Exploring Gluonic Matter with Electron-Ion Collisions Outline - - PowerPoint PPT Presentation

Exploring Gluonic Matter with Electron-Ion Collisions

J.H. Lee Brookhaven National Laboratory

1 QM2012, Washington D.C.

Outline

• Gluon, Saturation
• Electron-Ion Collider
• Signals of saturation/Selected key

measurements in eA

Glue in matter: What do we know

HERA F

2

1 2 3 4 5 1 10 10

10

10

10

F

2 em

• log

10

(x) Q

2

(GeV

2

)

ZEUS NLO QCD fit H1 PDF 2000 fit H1 94-00 H1 (prel.) 99/00 ZEUS 96/97 BCDMS E665 NMC x=6.32 10-5 x=0.000102 x=0.000161 x=0.000253 x=0.0004 x=0.0005 x=0.000632 x=0.0008 x=0.0013 x=0.0021 x=0.0032 x=0.005 x=0.008 x=0.013 x=0.021 x=0.032 x=0.05 x=0.08 x=0.13 x=0.18 x=0.25 x=0. 4 x=0.65

d2σep→eX dxdQ2 = 4πα2

e.m.

xQ4 ⇤ 1 − y + y2 2 ⇥ F2(x, Q2) − y2 2 FL(x, Q2) ⌅

2

• Gluons responsible for the visible mass and drive the vacuum

structure

• NLO QCD and the measurement “broadly similar”: limited success
• For smaller values of x, structure function F2 rises strongly with Q2:

Simple quark-parton model Bjorken scaling breaks

• Gluons dominate at low-x, but the underlying dynamics and the

evolution is not well established

0.2 0.4 0.6 0.8 1

• 4

10

• 3

10

• 2

10

• 1

10 1 0.2 0.4 0.6 0.8 1 HERAPDF1.7 (prel.)

• exp. uncert.

model uncert. parametrization uncert. HERAPDF1.6 (prel.)

x xf

= 10 GeV

Q

xu

xd 0.05) × xS ( 0.05) × xg (

HERAPDF Structure Function Working Group June 2011

HERA I+II inclusive, jets, charm PDF Fit

0.2 0.4 0.6 0.8 1

How gluons grow and saturate

• Saturation regime, where parton splitting is balanced by multi-

gluon fusion between self-interacting gluons, arises naturally through non-linear BK/JIMWLK evolution

• in the Color Glass Condensate (CGC) framework
• characterized by saturation momentum QS(x,A)
• Experimental establishment on the “theoretical evidence” of

saturation regime is fundamentally important for understanding of gluonic dynamics - strong interaction

3

10-5 10-4 10-3 10-2 1 10 0.1

Λ2

Q2 (GeV2)

200

120 4

A x

Proton Calcium Gold

P a r t

• n

G a s Color Glass Condensate Confinement Regime

EIC Coverage

(Qs

A)2 ≈ cQ0 2 A

x # $ % & ' (

1/3

Electron-Ion Collider (EIC) Exploring gluons (and sea quarks) - beyond HERA

• e + Ion : nuclear enhanced

(~x300) effective small-x reach - deeply into saturation regime

• wide energy range: kinematic

coverage with great leverage for measuring gluon distribution FL (√sA=~20-100 GeV)

• high luminosity (~x500 of

HERA) : rare and precision probe for gluonic properties: heavy flavor, exclusive measurements, ...

• polarized e and p: gluonic

contribution to spin degree of freedom of nucleon

4

1 10 10-3 103 10-2 102 10-1 1 10-4

x Q2 (GeV2)

0.1

Measurements with A ≥ 56 (Fe):

eA/μA DIS (E-139, E-665, EMC, NMC) νA DIS (CCFR, CDHSW, CHORUS, NuTeV) DY (E772, E866)

Q

A u , me d ian b C a, me d ian b p, m e d ia n b

EIC √s=90 GeV EIC √s=45 GeV

Characterizing glue in matter with EIC

• Precisely mapping momentum and space-time

distribution of gluons in nuclei in wide kinematic range including saturation regime through:

