Identified and Inclusive Charged Hadron Spectra from PHENIX Carla M Vale Iowa State University for the PHENIX Collaboration WWND, March 14 2006

Identified and Inclusive Charged Hadron

Spectra from PHENIXCarla M Vale

Iowa State Universityfor the PHENIX Collaboration

WWND, March 14 2006

WWND, La Jolla, CA 03/14/06

Carla M. Vale 2

Motivation

Particle distributions in transverse momentum provide the most basic tool to investigate the mechanisms of particle production, transport and hadronization

Low pT High pT

hydro evolution & thermalization

energy loss

jet production

chemical composition (through particle ratios)

fragmentation

recombination


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Detecting Particles in PHENIX

h+h-

Charged hadron tracking and momentum measurements use Pad Chambers (PC1 - PC3), Drift Chamber (DC)

||<0.35, =


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Identifying Particles in PHENIX


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RHIC-supplied data sets

p+p d+Au Au+Au Cu+Cu

200 GeV

130 GeV

62.4 GeV

22.4 GeV

en

erg

y

dep

en

den

ce

system size dependence

reference points


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Charged Hadron Spectra


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h± in Au+Au √sNN = 200GeV

PRC 69,034910 (2004)

Charged hadron spectra measured up to ~ 10 GeV


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h± in Au+Au √sNN = 62.4GeV

4M events divided in 3 centrality bins

p+p reference: interpolation of data from ISR, UA1 and PHENIX + fit using modified Hagedorn function


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h± in Cu+Cu √sNN = 200GeV

Collis

ion

cen

tralit

y


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Identified Particle Spectra


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π± in d+Au √sNN = 200GeV

Final results on identified particles in d+Au (and p+p) just released: nucl-ex/0306010


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K± in d+Au √sNN = 200GeV


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p, p in d+Au √sNN = 200GeV


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π, K, p in Cu+Cu √sNN = 200GeV

Same shapes as in Au+Au


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Nuclear Modification Factors


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Initial vs Final State Effects

PHENIX Preliminary

High pT suppression not observed in d+Au collisions, final state effects such as parton energy loss are the favored scenario but the energy loss mechanisms are not yet fully understood.

PRC 69, 034910 (2004)


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System size and Npart

Mid-central Au+Au very similar to central Cu+Cu, for bins with approximately the same <Npart>

Au+Au

Cu+Cu

<Npart> = 114

<Npart> = 98


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Energy Dependence

Au + Au at 62.GeV:

• Qualitatively similar to the 200GeV result

• Less suppression at intermediate pT

• Charged hadrons not as suppressed as π0


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h± ≠ π0

At intermediate pT, charged hadrons are less suppressed than π0s; at high pT the difference disappears we should look at identified hadrons

RAA (h+ + h-)/2


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RAuAu for π, K, p √sNN = 200GeV

nucl-ex/0603010

Protons are not suppressed like pions and kaons at intermediate pT in central collisions.


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RCuCu for π, K, p √sNN = 200GeV

Similarity between Cu+Cu and Au+Au for equivalent Npart also seen for identified particles


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Baryon Anomaly


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Initial Observation

PRL 91,172301 (2003)

Proton/pion > 1 for central Au+Au at intermediate pT

Much larger than expected from fragmentation alone (measured in e+e-)

Anti-proton/pion not as large


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At lower energy

The ratio p/π+ grows faster with pT than at higher energy, and appears to peak earlier

Anti-p/π- similar at both energies up to pT ~ 2 GeV


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Centrality dependence @ Au+Au √sNN = 62.4GeV

Weaker centrality dependence


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And in smaller systems

p/π+ not as high in central Cu+Cu as in central Au+Au

Npart scaling is seen here as well (pT = 2GeV)


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Baryons and mesons behave differently at RHIC in more ways than one…

p/π ratio, RAA, elliptic flow, all show same pattern at pT > 2GeV


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… and it’s not just due to the mass.

The mass is similar to that of a proton, but in both RAuAu and elliptic flow (?), the behaves like the lighter mesons.


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Recombination?

Fries, R et al PRC 68 (2003) 044902Greco, V et al PRL 90 (2003) 202302Hwa, R et al PRC 70(2004) 024905

At intermediate pT recombination of partons may be a more efficient mechanism of hadron production than fragmentation


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SummaryStudying spectra gives us a window into particle production at RHIC:

Study system size and energy dependence

Compare to reference systems

At high pT:

Suppression also seen at lower energy Au+Au and in Cu+Cu

Cu+Cu and Au+Au behave similarly for the same <Npart>

Charged hadrons and π0 appear to converge again at high pT

At intermediate pT :

Baryon enhancement is observed in several measurements

p/π+ reaches higher values at lower energy Au+Au


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Coming soon…

• More results:– Analyses of Cu+Cu 62.4GeV and

22.5GeV data sets are underway and first results will be out very shortly

• More data:– Reference p+p data sets at 62.4GeV

(and possibly 22.4GeV) will be collected during Run6, allowing for more precision in RAA results at those energies


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backup


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Trend at 62GeV Au+Au described by reco +

fragmentationnucl-th/0412043, Greco, Ko and Vitev


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p/π in d+Au, Au+Au

d+Au similar to peripheral Au+Au but much smaller than central Au+Au


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RdAu for π, K, p √sNN = 200GeV

nucl-ex/0603010

Species dependence of Cronin effect seen for pT>1.5GeV

Most peripheral collisions very similar to p+p

Calculation by Accardi & Gyulassy PLB586, 244 (2004)


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RAuAu RdAu for protons

Cronin effect in d+Au larger than Au+Au

No centrality dependence in Au+Au above 1.5 GeV

Documents

Identified and Inclusive Charged Hadron Spectra from PHENIX Carla M Vale Iowa State University for the PHENIX Collaboration WWND, March 14 2006