Charmonium production in pA collisions:results and perspectives

R.Shahoyan, IST Lisbon

Motivation

Production models and absorption parametrizations

Last results from NA50 on J/ and ’,

comparison with E866 and NA3

Prospects: NA60 experiment

HIC03, June 25-28 2003

Charmonium suppression was predicted as a signature of QGP formation in nucleus- nucleus collisions (T.Matsui and H.Satz, Phys. Lett. B178 (1986) 416)

Was found already in the normal nuclear matter due to interactions

NA50 observed in 158 AGeV/c PbPb collisions the anomalous suppression of J/Phys.Lett B477

(2000) 28 Its step pattern may be interpreted as initial melting of c states at the onset of QGP (T~Tc,) with subsequent melting of the J/ at higher temperatures.

Large fraction of J/ comes from the c (~32% HERA-B,hep/ex0211033) and ’ (~10% PDG, Phys. Rev. D 54 (1996) 1).

Introduction

XDDhcc }{

Need: Better understanding of J/, ’ and c production and absorption in normal nuclear matter (pA collision)

Detailed study of the Open Charm production and J/ anomalous suppression pattern in heavy ion interactions.

Charmonium Production Models

Color Singlet Model – perturbative creation of the static pair in color singlet state with subsequent binding to final meson without changing of quantum numbers (C-H. Chang, Nucl. Phys. B 172 (1980) 425.; R. Baier and R. Rückl, Phys. Lett. B 102 (1981) 364; Z. Phys. C 19 (1983) 251)Direct J/ and ’ are suppressed (hard gluon emission), main contribution from c decays. Describes high pT ISR data, but fails by the factor ~30 for the J/ and ~60 for the ’ to

reproduce CDF data at =1.8 GeV (F.Abe et al., CDF Collab., Phys. Rev. Lett. 79 (1997) 572)

Color Evaporation Model – perturbative creation of the pair in the color octet state with subsequent non-perturbative hadronization to color singlet via unsuppressed soft gluon emission (H. Fritzsch, Phys. Lett. B67, 217 (1977); F. Halzen, Phys. Lett. B69, (1977),105). Predicts unpolarized charmonium production.

Color Octet Model – uses NRQCD formalism to describe the non-perturbative hadronization of the color octet to the color singlet state via soft gluon emission (E.Braaten et al., Phys.Lett B 333 (1994) 548). Predicts transverse polarization at high Pt (but recently BaBar observed longitudinal polarization: Phys.Rev.Lett, 90, 162001 (2003) ).

CEM and COM correctly reproduce the energy dependence of the charmonium cross-section, although require parameters extracted from the experiment.

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s

Both assume production of non-singlet pair (without identity of final meson) with significant hadronic break-up cross-section, which evolves into charmonium state after some formation time (~1 fm). This may introduce the dependence of the absorption cross-sections at given XF on the charmonium type and collision energy: at smaller Lorentz factors higher fraction of pairs forms the final charmonium state still traveling in the nucleus.

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Parametrizations of Charmonium Absorption

Glauber Model: meson is produced in binary nucleon-nucleon interaction with cross section 0 and absorbed in nuclear matter with cross section abs

TA(s) - nuclear thickness function at impact vector s.

AabsA

abspA sTsd

)(10

<L> parametrization: meson is absorbed with cross section abs seeing in average <L> amount of matter from its production point to exit from nucleus:

(from expansion of Glauber formula: )

)(exp0 LA abspA

)(2

1 2 sTsdA

L A

A parametrization: (widely used but rough)

Connected with previousformulae as:

ApA 0

A

Labs ln

1

NA50 results for J/ and ’ p @ 450 GeVon Be, Al, Cu, Ag and W targets

Submitted to Physics Letters B

High intensity beam (1996-1998) [R.S at XXXVII Rencontres de Moriond, hep-ex/0207014] and Low intensity beam (1998-2000) [P.Cortese at QM2002, Phys.Lett. B 553 (2003) 167]

J/ acceptance

Analyzed domain:-0.5<ycm< 0.5

|cos|<0.5(-0.1<XF<0.1)

Fits to cross-sections integrated over rapidity (HI + LI data)

Glauber = 4.6 ± 0.8 mb

= 7.7 ± 1.1 mb

A = 0.928 ± 0.015

’ = 0.888 ± 0.018’- = -0.041 ± 0.009

exp(-L) = 4.3 ± 0.7 mb

= 6.6 ± 0.8 mb - ’ = 2.4 ± 0.05 mb

From ’/

XF - dependence of the absorptionfrom the absolute cross-sections of J/ and ’

(errors are dominated by the systematics of the normalization)

XF -0.1 : 0.1 -0.1 : -0.05 -0.05 : 0 0 : 0.05 0.05 : 0.1

J/ 0.925(15) 0.932(15) 0.923(15) 0.920(15) 0.929(16)

L 4.4(7) 4.1(7) 4.6(7) 4.7(7) 4.2(7)

G 4.9(8) 4.4(8) 5.0(8) 5.2(8) 4.6(8)

’

0.881(19) 0.844(27) 0.883(24) 0.879(27) 0.878(28)

L 7.0(8) 9.2(1.1) 6.9(1.0) 7.0(1.0) 7.0(1.1)

G 8.2(1.1) 11.4(1.8) 8.1(1.4) 8.4(1.5) 8.3(1.6)

’ with respect to J/ from the cross-sections ratios

(free of normalization errors, but full Glauber fit is not possible)

XF -0.1 : 0.1 -0.1 : -0.05 -0.05 : 0 0 : 0.05 0.05 : 0.1

-0.045(9) -0.091(18) -0.038(15) -0.043(15) -0.047(17)

L 2.5(5) 5.3(9) 2.2(8) 2.5(8) 2.6(9)

Evidence for the stronger suppression of slower ’ ?

