J/ production in In-In and p-A collisions

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J/ production in In-In and p-A collisions

E. Scomparin for the NA60 Collaboration

• Introduction• Centrality dependence of J/ and ’ suppression in In-In collisions• (Preliminary) results on J/ and ’ production in p-A collisions• Transverse momentum and rapidity distributions• Polarization• Outlook/conclusions

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J/ suppression in nuclear collisions

• Previous knowledge• 1986 – 1992: NA38 experiment (light ions and protons)• 1994 – 2000: NA50 experiment (Pb ions and protons)

• At CERN SPS energy (s ~ 20 GeV/nucleon) Study the onset of deconfinement (Matsui and Satz, 1986)

• Main topics (to be) studied• Normal vs anomalous suppression

needs accurate p-A data • Scaling variables(s) for the onset of the anomaly

needs comparison between different colliding systems• J/ vs c vs ’ suppression

needs high statistics (’) needs a sophisticated apparatus (c J/ )

Issues presently addressed by NA60

from H. Satz,hep-ph/0609197

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Results from p-A and Pb-Pb

• Absorption in cold nuclear matter (p-A) can explain S-U data• Anomalous suppression sets in for semi-peripheral Pb-Pb collisions

• But• p-A data taken in a different energy/kinematic range• Is there anomalous suppression for systems lighter than Pb-Pb ?

L. Ramello (NA50),Quark Matter 2005

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The NA60 experiment

hadron absorberMuonOther

and trackingMuon trigger

magnetic field

Iron wall

NA10/38/50 spectrometer2.5 T dipole magnet

Matching in coordinate and momentum space

targets

beam tracker

vertex tracker

ZDC

• In-In @ 158 GeV/nucleon ~ 2×108 dimuon triggers collected

• 2 event samples• Set A (low ACM current) mass resolution @ J/ ~ 125 MeV• Set B (high ACM current) mass resolution @ J/ ~ 105 MeV

• After muon matching mass resolution @ J/ ~ 70 MeV

• Both sets are used for J/ analysis maximize statistics

• Improved reconstruction algorithm and alignment with respect to QM2005 (~1 m accuracy)

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Event selection• 2 event selections have been used for J/ analysis1)• No matching required• Extrapolation of muon tracks must lie in the target region

Higher statistics Poor vertex resolution (~1 cm)

2)• Matching between muon tracks and vertex spectrometer tracks• Dimuon vertex in the most upstream interaction vertex (MC correction to account for centrality bias due to fragment reinteraction)

Better control of systematics Good vertex resolution (~200 m) Lose 40% of the statistics

• 2 analysesa) Use selection 1 and normalize to Drell-Yanb) Use selection 2 and normalize to calculated J/ nuclear absorption

• After quality cuts NJ/ ~ 45000 (1), 29000 (2)

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• Data points have been normalized to the expected J/ normal nuclear absorption, calculated with

as measured with p-A NA50 data at 400 and 450 GeV

J/ / DY vs. centrality (analysis a)

J/abs = 4.18 0.35 mb

• Qualitative agreement with NA50 results plotted as a function of Npart

bin1 Npart = 63 (EZDC> 11 TeV)

bin2 Npart = 123 (7< EZDC< 11 TeV)

bin3 Npart = 175 (EZDC< 7 TeV)

B. Alessandro et al., Eur. Phys. J. C39(2005) 335

3 centrality bins,defined through

EZDC

Anomalous suppression

present in Indium-Indium

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J/ yield vs nuclear absorption (analysis b)• Compare data to the expected J/ centrality distribution, calculated assuming nuclear absorption (with abs =4.18 mb) as the only suppression source

require the ratio measured/expected, integrated over centrality, to be equal to the same quantity from the (J/)/DY analysis (0.87 ± 0.05)

Nuclearabsorption

extrpA

centr all DYJ/ψμμ

meas

centr all DYJ/ψμμ

ZDCZDCnucl.abs.J/ψ

ZDCZDCmeasJ/ψ

σσB

σσB

dE dEdN

dE dEdN

Normalization of thenuclear absorption curve

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Results and systematic errorsSmall statistical errors

Careful study of systematicerrors is needed

• Sources• Uncertainty on normal nuclear absorption parameters (abs(J/) and pp(J/))• Uncertainty on relative normalization between data and absorption curve• Uncertainty on centrality determination (affects relative position of data and abs. curve)

• Glauber model parameters• EZDC to Npart

• ~10% error centrality indep. does not affect shape of the distribution• Partly common to analyses a and b• (Most) Central points affected by a considerable error

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Comparison with previous results (vs Npart)

• NA50: Npart estimated through ET (left), or EZDC (right, as in NA60)

• Good agreement with PbPb• S-U data seem to show a different behavior

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Various centrality estimators (,l)

• Suppression vs energy density and fireball’s transverse size• Anomalous suppression sets in at ~ 1.5 GeV/fm3 (0=1 fm/c)• What is the best scaling variable for the onset ?

