Transcript J/ suppression in p-A and In-In collisions at 158 GeV/nucleon 

J/ suppression in p-A and In-In
collisions at 158 GeV/nucleon
R. Arnaldi – INFN Torino (Italy)
for the NA60 Collaboration
• Introduction
• J/ suppression in In-In collisions
• New results from p-A collisions
at 158 GeV
 study of the pT distributions and
comparison with In-In
• v2 of the J/ in In-In
• Conclusions
1
J/ suppression at SPS energy
• Nuclear collisions results: Pb-Pb (NA50) and In-In (NA60)
• p-A reference results: from p-A collisions at 400/450 GeV (NA50)
In-In
Pb-Pb
R. Arnaldi et al. (NA60), PRL99, 132302 (2007)
• Observed suppression exceeds nuclear absorption
• Onset of the suppression at Npart  80
• Comparison between different systems  Npart scaling
• At RHIC (s  10 sSPS) a very similar suppression pattern is observed
2
Nuclear absorption reference
• Measuring J//DY in p-A collisions at 400/450 GeV, NA50 extracts
(Glauber analysis) absJ/ = 4.2±0.5 mb, and (J//DY)pp =57.5±0.8
• The expected J/ yield for In-In and Pb-Pb collisions is calculated
• assuming absJ/ (158 GeV) = absJ/ (400/450 GeV)
• rescaling (J//DY)pp to 158 GeV with a semi-theoretical procedure
(J/)/DY = 29.2  2.3
L = 3.4 fm
• Preliminary pA results from NA60 at 158GeV
(averaged over nuclear targets) seem to
validate the nuclear absorption normalization
extracted from 400/450 GeV data
• Results on absJ/ will appear soon (HP08)
 crucial to confirm (or modify) the
anomalous suppression pattern
Preliminary!
3
J/ transverse momentum
At SPS energy, previous results by NA50 seem to indicate that the shape of the pT
distributions of the J/ are dominated by initial state effects (multiple scattering of the
incoming gluons, i.e. Cronin effect)
• Main features:
• pT2 (and T) linearly increase with L
(mean thickness of nuclear matter)
• Phenomenological description with
the expression
pT2 ( L)  pT2
pp
  gN L
with an energy dependent pT2pp and
a common slope:
gN= 0.081±0.002 (GeV/c)2/fm
pT distributions for pA and AA never studied in the same energy/kinematical range
4
p-A collisions at 158 GeV
• A target system including 7 different nuclei (Be, Al, Cu, In, W, Pb, U) has been used
• Accurate target ID thanks to the NA60 vertex spectrometer (pixel)
W
Pb
Cu In
p-In
pCu
U
Be
Al
• Mass resolution: 100 MeV at the J/, 40 MeV at the 
• Under the J/
• Combinatorial background is zero
• Drell-Yan contribution is small (<2%)
 A simple event counting technique can be used to extract NJ/
5
Study of pT distributions in pA at 158 GeV
• The pT distributions of the J/ have been obtained using a 1D acceptance
correction method
• The input distributions for the other kinematical variables (y, cosCS) have been
obtained starting from a 3D correction algorithm and then adjusted iteratively on the
data
Al
In
Pb
• y distribution  gaussian with y=0.52
• cosCS distribution  flat
(no J/ polarization)
• Rapidity coverage 0<yCM <1
• Same as in NA50(Pb)/NA60(In)
 extrapolation needed for
upstream targets
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pT distributions for 158 GeV pA
Distributions fitted with the function
0<ycm<1
|cos|<0.5
 mT
1 dN
 mT K1 
T
pT dpT
 eff




in order to obtain the inverse slope
Teff values
Teff values slightly increase with A
7
mT distributions for 158 GeV pA
In the explored mT-M range,
no deviations from the
exponential behaviour can
be appreciated
8
Dependence of pT2 on L
<pT2>pp=1.13 ± 0.04 (GeV/c)2
gN=0.029 ± 0.011 (GeV/c)2/fm
• Systematic errors are mainly
due to the choice of the
generated y and cos
distributions in the
acceptance calculations
Pb
W
U
Cu
Be
Al
In
smaller than statistical errors
• Applying more severe event
selection cuts there is no
effect on the results
We observe a linear increase of <pT2> with L,
consistent with gluon scattering in the initial state
9
Comparison p-A vs In-In (Pb-Pb)
For the first time we compare the transverse momentum distributions of the J/
in p-A and A-A, in the same energy/kinematical range
p-A
<pT2>pp=1.13 ± 0.04 (GeV/c)2
gN=0.029 ± 0.011 (GeV/c)2 / fm
In-In
<pT2>pp=1.27 ± 0.09 (GeV/c)2
gN=0.058 ± 0.014 (GeV/c)2 / fm
Pb-Pb
<pT2>pp=1.19 ± 0.04 (GeV/c)2
gN=0.072 ± 0.005(GeV/c)2 / fm
• pT2 increases linearly with L in both p-A, In-In and Pb-Pb
• However, the scaling of pT2 with L is broken moving from p-A to A-A
• On one hand comparing p-A and peripheral In-In the suppression scales with L
• On the other hand the J/ pT distributions do not scale with L !
