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Heavy-quarkonium suppression in p A collisions from induced gluon radiation Fran cois Arleo LAPTH, Annecy Workshop pA@LHC CERN June 2012 Fran cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 1 / 18

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SLIDE 1

Heavy-quarkonium suppression in p A collisions from induced gluon radiation

Fran¸ cois Arleo

LAPTH, Annecy

Workshop pA@LHC CERN – June 2012

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 1 / 18

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SLIDE 2

Outline

Motivations

J/ψ suppression data in p A collisions

Revisiting energy loss

New scaling properties from medium-induced coherent radiation

Phenomenology

Model for J/ψ and Υ suppression in p A collisions Comparison with data and LHC predictions

References

FA, S. Peign´ e, T. Sami, 1006.0818 FA, S. Peign´ e, 1204.4609 + in preparation

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 2 / 18

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SLIDE 3

J/ψ suppression in p A collisions at forward rapidities

E866 √s = 38.7 GeV

0.2 0.4 0.6 0.8 1 0.25 0.5 0.75

xF RW/Be(xF)

E866 J/ψ √s = 38.7 GeV

PHENIX √s = 200 GeV

0.2 0.4 0.6 0.8 1

  • 3
  • 2
  • 1

1 2 3

y RdAu/pp(y) PHENIX √s = 200 GeV

Strong J/ψ suppression reported at large xF and y Weaker suppression in the Drell-Yan process Observed at various √s

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 3 / 18

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SLIDE 4

J/ψ suppression in p A collisions

Many explanations suggested. . . yet none of them fully satisfactory Nuclear absorption

requires unrealistically large cross section

nPDF effects and saturation

constrained by Drell-Yan

Intrinsic charm

assuming a large amount of charm in the proton

Parton energy loss

requires ∆E ∝ E . . . supposedly ruled out

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 4 / 18

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SLIDE 5

J/ψ suppression in p A collisions

Many explanations suggested. . . yet none of them fully satisfactory Nuclear absorption

requires unrealistically large cross section

nPDF effects and saturation

constrained by Drell-Yan

Intrinsic charm

assuming a large amount of charm in the proton

Parton energy loss

requires ∆E ∝ E . . . supposedly ruled out

This talk: revisiting energy loss processes

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 4 / 18

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SLIDE 6

Gavin–Milana model

Simple model assuming (mean) energy loss scaling like parton energy

[ Gavin Milana 1992 ]

∆E ∝ E L M−2 for both Drell-Yan and J/ψ (though larger due to final-state energy loss)

Caveats

Ad hoc assumption regarding E, L, and M dependence of parton energy loss, no link with induced gluon radiation Failure to describe Υ suppression ∆E ∝ E claimed to be incorrect in the high energy limit due to uncertainty principle — so-called Brodsky-Hoyer bound

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 5 / 18

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SLIDE 7

A bound on energy loss ?

Induced gluon radiation needs to resolve the medium

[ Brodsky Hoyer 93 ]

tf ∼ ω k2

⊥

L ω k2

⊥ L ∼ ˆ

q L2 Bound independent of the parton energy Energy loss cannot be arbitrarily large in a finite medium Apparently rules out energy loss models as a possible explanation However Not necessarily true in QCD

[ FA Peign´ e Sami 10 ]

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 6 / 18

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SLIDE 8

Revisiting energy loss scaling properties

Two cases whether gluon radiation is coherent or incoherent (i) Incoherent radiation in the initial/final state Radiation of gluons with large formation times cancels out in the induced gluon spectrum, leading to tf ∼ L ∆E ∝ ˆ qL2 Hadron production in nuclear DIS and Drell-Yan in p A collisions Jets and hadrons produced in hadronic collisions at large angle

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 7 / 18

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SLIDE 9

Revisiting energy loss scaling properties

Two cases whether gluon radiation is coherent or incoherent (ii) Coherent radiation (interference) in the initial/final state Induced gluon spectrum dominated by large formation times ∆E ∝ √ˆ qL M E Production of light and open heavy-flavour hadrons at forward rapidities in the medium rest frame (nuclear matter or QGP) Production of heavy-quarkonium if color neutralisation occurs on long time-scales toctet ≫ thard

