1. Quarkonium suppression at the SPS International Workshop on Heavy Quarkonium, DESY, Oct. 2007 Carlos Lourenço or Are the SPS J/  and  ’ suppression patterns “smoothy” or “steppy” ?

2. The QCD phase transition QCD calculations indicate that, at a critical temperature around 170 MeV, strongly interacting matter undergoes a phase transition to a new state where the quarks and gluons are no longer confined in hadrons quarks and gluons hadrons

3. The phase diagram of QCD Temperature net baryon density Early universe nuclei nucleon gas hadron gas quark-gluon plasma TcTc 00

4. N. Cabibbo and G. Parisi, Phys. Lett. B59 (1975) 67 The first QCD Phase Diagram

5. So Dark the Confinement of Man For details, see: “The Da Vinci colour Code” The really first QCD Phase Diagram Not easy to see... unless you know what you are looking for

6. How do we study bulk QCD matter? We heat and compress a large number of hadrons, in the lab, by colliding heavy nuclei at very high energies Pb 208 ++  p

7. One Pb-Pb collision seen by NA49 at the CERN SPS

8. A very large volume of compressed QCD matter

9. QGP ? We study the QCD matter produced in HI collisions by seeing how it affects well understood probes as a function of the temperature of the system (centrality of the collisions) Calibrated “probe source” Matter under study Calibrated “probe meter” Calibrated heat source Probe “Seeing” the QCD matter formed in heavy-ion collisions

10. vacuum QGP hadronic matter The good QCD matter probes should be: Well understood in “pp collisions” Only slightly affected by the hadronic matter, in a very well understood way, which can be “accounted for” Strongly affected by the deconfined QCD medium... Heavy quarkonia (J/ ,  ’,  c, ,  ’, etc) are good QCD matter probes ! Challenge: find the good probes of QCD matter

11. Challenge: creating and calibrating the probes The “probes” must be produced together with the system they probe (!) and very early, to be there before the matter to be probed:  quarkonia We need “trivial” (reference) probes, not affected by the dense QCD matter:  photons, Drell-Yan dimuons We need “trivial” collision systems, to understand how the probes are affected in the absence of “new physics”:  pp, p-nucleus, light ions

12. Tomography in medical imaging: Uses a calibrated probe and a well understood interaction to derive the 3-D density profile of the medium from the absorption profile of the probe. “Tomography” in heavy-ion collisions: - Jet suppression gives the density profile of the matter - Quarkonia suppression gives the confinement state (hadronic or partonic) of the matter “Tomography” of the produced QCD matter

13. The suppression of the J/  production yield in nuclear collisions should be a clear signal of the QCD phase transition from confined hadronic matter to a deconfined plasma of quarks and gluons In the beginning was the Verb, and the Verb was… “... colour screening prevents c-cbar binding...”

14. In the deconfined phase the QCD potential is screened and the heavy quarkonia states are “dissolved” into open charm or beauty mesons. Different heavy quarkonium states have different binding energies and, hence, are dissolved at successive thresholds in energy density or temperature of the medium; their suppression pattern woks as a “thermometer” of the produced QCD matter. Lattice QQbar free energy T The “melting” of the heavy-quarkonia states

15. The feed-down from higher states leads to a “step-wise” J/  suppression pattern 1.10 0.74 0.15 ’’ cc A “smoking gun” signature of QGP formation: steps “Well known” J/  cocktail: 60% direct J/  30% from  c decays 10% from  ’ decays HERA-B J/  cocktail: 72% direct J/  21% from  c decays 7% from  ’ decays

16. Drell-Yan dimuons are not affected by the dense medium they cross reference process The yield of J/  mesons (per DY dimuon) is “slightly smaller” in p-Pb collisions than in p-Be collisions; and is strongly suppressed in central Pb-Pb collisions Interpretation: strongly bound c-cbar pairs (our probe) are “anomalously dissolved” by the deconfined medium created in central Pb-Pb collisions at SPS energies p-Be p-Pb central Pb-Pb J/  normal nuclear absorption curve reference data J/  suppression: from theory predictions to SPS data

17.  2 /ndf = 0.7  2 /ndf = 1.4 The J/  and  ’ “normal nuclear absorption” in p-A collisions ’’ J/  NA50 p-A 400 GeV The Glauber model describes the J/  and  ’ “normal nuclear absorption”, in p-A collisions, in terms of the average path length, L, which they traverse in the target nucleus, from the production point to the nuclear “surface” NA50

18. normal nuclear absorption NA60 collected less J/  events in In-In than NA50 in Pb-Pb but they are directly compared to the normal nuclear absorption curve, calculated with “Glauber”, without using the “statistically challenged” Drell-Yan yield ~ 29 000 J/  dimuons The calculation of N part for each E ZDC bin uses the Glauber model, which reproduces distributions collected with minimum bias triggers (no dimuons) NA60: a third generation J/  experiment at the SPS

19. There is a good agreement between the Pb-Pb and In-In suppression patterns when plotted as a function of the N part variable, determined from the (same) ZDC detector. The statistical accuracy of the In-In points is, however, much better... The pink box represents the ±6% global systematic uncertainty in the relative normalization between the In-In and the Pb-Pb data points. J/  suppression at the SPS: In-In vs. Pb-Pb patterns

20. Now there isn’t...Now there is Question: Is there a “step” in the SPS J/  suppression pattern measured at the SPS ? Answer:

