light (anti-)nuclei production in the star experiment at rhic

Light (Anti-)Nuclei Production in the STAR experiment at RHIC

Jianhang Zhou

Bonner Lab, Rice University

Aug.2009 Jianhang Zhou, PhD thesis defense

2

Introduction

• Building blocks of the world: quarks and leptons

• Quark confinement: No free quarks

• Quark deconfinement: Quark Gluon Plasma (QGP)

• Ultra relativistic heavy Ion collision experiments

• Light nuclei study provides a probe for understanding the final freeze-out

• The relation to cosmology: early universe from Big Bang is similar to the heavy ion collision experiments

Thermal Freeze-out

Hadrons

Collision

QGP HadronsHadronization

Chemical Freeze-out

Light Nuclei


3

Outline

• Experiment facilities: RHIC, STAR, TPC, TOF

• Transverse momentum spectra and related techniques Particle identification Coalescence model Transverse momentum spectra in Cu+Cu 200 GeV collisions

• Elliptic flow and related techniques Event plane method, event plane shift, resolution Elliptic flow results in Cu+Cu 200 GeV

• Blast Wave model fit to Au+Au 200 GeV • Search for anti-alpha particles• Summary


4

Experiment FacilitiesRelativistic Heavy Ion Collider

(RHIC)　（ 2.4 miles circ.)

at Brookhaven National Lab (BNL)

Solenoidal Tracker at RHIC(STAR)

6 o’clock position at RHIC


5

Particle Identification (PID) in STAR

Time of Flight (TOF)Structure: pVPD and TOF tray

Time Projection Chamber (TPC)PID method: Ionization Energy Loss dE/dx

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

=> calculate Mass


6

TPC PID: N-sigma Distribution

Proton and deuteron N-sigma distributions are fit by a Gaussian

function plus a background.

ected

measured

dxdE

dxdE

exp/

/logz

With tight track cuts, z-distribution of helium is background free.

No need for background subtract.

ected

measured

XX dxdE

dxdEn

exp/

/log

1


7

Coalescence Model

AppPd

dNEB

Pd

dNE

Pd

dNEB

Pd

dNE Ap

A

p

ppA

N

n

nn

Z

p

ppA

A

AA /

3333

The relation of the light nuclei invariant yield and the proton yield

AfA V 1BThe coalescence parameter (A is atomic number)

23 /1B fVfV/1B2 For A=2, 3 :

Baryon density related to yields:

p

d

dydN

dydNyf

/

/

26

13


8

Data set

Data set:STAR Run-V Cu+Cu 200 GeV

Trigger: Minimum Bias

About 37 million events

TPC Track quality cuts:nHitsdEdx>15

nHitsFit>25|Zvtx|<30, DCA<1

|pseudo-rapidity|<0.9

centrality 0-10% 10-20% 20-30% 30-40% 40-50% 50-60% 0-60%

RefMult 139 98 67 46 30 16 >16

<Npart> 98.3 74.5 54.1 38.6 26.3 17.6 51.6

Centrality and Number of participants

Npart is the equivalent number of participant nucleons revolved in the collisons.RefMult is the number of primary tracks from the collision vertex.


9

Distance of Closest Approach (DCA)

• DCA distribution of d indicates contamination by background

• dbar is not contaminated by background

• dbar is used in the analysis of coalescence parameters

DCA of d DCA of dbar


10

Transverse momentum (pT) spectra

• Tracking efficiency is the ratio of TPC reconstructed tracks to all the tracks.

• Cu+Cu pbar and dbar spectra are calculated with tracking efficiency obtained from Au+Au for similar reference multiplicity.

pT spectra of dbarpT spectra of pbar


11

BA vs pT/A

• B2 and sqrt(B3) are close to each other in the same system

• BA from Cu+Cu is larger than Au+Au, consistent with smaller coalescence volumes

• BA increases slightly with increasing pT/A, consistent with decreasing coalescence volumes


12

1/B2 vs <Npart>

• <Npart> is the number of participant nucleons

• 1/B2 is found to be linear with <Npart>, in all pT ranges

• Consistent with that <Npart> is proportional to the coalescence volume


13

1/BA comparison to Au+Au

• B2 and sqrt(B3) in similar pT/A range

• All Cu+Cu and Au+Au results shows 1/BA is proportional to <Npart>


14

Comparison to pion HBT volume

HBT volume is calculated from the HBT correlation lengths along the longitudinal and transverse directions.