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 7 / 18

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SLIDE 10

Medium-induced gluon spectrum

Gluon spectrum dI/dω ∼ Bethe-Heitler spectrum of massive (color) charge

ω dI dω

  • ind

= Ncαs π

  • ln
  • 1 + E 2∆q2

⊥

ω2M2

⊥

  • − ln
  • 1 +

E 2Λ2

QCD

ω2M2

⊥

  • ∆E =
  • dω ω dI

dω

  • ind

= Ncαs

  • ∆q2

⊥ − ΛQCD

M⊥ E

∆E ∝ E neither initial nor final state effect nor ‘parton’ energy loss: arises from coherent radiation Physical origin: broad tf interval : L, thard ≪ tf ≪ toctet for medium-induced radiation

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 8 / 18

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SLIDE 11

Model for heavy-quarkonium suppression

[ FA Peign´ e 1204.4609 ]

dσψ

pA

dxF

  • xF , √s
  • =

ǫmax dǫ P(ǫ) dσψ

pp

dxF (xF + δxF(ǫ)) pp cross section fitted from experimental data dσψ

pp

dxF ∝ (1 − x′)n(√s)/x′ x′ ≡

  • x2

F + 4M2 ⊥/s

Shift given by δxF(ǫ) ≃ ǫ/Ebeam P(ǫ): quenching weight, scaling function of ˆ ω = √ˆ qL/M⊥ × E Length L given by L = 3/2 r0 A1/3

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 9 / 18

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SLIDE 12

Quenching weight

Poisson approximation assuming independent emission

[ BDMS 2001 ]

P(ǫ) ∝

∞

  • n=0

1 n!

  • n
  • i=1
  • dωi

dI(ωi) dω

  • δ
  • ǫ −

n

  • i=1

ωi

  • However, radiating ωi takes time tf (ωi) ∼ ωi
  • ∆q2

⊥ ≫ L

For ωi ∼ ωj ⇒ emissions i and j are not independent For self-consistency, constrain ω1 ≪ ω2 ≪ . . . ≪ ωn P(ǫ) ≃ dI(ǫ) dω exp

  • −

∞

ǫ

dω dI dω

  • Fran¸

cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 10 / 18

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SLIDE 13

Transport coefficient

ˆ q related to gluon distribution in a proton

[ BDMPS 1997 ]

ˆ q(x) = 4π2αsCR N2

c − 1 ρ xG(x, ˆ

qL) Typical value for x x = x0 ≃ (mNL)−1 for thard L ⇒ ˆ q(x) = constant x ≃ x2 for thard > L ⇒ ˆ q(x) ∝ x−0.3 For simplicity we assume ˆ q(x) = ˆ q0 10−2 x 0.3 x = min(x0, x2) ˆ q0 only free parameter of the model

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 11 / 18

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SLIDE 14

Procedure

1

Fit ˆ q0 from J/ψ suppression E866 data in p W collisions

2

Predict J/ψ and Υ suppression for all nuclei and c.m. energies

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 12 / 18

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SLIDE 15

Procedure

1

Fit ˆ q0 from J/ψ suppression E866 data in p W collisions

2

Predict J/ψ and Υ suppression for all nuclei and c.m. energies

0.2 0.4 0.6 0.8 1

  • 0.2

0.2 0.4 0.6 0.8

xF RW/Be(xF) E866 √s = 38.7 GeV (fit)

0.2 0.4 0.6 0.8 1

  • 0.2

0.2 0.4 0.6 0.8 1

xF RFe/Be(xF) E866 √s = 38.7 GeV

∧

q0 = 0.09 GeV2/fm

∧

q0 = 0.05 GeV2/fm + sat.

ˆ q0 = 0.09 GeV2/fm Fe/Be ratio well described, supporting the L dependence of the model

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 12 / 18

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SLIDE 16

Procedure

1

Fit ˆ q0 from J/ψ suppression E866 data in p W collisions

2

Predict J/ψ and Υ suppression for all nuclei and c.m. energies

0.2 0.4 0.6 0.8 1

  • 0.2

0.2 0.4 0.6 0.8

xF RW/Be(xF) E866 √s = 38.7 GeV (fit)

0.2 0.4 0.6 0.8 1

  • 0.2

0.2 0.4 0.6 0.8 1

xF RFe/Be(xF) E866 √s = 38.7 GeV

∧

q0 = 0.09 GeV2/fm

∧

q0 = 0.05 GeV2/fm + sat.

