Upsilon: the new golden probe?

Elena G. FerreiroUniversidade de Santiago de Compostela, Spain

Workshop AFTER@ECT* 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)

V(r)

Debye screeningDebye screening radius lD(T): maximum distance which allows the formation of a

bound qq pair decreases with the temperature T

If resonace radius r < lD(T)resonance can be formed

If resonace radius r > lD(T)resonance cannot be formed

c c

vacuum

J/

r

c c

Temperature T<Td

r

c c

Temperature T>Td

J/

DD

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/y 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/ , y 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 effectsA+A collisions

• dissociation by screening (“melting”) and/or collisions in hot QGP

• nuclear absorption• final energy loss• comovers

p

μ

μJ/

• shadowing, • saturation• intrinsic charm

Initial state Final stateCNM effectsp+A and A+A collisions

E. G. Ferreiro USC Upsilon golden probe February 2013

Absorption: ϒ vs J/y

uncertainty principle: time needed – in their rest frame to distinguish the energy levels of the 1S and 2S states

RHIC: sϒ

abs < 1 mb

E. G. Ferreiro USC Upsilon golden probe February 2013

nuclear PDF uncertainty on ϒ production in d+Au @ RHIC

Physical interpretation• backward: EMC effect• central: antishadowing

• forward : shadowing≈1

sabs=0 mb, sabs= 0.5mb , sabs= 1 mb in 3 nPDF shadowing parameterizations

16E. 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 dAu @ 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 dAu @ RHIC

E. G. Ferreiro USC Upsilon golden probe February 2013

Searching for new effects: saturation on ϒSaturation scale from which one expects effects beyond collinear factorisationto 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/ : y less affected by cold nuclear matter (CNM) effects

smaller nuclear absorptionsmall shadowing @ RHIC, not negligeable @ LHC

energy loss would not apply

Conclusions

1

• for ϒ in d+Au collisions @ RHIC:

EMC effect in the backward region accesible by AFTER

E. G. Ferreiro USC Upsilon golden probe February 2013

E. G. Ferreiro USC Upsilon golden probe February 2013

New: ϒ production @ 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 = 0shadowing effect is squared compared to pPb

20% suppression in PbPb at y=0!