Transcript “ pp and d-Au at RHIC“(ppt 727K)

pp and d-Au at RHIC
Fuming LIU (IOPP, Wuhan),
Tanguy Pierog, Klaus Werner
Contents:
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Interesting data from RHIC
High parton densities
pp and d-Au results
Conclusion
August 9-14, 2004, CCAST, Beijing
1. Interesting data from RHIC
The nuclear modification factor
shows interesting features:
1 AA
R
N coll pp
• AuAu: much smaller than one for central collisions
• d-Au: bigger than one for central collisions
charged hadrons / 2
minimum bias
STAR col. data
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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
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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?
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2. High parton densities
Parton-parton scattering:
Scattering with many partons:
rapidity
plateau
Same symbol for soft and hard.
No nuclear effect 
Nuclear modification factor R=1.
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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
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 elastic interaction
interference with simple
diagram and provide
negative contrib.
to cross section (screen)
F.M.Liu, CCAST, Beijing
Rapidity gap
(high mass
Diffraction)
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We try to put all possibilities together

In a simple and transparent way;
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Using only simple ladder diagrams between projectile and target;
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Putting all complications into “projectile/target excitations”, 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.
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For the screen contribution:
With
reduced
weight
The contribution of simple diagram
 ( x ) ( x ) '
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Adding the screening diagram gives the contribution
So we use
 
  '
 (x ) (x )
   max (1 
1
1  (log( 1  3ZT ))
2
)
Z should increase with collision energy, centrality and atomic number
So we use
with
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E b
Z P/T  
g( )
b0
nucleonsP/T E0
g ( x) 
1
a2  x2
exp(  x 2 )
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For the diffractive contribution:
The flat line represents
a projectile excitation.
For the multiple ladder contribution:
A target excitation
represents
Several ladders
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How to realize projectile/target excitation?

We suppose an mass distributed according to 1 / M 2

For masses exceeding hadron masses, we take strings.

To realize the effects of high parton density, string
properties are supposed to depend on Z , e.g.:
pt
with
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break

pt
0
f (Z )
break
f ( z )  min( f max , 1  Z ),
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f max  3,   0.3
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The formalism:
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Cut diagram technique
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Strict energy conservation

Markov chains for numerics
Our simulations tell that the number of “visible”
Partons in projectile by a parton in target,
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pp :
Z projectile  2
d - Au :
Zprojectile  6
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3. proton-proton results
a. multiplicity distribution:
Left to right: contributions from
0, 1, >=2 Pomerons
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3. proton-proton results
b. pseudo-rapidity distribution:
PHOBOS data
UA5 data
Central ladders (Pom’s)
Target excitations / Projectile excitations
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3. proton-proton results
c. Transverse momentum distribution:
data: PHENIX
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3. proton-proton results
c. Transverse momentum distribution:
At different rapidity regions, data: BRAHMS
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3. d-Au results
a. pseudo-rapidity distribution:
Minimum bias
Centrality dependence
Central ladders (N # Pom > 1)
Central ladder (N# Pom =1)
Target excitations / Projectile excitations
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3. d-Au results
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c. Transverse momentum distribution,
the nuclear modification factor R.
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The centrality dependence of nuclear modification factor R.
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The rapidity dependence of nuclear modification factor R.
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Some other good results
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Results on identified hadrons, e.g.
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The nuclear modification factor R for d-Au collisions
as a function of transverse momentum
The particle ratios as a function of transverse
momentum for pp and d-Au collisions
The number of triggered jets at near side
and away side for pp and d-Au collisions.
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Conclusions

Motivated by the recent RHIC data in pp and d-Au collisions,
we study the behaviors of nuclear modification factor.
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The behaviors change with collision energy and centrality
(including the atomic numbers of projectile and target).
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We simulate the R behavior for d-Au collisions successfully
and find the high parton density plays the key role for it.
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There are still something to do, e.g. adding the interactions of
produced particles, to explain well the target side data of d-Au
collision and explain Au-Au collisions.
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Thanks !