Published on October 29, 2007
Slide1: Quark Matter ’05 Budapest Aug 3-9, 2005 Marzia Nardi Centro Fermi (ROME) / CERN - TH Outline: Outline Introduction Normal suppression in nuclear matter : preresonance absorption Anomalous suppression : QGP (percolation, thermal dissociation) Normal hadronic interactions (comovers) Discussion : SPS and RHIC Conclusions Normal suppression: Normal suppression General definition : J/y suppression in p-A collisions is well described by a probabilistic formula z b p A Slide4: From a fit of experimental p-A data (NA38,NA50): sabs=4.18 +- 0.35 mb (hep-ex/0412036) In S-U collisions the same suppression is observed The normal suppression is interpreted as the absorption, in the nuclear environment, of the c-cbar pair before the J/y (or y’ or c) formation : preresonance absorption. Anomalous suppression: Anomalous suppression In peripheral Pb-Pb collisions the (J/y)/DY ratio is consistent with the normal suppression pattern In central Pb-Pb collisions (b<8-8.5 fm) a much stronger suppression is observed: Anomalous suppression New In-In data follow the same pattern ! (NA60) Slide6: The anomalous suppression is the candidate as the signal for deconfinement. There are two ways to prove it : compare to absorption in a hadronic gas: less trivial extrapolation of p-A and S-U. “Known” parameters. Negative approach. formulate a reasonnable model for a deconfinement scenario: define critical variable(s). Unknown parameters. Positive approach. More difficult ! Feed-down: Feed-down Only a fraction (~60%) of the observed J/y’s are directly produced. The rest come from the decay of higher excited states (~30% from c, ~10% from y’). The feed-down has been studied in pN and pN interactions. The medium (confined / deconfined) affects differently the different charmonium states. Different properties (binding energy, size,…) implies different dissociation temperatures or different cross-sections for interactions with hadrons. Comover interactions: Comover interactions After the normal absorption in the nuclear environment, the survived J/y’s interact with secondary hadrons: J/y+h->DD. Crucial parameter : J/y-hadron inelastic cross-section, (syhinel) a very uncertain parameter ! Theoretical estimates : syhinel ~0.1-1 mb Common assumptions: isoentropic, longitudinal expansion of the hadron gas (Monte Carlo calculations include transverse expansion); the density decreases as 1/t; the interactions stop at the freeze-out. From p-A and S-U to Pb-Pb: From p-A and S-U to Pb-Pb Constraints from p-A and S-U data : the cross-section is very small and/or the comover density in these systems is negligible. Can the comover density have such a strong increase in Pb-Pb collisions to produce the observed suppression ? ? Dual Parton Model: Dual Parton Model [A.Capella et al.,Z.Phys.C3,329,(1980); Phys.Rep.236,225(1994) A.Capella et al.,nucl-th/0303055; hep-ph/0505032] The number of secondary hadrons at the initial (formation) time is given by the sum of two contributions, proportional respectively to the number of participants and to the number of binary N-N collisions (s=coordinate in the transverse plane) : The coefficients C1 and C2 are predicted in the DPM. RHIC : shadowing corrections (to moderate the increase of the produced secondaries) DPM: results: DPM: results A.Capella,D.Sousa,nucl-th/0303055 A.Capella,E.Ferreiro,hep-ph/0505032 SPS: Pb-Pb SPS: In-In RHIC: Au-Au RHIC: Cu-Cu Comover absorption: problems: Comover absorption: problems To reproduce the observed suppression in Pb-Pb, the density of comovers must by very high : can a hadron gas exist in these extreme conditions ? Different approach by Maiani et al. [hep=ph/0408150] : the density and temperature of the hadron gas is limited (T=170-180 MeV). The experimental suppression can not be reproduced. Thermal dissociation: Thermal dissociation Potential extracted from lattice results [Digal et al., hep-ph/0110406; Phys.Rev.D64 ( 2001) 094015] below Tc above Tc Thermal dissociation/2: Thermal dissociation/2 Solve Schroedinger