Transcript Document

Столкновение релятивистских
тяжелых ядер и загадка
чармония
А.Б.Курепин – ИЯИ РАН, Москва
VI Марковские чтения
15 Мая 2008 г.
ОИЯИ, Дубна
Charmonium
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33 years ago: discovery of J/ψ, 21 years ago: Matsui & Satz
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colour screening in deconfined matter → J/ψ suppression
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→ possible signature of QGP formation
Experimental and theoretical progress since then
→ situation is much more complicated
–
cold nuclear matter / initial state effects
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“normal” absorption in cold matter
(anti)shadowing
saturation, color glass condensate
suppression via comovers
feed down from cc, y’
sequential screening (first: cc, y’, J/y only well above Tc)
regeneration via statistical hadronization or charm coalescence
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important for “large” charm yield, i.e. RHIC and LHC
NA50 experimental setup
The J/y is detected via its decay into muon pairs
Dimuon spectrometer: Centrality detectors: EM calorimeter (1.1< lab<2.3)
2.92 < ylab< 3.92
cos CS  < 0.5
ZDC calorimeter (lab> 6.3)
Multiplicity detector (1.9<lab<4.2)
Pb-Pb 158 GeV/c
Data period
1995
1996
1998
2000
p – A 400 GeV/c 2000 year
Subtargets Number of J/y
Target
7
7
1
1 in vacuum
Be
Al
Cu
Ag
W
Pb
50000
190000
49000
129000
Number of J/y
38000
48000
45000
41000
49000
69000
J/y suppression is generally considered as one of the most direct signatures of QGP formation
(Matsui-Satz 1986)
Fit to the mass spectrum
J/ψ suppression from p-A to Pb-Pb collisions
J/ψ production has been extensively studied in p-A, S-U and Pb-Pb
collisions by the NA38 and NA50 experiments at the CERN SPS
Projectile
J/y
Target
J/y normal nuclear
absorption curve
Jy
 abs
 4.18  0.35mb
• Light systems and peripheral Pb-Pb collisions: J/ψ is absorpted by nuclear matter .
The scaling variable - L (length of nuclear matter crossed by the J/ψ)
 (J/ψ) ~ exp( -abs L)
• Central Pb-Pb collisions: the L scaling is broken
- anomalous suppression
NA60 : is anomalous suppression present also in lighter In-In
nuclear systems ? Scaling variable- L, Npart, ε ?
NA60 experimental setup
~ 1m
Target
area
beam
Muon Spectrometer
Hadron absorber
MWPC’s
Iron
wall
Toroidal Magnet
m
m
ZDC
Trigger Hodoscopes
High granularity and radiation-hard silicon tracking telescope in the vertex region
before the absorber
Dipole field
2.5 T
Matching in coordinate
and in momentum space
BEAM
BEAM
TRACKER
not to scale
MUON
FILTER
VERTEX
TELESCOPE
IC

• Origin of muons can be accurately determined
• Improved dimuon mass resolution
ZDC