ˆ q0 = 0.09 GeV2/fm Fe/Be ratio well described, supporting the L dependence of the model Let’s investigate J/ψ suppression at other energies

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 12 / 18

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SLIDE 17

Extrapolating to other energies

Two competing mechanisms might alter heavy-quarkonium suppression Nuclear absorption if hadron formation occurs inside the medium tform = γ τform L

Low √s and/or negative xF Indicated later assuming τform = 0.3 fm

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 13 / 18

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SLIDE 18

Extrapolating to other energies

Two competing mechanisms might alter heavy-quarkonium suppression nPDF

  • saturation effects when Q2

s ∼ m2 c

RpA = RE.loss

pA

(ˆ q) × Ssat

A (Qs)/Ssat p (Qs)

Ssat

A (Qs) parametrized as [ Fujii Gelis Venugopalan 2006 ]

Ssat

A (Qs) =

  • 2.65

2.65 + Q2

s [GeV2]

0.417

No additional parameter: Q2

s (x, L) = ˆ

q(x)L

[ Mueller 1999 ]

Reduces fitted transport coefficient: ˆ q0 = 0.05 GeV2/fm Q2

s (x = 10−2) = 0.08 – 0.15 GeV2 consistent with fits to DIS data

[ Albacete et al AAMQS 2011 ]

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 13 / 18

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SLIDE 19

SPS predictions

0.2 0.4 0.6 0.8 1 1.2 0.2 0.4 0.6

RPt/p(xF) NA3 √s = 19.4 GeV

∧

q0 = 0.09 GeV2/fm

∧

q0 = 0.05 GeV2/fm + sat.

0.2 0.4 0.6 0.8 1 1.2 0.2 0.4 0.6 0.8

RPt/p(xF) NA3 √s = 22.9 GeV (π- beam)

0.2 0.4 0.6 0.8 1 1.2

  • 0.2

0.2

xF RW/Be(xF) NA60 √s =27.4 GeV

0.2 0.4 0.6 0.8 1 1.2

  • 0.4
  • 0.2

0.2

xF RW/C(xF) HERA-B √s = 41.6 GeV

Agreement when xF > xmin

F

Natural explanation from the different suppression in p A vs π A Room for J/ψ absorption, though weaker than previously thought

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 14 / 18

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SLIDE 20

RHIC predictions

0.2 0.4 0.6 0.8 1 1.2

  • 3
  • 2
  • 1

1 2 3

y RdAu/pp(y)

∧

q0 = 0.09 GeV2/fm

∧

q0 = 0.05 GeV2/fm + sat. PHENIX √s = 200 GeV

Energy loss model fails in the most backward bins Saturation effects improve the agreement Smaller experimental uncertainties would help

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 15 / 18

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SLIDE 21

LHC predictions

0.2 0.4 0.6 0.8 1 1.2

  • 5
  • 2.5

2.5 5

J/ψ

∧

q0 = 0.09 GeV2/fm J/ψ

∧

q0 = 0.05 GeV2/fm + sat. ϒ

∧

q0 = 0.09 GeV2/fm LHC √s = 5 TeV y RPb/p(y)

Moderate effects (∼ 10 – 15%) around mid-rapidity Large effects above y 2 – 3 Saturation might be the dominant effect at the LHC around y ≃ 0 Slightly smaller suppression expected in the Υ channel

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 16 / 18

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SLIDE 22

Summary

Energy loss ∆E ∝ E due to coherent radiation

Neither initial nor final state effect Parametric dependence of dI/dω and ∆E predicted

Heavy-quarkonium suppression predicted from SPS to LHC

Good agreement with all existing data Natural explanation for the large xF J/ψ suppression Model supplemented consistently by saturation effects Supports the assumption of long-lived color octet Q ¯ Q pair More precise J/ψ and Υ data (and larger y) would help

Similar phenomena expected for light

  • heavy hadrons

Work in progress

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 17 / 18

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SLIDE 23

Conference announcement

Heavy-ion collisions in the LHC era Dates: 15 – 20 July 2012 Place: Quy Nhon (Vietnam) Web: https://indico.cern.ch/event/heavyions2012 Organizers: F. Arleo, C.A. Salgado, J. Tran Thanh Van

Fran¸ cois Arleo (LAPTH) Quarkonia suppression from gluon radiation Workshop pA@LHC 18 / 18