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Why does high-pt suppression persist at forward rapidity?. I.G. Bearden ( for the BRAHMS collaboration) Niels Bohr Institute, Københavns Universitet. Outline. Introduction Experiment R AA Results 200GeV Au+Au 62GeV Cu+Cu & Au+Au Model Comparisons Summary. - PowerPoint PPT Presentation
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
1
HEHI BRAHMS
Why does high-pt suppression persist at forward rapidity?
I.G. Bearden ( for the BRAHMS collaboration)Niels Bohr Institute, Københavns Universitet
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
2
HEHI BRAHMS
Outline
Introduction– Experiment
– RAA
Results– 200GeV Au+Au– 62GeV Cu+Cu & Au+Au
Model Comparisons Summary
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
3
HEHI BRAHMS
Two small solid anglespectrometers (FS and MRS)
2.3°30°
that can rotate from 2.3° to 30°
90°
30°
and 30° to 90° (MRS)
provide excellent PID over broad range in y-pT
The BRAHMS ExperimentIt’s Broad RAnge Hadron Magnetic Spectrometers!
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
4
HEHI BRAHMS
Quantified by:
ddpNdN
ddpNdR
TNN
bin
TAB
AB /
/2
2
• Cronin Enhancement• Shadowing/Saturation• Jet-quenching
- yield relative to that fromN+N collisions, scaled forthe nuclear geometry (Nbin)
Nuclear Modification
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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HEHI BRAHMS
Charged hadron pT spectra 200GeV Au+Au
Nb: filled are +, open -, drawn lines are BRAHMS p+p data
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
6
HEHI BRAHMS
RAA for charged hadrons
at high pT, the charged hadron yields produced in
most central 0-10% Au+Au collisions are
suppressed compared to binary scaled p+p yields
Little change in RAA as function of eta
BRAHMS Preliminary
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAA @ 62.4 GeV ~3.1~0
Au+Au
Cu+Cu
BRAHMS Preliminary
BRAHMS Preliminary
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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HEHI BRAHMS
Caveat emptor!How to make pT=2GeV/c
p=2.8GeV/c p=28GeV/c
BRAHMS Preliminary
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMSRAuCu0- 10% & 40-60%
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAuCu with same Ncoll at Midrapidity
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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HEHI BRAHMS
RAuCu mid vs. forward 62.4GeV (10%)
0
0,2
0,4
0,6
0,8
1
1,2
0 1 2 3
forwardmid
pT
RA
uC
u
MidrapidityForward (3.1)
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAuCu with same ‘radius’
BRAHMS PRELIMINARY
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
13
HEHI BRAHMSRAA for identified particles
(200GeV)
the charged pion yields are suppressed by a factor of ~ 2-3 as
compared with binary scaled p+p pion yields.
RAA for pions is independent of rapidity
the proton and antiproton yields in central Au+Au at 200 GeV
do not show suppression, baryon meson difference remains
protons
BR
AH
MS P
relim
inarypions
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAA at 62.4 GeV, y=0BRAHMS PreliminaryBRAHMS Preliminary
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAA, y>3, 62GeV, top 10% central
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
16
HEHI BRAHMS
Interesting regionIntermediate pT
(2<pT<3.5 GeV/c)Pion hard, Proton soft
PT, cross~ 1.8 GeV/c for 1.8 GeV/c for
2.7 GeV/c for K2.7 GeV/c for K3.7 GeV/c for p3.7 GeV/c for p
Hydro+Jet: Interplay between Soft and Hard
T.H
irano &
Y.N
ara
(’0
3),
PR
C6
9(2
00
4)0
34
90
8
Au
+A
u a
t b
=2 f
m
Calculation based on two models with
CGC as initial conditions:
3D hydrodynamic model (Hydro)
dynamics of high pT partons (Jet)
pT,cross is the point for Yieldsoft=Yieldhard
pT,cross moves toward high pT with mass
of particles because of the effects of
radial flow.
y=0
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
17
HEHI BRAHMS
Model comparison I
pT spectra for charged hadrons in 200 GeV Au+Au reasonably
well described by the hydro+jet model calculation at η=3.2
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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HEHI BRAHMS
Model comparison II
opacity n = L/l
L – effective length of matter
l – mean free path
less jet quenching +
stronger initial effects
at higher rapidities
maintain rapidity independent NMF
Barnafoldi et al. hep-ph 0609023
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
19
HEHI BRAHMS
Is RAA an appropriate measure?
~15 GeV
Re
nk,
Esk
ola
, P
RC
75
, 0
54
91
0 (
20
07
)
Wicks,H
oro
witz,D
jord
jevic,G
yula
ssyN
PA
78
4, 4
26
(20
07
)
Two rather differentModels both reproduceRAA. RAA only tells us that we only ‘see’ particles from near Hot&dense surface?
5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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HEHI BRAHMS
Summary
At 200GeV, intermediate pT constant behavior vs. y
For 62.4GeV, pronounced changes from mid to forward rapidity.
+ suppressed for 62.4 y=3.4, p “suppressed” but not partonically
RAA flat for same mean radius (<R>). Why?
Hydro+jet looks good, but... RAA not a good model descriminator