Hot Quarks 2004, Taos Valley 1

Meson Production in d Au Collisions at √s = 200 GeV

Dipali Pal

Vanderbilt University

(for the PHENIX Collaboration)

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Outline

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• Physics motivation• PHENIX experiment• Particle identification• Data analysis

meson reconstruction Corrections

• Results ( K+K- and e+e-)• Summary and outlook

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Physics motivation

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mesons

• Chiral symmetry restoration and medium effects - mass shift, width broadening - branching ratios in K+K- and e+e- decay channel Simultaneous measurement of K+K- and e+e-

• Strangeness production - meson yield

• Particle production mechanism - Rcp, elliptic flow

• Au – Au & d – Au collisions– Distinguish between hot and cold partonic matter– Evolution of medium properties with density and temperature– Probing nuclear effects

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K+K-

Minimum-bias|zVertex| < 30 cm

Nevt = 54 M

Tracking : DC – PC1 – PC3 Momentum

PHENIX Setup

Collision vertex and centrality: Beam-beam Counter

e+e-

Electron identification: RICH + EMC || < 0.35, = 90o, both arms

Kaon identification: TOF: || < 0.35, = 45o PbSc (East): || < 0.35, = 45o

PbSc (West): || < 0.35, || = 90o

K-

K+K+K-

K+K-

K+

K

-

e+e-

ERT_Electron trigger|zvertex| < 30 cmNevt (ERT) = 31M 1.9 G Minimum bias

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Kaon identification

Time of flight (TOF):0.3 < p (GeV/c) < 2t = 130 ps

PbSc East and West:0.3 < p(GeV/c) < 1.0t ~ 450 ps

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Electron identification

Energy / Momentum

Electron PID cutsNRICH PMT 20.5<E/p<1.5 E - from EMCp from tracking

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Data analysis and corrections

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• Same event K+K- and e+e- invariant mass distributions (R).

• Combinatorial background (CB) Event mixing within same centrality and Zvertex

Normalization to 2√N++N—

• Signal = R - CB

• Acceptance correction: PHENIX Single particle Monte-Carlo simulation - Event generation + Detector hit + Detector response + offline analysis

• Other experimental quality control correction: Run (time) dependent corrections

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Invariant mass distributions

MixedBackground

Co

un

ts p

er 1

0 M

eV/c

2

e+e- invariant mass (GeV/c2)

K+K- @ d – Au, √sNN = 200 GeVK+ and K- are selected from TOF

e+e- @ d – Au, √s = 200 GeV

S ~ 120S/B = 1/4

= 4.409 ± 0.711 MeV/c2

Co

un

ts p

er 1

MeV

/c2 b

in

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meson transverse mass spectra (I)

)(syst 0.00950.0092 )stat ( 0.0092 0.0468

dydN

mT(GeV/c2)

e+e-

1/2

mT d

N/d

mTd

y (G

eV

/c2)-

2

PHENIX Preliminary PHENIX Preliminary

Fitted with exponential function in mT

)23(syst31(stat)414T

dN/dy=0.0560.015(stat) 50%(syst)T=326 94(stat) 53%(syst) MeV

PHENIX PreliminaryPHENIX Preliminary

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meson transverse mass spectra (II)SPS result

Central Pb-Pb 158 A GeV

49: K+K- T = 305 MeV dN/dy ~ 2.35

NA50: T = 227 MeV No specific quote of dN/dyIntegrating the mT spectrum gives dN/dy ~ 13

D. Rohrich et al, J Phys. G 27 (2001) 355

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1/2

mT d

N/d

mTd

y (G

eV

/c2)-

2

Minimum-bias mT distribution of

MT(GeV/c2)Overall fitdN/dy~ 0.0485T~4082/DOF=6.7/7

dN/dy T

yields in d-Au collisions in K+K- and e+e- channels are consistent witheach other

K+K-

K+K-

e+e-e+e-

K+K-

e+e-

PHENIX Preliminary PHENIX Preliminary PHENIX Preliminary

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Comparison between yields in d-Au and Au-Au collisions

( K+K- )

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yield increases from d-Au to Au-Au system

Inverse slope remains constant in Au-Au and d-Au collisions.

(Preliminary)(Preliminary)

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Factor of ~4 more statistics is now available by including the PbSc detectors in east and west arm. Scope of centrality dependence studies.

Invariant mass spectra from TOF and PbSc analysis

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Full east arm ( TOF + PbSc) West arm (PbSc)

Work in progressWork in progress

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Summary

• First simultaneous measurement of K+K- and e+e- in d-Au collisions at RHIC.

K+K-

)(syst 0.00950.0092 )stat ( 0.0092 0.0468

dydN

dN/dy=0.056.015(stat) 50%(syst)T=326 94(stat) 53%(syst) MeV

e+e-

Consistent with each other within errors.

• yield jumps from d-Au minimum-bias to Au-Au peripheral collisions. Then it increases slowly upto Au-Au mid-central, finally saturates.

)23(syst31(stat)414T

(PHENIX Preliminary) (PHENIX Preliminary)

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Outlook

• Extended K+K- measurement in d-Au collisions with kaons identified with PbSc modules.

Total yield increases by almost a factor of 4.

Better understanding of the systematics is possible.

Centrality dependence of yield

Particle ratio

Rcp measurements.