• Inclusive measurements of structure functions

(F2,FL, F2D, FLD): eA→eX, eA→eX+gap

• Semi-inclusive measurements of final state

distributions: eA→eA{π,K,Φ,D,J/Ψ...}X

• Exclusive final states: eA→eA{ρ,Φ,J/Ψ,γ}+gap
• Multiple controls: x, Q2, t, MX2 for light and heavy nuclei

5

k p X k' q

k k' p' p q

gap

Mx

X A gap

}

e e

Selected Key Measurement I: Integrated gluon distribution: non-linear QCD in FL

6

• Saturation signal in nuclear structure function: FLA is sensitive to higher

twist (non-linear) effects at low Q2 / small-x - correction to leading-twist DGLAP

• Higher twist effect cancelation in F2 (=FL+FT)
• Based on saturation inspired model (GBW) describing HERA ep data
• wide energy range of EIC is essential for the measurement

F A

L (x, Q2) ∝ x GA(x, Q2)

(FL - FL

(FL - FL

Au (A=197) proton

• 5
• 4
• 3
• 2

1 2 3

• 10
• 8
• 6
• 4
• 2

log

(x) log10(Q2) log

(x) log10(Q2)

• 5
• 4
• 3
• 2

1 2 3

• 10
• 8
• 6
• 4
• 2

Bartels, ¡Golec-­‑Biernat, ¡Motyka, ¡PRD ¡ ¡81 ¡(2010)

Integrated gluon distribution at EIC: F2 and FL

• F2,LA extracted from pseudo-data generated at 3 EIC energies (2-4 fb-1)
• 5+50 GeV 5+75 GeV 5+100 GeV
• Data, with errors, added to theoretical expectations from EPS09 PDF and rcBK
• at Q2 = 2.7 GeV2x=10-3

7

A¹⁄³ A¹⁄³

rcBK EPS09 (CTEQ) Q2 = 2.7 GeV2, x = 10-3 Q2 = 2.7 GeV2, x = 10-3 rcBK EPS09 (CTEQ)

• stat. errors enlarged (× 50)
• sys. uncertainty bar to scale

errors to scale

Cu Au Beam Energies A ∫Ldt 5 on 50 GeV 2 fb-1 5 on 75 GeV 4 fb-1 5 on 100 GeV 4 fb-1 1 2 3 4 5 6 7 0.2 0.4 0.6 0.8 1 1.2 1 2 3 4 5 6 7 0.2 0.4 0.6 0.8 1 1.2

R2 = F2

A/(A F2 p)

RL = FL

A/(A FL p) Beam Energies A ∫Ldt 5 on 50 GeV 2 fb-1 5 on 75 GeV 4 fb-1 5 on 100 GeV 4 fb-1

σr(x, Q2) = F A

2 (x, Q2) − y2

Y + F A

L (x, Q2)

Q2=sxy

Selected Key Measurement II: Di-hadron correlation: Measurements at RHIC

• Multiple scattering in the dense nucleus at forward in dAu lead to mono-jet (decorrelation

at ΔΦ=π) in CGC frame work ( J. Albacete and C. Marquet, PRL 105 (2010))

• Alternative interpretation: Multiple parton scattering (Energy loss+dynamical shadowing)

without saturation at “moderate” x (Kang, Vitev, Xing PRD85 (2012))

• Estimated xA in dAu at RHIC ~ 10-3

8

20

STAR Preliminary

Uncorrected Coincidence Probability (rad-1)

p+p → π0 π0 + X, √s = 200 GeV d+Au → π0 π0 + X, √s = 200 GeV d+Au → π0 π0 + X, √s = 200 GeV STAR Preliminary STAR Preliminary d+Au peripheral d+Au central p+p

pT,L > 2 GeV/c, 1 GeV/c < pT,S < pT,L 〈ηL〉=3.2, 〈ηS〉=3.2 pT,L > 2 GeV/c, 1 GeV/c < pT,S < pT,L 〈ηL〉=3.2, 〈ηS〉=3.2 pT,L > 2 GeV/c, 1 GeV/c < pT,S < pT,L 〈ηL〉=3.1, 〈ηS〉=3.2

