Is there a peak ? At what pT do we get to the pQCD ratios ?
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If protons are soft up to 4 Gev/c
R < 1 in regime of soft physics R = 1 at high-pT where hard scattering dominatesR< 1 at high-pT suppression
pp
centralbinarycentral
Yield
NYield / R=
pionsprotons
Tslope~ sqrt [ (1+<<
For mT > 2 m0
central
peripheral
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Scaling the proton+anti-proton spectra
Radial flow
Collision scaling ?
Nbin
97542213514.8
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How does the ratio Central/peripheral look ?
…. and more details See PHENIX talk by Jiangyoung Jia And overview talk by David d’Enterria
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Conclusions
A wealth of spectra, yields, ratios measurements from the first 2 years of RHIC
Spectral shapes consistent with strong radial expansion
Success of thermal chemical models Almost net baryon free system with Tch close to
critical temperature
Resonance studies show time-scale for emission is short , Tch close to Tfo
Abundant protons+anti-protons at intermediate/high pT . How do they get there ?