Would be expected due to the faster formation of the final state

Comparison with E866/NuSea and NA3

E866 at 800 GeV finds (Phys.Rev.Lett 84 (2000) 3256) ~0.95 at XF~0, vs ~0.92 of NA50 at 450 GeV.

Also, NA50 shows larger difference between the J/ and ‘.

NA3 at 200 GeV reported (Z.Phys.C 20 (1983) 101) value close to E866 and similar XF behaviour.

NA3 used p and Pt targets while NA50 and E866: Be ... W. ’s may be misleading => use Glauber model

Does normal nuclear absorption depend on or scales with XF?

It does not scale neither with x of the struck parton in the target (parton energy loss scenario) nor with Plab (~charmonium formation time)

s

E866,800 GeV

Absorption decreases as pT increases and turns to enhancement: understood as an effect of the partons rescattering before interaction amplified by the absorption: J/ produced in the end of the nucleusby rescattered gluon sees less matter and vice-versa.

But <pT2> increases already at the p-p level: can this

be the reason of the stronger suppression at SPS thanat FNAL?

Oliver Drapier, Mémoire de l’habilitation

SPS and FNAL experiments are far from the strong shadowing x domains, at least for small XF.

Open Charm cross-section/nucleon in pA does not show dependence on A at XF ~ 0 : = 1.02 ±0.03 ±0.02 (E789 800GeV, Phys.Rev.Lett. 72 (1994) 2542) => suppression dueto the structure functions nuclear modifications and initial state interactions at SPS-FNAL energies may be relevant only at large XF.

Fraction of from gg fusioncc

shadowing

anti-shadowing

EKS 98

from H.Wöhri, CINANP03

at XF~0with EKS 98cc

Can modification of PDF’s in the nucleus or Initial State interactions affect charmonium suppression?

c production

HERA-B, hep-ex/0211033

CEM and COM (NRQCD) predict different A-dependence for the c1,2 production (R.Vogt, Nucl.Phys. A 700 (2002) 539)

CEM: all charmonia are produced from the color octet Only at very negative XF it is slow enough to form the final meson still inside the nucleus. The suppression observed at XF ~0 is dominantly due to the color octet absorption => J/, ’ and c1,2 should have the same A-dependence

COM: c1,2 production is dominated by the point-like color

singlet contribution (in opposite to J/ and ’) => c1,2 should suffer much less absorption.

Due to the large contribution to the observed J/ cross-section the c1,2 A-dependence may be crucial for the understanding of the charmonium suppressionpattern in heavy ion collisions

A-dependence was not measured yet:

Most recent measurement of HERA-B: 920 GeV/c p on C and Ti targets. But obtained relative error on the fraction of the J/ from the c1,2 decays is still ~30%...

E771, Phys.Rev.D62(2000)03206

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Muon Spectrometer

beam

2.5 T dipole magnet

vertex tracker

Micro-Strips

Pixels

Beam Tracker

D

} offset

vertex

Muon track matching through the absorber

Muon track offset measurement :Separate charm from prompt dimuons

< 1 mm

ZDC Quartz Blade Interaction

Counter

Overview of NA60 Experiment

pA runs

Planed for 2004

2 months of beam requested.

Primary aim: c A-dependence study

~ 1% precision on nuclear absorption cross-section to be achieved

2002 : 400 GeV (low statistics)

after addition

of vertex detector

Z (cm)-10 -8 -6 -4 -2 0 2 4 6 8 10

0

500

1000

1500

2000

2500

3000

3500

4000

30 GeV/n

~20m XY resolution

Heavy Ion runs2002: Pb-Pb 30 and 20 GeV/A

Planed: October 2003, In-In 158 GeV/A

Primary aims: study ofcharmonium anomalous suppression onset,Intermediate mass region (open charm vs prompt dimuons), Low mass region

3 pixel planesMuon Spectrometer

was not operated.

Centrality Bin max (dN/d)max

0-10 % 2.2 ± 0.1 166 ± 5 10-20% 2.2 ± 0.1 128 ± 7 20-35% 1.9 ± 0.2 90 ± 4

J/

su

rviv

al

pro

ba

bil

ity

by M.Nardi

0 100 200 300 400 500 600 700offset (m)

promptdimuons

open charm

muon track offset resolution

better than 35 m for p 15 GeV/c

D+ : c = 317 mD0 : c = 124 moffset 90 m

90 offset 800 m and muons away from each other 180 min the transverse plane at Zvertex

Background

Background

Signal

Signal

Separating charm decays from prompt dimuons