# Presentation: 806982

## Various Aspects of (anti)deuteron Spectra in Au+Au Collisions

- Ron Belmont
- Vanderbilt University
- PHENIX Collaboration

## Outline

- Motivation
- Particle Identification
- Spectra
- Coalescence Parameter and Source Dynamics
- Particle Ratios and Constraints on Neutron Production
- Conclusion

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Physics Motivation

- Source dynamics
- Spectral shapes change with mass due to radial flow
- Deuteron spectra can be used to infer source radius, complimentary to HBT measurements

- Neutron production
- Deuterons are produced by coalescence of neutrons and protons, and so can be used to place constraints on neutron production

- PRC 72 (2005) 014903

- PRC 72 (2005) 014903

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Particle Identification

- PHENIX Run 7
- Au+Au 200 GeV
- 1.9 out of 5.5 billion events total used for this study
- TOFW
- 75 ps timing resolution
- Excellent PID capabilities

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Particle Identification and Yield Extraction

- pT

- pT

- m2

- Fit the mass peak
- Gaussian + exponential for background
- Extract the yield
- Integrate under the gaussian

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## pT Spectra

- 5 centrality classes + MinBias
- pT from 1.1 GeV/c to 4.2 GeV/c (5 GeV/c for MinBias)
- Slope gets flatter with increasing centrality
- Consistent with radial flow

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## mT Spectra

- For central collisions deuteron is flatter than proton due to radial flow
- For peripheral collisions the d and p are have roughly the same slope

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Mean pT

- Mean pT inceases with Npart
- Consistent with collective expansion
- Radial flow velocity increases with centrality
- Heavier particles get the largest increase of <pT>

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Blastwave Fits I

- All particles are fit individually
- Consistent overlap for produced hadrons
- NO consistent overlap between deuterons and produced hadrons

- 1/pT dN/dpT = A∫f(x)xdx mT K1(mT cosh ρ/Tfo) I0(pT sinh ρ/Tfo)

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Blastwave Fits II

- The fit from the produced particles poorly reproduces the deuteron spectra

- π K p -
- PRC 69 (2004) 034909

- d -
- PHENIX PRELIMINARY
- (this study)

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Blastwave Fits III

- We use a simultaneous fit to produced hadrons and a separate fit for the deuterons
- These describe the data well, and either a gaussian or box density profile can be used

- π K p -
- PRC 69 (2004) 034909

- d -
- PHENIX PRELIMINARY
- (this study)

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Coalescence Parameter I

- Defined mathematically as:
- pd = 2pp
- Defined conceptually as probability of proton and neutron to coalesce into deuteron
- Depends on momentum and fireball size

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Coalescence Parameter II

- B2 increases with pT
- This is consistent with an expanding source
- B2 decreases with centrality

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Coalescence Parameter III

- B2 decreases hyperbolically with Npart
- Effective volume (~1/B2) increases linearly with Npart
- Bulk particle production also goes as Npart
- This implies that freezeout happens at constant particle density

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Coalescence Parameter and Source Radius

- Radius increases linearly vs Npart1/3
- Good consistency with HBT results

- PRL 93 (2004) 152302

- PRC 17(3)  1051-1070 (1978)

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Ratios I

- dbar/d is consistent with (pbar/p)2
- This suggests that nbar/n is similar to pbar/p
- dbar/d can be used to calculate deuteron fugacity -> deuteron chemical potential
- Since proton chemical potential is known, neutron chemical potential can be determined and therefore so can nbar/n
- nbar/n = 0.64 +/- 0.04

- PRL 94 (2005) 122302

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Ratios II

- This measurement constrains the neutron RCP to be similar to that of the proton

- deuteron pT divided by 2 to match the proton

- R. Belmont - Hot Quarks 2008

- 8/23/2008

## Conclusion

- Deuteron spectra
- This new study has an expanded pT reach and more centrality classes than previous studies at RHIC energies
- The pT and mT spectra are consistent with radial flow
- Mean pT vs Npart also consistent with radial flow
- Blastwave fits
- (Anti)deuterons do not freeze out contemporaneously with produced hadrons
- Coalescence parameter
- Source radius decreases with pT
- Source radius increases with Npart
- Coalescence probability increases with pT (expanding source)
- Effective volume goes as Npart (freezeout occurs at common particle density)
- Deuteron ratios
- dbar/d shows that nbar/n is similar to pbar/p
- RCP of d+dbar shows that neutron and proton have similar RCP

- R. Belmont - Hot Quarks 2008

- 8/23/2008