Upsilon: the new golden probe?

1. Workshop AFTER@ECT* Trento, February 2013 Upsilon: the new golden probe? Elena G. Ferreiro Universidade de Santiago de Compostela, Spain E. G. Ferreiro USC Upsilon golden probe February 2013

2. Debyescreening V(r) r What happens to a q-qbar pair in a QGP? • The high color density induces a screening of the coulombian term of the potential • The “confinement” contributiondisappears Screeningof long range confining potential at high enough temperature or density. V(r) E. G. Ferreiro USC Upsilon golden probe February 2013

3. Debyescreening D J/ D c c c J/ Temperature T<Td c r Debye screening radius lD(T): maximumdistancewhichallowsthe formation of a bound qq pair decreases with the temperature T vacuum Temperature T>Td c c r r Ifresonaceradiusr < lD(T) resonance can be formed Ifresonaceradiusr > lD(T) resonance cannot be formed Validalsoforϒ Whathappenswhentherange of thebindingforcebecomessmallerthantheradius of thestate? different states “melting” at different temperatures due to different binding energies. Matsui and Satz: J/y destruction in a QGP by Debye screening E. G. Ferreiro USC Upsilon golden probe February 2013

4. The quarkonia thermometer E. G. Ferreiro USC Upsilon golden probe February 2013

5. Charmonia E. G. Ferreiro USC Upsilon golden probe February 2013

6. Bottomonia ContrarytoJ/y, everythingseemstoworkforϒ WHY? E. G. Ferreiro USC Upsilon golden probe February 2013

7. Quarkoniumsupression in p+Acollisions: CNM effects Quarkoniumproductionissuppressed in nuclear collisions...but for a variety of reasons QGP effects A+A collisions • dissociation by screening (“melting”) and/or collisions in hot QGP • nuclear absorption • final energy loss • comovers • shadowing, • saturation • intrinsic charm CNM effects p+A and A+A collisions Initial state Final state μ To understand quarkoniumbehaviour in the hot medium, it’s important to know its behaviour in the cold nuclear matter. This information can be achieved studying pA collisions J/ μ p The cold nuclear matter effects present in pA collisions are of course present also in AA and can mask genuine QGP effects It is very important to measure cold nuclear matter effects (CNM) before any claim of an “anomalous” (QGP) suppression in AA collisions CNM, evaluated in pA, are extrapolated to AA, in order to build a reference for the quarkoniumbehaviour in hadronic matter E. G. Ferreiro USC Upsilon golden probe February 2013

8. Absorption: ϒvs J/y uncertaintyprinciple: time needed – in their rest frame to distinguish the energy levels of the 1S and 2S states RHIC: sϒabs< 1 mb E. G. Ferreiro USC Upsilon golden probe February 2013

9. nuclear PDF uncertaintyonϒproduction in d+Au @ RHIC sabs=0 mb, sabs= 0.5mb , sabs= 1 mb in 3 nPDF shadowing parameterizations Physical interpretation • backward: EMC effect • central: antishadowing • forward : shadowing≈1 energy loss is needed Not really… new data! 16 E. G. Ferreiro USC Upsilon golden probe February 2013

10. Searchingfor new effects: gluonEMConϒ in dAu @ RHIC E. G. F., F. Fleuret, J. P. Lansberg and A. Rakotozafindrabe arXiV:1110:5047 Let us try to increase the suppression of g(x) in the EMC region, thr shadow incert.: Wehaveusedthreeof the EPS09 LO sets: one with a quark-like EMC gluon suppression, and the two limiting curves Presence of a strong EMC effect in the backward region What about the forward region? E. G. Ferreiro USC Upsilon golden probe February 2013

11. Searchingfor new effects: energylossonϒin dAu @ RHIC E. G. Ferreiro USC Upsilon golden probe February 2013

12. Searchingfor new effects: saturationonϒ Saturation scale from which one expects effects beyond collinear factorisation tobeimportant Saturationscale in the Au nucleus at RHIC Saturationscale in the Pb nucleus at LHC •No saturationeffectsonϒat RHIC and LHC energies •Saturationscalewellbelowthescale of theprocess •Theshadowing of thegluons as encoded in thenPDFfitsgive a reliableaccount of theeffects in the forward region E. G. Ferreiro USC Upsilon golden probe February 2013

13. Conclusions • Upsilon vs J/y: less affected bycold nuclear matter (CNM) effects smallernuclear absorption smallshadowing @ RHIC, notnegligeable @ LHC energylosswouldnotapply • forϒin d+Aucollisions @ RHIC: EMC effectin thebackwardregion accesible byAFTER 1 E. G. Ferreiro USC Upsilon golden probe February 2013

14. E. G. Ferreiro USC Upsilon golden probe February 2013

15. New: ϒproduction @ LHC While nuclear effects are small at RHIC energies, shadowing effect is not small at LHC energies! Remember that in PbPb collisions at y = 0 shadowing effect is squared compared to pPb 20% suppression in PbPb at y=0! E. G. Ferreiro USC Upsilon golden probe February 2013