DNP2008 Jianhang Zhou, Rice University 1

Nuclei yields and elliptic flow in Au+Au 200GeV collision

and comparison to the models

Jianhang Zhou (Rice University)

For STAR collaboration

DNP2008 Jianhang Zhou, Rice University 2

Motivation

1) To study light nuclei yield together with coalescence model as a tool to measure collective motion and freeze-out properties, such as particle density and correlation volume. The coalescence parameters obtained from nuclei and nucleon yields could be compared to HBT results.

2) To study the elliptic flow scaled by atomic mass number A of protons and nuclei, which might suggest the formation of light nuclei of their constituent nucleons through final-state coalescence.

3) To fit pi/K/p spectra and elliptic flow with blast-wave model, to retrieve the parameters related to the final state coalescence, and use them to predict d/He3 spectra and flow to compare with experimental data.

4) To use the blast-wave model to predict the flow of nuclei for different centralities, and compare with the experimental data.

5) To study the baryon density and compare with cosmology results :Big Bang Nucleosynthesis (BBN).

DNP2008 Jianhang Zhou, Rice University 3

TPC(Time Projection Chamber)TOF (Time of Flight)

STAR PID Capable Detectors: TPC and TOF

TOF PID method: measure TOF=T(stop)-T(start), along with p from TPC,

=> calculate Mass

• Run IV Au+Au 200 GeV full stat

• ---------TPC only------• 24M central triggered events (0~12%)• 25M minBias triggered events (0~80%)

• --------TPC+TOF ------• 16M central triggered events (0~12%)• 15M minBias triggered events (0~80%)

Data Set

DNP2008 Jianhang Zhou, Rice University 4

Blast-Wave model parameters

The 8 parameters of the blast-wave model are:

T, rho0, rho2, Ry, Rx, s, , Δ

The freeze-out distribution is infinite in z-direction, and elliptical in transverse(x-y) plane.

The transverse shape is controlled by Rx, Ry.

x

y

Ry

Rx

r

The parameter s corresponds to a surface diffuseness of the emission source. s =0 corresponds to a hard edge source.

The flow rapidity is given by: Rho(r,φs) = r~ (rho0+rho2*cos(2φb))where r~=sqrt((rcos(φs))2/Rx2+(rsin(φs))2/Ry2)

The freeze-out is supposed to occur with a given distribution in longitudinal proper time =sqrt(t2-z2). We assume a Gaussian distribution peaked at 0 and with a width Δ

Ref: F.Retiere and M.Liza, Phys.Rev.C70,(2004) 044907

DNP2008 Jianhang Zhou, Rice University 5

Blast-Wave Fitting

spectra fit (pi,K,p) : [1] V2 fit (pi,K,p) : [2]

Fit spectra and v2 for pi, K, p:(MinBias triggered)

Total 2/ndf = 745.126/157

T (MeV) = 124.2 +-1.8 rho0 = 0.88 +- 0.08 rho2 = 0.061 +-0.002

Rx (fm) = 12.33 +- 0.02 Ry (fm) = 13.86 +- 0.03

s = 0 +- 0 (fixed) (fm/c) = 9.2 +- 0 (fixed) (fm/c) = 0.03 +- 0 (fixed)

Ref[1]: STAR Phy. Rev. Lett. 97(2006) 152301Ref[2]: STAR Phy. Rev. C72(2005) 014904

DNP2008 Jianhang Zhou, Rice University 6

Spectra and Blast-Wave Fitting

Spectra of d (dbar) and He3 (He3bar) v.s. pT, for both central and MinBias.The corresponding BW fitting results are shown by solid and dashed lines.The green bands show proton data/BW ratio, as a comparison. BW describes proton very well, but overpredicts radial flow of d and He3. (chi2/ndf is 36.9/4 for d, and 52.8/3 for He3)This indicates the coalescence might differ from a simple mass effect.

STAR Preliminary

DNP2008 Jianhang Zhou, Rice University 7

V2 and Blast-Wave Fitting

(a) MB v2 vs. pT for He3+He3bar, d+dbar and dbar, and BW fitting.

(b) d+dbar and He3+He3bar v2/A  v.s. pT/A. pbar and the Λ+Λbar v2 are also shown as comparison.

BW fit 2/ndf = d+dbar : 3.1/2 He3+He3bar: 4.3/2

(c) Low pT dbar and pbar v2/A v.s. Npart, and BW predictions.

pT range for dbar: upper: 0.2<pT<0.7 GeV/c; lower: 0.7<pT<1.0 GeV/c. pT range for pbar: upper: pT<0.24 GeV/c; lower: 0.4<pT<0.48 GeV/c.

Pbar and Λ+Λbar v2 from: Phy. Rev. C72(2005) 014904

Heavier nucleus deviates more from the scaling.Negative v2 is not correctly predicted by BW.

STAR Preliminary

DNP2008 Jianhang Zhou, Rice University 8

Coalescence parameters and HBT volume

B2 and sqrt(B3) as a function of Npart. HBT volume is calculated from the HBT correlation lengths along the longitudinal and transverse directions.

The extracted B2 and sqrt(B3) are smaller for larger Npart, which is consistent with larger volume for more central collisions.

The B2 & sqrt(B3) are consistent with HBT volumes

STAR Preliminary

DNP2008 Jianhang Zhou, Rice University 9

Baryon density and Big Bang Nucleosynthesis (BBN)

dbar/pbar ratio as a measure of antibaryon phase space density v.s. beam energy. The ratio of the baryon density in the universe (from BBN) to the baryon density from collider experiment is 3.6+-0.4%

The ratio of the observed baryon in the universe to the total matter in the universe is about 4%.

Is this just a coincidence, or ……… ?

DNP2008 Jianhang Zhou, Rice University 10

Summary1) Using STAR TPC and TOF detectors, we measured the d(dbar) and He3(He3bar) pT spectra.

The extracted B2 and sqrt(B3) have similar values.

2) The freeze-out volume for nuclei obtained from coalescence parameters is proportional to the freeze-out volume estimated using the pion HBT radii in different centrality classes. The spectra of nucleus with A=2 and 3 are in general described by the Blast-Wave model. However, the model overpredicts the radial flow.

3) The v2 values of d(dbar) when scaled by atomic mass number A follows the baryon v2, thereby providing evidence of d(dbar) formation through final-state coalescence of nucleons. We also observed the v2 for dbar to be negative at low pT in the mid-central collisions. Comparison with blast-wave predictions shows this is consistent with a large radial flow in Au+Au collisions at small impact parameter.

4) We showed that there is a universal baryon density at zero chemical potential. The baryon density measured by dbar/pbar is compared to nucleus abundance (D/H) measured in the universe. The ratio is 0.036±0.004, in coinsidence with baryon density from the standard BBN and CMB.

Outline:

The next step is to get identified pbar and dbar v2 from Cu+Cu, and using the same blast wave fit algorithm, and compar

e the fitting parameters with Au+Au system.