production of meson, baryon and light nuclei in au+au collisions at rhic haidong liu univ. of...

Production of meson, baryon and light nucleiin Au+Au collisions at

RHIC

Haidong LiuUniv. of Science & Technology of

China

UC Davis, Aug 21, 2007 Haidong Liu 2

Outline

Motivation and introductions Detectors and techniques Results (RHIC run 4 AuAu 200

GeV) Conclusions & Discussions


Motivations

&

Introductions


Heavy-ion collisions at RHIC

Time

initial state

pre-equilibrium(high Q2 interactions)

QGP andhydrodynamic expansion

hadronization

freeze-out

Physics: 1) Parton distributions in nuclei 2) Initial conditions of the collision 3) A new state of matter – Quark-Gluon Plasma and its properties 4) Hadronization and freeze-out


Particles production

Pions and protons production Low pT – hydrodynamic Intermediate pT – partonic coalescence High pT – jet fragmentation

Light nuclei production Final-state coalescence


The success of hydrodynamic

At low pT, hydrodynamical models successfully reproduce the spectra and v2

STAR PRC.72 (2005) 014904


Coalescence at intermediate pT

STAR PRC.72 (2005) 014904

NQ scaling of v2 is a strong evidence

Coalescence

fragmenting parton:ph = z p, z<1

recombining partons:p1+p2=ph


STAR: Nucl. Phys. A 757 (2005) 102

The difference is not sensitive to the mass of the hadron, but rather depends on the number of valence quarks contained within it.

Coalescence at intermediate pT


High pT – from pp to AuAu

p+p collisions Parton Distribution Function

(derived from e-h scattering) pQCD (parton-parton interaction

cross section calculation) Fragmentation Function (derived

from e+e- collisions) Au+Au collisions

pp collisions + Nuclear effect

We understand pp collisions


Jet fragmentation in pp collisions

1. Improved FF reasonably reproduces data 2. pbar/ ~ 0.2 at RHIC, <<0.1 at low energy

pbar dominated by gluon FFPLB 637 (2006) 161


Jet quenching in Au+Au

STAR: Nucl. Phys. A 757 (2005) 102

Significant suppression of inclusive charged hadron is observed in central Au+Au collisions: Fragmentation+parton energy loss


X.N. Wang: PRC58(2321)1998.

Study the PID spectra and pbar/p ratios can help to further understand how the g/q jets interact with the medium

Parton energy loss in HIJING

HIJING calculation


pQCD: Color charge and flavor dependence of parton energy loss

dE/dx(c/b)<dE/dx(uds)< dE/dx(g)

S. Wicks et al., NPA 784(2007)426


The roles of energetic parton --- source of the meson/baryon production

(1)In LEP e+e- experiment, identified charged particle spectra can be measured from 2 kinds of hadronic Z decays: quark jets and gluon jets (DELPHI EPJC 17 (2000) 207)

(2) The anti-baryon phase space density can be accessed by measuring dbar/pbar

p

d

dydN

dydNyf

/

/

26

13

F.Q. Wang, N. Xu, PRC 61 021904 (2000)


Different mechanisms govern hadron formation in the different kinematic region

Different hadron species may have different sources

Those sources (g/q) may have different behavior when propagating the medium

To study those behaviors,PID in large pT range is required!


Light nuclei formation – final-state coalescence

ChemicalFreeze-out

ThermalFreeze-out

InitialCollisions “QGP”

“De-confinement”Hadronization Late stagescattering

Due to the small binding energy, light nuclei cannot survive before thermal freeze-out. Therefore, light nuclei production and their elliptic flow are sensitive to the freeze-out conditions, such as temperature, particle density, local correlation volume and collective motion.

