pp and d-au at rhic contents: interesting data from rhic high parton densities pp and d-au results...

pp and d-Au at RHICpp and d-Au at RHIC

Contents: • Interesting data from RHIC• High parton densities• pp and d-Au results• Conclusion

Fuming LIU (IOPP, Wuhan),Tanguy Pierog, Klaus Werner

August 9-14, 2004, CCAST, Beijing

2004-8-102004-8-10 F.M.Liu, CCAST, BeijingF.M.Liu, CCAST, Beijing 22

1.1. Interesting data from Interesting data from RHICRHIC

The nuclear modification factor

shows interesting features: pp

AA

NR

coll

1

• AuAu: much smaller than one for central collisions

• d-Au: bigger than one for central collisions

charged hadrons / 2

minimum bias

STAR col. data


Centrality dependence of

the nuclear modification factor

from top to bottom: 0-20%,

20-40%, 40-60%, 60-88%

Rapidity dependence of the nuclear modification factor from top to bottom: eta=0, 1, 2.2, 3.2


Nuclear modification factor R > 1 implies that

partons with higher density in d-Au than in pp

involve the interactions.

How to formulize and simulate this high parton

densities in a Monte Carlo generator?


2. High parton densities2. High parton densities

Parton-parton scattering:

Same symbol for soft and hard.

rapidity plateau

Scattering with many partons:

No nuclear effect Nuclear modification factor R=1.


With high parton densities in target, a parton in projectile may interact with more partons in the target, e.g.:

Multiple ladders

Affects:• multiplicites• hadronization properties

elastic interaction

interference with simple diagram and provide negative contrib. to cross section (screen)

Rapidity gap

(high mass Diffraction)


We try to put all possibilities We try to put all possibilities togethertogether

In a simple and transparent way;In a simple and transparent way;

Using only simple ladder diagrams between projectile and Using only simple ladder diagrams between projectile and

target;target;

Putting all complications into “projectile/target excitations”, Putting all complications into “projectile/target excitations”,

to be treated in an effective way.to be treated in an effective way.The number of partons in projectile/target

which can interact with a parton in target/projectile

is the key quantity, we define it as Z p/T.


The contribution of simple diagram

')()( xx

For the screen contribution:

With reduced weight


)))31(log(1

11(

2max

TZ

)exp(1

)(

)(

2

22

0P/Tnucleons 0P/T

xxa

xg

b

bg

E

EZ

So we use

Z should increase with collision energy, centrality and atomic number

with

So we use

Adding the screening diagram gives the contribution

')()( xx


For the diffractive contribution:

The flat line represents a projectile excitation.

For the multiple ladder contribution:

A target excitation representsSeveral ladders


How to realize projectile/target

excitation? We suppose an mass distributed according toWe suppose an mass distributed according to For masses exceeding hadron masses, we take strings.For masses exceeding hadron masses, we take strings. To realize the effects of high parton density, string proTo realize the effects of high parton density, string pro

perties are supposed to depend on perties are supposed to depend on ZZ , e.g.: , e.g.:

2/1 M

),1 ,min()( max Zfzf

)(t

0

breakbreakt Zfp p

0.3 ,3max fwith


The formalism:The formalism: Cut diagram techniqueCut diagram technique Strict energy conservationStrict energy conservation Markov chains for numericsMarkov chains for numerics

Our simulations tell that the number of “visible”Partons in projectile by a parton in target,

6 Z:Au-d

2 :pp

projectile

projectile

Z


3. proton-proton results a. multiplicity distribution:

Left to right: contributions from 0, 1, >=2 Pomerons


3. proton-proton results b. pseudo-rapidity distribution:

UA5 data

PHOBOS data

Central ladders (Pom’s)Target excitations / Projectile excitations


3. proton-proton results c. Transverse momentum distribution:

data: PHENIX


3. proton-proton results c. Transverse momentum distribution:At different rapidity regions, data: BRAHMS


3. d-Au results a. pseudo-rapidity distribution:

Central ladders (N Pom > 1) Central ladder (N Pom =1)

Target excitations / Projectile excitations

Minimum bias

Centrality dependence

#

#


3. d-Au results c. Transverse momentum distribution,

the nuclear modification factor R.


The centrality dependence of nuclear modification factor R.


The rapidity dependence of nuclear modification factor R.


Some other good resultsSome other good results

Results on identified hadrons, e.g. Results on identified hadrons, e.g. The nuclear modification factor R for d-Au The nuclear modification factor R for d-Au

collisions as a function of transverse collisions as a function of transverse momentum momentum

The particle ratios as a function of transverse The particle ratios as a function of transverse momentum for pp and d-Au collisionsmomentum for pp and d-Au collisions

The number of triggered jets at near The number of triggered jets at near side and away side for pp and d-Au side and away side for pp and d-Au collisions.collisions.


ConclusionsConclusions

Motivated by the recent RHIC data in pp and d-Au collisions, we sMotivated by the recent RHIC data in pp and d-Au collisions, we study the behaviors of nuclear modification factor.tudy the behaviors of nuclear modification factor.

The behaviors change with collision energy and centrality (incluThe behaviors change with collision energy and centrality (including the atomic numbers of projectile and target).ding the atomic numbers of projectile and target).

We simulate the R behavior for d-Au collisions successfully and fiWe simulate the R behavior for d-Au collisions successfully and find the high parton density plays the key role for it.nd the high parton density plays the key role for it.

There are still something to do, e.g. adding the interactions of prThere are still something to do, e.g. adding the interactions of produced particles, to explain well the target side data of d-Au collioduced particles, to explain well the target side data of d-Au collision and explain Au-Au collisions.sion and explain Au-Au collisions.

Thanks !Thanks !

pp and d-au at rhic contents: interesting data from rhic high parton densities pp and d-au results...

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