equation to get binding energy (Mi(T)) and binding radius ri(T) Below Tc: no bound state if Mi(T) > Vlim(T) Above Tc: No bound state if ri(T)>r0(T) [Digal et al., hep-ph/0110406; Phys.Rev.D64 ( 2001) 094015] Thermal dissociation/3: Tdiss(y’) ~ 0.2 Tc Tdiss(c) ~ 0.7 Tc Tdiss(J/y) ~ 1.1 Tc To compare to the experimental data : introduce the T <-> r <-> b correlation introduce ET <-> b One gets a curve qualitatively similar to the experimental pattern Thermal dissociation/3 J/y suppression pattern: Thermal Dissociation: new developments: ‡ Datta et al., hep-lat/0312037 ; hep-lat/0403017 ¶ Datta et al., hep-lat/0409147 The threshold is lowered if the relative momentum is taken into account ¶. T dependence of the width ? Thermal Dissociation: new developments New calculation of Tdiss: New calculation of Tdiss [W. Alberico et al. , hep-ph/0507084 ; C.Y. Wong hep-ph/0408020 ] Extract the internal energy from lattice results and use it in the Schroedinger equation : Tdiss(y’) ~ Tdiss(c) ~ 1.1 Tc Tdiss(J/y) ~ 1.7 - 2 Tc In good agreement with the dissociation temperatures given by lattice ! Percolation: Percolation critical phenomenon pre-equilibrium deconfinement prerequisite for QGP applicable to finite-size systems [First works: Baym , Physica (Amsterdam) 96A, 131 (1979) Celik et al., Phys. Lett. 97B (1980) 128] Percolation/2: Circular surface of radius R and N small discs of radius r<<R randomly distributed. Percolation/2 nc Percolation/3: Cluster formation shows critical behaviour: in the limit of infinite R and N with constant n the cluster size diverges at a critical density nc. Onset of percolation : with g = 43/18 ; nc~1.12-1.13 Percolation/3 Percolation/2: The transverse size rcof the percolating partons is determined by the condition (Qc=1/rc) : the density of the largest cluster at the percolation point is : with hc=1.72 (local percolation condition) Percolation/2 Percolation/3: Percolation/3 For Pb-Pb at SPS: 1/rc ~ Qc~ 0.7 GeV, Npart = 150 (b ~ 8fm) [S. Digal et al, hep-ph/0310354] Percolation:results: Percolation:results Q(c) ~ 0.6 GeV Q(y’) ~ 0.5 GeV and y’ are dissociated at the percolation (onset of deconfinement). Directly produced J/y’s survive because Q(J/y)~1GeV; second threshold at Npart=200-300 Results : Data: NA50 Coll. Percolation: results: Percolation: results Predictions for In-In : Predictions for Au-Au : Regeneration: Regeneration [L. Grandchamp et al., Nucl.Phys.A715 (2003) 545; Phys.Rev.Lett.92 (2004) 212301.] “Two component” model: suppression in hadronic and QGP phase + statistical production at hadronization. In the QGP phase: in-medium properties of open- and hidden-charm states as deduced from lattice calculations. The regeneration is very important at higher energies. Results: Results At SPS energy the regeneration contribution is small; at RHIC it is the dominant one. Experiment : SPS: Experiment : SPS L. Ramello, R.Arnaldi Theory…: Theory… Thermal model: Percolation : Experiment : RHIC: Experiment : RHIC H. Buesching : More data on p-A are needed to define the normal suppression ! Slide33: Lattice and potential models : J/y dissolves at T~2Tc, the corresponding energy density is very high ! RHIC suppression is compatible with the one observed at SPS (?) RHIC data could be explained by the suppression of the c and y’ components only, without recombination !!! Improving models…: Improving models… Generally, deconfinement models assume the complete suppression for the charmonium states inside the “QGP” bubble: this is a really extreme assumption ! Finite-size effects can modify the suppression pattern in small systems and in peripheral collisions. Conclusions: Conclusions The observed J/y suppression at SPS is qualitatively very similar to the pattern expected by deconfinement models. None of the models so far is completely satisfactory in the comparison with data; new effects: finite size, life-time, surface… RHIC data : recombination or higher states suppression ? There is room for work and progress !
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