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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

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In-InPb-Pb

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)

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

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• Measuring J//DY in p-A collisions at 400/450 GeV, NA50 extracts (Glauber analysis) abs

J/ = 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 abs

J/ (158 GeV) = absJ/ (400/450 GeV)

• rescaling (J//DY)pp to 158 GeV with a semi-theoretical procedure

(J/)/DY = 29.2 2.3L = 3.4 fm

Preliminary!

Nuclear absorption reference

• 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

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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

LpLp gNppTT 22 )(

with an energy dependent pT2pp 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

J/ transverse momentum

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• 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)

pCu

• 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/

p-A collisions at 158 GeV

Al

U

Cu In

W

Be

Pb p-In

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• The pT distributions of the J/ have been obtained using a 1D acceptance correction method• The input distributions for the other kinematical variables (y, cosCS) have been obtained starting from a 3D correction algorithm and then adjusted iteratively on the data

• Rapidity coverage 0<yCM <1• Same as in NA50(Pb)/NA60(In) extrapolation needed for upstream targets

Al

In

Pb

Study of pT distributions in pA at 158 GeV

• y distribution gaussian with y=0.52• cosCS distribution flat (no J/ polarization)

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Distributions fitted with the function

eff

TT

TT T

mKm

dp

dN

p 1

1

Teff values slightly increase with A

0<ycm<1|cos|<0.5

pT distributions for 158 GeV pA

in order to obtain the inverse slope Teff values

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In the explored mT-M range, no deviations from theexponential behaviour canbe appreciated

mT distributions for 158 GeV pA

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• Systematic errors are mainly due to the choice of the generated y and cos distributions in the acceptance calculations

• 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

Dependence of pT2 on L

smaller than statistical errors

<pT2>pp=1.13 ± 0.04 (GeV/c)2

gN=0.029 ± 0.011 (GeV/c)2/fm

BeAl

Cu In

WPb

U

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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

<pT2>pp=1.13 ± 0.04 (GeV/c)2

gN=0.029 ± 0.011 (GeV/c)2 / fm

<pT2>pp=1.27 ± 0.09 (GeV/c)2

gN=0.058 ± 0.014 (GeV/c)2 / fm

<pT2>pp=1.19 ± 0.04 (GeV/c)2

gN=0.072 ± 0.005(GeV/c)2 / fm

Comparison p-A vs In-In (Pb-Pb)

Pb-Pb

In-In

p-A

• 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 !• gN

AA ~ 2 gN

pA does one simply add up projectile and target broadening ?

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Comparison p-A In-In vs. Npart

We find an approximatescaling of pT

2 with the logarithm of the number of participant nucleons

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• 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 GeVgN=0.104 ± 0.013

NA50 p-A 400 GeVgN=0.087 ± 0.004

New 158 GeV data show that at SPS gN depends on the energy of

the collision

Comparison pA 158 GeV vs pA 400 GeV

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• We have not measured reference p-p collisions at 158 GeV• Build a J/ pT distribution using the functional form

RAA for In-In at 158 AGeV

eff

TT

TT T

mKm

dp

dN

p 1

1 with T obtained from the value of pT2 pp

coming from the fit of the p-A data

0-1.5% 1.5-5 % 5-10% 10-16%

16-23% 23-33% 33-47% 47-57%

pT (GeV/c)

RA

A

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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

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Normalize pT distributions to the most peripheral In-In bin, corresponding to Npart50

We see that moving towards central collisions there is an increasingly large suppression at low pT (already seen in Pb-Pb)

RCP for In-In at 158 A GeV

pT (GeV/c)

RC

P

0-1.5% 1.5-5% 5-10% 10-16%

16-23% 23-33% 33-47%

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Comparison with PHENIX

RAA similar at SPS and RHIC at low transverse momentum (pT < 1.5 GeV/c)

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● NA60 acceptance: ~ 0 < ycm