21. Capella and Ferreiro hep-ph/0505032 Digal, Fortunato and Satz EPJ C32 (2004) 547 Grandchamp and Rapp NP A715 (2003) 545 PRL 92 (2004) 212301 Pb-Pb @ 158 GeV CF: suppression by “comovers” DFS: percolation phase transition GR: dissociation and regeneration in QGP and hadron gas, inc. in-medium properties of open charm and charmonium states J/  suppression at the SPS: model tuning on the Pb data

22. None of these predictions describes the measured suppression pattern... Homework exercise: calculate the  2 /ndf for each of these curves (ndf = 8) Note: the In-In data set was taken at the same energy as the Pb-Pb data... to minimise the “freedom” of the theoretical calculations Note: by moving up or down all the data points, within the 6% uncertainty on their global normalisation, we can get better (and worse) agreements... but even in the best cases, the  2 /ndf remains very high... S. Digal et al. EPJ C32 (2004) 547 A. Capella, E. Ferreiro EPJ C42 (2005) 419 R. Rapp EPJ C43 (2005) 91 centrality dependent  0 R. Rapp EPJ C43 (2005) 91 fixed termalization time  0 In-In 158 A GeV Data vs. theoretical predictions: the results Capella & Ferreiro = 49 Digal et al. = 21 Rapp (fixed  0 ) = 14 Rapp (variable  0 ) = 9 Solutions:

23. Nuclear plus hadron gas absorption L. Maiani et al., NP A748 (2005) 209 F. Becattini et al., PL B632 (2006) 233 Nuclear absorption only... plus largest possible absorption in a hadron gas (T = 180 MeV) This figure Data vs. theoretical post-dictions...

24.  2 /ndf = 7.4  2 /ndf = 16 ndf = 8 The probability that the measurements should really be on any of these two curves and “statistically fluctuated” to where they were in fact observed is... zero In-In 158 A GeV HSD Charmonium dynamics in heavy ion collisions O. Linnyk et al., SQM 2007, June 28, 2007 and Nucl. Phys. A 786 (2007) 183.

25. Step at N part = 86 ± 8 A1 = 0.98 ± 0.02 A2 = 0.84 ± 0.01  2 / ndf = 0.75 (ndf = 8  3 = 5) Taking into account the E ZDC resolution, the measured pattern is perfectly compatible with a step function in N part N part Measured / Expected 1 Step position A1 A2 In-In data vs. a step function in Npart

26. N part is convenient to compare the measured In-In and Pb-Pb data, since it is derived from the same E ZDC variable (measured by the same detector) using the same Glauber formalism (except for different nuclear density functions). Also, the derivation of N part from E ZDC is trivial and essentially model independent. Maybe the “real variable” driving charmonia suppression is not N part. Then, the measured smearing is the convolution of the detector resolution with the “physics smearing”, due to the conversion from the “real variable” to N part But the N part “detector resolution” is 20 and the “total resolution” from fitting the measured pattern is 19 (!) indicating that the “physics smearing” is negligible with respect to the detector resolution... In summary, the In-In pattern indicates that:1) there is a step and 2) the “physics variable” is N part A step function in Npart or in another “physics variable” ?

27. Steps: N part = 90 ± 5 and 247 ± 19 A1 = 0.96 ± 0.02 A2 = 0.84 ± 0.01 A3 = 0.63 ± 0.03  2 / ndf = 0.72 (ndf = 16  5 = 11) N part Measured / Expected 1 Step positions A1 A2 A3 If we try fitting the In-In and Pb-Pb data with one single step we get  2 /ndf = 5 !.. In summary, the Pb-Pb pattern1) rules out the single-step function and 2) indicates the existence of a second step... What about the Pb-Pb pattern? Another step?

28. The  ’ suppression pattern also shows a significantly stronger drop than expected from the “normal extrapolation” of the p-A data  abs ~ 20 mb ’’ The “change of slope” at L ~ 4 fm is very significant and looks very abrupt... The third step of the day ! Starts to look like a “stairway to heaven”... ’’  ’ suppression in heavy-ion collisions at the SPS

29. We made measurements, to rule out one of these two scenarios (or both) normal nuclear absorption suppression by QGP J/  survival probability Back to the ideal world The predicted patterns, before any data points were available, were quite different from each other  We thought it was going to be very easy to discriminate between the two theories... Energy density cc

30. Can any of the models describe the experimental data points? Observations made at CERN

31.  All kept data points agree with the expected normal nuclear absorption pattern! “outlier” point; to be rejected normal nuclear absorption Data versus the “no new physics” model

32. calibration error anomalous suppression  All kept data points agree with the expected QGP suppression pattern! Data versus the “new physics” model

33. New and improved data points are needed B decays direct J/  suppression  ’,  c suppression gluon anti-shadowing recombination of uncorrelated ccbar pairs J/  survival probability A more detailed theoretical framework J/  survival probability Energy density

34. Once again, the model prediction agrees with the measurements... Improved model versus new experimental data

35. 1) There is a BIG difference between “the measurements are compatible with the model expectations...” and “the measurements show beyond reasonable doubt that the model is good” 2) “Nature never tells you when you are right, only when you are wrong” You only learn something when the theory fails to describe the data... [Bacon, Popper, Bo Andersson]  Be happy if your model is shown to be wrong… 3) Today, none of the “fancy theories” describes the In-In suppression pattern  All the “fancy theorists” should be happy 4) The very simple step function gives a perfect description of the In-In pattern; a second step is needed to describe the Pb-Pb pattern  We found what we were told to look for, as a “smoking gun QGP signal” the experimentalists should be happy Take-home messages...