CT: QUARKONIA IN DECONFINED MATTER
SEZIONE DI CATANIA
The in-medium behavior of the different quarkonium states has for quite some time been studied as suitable tool to test strongly interacting matter. Originally it was proposed as a probe of the early, deconfined stage of the medium produced in high energy nuclear collisions. Ab initio calculations for the quarkonium dissoci- ation points could thus provide a tool to determine experimentally the tempera- ture/energy density of the primordial medium. More recently, secondary quarko- nium production through statistical combination of charm quark pairs from different primary collisions has been proposed as a competing production mechanism. This should become more and more effective with increasing charm production rates, i.e., with increasing collision energy. At present, we thus have two very distinct scenarios for charmonium production in nuclear collisions at the LHC: – Sequential quarkonium suppression, predicting that for central AA collisions at the LHC essentially only charmonia from B decay and from corona production will remain. – Secondary charmonium production through statistical combination of charm quarks from different nucleon-nucleon collisions, predicting for the LHC an enhanced J/ψ production relative to the scaled proton-proton rates. Several further features enter in both approaches, such as the nuclear charm pro- duction rates and initial state effects (shadowing, parton energy loss). The LHC will open up a decisive energy range for these considerations, and it will moreover provide the necessary reference measurements to cross-check the conclu- sions. Both open and hidden charm/bottom production will be measured (or is already) in proton-proton collisions, providing the reference rates in the absence of a medium. In AA collisions, open charm and open bottom rates will be measured with considerable precision and thus allow independent studies of shadowing for nuclear PDF’s. The study of charmonium production in nuclear collisions can thus be performed relative to the ideal reference, open charm in AA and in pp collisions. This will, if the planned experiments are successfully completed, provide a situation more suitable for conclusions than ever before. The aim of the proposed workshop is an in-depth dedicated discussion of the results as compared to the predictions. By the fall of 2011, much of the data should be analysed and generally available. We therefore want to bring together the leading experts in the field to assess the situation at this crucial point in the experimental development. In addition, one may also expect further theoretical progress by that time. Lattice calculations have presently achieved a degree of reliability for T ≤ Tc , but the extension to T > Tc is still in progress. Present work addresses calculations at several temperatures above the deconfinement point and with higher statistics. Hopefully, the results will become available in the coming months, so that they should enter the discussion at the workshop. Moreover, the past years have brought considerable new analytical work, in NRQCD, effective field theories and in AdS/CFT gauge-gravity dual theory. In initial state considerations, the role of color glass condensate formation on charmonium pro- duction has been addressed. It would obviously be of great interest to see if these different studies can also shed light on the in-medium behavior of quarkonia. Weak coupling arguments are expected to be more applicable for bottomonia, and hence first detailed Υ data will also be of considerabel interest. The workshop organization will pay particular attention to assure that the (quite numerous) young post-docs and graduate students beginning their work in this challenging field will be able to attend and we will, as in the previous meeting, arrange a special session for the representation of their work. As is evident from what was said, a complete presentation of the experimental results available at that time, as well as a good overview of the different theoretical approaches, are both essential for the success of the workshop. We have therefore tried to chose for our key participants the leading experts for the different aspects of the topic, and we were very pleased that the proposed meeting found strong resonance.

DATA: 26-09-2011

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