< 1● Use elliptic flow v

2 to estimate the reaction plane (v

1 = 0 at midrapidity)

● Determination from charged particle tracks as measured in the vertex tracker

v2 measurements at NA60

v2 for charged particles

h±

v 2

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peripheral central

J/ azimuthal anisotropy (1)

• Limited statistics (<30000 J/ events) prevents a fine binning in centrality/pT

• Define 2 broad centrality classes

v2 consistent with zero for central events, v2 > 0 (2.3) for peripheral

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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

J/ azimuthal anisotropy (2)

• 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

• Introduce a rough pT binning

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• First results on the J/ transverse momentum distributions in pA at 158 GeV• We observe a linear increase of <pT

2> 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 <pT

2> different by ~ 200 MeV

• 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

Conclusions

• 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

• One key ingredient in the overall J/ suppression picture still missing abs

J/ (158 GeV) • Results are coming…. stay tuned!

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Lisbon

CERN

Bern

Torino

Yerevan

CagliariLyon

Clermont

Riken

Stony Brook

Palaiseau

Heidelberg

BNL

~ 60 people13 institutes8 countries

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

The NA60 Collaborationhttp://cern.ch/na60

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Backup

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hadron absorberMuonOther

magnetic field

Iron wall

2.5 T dipole magnet

targets

beam tracker

vertex tracker

ZDC

Muon trigger and tracking(NA10/NA38/NA50 spectrometer)

Matching in coordinate and momentum space

Origin of muons can be accurately determined ~20 MeV/c2 (vs. 80 MeV/c2)

J/ ~70 MeV/c2 (vs. 105 MeV/c2)

Improved dimuon mass resolution:

or!

prompt

displaced

The experimental apparatus

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• 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

• Assume the usual dependence of pT2 on L,

<pT2> = <pT

2>pp + qN * L, with qN = 4/9 gN

• Use pT2pp = 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)

a)

Teff changes by less than 0.4 MeVpT

2 changes by less than 0.01 (GeV/c)2

p-Pb

Influence of Drell-Yan contamination

DY subtracted

DY not subtracted

DY

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<pT2> vs NPart

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Comparison peripheral In-In vs p-Pb

Comparison p-A and In-In

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<pT2> vs L – different y ranges

<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

p-A

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• 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 anenhancement at high pT

(is the L extrapolation from p-A to A-A a good one?)

RAA*(pT) for In-In at 158 AGeV

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RAA

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Systematic errors

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Suppression by hadroniccomovers (co = 0.65 mb,tuned for Pb-Pb collisions)

Dissociation andregeneration in QGPand hadron gas

Percolation, withonset of suppression at Npart~140

• Size of the anomalous suppression reasonably reproduced• Quantitative description not satisfactory

centrality dependent 0

fixed termalization time 0

A. Capella, E. Ferreiro EPJ C42(2005) 419

R.Rapp, EPJ C43(2005) 91

S. Digal, S. Fortunato, H. Satz, EPJ C32(2004) 547

Comparison with theoretical predictions

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• Compare J/ yield to calculations assuming

• Nuclear absorption• Maximum possible absorption in a hadron gas

(T = 180 MeV)

• Both Pb-Pb and (to a lesser extent) In-In show extra-suppression

L. Maiani et al.,Nucl.Phys. A748(2005) 209F. Becattini et al.,Phys. Lett. B632(2006) 233

Maximum hadronic absorption

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J/ suppression in In-In collisions

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• Use matching of muon spectrometer tracks• Study limited by statistics (N’ ~ 300)• Normalized to Drell-Yan yields

• Most peripheral point (Npart ~ 60) does not show an anomalous suppression

• Good agreement with Pb-Pb results

Preliminary

450, 400 and 200 GeV points rescaled to 158 GeV

’ in In-In collisions

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’/DY = 0.51 0.07L = 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!

450, 400 and 200 GeV points rescaled to 158 GeV

’ in p-A collisions