Δφ Δφ Δφ

CGC+offset

σ 0.41 ± 0.01 0.68 ± 0.01

Δφ π σ 0.46 ± 0.02 0.99 ± 0.06

Δφ π σ 0.44 ± 0.02 1.63 ± 0.29

Δφ π

• 1

1 2 3 4 5

• 1

1 2 3 4 5

• 1

1 2 3 4 0.02 0.15 0.01 0.05 0.03 0.025 0.02 0.015 0.01 0.005 0.016 0.014 0.012 0.01 0.008 0.006 0.004 0.002

p q

x y

p q

x y

Di-hadron correlation at EIC

• EIC reach small-x regime with clean kinematic control in di-hadron

correlation measurement

• EIC expected data from10 fb-1 integrated luminosity at 30(e)x100(p/Au) GeV
• Factor of ~2 suppression expected in eAu/ep with saturation

compared with non-saturation model: Pythia+nPDF+DPMJETIII

• Q2=1 GeV2 <x>=1x10-4
• hadron pT cut: trigger / associate = 2 / 1 GeV/c
• Systematic differential measurement: crossing onset of saturation using √s, Q2, A

9

2 2.5 3 3.5 4 4.5 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 eAu eAu - sat eAu - nosat eCa pT

ep

Q2 = 1 GeV2

Δϕ Δϕ C(Δϕ) CeAu(Δϕ)

2 2.5 3 3.5 4 4.5 0.05 0.1 0.15 0.2 EIC stage-II ∫ Ldt = 10 fb-1/A

sampling

Bowen, Dominguez, Yuan 2011/2012

Di-hadron correlation vs x at EIC: Nuclear modification JeAu

10

log10(xg) JeAu

• 3
• 2.5
• 2
• 1.5
• 1

1 eAu - sat eAu - nosat

Q2 = 1 GeV2 pT

trigger > 2 GeV/c

1 < pT

assoc < pT trigger

|η|<4

EIC stage-II ∫ Ldt = 10 fb-1/A 10-3 10-2 1 10-1

peripheral central

xA

frag

JdAu

RHIC dAu, √s = 200 GeV

• JeAu - relative yield of di-hadrons produced in eAu compared to ep collisions
• Curves from saturation model (B. Xiao (2012) )

forward-forward mid-forward

Data:Phenix

Selected Key measurement III: Gluon spatial distribution and correlations in exclusive diffractive Vector Meson production

• Novel “strong” probe to investigate gluonic structure of nuclei: color dipole

coherent and incoherent diffractive interaction: Sensitive to saturation (s,b,A)

• Large σdiff/σtotal in e+A (~25-40%) compared to e+p (~10-15%)
• Coherent: Access to spatial distribution of gluons
• Precise transverse imaging of the gluons
• Modification due to small-x evolution
• Tagging with vetoing spectator neutrons in Zero Degree Calorimeter
• Incoherent: Gluon correlations in the transverse plane

gap gap A A A A’ p n e e e e

coherent incoherent

11

Exclusive diffractive vector meson production: J/Ψ and Φ

• Probe (vector meson dipole size) dependent exclusive t-dependent production
• Coherent: Fourier transform of dσ/dt gives source distribution ρg(b): gluonic form factor
• Incoherent: gluon correlation in transverse plan - constraining initial wave function in RHIC/LHC AA
• High precision measurement available with A∫Ldt = 10 fb-1
• Simulation: Sartre (Toll, Ullrich) + experimental smearing

12

|t | (GeV2) |t | (GeV2)

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

)

/dt (nb/GeV

σ d )