TARGET
BOX
allows studies vs.
collision centrality
Comparison of NA50 and NA60 results
An “anomalous suppression” is presented already in In-In
The normal absorption curve is based on NA50 results. Its uncertainty (~ 8%) at 158
GeV is dominated by the (model dependent) extrapolation from the 400 and 450 GeV
p-A data.
 need p-A measurements at 158 GeV
Сomparison J/y results versus Npart
NA50: Npart ftom Et (left) and from Ezdc (right, as in NA60)
J/y suppression in In-In is in agreement with Pb-Pb
S-U has different behaviour
y’ suppression (NA38, NA50, NA60)
abs=8±1 mb
abs~20 mb
Preliminary!
Small statistics in NA60 In-In for y’ (~300)
The most peripheral point (Npart~60) – normal nuclear absorption
Suppression by produced hadrons (“comovers”)
The model takes into account nuclear absorption and comovers interaction
J/y / NColl
with σco = 0.65 mb (Capella-Ferreiro) EPJ
C42(2005) 419
In-In 158 GeV
nuclear absorption
comover + nuclear absorption
(E. Ferreiro, private communication)
Pb-Pb 158 GeV
NA60 In-In 158 GeV
QGP + hadrons + regeneration + in-medium effects
The model simultaneously takes into account dissociation and regeneration processes in
BmmJ/y/DY
both QGP and hadron gas (Grandchamp, Rapp, Brown EPJ
fixed thermalization
time
centrality dependent
thermalization time
In-In 158 GeV
Nuclear Absorption
Suppression +
Regeneration
QGP+hadronic suppression
Regeneration
Number of participants
centrality dependent
thermalization time
fixed thermalization time
NA60 In-In 158 GeV
Pb-Pb 158 GeV
C43 (2005) 91)
Suppression due to a percolation phase transition
Model based on percolation (Digal-Fortunato-Satz)
Eur.Phys.J.C32 (2004) 547.
Prediction: sharp onset (due to the disappearance of
the cc meson) at Npart ~ 125 for Pb-Pb and
~ 140 for In-In
Pb-Pb 158 GeV
NA60 In-In 158 GeV
The dashed line includes the
smearing due to the resolution
J/y transverse momentum distribution
Study <pT2> and T
dependence on
centrality
NA60 In-In
J/y transverse momentum distribution
<pT2> versus L
Fitting : <pT2>(L) = <pT2>pp + αgN L
<pT2>pp= 1.08 ± 0.02 GeV2/c2
χ2= 0.85
αgN = 0.083 ± 0.002 GeV2/c2fm-1
The observed dependence could simply
result from parton initial state multiple
scattering
NA50 and NA38 Teff recalculated to
158 GeV vs energy density
T(=0) =( 182)2 MeV
Tslope = ( 20.16  1.04)  10-3 fm3
Tslope(cent Pb-Pb)=(8.87  2.07) 10-3 fm3
R(slopes)=2.27 +/- 0.54
In NA38 and NA50 TJ/ ψ grows linearly with the energy density and with L.
Model dependent recalculation 400 and 200 GeV data to 158 GeV- scaling.
For the most central Pb-Pb collisions more flat behaviour could be seen.
J/ψ suppression versus pT.
F=(J/y/DY>4.2 )acc vs pT in 5 ET bins
NA50
Pb-Pb
2000
F
F
Et bins in GeV
1.
2.
3.
4.
5.
pT
5 - 20
20 - 40
40 - 70
70 - 100
>100
Suppression vs pT for p-A, S-U and Pb-Pb
Rcp
p-A
S-U
~Aα
Cronin effect- enhancement at
pT>2 GeV/c
Et bins GeV
5 - 40
40 - 80
80 – 125
Rcp
Pb-Pb 2000
Rcp vs pT.
NA60 In-In
RCP
Rcp = (J/ψi(pT)/Ncoll i)/(J/ψ1(pT)/Ncoll1)
0-1.5%
16-23%
1.5-5%
5-10%
23-33%
33-47%
10-16%
pT (GeV/c)
The ratios to the peripheral i=1 (47-57%) bin.
Large suppression at low pT, growing with centrality- as in RAA NA60
and in Rcp NA50.
J/ in PHENIX
J/  e+e–
identified in RICH and
EMCal
– |y| < 0.35
– Pe > 0.2 GeV/c
–  = 
J/μ+μ–
identified in 2 fwd
spectrometers
South :
• -2.2 < y < -1.2
North :
• 1.2 < y < 2.4
– Pm > 2 GeV/c
–  = 2 
Centrality is calculated to Npart (Ncoll)
using Glauber model
Event centrality and
vertex given by
BBC in 3<||<3.9 (+ZDC)
Suppression RAA vs Npart at RHIC.
PHENIX Au-Au data
All models for
y=0 J/y,y’,c
nucl-ex/0611020
c
Yan, Zhuang, Xu
nucl-th/0608010
nucl-ex/0611020
Models for mid-rapidity Au-Au data
Without regeneration
With regeneration
J/ψ suppression (SPS and RHIC)
J/ψ yield vs Npart,
normalized on Ncoll.
Unexpected good
scaling.
Coherent interpretationproblem for theory.
Work start - : Karsch,
Kharzeev and Satz.,
PRL637(2006)75
J/ψ suppression RAA vs pT at PHENIX.
Au-Au
Cu-Cu
nucl-ex/0611020
arXiv:0801.0220 [nucl-ex]
For low pT suppression grows with centrality.
Comparison SPS (NA60) and RHIC (PHENIX) data
The same suppression at
low pT.
Larger values of <pT2> at
RHIC
Suppression RAA in Au-Au (PHENIX) vs pT.
P
J/ψ up to only 5 GeV
Central events
The same RAA for
0,  at all pT
and J/y (up to 4 GeV/c).
RAA for  is higher.
RAA for direct  <1 for
high pT.
J/ψ suppression RAA at RHIC.
PHENIX and STAR Cu-Cu data
• Data consistent with no suppression at
high pT: RAA(pT > 5 GeV/c) = 0.9 ± 0.2
• At low-pT RAA: 0.5—0.6 (PHENIX)
• RAA increase from low pT to high pT
• Most models expect a decrease RAA at
high pT:
X. Zhao and R. Rapp, hep-ph/07122407
H. Liu, K. Rajagopal and U.A. Wiedemann,
PRL 98, 182301(2007) and hep-ph/0607062
 But some models predict an increase RAA
at high pT:
K.Karch and R.Petronzio, 193(1987105;
J.P.Blaizot and J.Y.Ollitrault, PRL (1987)499
Conclusions
• At SPS energies the J/y shows an anomalous suppression
discovered in Pb-Pb and existing already in In-In
• None of the available models properly describes the observed
suppression pattern simultaneously in Pb-Pb and In-In
•The y shows an anomalous suppression for S-U, In-In
and Pb-Pb
•At RHIC energies the J/y suppression is of the same order as at SPS
•None of the theoretical model could describe all the data
•The transverse momentum dependence of J/ψ suppression shows
suppression mainly ay low pT, growing with centrality
Need information at high pT.