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

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~T c, ) with subsequent melting of the J/  at higher temperatures. Large fraction of J/  comes from the  c (~32% HERA-B,hep/ex ) and  ’ (~10% PDG, Phys. Rev. D 54 (1996) 1 ). Introduction E866/NuSea collaboration observed stronger suppression of  ’ compared with J/  already in interactions of 800 GeV/c protons on Be, Fe and W targets (Phys.Rev.Lett.84(2000) 3256). The motivation of the present study is to look for similar effect in NA50 pA data. 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 p T 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, (2003) ). CEM and COM correctly reproduce the energy dependence of the charmonium cross-section, although require parameters extracted from the experiment. 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 X F 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.

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 T A (s) - nuclear thickness function at impact vector s. parametrization: meson is absorbed with cross section  abs seeing in average amount of matter from its production point to exit from nucleus: (from expansion of Glauber formula: ) A  parametrization: (widely used but rough) Connected with previous formulae as:

NA50 results for J/  and  ’ 450 GeV on Be, Al, Cu, Ag and W targets Submitted to Physics Letters B High intensity beam ( ) [R.S at XXXVII Rencontres de Moriond, hep-ex/ ] and Low intensity beam ( ) [P.Cortese at QM2002, Phys.Lett. B 553 (2003) 167] J/  acceptance Analyzed domain: -0.5<y cm < 0.5 |cos  |<0.5 (-0.1<X F <0.1) Fits to cross-sections integrated over rapidity (HI + LI data) Glauber   = 4.6 ± 0.8 mb   = 7.7 ± 1.1 mb A    = ±   ’ = ±   ’ -   = ± exp(-  L)   = 4.3 ± 0.7 mb   = 6.6 ± 0.8 mb   -   ’ = 2.4 ± 0.05 mb From  ’/ 

X F - dependence of the absorption from the absolute cross-sections of J/  and  ’ (errors are dominated by the systematics of the normalization) XFXF -0.1 : : : 00 : : 0.1 J/   0.925(15)0.932(15)0.923(15)0.920(15)0.929(16) LL 4.4(7)4.1(7)4.6(7)4.7(7)4.2(7) G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L 7.0(8)9.2(1.1)6.9(1.0)7.0(1.0)7.0(1.1) G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XF -0.1 : : : 00 : : 0.1  (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 X F ~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 X F 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 X F ? It does not scale neither with x of the struck parton in the target (parton energy loss scenario) nor with P lab (~charmonium formation time)

E866,800 GeV Absorption decreases as p T 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 nucleus by rescattered gluon sees less matter and vice-versa. But increases already at the p-p level: can this be the reason of the stronger suppression at SPS than at FNAL? Oliver Drapier, Mémoire de l’habilitation

SPS and FNAL experiments are far from the strong shadowing x domains, at least for small X F. Open Charm cross-section/nucleon in pA does not show dependence on A at X F ~ 0 :  = 1.02 ±0.03 ±0.02 (E GeV, Phys.Rev.Lett. 72 (1994) 2542 ) => suppression due to the structure functions nuclear modifications and initial state interactions at SPS-FNAL energies may be relevant only at large X F. Fraction of from gg fusion shadowing anti-shadowing EKS 98 from H.Wöhri, CINANP03 at X F ~0 with EKS 98 Can modification of PDF’s in the nucleus or Initial State interactions affect charmonium suppression?

 c production HERA-B, hep-ex/ 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 X F it is slow enough to form the final meson still inside the nucleus. The suppression observed at X F ~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 suppression pattern 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

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 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

~20  m XY resolution Heavy Ion runs 2002: Pb-Pb 30 and 20 GeV/A Planed: October 2003, In-In 158 GeV/A Primary aims: study of charmonium anomalous suppression onset, Intermediate mass region (open charm vs prompt dimuons), Low mass region  3 pixel planes Muon Spectrometer was not operated. Centrality Bin  max (dN/d  )  max 0-10 % 2.2 ± ± % 2.2 ± ± % 1.9 ± ± 4 J/  survival probability by M.Nardi

offset (  m) prompt dimuons open charm muon track offset resolution better than 35  m for p  15 GeV/c D + : c  = 317  m D 0 : c  = 124  m offset  90  m 90  offset  800  m and muons away from each other  180  m in the transverse plane at Z vertex Background Signal Separating charm decays from prompt dimuons