Henppdnp 3

Time


Final-state Coalescence

AppPd

dNEB

Pd

dNE

Pd

dNEB

Pd

dNE Ap

A

p

ppA

N

n

nn

Z

p

ppA

A

AA /

3333

11

A

A VB R. Scheibl, U. Heinz, PRC 59 1585 (1999)

•Coalescence parameters BA

•Light nuclei v2 – atomic mass number (A) scaling?(consequence of the final-state coalescence)


Detectors

&

Techniques


STAR detectors: TPC & TOF

A new technology (TOF) ----Multi-gap Resistive Plate Chamber

1. Good timing resolution (<100ps)2. Two trays (TOFr+TOFp) for run 4,

acceptance~0.01, 120 trays (TOFr) in the future

Time Projection Chamber

1. Tracking2. Ionization energy loss (dE/dx)


PID – Hadrons

TPC

Relativistic rising of dE/dx

High pT

High performance of time resolution

Low & intermediate pT2.5<pT<3.0

PID up to 12 GeV/c


Light Nuclei Identification

PID Range (GeV/c):

6p2 :HeHe

3p0.2 :d

4p1 :d

T33

T

T

TOF

)expdEdx

measuredEdxLog(Z

)( 33 HeHe

GeV/c 6p2 T

GeV/c 1p7.0 T GeV/c 3p2.5 T


Feed-down correction for (anti-)protons

Method 1: Primordial protons and the protons come from weak decays have different DCA distribution

Primordial (MC) From decay (MC)

Method 2: From the measurements of and spectra, we can estimate the FD contribution


Results

(Au+Au 200 GeV)

Pion and proton spectra: STAR Phys. Rev. Lett. 97 (2006) 152301

Nuclei spectra and v2: QM06 proceeding, J. Phys. G: Nucl. Part. Phys. 34 (2007) S1087-S1091


Pion & proton spectra

PID up to 12 GeV/c

STAR Collaboration PRL 97 (2006) 152301PAs: O. Barannikova, H. Liu, L. Ruan and Z. Xu


Nuclear Modification factor

In central Au+Au collisions:

At 1.5<pT<7 GeV/c, RCP(p+pbar) > RCP() , RCP(p+pbar) shows obvious decreasing trend.

At 4<pT<12 GeV/c, both and p are strongly suppressed. They approach to each other at about 0.3

Curve:I. Vitev, PLB 639 (2006) 38.pT


Anti-particle to particle ratios

1. -/+ are consistent with flat at unity in all pT, no significant centrality dependence.

2. pbar/p ratio: no significant centrality dependence, parton energy loss underpredicts the ratios (X.N. Wang, PRC 58 (2321) 1998).


Proton over pion ratios

1. The p(pbar)/ ratios in Au+Au collisions show strong centrality dependence.

2. In central Au+Au collisions, the p(pbar)/ ratios reach maximum value at pT~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>5 GeV/c.

3. In general, parton energy loss models underpredict p/ ratios. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).


Light Nuclei SpectraDeuteron Helium-3

QM06 proceeding: J. Phys. G: Nucl.Part. Phys. 34 (2007) S1087-S1091


Coalescence Parameters B2 & B3

•B2 & sqrt(B3) are consistent•Strong centrality dependence

11

A

A VB

(anti-)proton spectra: STAR Phys. Rev. Lett. 97, 152301 (2006)

A

p

ppA

A

AA Pd

dNEB

Pd

dNE

33


Coalescence Parameters B2 & B3

•Compare to pion HBT results•Beam energy dependence

11

A

A VB

A

p

ppA

A

AA Pd

dNEB

Pd

dNE

33

22

3

2 sidelongf RRV

HBT parameters: STAR Phys. Rev. C71 (2005) 044906

Assuming a Gaussian shape in all 3 dimensionsR. Scheibl et al.Phys.Rev.C59 (1999)1585


Scaled by A

Baryon v2 -- X.Dong et al, Phys. Lett. B597 (2004) 328-332

Light Nuclei v2

•This is the 1st helium-3 v2 measurement at RHIC

•Deuterons v2 follows A scaling within error bars

•Helium-3 v2 seems deviating from A scaling at higher pT

(need more statistics)

minBias


Low pT v2

The 1st observation of negative v2 at RHIC

No model can readily reproduce the data

dbar centrality bins: 0~12%, 10~20%, 20~40%, 40~80%pbar v2: STAR Phys. Rev. C72 (2005) 014904

d

BW parameters:F. Retiere, M. Lisa, Phys.Rev. C70 (2004) 044907


Accessing anti-baryon density by &

Source of anti-baryon production

pd /

H. Liu & Z. Xu, nucl-ex/0610035Submitted to PLB


In nucleus+nuclues collisions, the anti-baryon density increases with beam energy and reaches a plateau above ISR beam energy regardless the beam species (pp, pA, AA).It can be fitted to a thermal model : ppTmpd B //exp/

