1. Nuclear matter effects in charmonium production in proton-nucleus collisions‏ Hermine K. Wöhri LIP – Lisbon, Portugal QWG 2008, Nara, Japan, December 2008 Initial state versus final state “cold nuclear effects” Energy dependence of the J/  “absorption cross section”  abs values estimated for the SPS heavy-ion conditions A joint analysis of the J/  and  ’  abs values Work done in collaboration with Carlos Lourenço, Ramona Vogt, Pietro Faccioli and João Seixas

2. The charmonium production yields should be considerably suppressed if a medium of deconfined quarks and gluons is formed in high-energy heavy-ion collisions But already in p-nucleus collisions the charmonium states are absorbed This “normal absorption” must be well understood before high-density QCD signals can be extracted from the nucleus-nucleus data “Anomalous suppression” vs. “normal nuclear absorption” Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 2 J/  normal nuclear absorption curve heavy-ion ’’ J/  proton-nucleus Be Al Cu Ag W Pb

3. 1.Collect the J/  production cross sections measured in proton-nucleus collisions by NA3, NA50, E866 and HERA-B (plus the PHENIX d-Au values) 2.Compare the measured “heavy / light” cross-section ratios to those calculated with the Glauber model, to get a  abs value from each data set (energy, rapidity window) 3.Derive the  abs value suitable for the SPS heavy-ion kinematical conditions Remark : Feed-down contributions from  c and  ’ decays should be taken into account. We first present results effectively convoluting all J/  sources: Strategy to evaluate the “normal nuclear absorption” Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 3

4. Within the Glauber model the J/  “normal nuclear absorption” can be described with one single parameter : the “absorption cross section”,  abs From 400 GeV J/  and  ’ cross sections in p-A collisions (6 nuclei), NA50 obtained  abs (J/  = 4.6 ± 0.6 mb  abs (  ’) = 10.1 ± 1.6 mb using free proton PDFs, i.e. not considering nuclear effects on the PDFs Such effects can be modelled by using EKS 98 or other parameterisations, which indicate sizeable anti-shadowing at x values around 0.1–0.4 → It is important to separate this initial state nuclear matter effect from final state absorption Initial state nuclear matter effects: modification of PDFs gluon density function in Pb gluon density function in p Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 4

5. Nuclear effects on the PDFs vs. final state absorption At SPS energies, the gluon anti-shadowing makes the J/  production cross section per nucleon increase from pp to p-Pb (before final state absorption)   abs = 4.5 mb assuming no nuclear effects on the PDFs (“NONE”) is equivalent to  abs = 7.0 mb with EKS 98‏  The  abs values quoted by PHENIX (obtained with EKS 98) cannot be directly compared to the NA50 (“NONE”) numbers…  When comparing different data sets, we must consistently use the same shadowing model Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 5 0 < y cms < 1 EKS 98  abs = 0 mb  abs = 4.5 mb no n.e. EKS 98  abs = 7.0 mb J/  NONE Be Al Cu W

6. Nuclear effects on the PDFs vs. x F : E866 The nuclear effects on the PDFs are a function of Bjorken-x  they are energy and x F (or y) dependent At x F < 0.2 : strong anti-shadowing in EKS98 and EPS08 :  In the absence of other effects, the E866 data should be higher than unity Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 6

7. The J/   was measured in p-A collisions at different energies (E lab = 200  920 GeV) and using several target nuclei (the  s = 200 GeV PHENIX d-Au / pp y-dependent ratios were also analysed but will not be shown today because of their large errors) NA50 provided absolute production cross sections for each of the 5 (6) targets, while the others provided “heavy / light” cross-section ratios NA3 is different in several respects: secondary proton beam; long liquid target; only two target nuclei and one of them being a proton (not exactly a “nucleus”); took data 25 years ago (and was not yet cross-checked by a newer experiment) Available measurements : a global summary Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 7

8. Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 8

9. For each energy and kinematical window, the relevant cross-section ratios were calculated as a function of a running  abs value, with several (nuclear) PDF sets Comparing calculations to data gives the corresponding  abs (and error)   abs is insensitive to the PDFs ( GRV94, GRV98, CTEQ6L, MRST2001 )‏ but depends on the nuclear effects ( EKS98, EPS08, nDS, nDSg )‏ Extracting  abs from cross-section ratios GRV94-NONE CTEQ6L-NONE GRV94-EKS98 CTEQ6L-EKS98  0.1 < x F < 0.14  abs [mb]‏ 4.2  0.5 EKS98 2.4  0.5 NONE Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 9

10. J/ ’’ The fits are equally good using EKS98 or “ NONE”, but give very different  abs values A simultaneous fit of the six p-A cross sections measured by NA50 at 400 GeV (using “NONE”) gives  abs (J/   ) = 4.8 ± 0.6 mb and  abs (  ') = 10.8 ± 1.8 mb, in good agreement with the values published by NA50  0.425 < y cms < 0.575 Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 10

11. Extracted  abs from each data set, x F dependent Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 11

12. E866 Another influence of nuclear PDFs on  abs If no nuclear effects are considered, we see a flat nuclear dependence at x F ~ 0, both in  and in  abs For nDSg, EKS98 or EPS08 the x F ~ 0 values require an x F dependent study, with  abs values decreasing as x F increases  pA =  0 A  ‏ Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 12

