qm2006 shanghai, china 1 high-p t identified hadron production in au+au and cu+cu collisions at...

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QM2006 Shanghai, China

High-pT Identified Hadron Productionin Au+Au and Cu+Cu Collisions

at RHIC-PHENIX

Masahiro Konno (Univ. of Tsukuba)

for the PHENIX Collaboration

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Outline

- Physics Motivation- Method- New Data Set (full statistics now available) :

Cu+Cu 200GeV / p+p 200 GeV- Results and Comparisons:

- p/ ratios- Npart Scaling of p/ in Au+Au, Cu+Cu- RAA in Au+Au, Cu+Cu

- Summary

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Physics Motivation

- High-pT suppression due to parton energy loss in the medium (jet quenching).- The suppression patterns depend on particle type. Protons are enhanced, while pions and kaons are suppressed.

Au+Au 200 GeV

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RAA =YieldAA/⟨Nbinary⟩AA

Yield pp

- Baryon Enhancement -

PRL 91, 172301 (2003)p/ ratioPRC 74, 024904 (2006)

- What is the origin of (anti-)proton

enhancement at intermediate pT(2~5 GeV/c) ?- A systematic study at intermediate pT is necessary over different collisions systems.

RAA

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PHENIX detector

Aerogel Cherenkov (PID)

EM Calorimeter (PID)TOF (PID)

Drift Chamber (momentum meas.)

Tracking detectors (PC1,PC2,PC3)

- Central Arm Detectors (magnetic spectrometer)- Event Characterization detectors- PID (particle identification) is a powerful tool to study hadron production.

p (p) ID up to 7 GeV/c-

p (p) ID up to 4 GeV/c-

Time of Flight (TOF)

Veto for proton ID

π+

K+p

Aerogel Cherenkov (ACC)

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pT spectra (Cu+Cu √sNN = 200 GeV)

NOTE: No weak decay feed-down correction applied.

Phenix preliminary

- pT reach extended for (anti-)protons with fine centrality bins. <= (1) Aerogel Cherenkov, (2) Enough statistics in Au+Au/Cu+Cu

(Anti-) protons ACC

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pT spectra (p+p √s = 200 GeV)

- High statistics 200 GeV p+p data. More than10 times statistics used compared to previous Run3 p+p analysis.- The p+p data provides baseline spectra to heavy ion data, and it is important to quantify in-medium nuclear effects in heavy ion collisions at RHIC


Phenix preliminary

TOF

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p/ vs. pT

p/ p/

- p/ (pbar/) ratios seem to turn over at intermediate pT, and be close to the value of fragmentation at higher pT.- Clear peak in central events than that in peripheral.- Indicating a transition from soft to hard at intermediate pT.

NOTE: - No weak decay feed-down correction applied. - p+p data (PRC 74, 024904 (2006))

Au+Au 200 GeV

ACC

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- Baryon enhancement observed in Cu+Cu at 200 GeV.

- pT dependence in Cu+Cu is similar to that in Au+Au. => How about the magnitude as a function of centrality? see Next.


Phenix preliminaryACC

p/ vs. pT Cu+Cu 200 GeV

p/ p/

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p/ vs. Npart1/3

Phenixpreliminary

Cu+Cu 200 GeV vs. Au+Au 200 GeV


TOF (<3 GeV/c)ACC (>3 GeV/c)

0.6 - 1.5 GeV/c1.0 - 2.0 GeV/c2.0 - 3.0 GeV/c3.0 - 4.0 GeV/c4.0 - 5.0 GeV/c

pT

pT

Phenix preliminary

Npart dependence in Cu+Cu looks similar to that in Au+Au (Npart scaling !). Slight difference in the magnitude seen.

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p/ vs. pT (Low pT)

At low pT, p/ shows weak and decreasing Npart dependence because inverse slope (from mT exponential fitting) also shows it.


- Radial flow -

(Anti-)protonsTOF

Phenix preliminary Phenix preliminary

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- Radial flow (ex. blast-wave fit) -

p/ vs. pT (Intermediate pT)

Au+Au 200 GeV

- Spectra for heavier particles has a convex shape due to radial flow.- Using Blast-wave fitting, try to estimate p/ ratio as a function of pT.

(hydro p)/(hydro ) (hydro p)/(real )


TOF, ACC

Central Peripheral

- Hydrodynamic contribution for protons is one of the explanations (baryon enhancement).- Other contribution is also needed: Recombination, Jet fragmentation

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A number of models predicted a turnoverin the B/M ratio at pT just above where the available data finished…

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

qq M→

qqq B→

- Quark Recombination -

At intermediate pT, recombination ofpartons may be a more efficient mechanismof hadron production than fragmentation.

p/ vs. pT (Intermediate pT)


ACCp/

Phenix preliminary

Now, we find a similar trend.

ACCTOF

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- Similar tendencies as at 200 GeV.

p/ vs. pTCu+Cu 62 GeV vs. Au+Au 62 GeV

TOFPhenix preliminary

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p/ vs. Npart1/3 Cu+Cu 62 GeV

vs. Au+Au 62 GeV

- Npart scaling of p/ also at 62 GeV in Au+Au/Cu+Cu.

Phenix preliminary


TOF

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p/ vs. Npart1/3

,(dET/dy)1/3 Au+Au 200 GeV vs. Au+Au 62 GeV

- No Npart scaling of p/ (pbar/) in Au+Au between 62 GeV and 200 GeV.- dET/dy scaling of pbar/ seen. => Proton production (this pT range) at 62 GeV is partly from baryon transport, not only pair production.


TOF

Phenix preliminary Phenix preliminary

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RAA vs. pT

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RAA =Yield AA/⟨Nbinary⟩AA

Yield pp

- Proton, antiproton are enhanced at 1.5 - 4 GeV/c for all centralities. (enhancement > suppression)- Suppression is seen for pions, kaons.


TOFPhenix preliminary

NOTE: Systematic errors (~10%)for overall normalization not shown.

- Similar Npart dependence for Au+Au / Cu+Cu.- Cronin effect in peripheral

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Summary- pT reach of PID (especially for p, pbar) extended with:

(1) High statistics Au+Au/Cu+Cu data(2) New PID detector (Aerogel)

- (Anti-)Proton enhancement is observed in Au+Au/Cu+Cu collisions at 200/62 GeV.

- p/ ratios: (1) Indicating a transition from soft to hard production at intermediate pT.

(2) Npart scaling (dET/dy scaling) over different collision systems.

(3) Recombinatio + radial flow would explain the pT, Npart dependencies.

- Systematic study of PID spectra (and jet correlations) for different collision systems can provide information to understand the hadron production mechanisms.

qm2006 shanghai, china 1 high-p t identified hadron production in au+au and cu+cu collisions at...

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