Anti-baryon Phase Space DensitySTAR preliminary

p

d

dydN

dydNyf

/

/

26

13

F.Q. Wang, N. Xu, PRC 61 021904 (2000)


Anti-baryon Phase Space Density

STAR preliminary ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar low



ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar lowALEPH(LEP) e+e-

sqrt(s)=91(Z) q+qbar low

STAR preliminary



ARGUS e+e-


sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q low

STAR preliminary



ARGUS e+e-


sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q lowH1(HERA) pWp =200 qqbar+g high

STAR preliminary


ARGUS e+e-


sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q lowH1(HERA) pWp =200 qqbar+g high

In e+e-, the density through qqbar processes is a factor of strong coupling constant less than that through ggg processes (s=0.12)

(q+qbar->q+qbar+g)

s

STAR preliminary


H. Liu, Z. Xu nucl-ex/0610035


Where does (anti-)baryon come from?

In short, anti-baryon phase space density from collisions involving a gluon is much higher than those without gluons

Conclusions:

(1) Collisions which contain ggg, qbar+g or qqbar+g processes have higher anti-baryon phase space density

(2) Processes q+qbar create few anti-baryons

(3) Processes q+g create few anti-baryons at low energy – energy too low?

STAR preliminary


Conclusions

&

Discussions


B/M enhancement at intermediate pT

The relative baryon enhancement is clearly observed in the p/pi ratios at intermediate pT, the similar behavior can also be seen in the /Ks

0 ratios. At the same pT region, the NQ scaling of v2 has also been observed. This can be explained by the parton coalescence phenomena.

STAR Nucl-ex/0601042


Freeze-out volumes

•B2 and B3 have strong centrality dependence, the system has larger freeze-out volumes in more central collisions.

•B2 and sqrt(B3) have similar values in different centrality collisions, which indicates that the deuteron and helium-3 have similar freeze-out volume.

•B2 has little beam energy dependence when sqrt(sNN)>20 GeV, which indicates that the freeze-out volume won’t change with the beam energy.


Light nuclei v2

•At intermediate pT, deuteron v2 follows A scaling within errors while helium-3 v2 seems deviates from this scaling, we need more statistics to draw further conclusion.

•At low pT, the dbar v2 is found to be negative. The BW model, which includes large radial flow scenario, also shows a negative flow prediction. But the BW model fails to reproduce our data since there is only mass input for light nuclei.


Color charge and flavor dependence of parton energy loss

High pT Rcp measurements: , p(pbar), e, , 0

pT

Nucl-ex/0607012 PRL 96 (2006) 202301

Rcp(RAA)~0.2 for all these particles!


Color charge and flavor dependence of parton energy loss

The partonic source:, , 0 – light quarks •p(pbar) – glouns •e – heavy quarks

pQCD calculations

dE/dx(c/b)<dE/dx(uds)< dE/dx(g)

S. Wicks et al., NPA 784(2007)426

Rcp(RAA)~0.2 for all these particles!???


Physics possible:g/q jets conversion in the medium

soft q(qbar)+

hard g

hard q(qbar)+

soft gCompton-like scattering:

W. Liu et al., nucl-th/0607047

A much larger cross-section is needed to explain our data


The future – a good time for discovery

Inv. Yield~Anti-3He : dbar : pbar 1 : 1K : 1M

In the RHIC upcoming high statistics AuAu runs, with STAR large acceptance detector TPC/TOF, we should try to search for anti-, which has never been observed before.

HeH

Hnp

33

3

And, there is also possible to discover Antihypernucleus

STAR Phys. Rev. Lett. 87 (2001) 262301

E864 Phys. Rev. Lett. 85 (2000) 2685

Thanks!

production of meson, baryon and light nuclei in au+au collisions at rhic haidong liu univ. of...

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