13.  abs in the forward hemisphere At x F ~ 0, the E866 and HERA-B differential  abs values, extracted with nDSg, EKS98 or EPS08, can be parameterised by an asymmetric Gaussian At forward x F other effects than “absorption” play a leading role  Glauber-like absorption must be studied at x F ~ 0 (i.e. |y cms | < 1.0)‏ Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 13

14. The E866 and HERA-B patterns set the shape of the rapidity dependence of  abs : an asymmetric Gaussian if EKS98 is used; flat if free proton PDFs are used Rapidity dependence of  abs Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 14 NONE EKS98

15. The nDSg and EPS08 cases are similar to the EKS98 case The leftmost NA3 point is consistently below the trend suggested by other points We can now see how the y cms =0 value of  abs evolves with collision energy,  s nDSgEPS08 Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 15

16. EKS98  abs (y cms =0) decreases with increasing NN collision energy NONE  Using EKS98,   abs (y cms =0) extrapolated to 158 GeV is 9.9±0.6 mb excluding the lowest x F NA3 point and 8.7±0.7 mb otherwise Using free proton PDFs, the respective values are: 5.9±0.8 mb and 5.4±0.8 mb Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 16 power law curves

17. Also with nDSg and EPS08, we see that  abs significantly drops with increasing NN collision energy The impact of the first NA3 point is even more visible with these nuclear PDFs power law curves nDSg EPS08 Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 17

18.  abs extrapolated to the SPS heavy-ion kinematical conditions Remark: the absorption cross section used in the SPS heavy-ion analyses, with free proton PDFs, has been 4.2 ± 0.5 mb Using EKS98 nuclear PDFs, the absorption cross section integrated in the NA50/60 rapidity window (0<y cms <1) is 8.2 ± 0.5 mb. Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 18

19. N-N J/  -N If the absorption process depends on the J/  energy (rather than on the proton beam energy), we should study the J/  nuclear absorption as a function of the J/   nucleon c.m.s. energy...  abs vs. J/  kinematics: an alternative scenario for x F = p T = 0 Also in terms of this alternative variable no scaling is seen: the magnitude of  abs depends on the data set Similar results are obtained with the other sets of nuclear PDFs (including “NONE”) Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 19

20. What can we learn from a joint J/  and  ’ analysis? The observed J/  yield is affected by  c and  ’ feed-down decays and these two states should have different (larger) break-up cross sections The  ’ component is directly measurable: Can both measurements, J/  and  ’, be described in a global and simple way ? Our assumptions : 1. Feed-down fractions: F 1P = 25 ± 5% and F 2S = 8.1 ± 0.3% see JHEP 10 (2008) 004 and talk of P. Faccioli on Wednesday 2.  abs values are geometrically related, with r 1P / r 1S = 1.44 and r 2S / r 1S = 1.80 see H. Satz, NPA 783 (2007) 249c. With these values, we can evaluate  abs (1S) from the J/  and  ’ data sets in a global fit, as well as obtaining two independent estimates Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 20

21. NA50 published J/  and  ' production cross sections at 400 at 450 GeV (at |y|<0.5)‏ A single  abs (1S) value (3.05±0.25 mb) describes both data sets with a good quality Independent  abs (1S) values: 3.94±0.40 mb (from J/  ) and 2.74±0.31 mb (from  ’) E866 reported J/  and  ’ p-W / p-Be cross-section ratios at 800 GeV vs. x F We use the |x F |<0.1 window, analogous to the NA50 rapidity window. Again, a single  abs (1S) value (1.60±0.24 mb) describes very well both data sets Independent  abs (1S) values: 2.04±0.50 mb (from J/  ) and 1.46±0.27 mb (from  ’) Both NA50 and E866 indicate a ~30% larger  abs (1S) value from the J/  data than from the  ’ data but with a large uncertainty Side-remark: also the  ’ data show that  abs decreases with collision energy: 8.9±1.0 mb (400/450 GeV)  4.7±0.9 mb (800 GeV) with free proton PDFs Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 21

22. Summary The nuclear dependence of the J/  production cross section, in p-A collisions, cannot be described by the Glauber model with a “universal”  abs value : 1.  abs changes significantly with collision energy 2. and with rapidity (even at mid-rapidity, when using n-PDFs) A power-law extrapolation gives  abs values in the SPS heavy-ion kinematical conditions larger than currently used in the J/  suppression analyses :  abs (J/  ) = 8.2 ± 0.5 mb with EKS98 and 5.9 ± 0.8 mb with free proton PDFs The J/  and  ’ data sets can be simultaneously described assuming geometrical scaling of the charmonium break-up cross sections. Including a pre-resonant state improves the global description... Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 22

23. Backup Slides

24. “450-LI”“450-HI”“400” “450-LI”“450-HI”“400” NA50 data sets J/  ’’ Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 24

25. The J/  (and  ’) absorption is much stronger at forward x F than at mid-rapidity… clearly indicating that extra absorption mechanisms come into play at high x F To stay away from such extra issues, we start our study by only looking at mid-rapidity values x F dependence of charmonium absorption Note:  is “inversely proportional” to  abs  pA =  0 A  =  0 A exp(  L  abs )‏ J/   xFxF E866  xFxF  Hermine Wöhri — QWG 2008 — Nara, Japan, December 2008 25