Elementary Process and d+Au Collision at RHIC Energy

@ 大阪大学 RCNP, 28 Oct., 2003

北大理　一瀬 昌嗣 (M.Isse)☆ 共同研究　　　　　　　　　　　　　　　　　　

原研東海研　 大塚 直彦 (N.Otuka)インド物理学研 Ｐ．Ｋ．サフ (P.K.Sahu)

北大理　 　大西 明 (A. Ohnishi)IntroductionAdditional Jets study (Au+Au)Elliptic flow with two analysis methodElementary Process study (p+p, d+Au)pt-spectrum and Azimuthal CorrelationSummary

Introduction

p+p and d+Au collision has been done at RHIC (√s =200 AGeV). d+Au collision dose not show signature of QGP formation seen in Au+Au (√s = 130, 200 AGeV), like Jet Quenching.d+Au collision is not expected to form QGP. Then, Hadronic Cascade should reproduce d+Au collisions.We would like to estimate how the Jet events occur in each event at RHIC.

Today’s Two Topic

Additional Jets study -> Au+Au High pT hadrons, underestimated in hadronic cascade, seems to come from jets in both Au+Au, d+Au collisions.Elliptic flow v2 of Au+Au (130,200 AGeV) collision at RHIC is available, which may be a sensitive probe to see jet effect.We introduce jets additionally in Hadronic Cascade model JAM 1.010 and study elliptic flow v2.

Elementary Process study -> d+Au

Additional Jets study

Au+Au

Final State Interaction and Jet production

Final State InteractionHadron multiple scatteringResonance and String production and decaySoft process is dominant.

Jet productionHard process.QCD based scenario has to be considered.Jet-quenching or Cronin effect or shadowing are not considered in this result, but we include independent jets.

Additional JetsAu+Au pT- spectrum produced by JAM1.010 is not enough at high-pT.Add some (Ncentral=7 (Au+Au), 1.5(d+Au)) jets of p+p collision by PYTHIA 6.2 to reproduce high-pT hadrons in central events.Additional jet number is determined by Njet(b)= Ncentral*<Nbin>/<Nbin>max, proportional to the number of binary collision assuming Glauber geometry.

Glaubergeometry

Additional Jets

Ncentral

(h++h-)2

Analysis Methods of Elliptic Flow

Reaction Plane Method

The R.P. is initially known in the simulation. vn(pT,)=<cos(n())>

Correlation Method

Calculate the angle of each particles vn(pT,)=<cos(n)> (pT,) / √<cos(n)> ()

)))(cos(21()(/10

nvNddN

n n

))cos(21(/1

20

nvNddN

n n

squared

Elliptic flow v2 (Nch/Nmax)

Jets do not affect so much on v2

Two Analysis Methods (Reac. and Corr.) do not have significant differences.

Reac.

Corr.

Au+Au√s

=130AGeV

h±

Elliptic flow v2 (pT)

Additional Jets reduce v2 at high-pT .

Including additionalJets make v2 reduce!!Both in Reaction Plane Method and Correlation Method.

Au+Au√s

=130AGeV

h±

Summary of Additional Jets study

We have investigated Au+Au collision at RHIC by using hadron-string cascade model JAM 1.010 with additional jets by using PYTHIA 6.2. They are determined to fit experimental pT-spectra.We calculate elliptic flow v2 by JAM with additional jets. In Nch/Nmax distribution, v2 change little. While, in pT distribution, v2 at high-pT is largely suppressed, both in Reaction Plane and Correlation method.

Elementary process study

p+p, d+Au

Elementary Process

)],()(exp[12 sbTbd Njetsoft

Inelastic cross sections of p+p collision. eltotinel

)],(2exp[12 sbbd

)0,(Im4 tsftot

)],(exp[12 2 sbbd

Total cross sections of p+p collision.

Lower limit of allowed pT

We choose a parameter in JAM (i.e. PYTHIA 6.1), which give the lower limit of allowed pT value for hard 22 processes. Here we denote it “c”. (“ckin(3)” in PYTHIA)

The default value of “c” in JAM is 2, it is same in HIJING.

p+p √s= 200 AGeV pt-spectrum

(h++h-)2

c=2.7 seems good

Nuclear coherent thickness

)],()(exp[12 sbTbd Njetsoftinel

(1+a)

In nucleus-nucleus collisions, we increase thickness for hard processes.

Put a factor “a” onjet

Calculate pT –spectrum and Azimuthal Correlation of d+Au collision.

d+Au √s=200 AGeV pt-spectrum

(h++h-)2

Dose not increased thickness “a”

Increased thickness

“a”

d+Au M.B. Azimuthal correlation

Jet

Jet

•Much far-side @high-pT

•Little near-side @low&high-pT

We need more consideration.

SummaryWe have investigated p+p, d+Au collision at RHIC by using hadron-string cascade model JAM 1.010.When we put a factor “a” on jet as nucleon coherent thickness, pT -spectrum of d+Au collision is reproduced. Independent h+h collision is not suitable for A+A collisions at RHIC energies.correlation should be considered more carefully. High-pT (<4GeV/c) component may not come from back-to-back jets.