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

Debye screening 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” contribution disappears E. G. Ferreiro USC Upsilon golden probe February 2013 Screening of long range confining potential at high enough temperature or density. r V(r)

Debye screening Debye screening radius D (T): maximum distance which allows the formation of a bound qq pair decreases with the temperature T If resonace radius r < D (T) resonance can be formed If resonace radius r > D (T) resonance cannot be formed c c vacuum J/  r c c Temperature T<Td r c c Temperature T>Td J/  D D r E. G. Ferreiro USC Upsilon golden probe February 2013 different states “melting” at different temperatures due to different binding energies. Matsui and Satz: J/  destruction in a QGP by Debye screening What happens when the range of the binding force becomes smaller than the radius of the state? Valid also for ϒ

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

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

Bottomonia E. G. Ferreiro USC Upsilon golden probe February 2013 Contrary to J/  everything seems to work for ϒ WHY?

Quarkonium supression in p+A collisions: CNM effects To understand quarkonium behaviour in the hot medium, it’s important to know its behaviour in the cold nuclear matter. This information can be achieved studying pA collisions 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 quarkonium behaviour in hadronic matter Quarkonium production is suppressed 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 p μ μ J/ shadowing, saturation intrinsic charm Initial stateFinal state CNM effects p+A and A+A collisions E. G. Ferreiro USC Upsilon golden probe February 2013

Absorption: ϒ  vs J/  uncertainty principle: time needed – in their rest frame to distinguish the energy levels of the 1S and 2S states RHIC:  ϒ abs < 1 mb E. G. Ferreiro USC Upsilon golden probe February 2013

nuclear PDF uncertainty on ϒ  production in RHIC Physical interpretation backward: EMC effect central: antishadowing forward : shadowing≈1  abs =0 mb,  abs = 0.5mb,  abs = 1 mb in 3 nPDF shadowing parameterizations 16 E. G. Ferreiro USC Upsilon golden probe February 2013 Not really… new data! energy loss is needed

Searching for new effects: gluon EMC on ϒ in RHIC Let us try to increase the suppression of g(x) in the EMC region, thr shadow incert.: We have used three of 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 E. G. F., F. Fleuret, J. P. Lansberg and A. Rakotozafindrabe arXiV:1110:5047 What about the forward region? E. G. Ferreiro USC Upsilon golden probe February 2013

Searching for new effects: energy loss on ϒ in RHIC E. G. Ferreiro USC Upsilon golden probe February 2013

Searching for new effects: saturation on ϒ Saturation scale from which one expects effects beyond collinear factorisation to be important E. G. Ferreiro USC Upsilon golden probe February 2013 Saturation scale in the Au nucleus at RHIC Saturation scale in the Pb nucleus at LHC No saturation effects on ϒ at RHIC and LHC energies Saturation scale well below the scale of the process The shadowing of the gluons as encoded in the nPDF fits give a reliable account of the effects in the forward region

Upsilon vs J/  less affected by cold nuclear matter (CNM) effects smaller nuclear absorption small RHIC, not LHC energy loss would not apply Conclusions 1 for ϒ in d+Au RHIC: EMC effect in the backward region accesible by AFTER E. G. Ferreiro USC Upsilon golden probe February 2013

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