Cu+Cu results at pT/A= 0.45GeV/c are consistent with pT=0.5 GeV/c pion HBT volume.

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


15

Baryon density

dbar/pbar ratio as a measure of antibaryon phase space density v.s. beam energy. Data points from e+e- and γp collisions are also shown.


16

He3 and He3bar production


17

Elliptic Flow (v2)

1

2

3

3

)](cos[212

1E

nn

TT

nvdydpp

Nd

dp

Nd

The azimuthal dependence of yield:

i

iinn nwnQ )cos()cos(

i

iinn nwnQ )sin()(sin

iii

iii

nw

nw

n )cos(

)sin(arctan

1n

Determine the event plane angle:

The weight factors wi are chosen to be the transverse momentum pT.


18

Event plane angle shift

1' ( sin 2 cos 2 cos 2 sin 2 )

n

n n n nn

(n=1,2,3,4…… )

Formula used for shift correction


19

Event Plane from FTPC


20

dbar yield versus azimuthal angle

　

)](2cos[21 10 pp


21

pbar and dbar v2 for different background

Use different background estimation to fit the N-sigma plots:

Gaussian, Exponential, or no background


22

pbar and dbar v2 compared to Au+Au

Negative dbar v2 was first observed in Au+AuNegative dbar v2 is observed again, in Cu+CuSystematic errors are smaller than statistical

errors

Pbar and Lambda v2: slightly higher in Cu+Cu than in Au+Au, for

pT<1GeV/c.

Mass dependence: larger v2 for smaller mass, in both Au+Au an

d Cu+Cu


23

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


24

Blast-Wave Fitting spectra fit (pi,K,p) : V2 fit (pi,K,p) :

Fit all spectra and v2 for

pi, K, p:

(MinBias triggered)

Total 2/ndf = 711.422/154

T (MeV) = 124.2 +-1.9

rho0= 0.88 +- 0.01

rho2 = 0.061 +-0.002

Rx/Ry= 0.89 +- 0.003

s = 0 +- 0 (fixed)

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

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


25

Spectra and Blast-Wave Prediction

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.


26

V2 and Blast-Wave prediction

(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.

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


27

Search for anti-alpha

• Anti-alpha has never been found.

• Using TPC, 2 candidates are found in STAR Run-VII Au+Au collisions.


28

Track validity check

• The candidate tracks are checked to be valid.

• Confirmation needs further investigation or more candidates.

• Upgraded TPC and TOF will provide enough statistics in the future


29

Summary

• The pT spectra of pbar, dbar and He3bar in STAR Run-V Cu+Cu are studied and the coalescence parameters B2, B3 are calculated. B2 and sqrt(B3) are demonstrated to be comparable with each other and linear with <Npart> for different centralities.

• B2 and sqrt(B3) from both Cu+Cu and Au+Au are compared. In similar pT range, they are consistent with each other and proportional with <Npart>. It is consistent with that the final freeze-out volume is proportional to <Npart>.

• B2 and sqrt(B3) are also compared to pion HBT volumes. They are consistent with each other.

• He3bar/He3 ratio in Cu+Cu are compared to pbar/p ratio. The comparison is consistent with coalescence model.

• The elliptic flow (V2) of pbar and dbar in Cu+Cu are studied and compared to Au+Au. The comparison is consistent with mass dependence. A negative dbar v2 is observed.

• Blast Wave model is used to fit pi/K/p pT spectra and v2. The fit results are used to predict light nuclei (d,He3) spectra and v2. The comparison shows consistence between data and BW predictions.

• Search for anti-alpha in STAR Run-VII results in two candidates. Tracking information is checked. Further confirmation is needed. Future hope in finding more candidates depends on the upgraded TPC and the large area TOF system.


30

THE END

THANK YOU!


31

Comparison to Big Bang Nucleosynthesis baryon density

The ratio of the baryon density (D/H) in the universe (from BBN) to the baryon density from collider experiment is 3.60.4%.

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

Possible explanation of the relation between these 2 numbers is unknown.

light (anti-)nuclei production in the star experiment at rhic

Documents

cu cu results

cu cu pbar

phd thesis defensecomparison

similar pta rangeall

phd thesis defense1b2

phd thesis defensetpc

star runv cu cu

starjianhang zhou