Source Dynamics from Deuteron and Anti-deuteron Measurements in 200 GeV

Au+Au Collisions

Hugo E Valle

Vanderbilt University

(For the PHENIX Collaboration)

Quark Matter 2008, Jaipur India

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Outline

Motivation Deuteron Identification and the Time of Flight

Detector Spectra and Ratios Coalescence Parameter (B2) and Source

Radius RCP

Conclusion

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Physics MotivationWhy are deuterons interesting?-Low pT :

-Spectral shapes change with mass due to radial flow- Information on source size complementary to HBT measurements

PHENIX: Phys. Rev. C 72, 014903 (2005) Au+Au collisions at sNN = 200 GeV

-Intermediate-High pT:–Baryon-Meson difference in suppression–Possibly due to quark recombination–Study the coalescence of baryons with deuteron Rcp

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TOF.W New MRPC TOF in

West arm for Run 7 ~75 ps resolution Coverage

|η|<0.35 Δφ = 22°

Drift Chamber (DC) andPad Chamber 1 (PC1)- for momentumPad Chamber (PC3) outer trackingTime of Flight (TOFW) for timing

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Data Set RHIC Run 7 200 GeV Au+Au Collisions Analyzed 1.9 billion events (half of available

data) Tracks reconstructed using TOF.W, and

central tracking chambers. High quality Drift Chamber tracks 2.0 TOF.W and PC3 spatial matching cuts in

azimuth and z (beam-axis)

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Deuteron & Anti-deueron Extraction

•Fitted a Gaussian + background function (e-x), to obtain yield.

pT

pT

m2

Large data sample analyzed in centrality classes:•0-10% •10-20%•20-40%•40-60%•60-92%Extend both pT range and centrality selection from previous measurementsRef Phys. Rev. Lett. 94, 122302 (2005)

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Deuteron and anti-deuteron Spectra

MC Correction Factors: • Acceptance•MRPC (TOF.W) Efficiency•Tracking Efficiency•Survival Probability•Tracks Cuts

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Anti-deuteron/Deuterons Ratio ratio vs pT

•No pT. and no centrality dependence (within

errors)•Consistent with (pbar/p)2 ratio0.73 ± 0.01

0.46 ± 0.01(stat) ± 0.05 (syst)

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Radial Flow in Hadron mT Spectra

Slope of spectra for deuterons at 0-10% is smaller due to Radial Flow Consistent with other particles in peripheral collisions.

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Coalescence Parameter B2 Defined as:

with pd = 2pp

The coalescence factor B2, characterizes the coalescence probability, depends on the fireball size.

€

Edd3Nddpd

3= B2 E p

d3N p

dpp3

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

2

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Coalescence Parameter

B2 increases from central to peripheral collisionsB2 rises with pT

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B2 and System Volume

Significant change in B2 from 14.5 to 60 Npart

1/B2 vs Npart shows a consistent linear rise

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Centrality dependence of Source size

€

R3 =αRnp hc( )3 mdmp

2B2( )

−1

• Shows linear increase as the cubic root of the number of participants (Npart). • Consistent with HBT radii for pions.

Phys.Rev.Lett.93, 152302 (2004)

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Energy Dependence of B2 Parameter

Comparison of B2 parameter for deuterons and anti-deuterons (pT =1.3 GeV) with other experiments at different values of sqrt(s)

Seems consistent between SPS and RHIC

AGS SPS RHIC

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Deuterons Rcp

Deuterons’ pT divided by 2

Proton spectra from:Phys. Rev C 69, 034909 (2004)

€

RCP =Yield central • Ncoll

peripheral

Ncollcentral • Yield peripheral

Rcp for deuteron affected by two factors:• Centrality dependence of B2

• Scaling of production yields for protons and neutronsRcp of neutrons is consistent with that of protons

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Conclusions Measured (Anti-)Deuteron spectra for Run7

Expanded the range of our previous measurement both at low and at high pT

Detailed study as a function of centrality mT spectra are consistent with radial flow

Extracted coalescence parameter (B2) and source radius at freeze-out as a function of pT and Npart Source radius decreases with pT

Source radius increases linearly with Npart1/3 consistent with

expanding source B2 measurement indicates that the freeze-out

conditions are similar at SPS and RHIC energies. Rcp for (Anti-)Deuterons reveals that neutron

production is similar to that of protons

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BACKUP

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Rcp for neutrons

€

Rcpd =

B2cent

B2per

•Yncent

Ynper

• RCPp

Rcpd =

N partper

N partcent

•Yncent

Ynper

• RCPp

Since Rcp for deuterons reaches 2.7, the neutron yield has to increase faster than Npart from central to peripheral collisions. Assuming it increases as Ncoll we get:

€

RCP (pT =1.5GeV /c) =14.5

280•

779

14.5• 1 = 2.78

ppnn // =

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Raw (Anti-)Deuteron Spectra

Large data sample analyzed in centrality classes:•0-10% •10-20%•20-40%•40-60%•60-92%Extend both pT range and centrality selection from previous measurementsRef Phys. Rev. Lett. 94, 122302 (2005)

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PHENIX acceptance for different particles

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Survival Probability

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Implications for

It has been shown pT shape of

It has been shown pT shape of

Since scaled yields (or B2) are equal within errors, it is suggestive:

pbar/p = 0.73 ± 0.01

nn /

pp =dd =

ppnn // =