/dt (nb/GeV

σ d

J/ψ φ

104 103 102 10 1 10-1 10-2 105 104 103 102 10 1 10-1 10-2

Φ J/Ψ

Exclusive Diffractive Vector Meson at EIC

• Q2 dependence of cross-section from coherent vector meson diffraction
• σ(eA)/σ(ep) saturation vs non-saturation
• With A∫Ldt = 10 fb-1
• Φ more sensitive to saturation effects than J/ψ due to a larger wave

function

13

0.2 0.4 0.6 0.8 1 1.2 coherent events only ∫Ldt = 10 fb-1 x < 0.01 Experimental Cuts: |η(edecay)| < 4 p(edecay) > 1 GeV/c coherent events only ∫Ldt = 10 fb-1 x < 0.01 1 2 3 4 5 6 7 8 9 10

(1/A4/3) σ(eAu)/σ(ep) Q2 (GeV2)

no saturation saturation (bSat) no saturation saturation (bSat)

e e e p(Au) → e’ p’(Au’) J/ψ

1 2 3 4 5 6 7 8 9 10

(1/A4/3) σ(eAu)/σ(ep) Q2 (GeV2)

2.2 2.0 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2

e p/Au → e’ p’/Au’ φ K K

Experimental Cuts: |η(Kdecay)| < 4 p(Kdecay) > 1 GeV/c

Coherent Diffraction (γ*+IP ) in Ultra Peripheral Collisions at RHIC

• Coherent

diffractive ρ production in Au +Au at √sNN=200 GeV

• Data: STAR/RHIC

Ultra-peripheral AuAu Collision

• Simulation: Sartre

14

]

2

• t [(GeV/c)

0.05 0.1 0.15 0.2 ]

2

/dydt [mb/GeV σ d

• 3

10

• 2

10

• 1

10 1 10

2

10

STAR Preliminary Sartre (coherent)

Selected Key measurement IV: semi-inclusive DIS at large-x

• Nuclei as space-time analyzer
• EIC can measure
• fragmentation time scale to understand dynamics
• in medium energy loss to characterize medium
• gluon bremsstrahlung: hadronization outside media
• pre-hadron absorption: color neutralization inside

the medium

• Observable
• pT distribution broadening: link to saturation
• attenuation of hadrons (multiplicity ratio) : energy loss

mechanism

15 h

q q q

l lf

p q

γ∗

z

Multiplicity Ratio

z Multiplicity Ratio

Attenuation of hadrons in nuclei

16 ν = virtual photon energy in nucleon rest frame zh = Eh/ν

• Unprecedented precision to distinguish between different models/mechanisms in wide ν range
• gluon radiation, parton scattering, hadron absorption..
• Hadronization in and out of nucleus
• First time access to Charm

RM(multiplicity ratio)

D0 π

Hermes EIC EIC Hermes

Summary

The new proposed versatile and high-luminosity electron-Ion collider (EIC) is to study one of the outstanding fundamental questions in QCD:

• Establish and explore new degree of freedom of gluonic property of

matter - saturation regime by systematically studying the unprecedentedly accessed kinematic regime with the probes sensitive to saturation

• inclusive structure function: integrated gluon distribution
• di-hadron correlation: kT dependent gluons, correlations
• exclusive diffraction vector meson: spatial distributions, gluon

correlations

• large-x SIDIS, jets: transport coefficients in cold matter
• Characterizing the initial gluon dynamics in eA is crucial to

disentangle initial and final state effects in RHIC and LHC heavy-ion results

17

Back-up slides

18

Estimating saturation scale

• Gluonic saturation/recombination
• number of gluons per unit of transverse area:

ρ~xG(x,Q2)/πR2

• cross-section for gluon recombination:

σ~ αs/Q2

• saturation occurs when 1 < ρσ ⇒

Q2 < Qs2(x)

• saturation Qs varies
• Qs ∝ x1/3 (phenomenological “geometrical scaling” at HERA)
• Qs ∝ A1/3 (Gluons act coherently)
• Nuclear enhanced saturation scale
• To access saturation: increase energy (~1/x) or increase Qs (~A1/3)
• HERA (ep) energy range higher G(x,Q2) very limited reach of the

saturation regime: Need √s=1-2 TeV in ep

19

e+A physics science matrix: Key measurements

20