Studies of e+A physics at an Electron-Ion Collider

Liang ZhengOn behalf of the BNL EIC Science Task Force

Brookhaven National LabInstitute of Particle Physics, Central China Normal

University

Division of Nuclear PhysicsAmerican Physical Society October 23-26, 2013Newport News, VA

DNP 2013, Liang Zheng 2

Overview• EIC eA physics program– Nuclear PDF• Nuclei F2/FL

– Nuclear Imaging• Coherent t distribution in diffraction

– Saturation• Inclusive diffraction• Dihadron correlation

– Parton propagation and hadronization in nuclear medium

2013/10/25

DNP 2013, Liang Zheng 3

Explore the small x regime• Gluons dominate at small x

– 99% of proton mass accounted by QCD interaction

– Gluon PDF grows explosively at small x

2013/10/25

Must be tamed at some point

DNP 2013, Liang Zheng 4

Explore the small x regime• Gluons dominate at small x

– 99% of proton mass accounted by QCD interaction

– Gluon PDF grows explosively at small x

• Nonlinear evolution like BK alternative to DGLAP, BFKL due to gluon recombination.

• Saturation regime, Q2<<Q2

s(x)

2013/10/25

DNP 2013, Liang Zheng 5

Nuclear amplification

2013/10/25

•Gluon density scales as nuclear size

•Effective x much smaller in a nuclei

DNP 2013, Liang Zheng 6

EIC eA kinematics coverage

2013/10/25

• Largely extend current reach

• Possible to explore the saturation regime

DNP 2013, Liang Zheng 7

Diffractive cross section

2013/10/25

• σdiff/σtot 15% at HERA, predicted 25-40% in eA

• σdiff ～ g(x,Q2)2

Rapidity gap: Signature of a diffractive event.

Color-neutral exchange

t=(p-p’)2

DNP 2013, Liang Zheng 8

Diffractive cross section

2013/10/25

• Significant difference between saturation and non-saturation

• Strong discrimination power within a few months of running.

DNP 2013, Liang Zheng 9

Dihadron correlation

• Back to back hadron pairs decorrelate

• Strong suppression at away side predicted by saturation

• Probe nuclei in kT space.2013/10/25

Xiao, Dominguez, Yuan 2011/2012

y=0.7zh1 = zh2 = 0.3p1T>2GeV1GeV < p2T < p1T

trigger

associateDf

transverse plane

DNP 2013, Liang Zheng 10

Dihadron correlation: non-saturation

2013/10/25

ep/eAu 20x100 GeV0.6<y<0.81 <Q2<2 GeV2

pt1>2 GeV, 1 GeV<pt2<pt10.2<z1,z2<0.42559 < ν < 3412 GeV<xbj>=2.59x10-4

<xg>=3.42x10-2

Charged particlesNuclear effect:• nPDF EPS09• Cold nuclear medium energy loss

DNP 2013, Liang Zheng 11

Dihadron correlation: saturation• Constrain sat/nosat models a lot with limited

statistics of 1fb-1.• Strong suppression can not be reproduced by the

nosat model.

2013/10/25

DNP 2013, Liang Zheng 12

Summary• Key eA measurements at EIC:

– Ratio of diffractive cross section to total, “day one” measurement

– Dihadron correlation in ep/eA, mark out the saturation region with a low luminosity requirement and ep baseline

– More details :• arXiv:1212.1701 EIC White paper• wiki.bnl.gov/eic/index.php/Main_Page

• What can we learn from this– Understand the collective dynamics of

gluons– Investigate inner landscape of a nuclei– Provide initial state input to pA/AA

2013/10/25

Back up

DNP 2013, Liang Zheng 14

Structure functions

2013/10/25

eAu:5x50 2 fb-1

5x75 4 fb-1

5x100 4 fb-1

Running combined 6 months total (50% eff)

Systematics-error dominated

Sensitive to gluons

DNP 2013, Liang Zheng 15

Diffraction

2013/10/25

Exclusive Vector meson productionCoherent: nuclei intactIncoherent: break up

Finding the source

eic-tf-meeting 16

10x100 GeVLc = z0.35(1-z) ν y = 0.3, z = 0.3, ν = 640 GeV, Lc = 420 fmy = 0.7, z = 0.3, ν = 1492 GeV, Lc = 979fm

charged pionz>0.1, ν>6 GeV, xFeynman>0, pT>0.1 GeV

Where we are

2013/9/19

Dihadron correlation at an EIC

eic-tf-meeting 172013/9/19

Kinematics coverage in the Dihadron correlation at an EIC

Qs2 for Au

Qs2 for Ca

Qs2 for

proton

10x100

20x100

Black box:0.6<y<0.8Red box:0.25<y<0.35

eic-tf-meeting 182013/9/19

Dihadron correlation in different kinematics bins (no sat)10x100 GeV

1fb-1

eic-tf-meeting 192013/9/19

10x100 GeV 1fb-1

Dihadron correlation in different kinematics bins (sat)