why does high-pt suppression persist at forward rapidity?
DESCRIPTION
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 PresentationTRANSCRIPT
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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
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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
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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!
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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
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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
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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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
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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
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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
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMSRAuCu0- 10% & 40-60%
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAuCu with same Ncoll at Midrapidity
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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)
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAuCu with same ‘radius’
BRAHMS PRELIMINARY
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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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
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAA at 62.4 GeV, y=0BRAHMS PreliminaryBRAHMS Preliminary
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
HEHI BRAHMS
RAA, y>3, 62GeV, top 10% central
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
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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
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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
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
18
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
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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?
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5. Februar 2008 Quark Matter '08 Jaipur IndiaI.G.Bearden, Niels Bohr Institute
20
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