• gNAA ~ 2 gNpA  does one simply add up projectile and target broadening ?
10
Comparison p-A In-In vs. Npart
We find an approximate
scaling of pT2 with the
logarithm of the number of
participant nucleons
11
Comparison pA 158 GeV vs pA 400 GeV
• NA60 has also taken p-A data at 400 GeV, i.e. in the same energy and kinematical
domain covered by p-A data previously collected by NA50
• Compare (as a check) the results of the two experiments
• The slope of the p-A points at 400 GeV
is compatible between NA50 and NA60
(1.2 )
NA60 p-A 400 GeV
gN=0.104 ± 0.013
NA50 p-A 400 GeV
gN=0.087 ± 0.004
New 158 GeV data show that at
SPS gN depends on the energy of
the collision
12
RAA for In-In at 158 AGeV
• We have not measured reference p-p collisions at 158 GeV
• Build a J/ pT distribution using the functional form
RAA
 mT
1 dN
 mT K1 
T
pT dpT
 eff
0-1.5%
16-23%




with T obtained from the value of pT2 pp
coming from the fit of the p-A data
1.5-5 %
23-33%
5-10%
33-47%
10-16%
47-57%
pT (GeV/c)
13
RAA for In-In at 158 AGeV (2)
• Clear rise at high pT consistent
with the Cronin effect
• RAA much lower than 1 at low pT
• Effect seen dominated by
nuclear absorption
• A systematic error (11%) due to
the data normalization is common
to all points
14
RCP for In-In at 158 A GeV
RCP
Normalize pT distributions to the most peripheral In-In bin,
corresponding to Npart50
0-1.5%
16-23%
1.5-5%
5-10%
23-33%
33-47%
10-16%
pT (GeV/c)
We see that moving towards central collisions there is an increasingly
large suppression at low pT (already seen in Pb-Pb)
15
Comparison with PHENIX
RAA similar at SPS and RHIC at low transverse momentum (pT < 1.5 GeV/c)
16
v2 measurements at NA60
NA60 acceptance: ~ 0 < ycm < 1
● Use elliptic flow v to estimate the reaction plane (v = 0 at midrapidity)
2
1
● Determination from charged particle tracks as measured in the vertex tracker
●
h±
v2
v2 for charged particles
17
J/ azimuthal anisotropy (1)
• Limited statistics (<30000 J/ events) prevents a fine binning in centrality/pT
• Define 2 broad centrality classes
central
peripheral
v2 consistent with zero for central events, v2 > 0 (2.3) for peripheral
18
J/ azimuthal anisotropy (2)
• Introduce a rough pT binning
Centrality
pt<1GeV/c
pt>1GeV/c
0.5% < σ/σgeo <
28%
0.00±0.03
-0.01±0.03
28% < σ/σgeo < 83% 0.03±0.05
0.11±0.05
• In spite of the relatively low statistics, we
see an anisotropy for peripheral events,
concentrated at high pT
• Hardly a signal of elliptic flow (charm
collective motion), since at SPS
• Ncc is low (no recombination)
• Difficult to have charm thermalisation
• Effect likely to be connected with
anisotropic absorption in QGP/nuclear
matter
19
Conclusions
• First results on the J/ transverse momentum distributions in pA at 158 GeV
• We observe a linear increase of <pT2> with L, consistent with gluon scattering
in the initial state
• However
• The slope is smaller than in In-In and Pb-Pb at the same energy
• Peripheral In-In and p-A collisions with approximately the same L
have <pT2> different by ~ 200 MeV
• The J/ suppression scales with L in p-A and peripheral In-In and Pb-Pb
• The L scaling is broken when looking at the pT distributions
• First results on the v2 of the J/ at SPS energy
• v2 significantly larger than zero for non central events at pT >1 GeV/c
• Effect likely to be connected with anisotropic absorption
in QGP/nuclear matter
• One key ingredient in the overall J/ suppression picture still missing
 absJ/ (158 GeV)
• Results are coming…. stay tuned!