Clear answer requires more accurate Pb-Pb suppression pattern

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Comparison with theoretical predictions

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

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Maximum hadronic absorption

• 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

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Comparison between SPS and RHIC• Plot J/ yield vs Npart , normalized to collision scaling expectations

Work in this direction has already started

(see e.g. Karsch, Kharzeev and Satz, PLB 637(2006) 75)

Coherent interpretation of SPS vs RHIC

We see a nice scaling(really surprising....)

challenge for theorists

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’ suppression in In-In collisions• Use selection 2 (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

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p-A collisions at 158 GeV

• Accurate proton data are an essential reference for A-A

• NA60 has taken p-A data at 158 GeV

Obtain for the first time at SPS energy information on nuclear absorption and production yields at the same energy of A-A data

• Reduce systematic errors on the reference curve for A-A collisions, due to energy and kinematic rescaling

Pb

Be

InCu

W

U

Al

All targets

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Data analysis• Final analysis needs a complete understanding of the (local) efficiency of the vertex spectrometer still in progress

• For the moment use info from muon spectrometer only• Calculate –related quantities averaged over the various targets

• Obtain ratio of charmonia production to Drell-Yan (à la NA50)

• Kinematic region• 0 < yCM <1• -0.5 < cos CS < 0.5

• Acceptances• J/ : 0.156• ’ : 0.173• DY (2.9<m<4.5) : 0.150

2/ndf = 1.24

DYJ/, ’DD

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(J/)/DY at 158 GeV

0.081.03

σσB

σσBextrap GeV, (400) 450

LDYJ/ψμμ

meas GeV, 158

LDYJ/ψμμ

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

Preliminary!

• Preliminary NA60 result shows that the rescaling of the J/ production cross section from 450(400) GeV to 158 GeV is correct !

Rescaled to 158 GeV

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’ / DY

’/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

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Transverse momentum distributions

Kinematical region0.1 < yCM < 0.9

-0.4 < cosH < 0.4

Transverse momentum distributions fitted with

Tm

TT

Tedp

dN

p

1

• Study evolution of T and pT

2 with centrality

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pT2 vs centrality

gNInIn = 0.067 0.011 (GeV/c)2/fm

pT2pp

InIn = 1.15 0.07 (GeV/c)2

2/ndf = 0.62

• If pT broadening is due to gluon scattering in the initial state pT

2 = pT2pp + gN · L

gNPbPb = 0.073 0.005 (GeV/c)2/fm

pT2pp

PbPb = 1.19 0.04 (GeV/c)2

2/ndf = 1.22

• NA60 In-In points are in fair agreement with Pb-Pb results

• We get

to be compared with

(NA50 2000 event sample)

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T vs centrality

1) dN/dpT = pT mT K1(mT/T)

2) dN/dpT = pT e -mT/T

• Used by NA50• Gives slightly higher T values (~ 7 MeV)

Fitting functions

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J/ polarization • Quarkonium polarization test of production models

• CSM: transverse polarization• CEM: no polarization• NRQCD: transverse polarization at high pT

CS = -0.03 0.17

2/ndf =1.42

0 < pT < 5 GeV0.4 < yCM < 0.75

H = 0.03 0.06

2/ndf =1.01

0.5 < pT < 5 GeV0.1 < yCM < 0.6

• Deconfinement should lead to a higher degree of polarization (Ioffe,Kharzeev PRC 68(2003) 094013)

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Polarization vs pT, y, centrality

• Helicity reference system (good coverage in NA60, -0.8<cosH<0.8)

• No significant polarization effects as a function of• Centrality• Kinematical region

• Similar results in the Collins-Soper reference frame, albeit with much narrower coverage (-0.4<cosCS<0.4)

0.1<yCM<0.80.5<pT<50.1<yCM<0.60.2<pT<5

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J/ rapidity distributions

y = 0.68 0.022/ndf = 0.60

0<pT<5, -0.4 < cosH < 0.4

• Data are consistent with a gaussian rapidity distribution

• Centrality independent• Slightly narrower at high pT ?

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Azimuthal distribution of the J/central peripheral

More peripheral data hint for a non isotropic emission pattern?

Only 50% of the statistics analyzed

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Conclusions and perspectives

• NA60 has performed a high-quality study of J/ production in Indium-Indium collisions at the SPS

• Confirms, for a much lighter system, the anomalous suppression seen in Pb-Pb collisions by NA50

• Onset of anomalous suppression at Bj ~ 1.5 GeV/fm3

• Preliminary results from p-A collisions at 158 GeV show that the normalization of the absorption curve is correct• Peripheral In-In and Pb-Pb results are compatible with p-A

• Absence of J/ polarization in the kinematical window probed by NA60

• pT distributions sensitive to initial state effects

• Study of J/ suppression for other collision systems, with the accuracy allowed by a vertex spectrometer, would be very interesting

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The NA60 collaborationhttp://cern.ch/na60

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