20
The NA60 Collaboration
http://cern.ch/na60
CERN
Heidelberg
~ 60 people
13 institutes
8 countries
Bern
Palaiseau
BNL
Riken
Yerevan
Stony Brook
Torino
Lisbon
Clermont
Lyon
Cagliari
R. Arnaldi, R. Averbeck, K. Banicz, K. Borer, J. Buytaert, J. Castor, B. Chaurand, W. Chen, B. Cheynis,
C. Cicalò, A. Colla, P. Cortese, S. Damjanović, A. David, A. de Falco, N. de Marco, A. Devaux, A. Drees,
L. Ducroux, H. En’yo, A. Ferretti, M. Floris, P. Force, A.A. Grigoryan, J.Y. Grossiord, N. Guettet, A. Guichard,
H. Gulkanyan, J. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenço, J. Lozano, F. Manso, P. Martins, A. Masoni,
A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher,
P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan,P. Sonderegger, H.J. Specht,
R. Tieulent, E. Tveiten, G. Usai, H. Vardanyan, R. Veenhof and H. Wöhri
21
Backup
22
The experimental apparatus
Muon trigger and tracking
(NA10/NA38/NA50 spectrometer)
2.5 T dipole magnet
targets
ZDC
hadron absorber
Iron wall
magnetic field
vertex
tracker
beam
tracker
Muon
Other
Matching in coordinate and momentum space
Origin of muons can be accurately
determined
prompt
or
displaced
!
Improved dimuon mass resolution:
 ~20 MeV/c2 (vs. 80 MeV/c2)
J/ ~70 MeV/c2 (vs. 105 MeV/c2)
23
Influence of Drell-Yan contamination
• The Drell-Yan contribution under the J/ is ~ 2%
and its pT distribution is not known
• Describe the Drell-Yan pT shape with the
same function used to fit the J/ distributions
p-Pb
a)
DY subtracted
DY not subtracted
DY
• Assume the usual dependence of pT2 on L,
<pT2> = <pT2>pp + qN * L, with qN = 4/9 gN
• Use pT2pp = 1.25 (GeV/c)2, as given by PYTHIA
• 2 assumptions for qN:
a) qN = 0 (no dependence on L)
b) qN = 4/9  0.081 (GeV/c)2/fm (dependence
on L as measured by NA50 in PbPb)
b)
Teff changes by less than 0.4 MeV
pT2 changes by less than 0.01 (GeV/c)2
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<pT2> vs NPart
25
Comparison p-A and In-In
Comparison peripheral In-In vs p-Pb
26
<pT2> vs L – different y ranges
p-A
<pT2>pp=1.13 ± 0.04 (GeV/c)2
gN=0.029 ± 0.011 (GeV/c)2 / fm
p-A
<pT2>pp=1.14 ± 0.04 (GeV/c)2
gN=0.015 ± 0.012 (GeV/c)2 / fm
27
RAA*(pT) for In-In at 158 AGeV
• In p-A we find a good correlation between pT2 (and therefore T) and L
• Effects connected with Cronin and nuclear absorption should scale with L
• Extrapolate T to the L values reached in In-In and build the corresponding pT
distribution, which is then used to normalize the measured In-In distributions
The suppression effect is
mainly present at low pT
But we still observe an
enhancement at high pT
28
(is the L extrapolation from p-A to A-A a good one?)
RAA
29
Systematic errors
30
Comparison with theoretical predictions
A. Capella, E. Ferreiro
EPJ C42(2005) 419
R.Rapp,
EPJ C43(2005) 91
S. Digal, S. Fortunato, H. Satz,
EPJ C32(2004) 547
centrality dependent t0
fixed termalization time t0
Suppression by hadronic
comovers (co = 0.65 mb,
tuned for Pb-Pb collisions)
Dissociation and
regeneration in QGP
and hadron gas
Percolation, with
onset of suppression
at Npart~140
• Size of the anomalous suppression reasonably reproduced
• Quantitative description not satisfactory
31
Maximum hadronic absorption
• Compare J/ yield to
calculations assuming
• Nuclear absorption
• Maximum possible
absorption in a
hadron gas
(T = 180 MeV)
L. Maiani et al.,
Nucl.Phys. A748(2005) 209
F. Becattini et al.,
Phys. Lett. B632(2006) 233
• Both Pb-Pb and (to a lesser extent) In-In show extra-suppression
32
J/ suppression in In-In collisions
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’ in In-In collisions
• Use matching of muon spectrometer tracks
• Study limited by statistics (N’ ~ 300)
• Normalized to Drell-Yan yields
450, 400 and 200 GeV points
rescaled to 158 GeV
• Most peripheral point
(Npart ~ 60) does not show
an anomalous suppression
• Good agreement with
Pb-Pb results
Preliminary
35
’ in p-A collisions
450, 400 and 200 GeV points
rescaled to 158 GeV
’/DY = 0.51  0.07
L = 3.4 fm
Also the ’ value measured
by NA60 at 158 GeV is in
good agreement with
the normal absorption
pattern, calculated from
450 (400) GeV data
Preliminary!
36