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

American Physical Society

October 23-26, 2013

Newport News, VA

Liang Zheng

On behalf of the BNL EIC Science Task Force

Brookhaven National Lab

Institute of Particle Physics, Central China Normal University

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

DNP 2013, Liang Zheng

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

Must be tamed at some point

DNP 2013, Liang Zheng

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<<Q2s(x)

DNP 2013, Liang Zheng

Nuclear amplification

- Gluon density scales as nuclear size
- Effective x much smaller in a nuclei

DNP 2013, Liang Zheng

EIC eA kinematics coverage

- Largely extend current reach
- Possible to explore the saturation regime

DNP 2013, Liang Zheng

Diffractive cross section

- σdiff/σtot 15% at HERA, predicted 25-40% in eA
- σdiff～g(x,Q2)2

Color-neutral exchange

Rapidity gap: Signature of a diffractive event.

t=(p-p’)2

DNP 2013, Liang Zheng

Diffractive cross section

- Significant difference between saturation and non-saturation
- Strong discrimination power within a few months of running.

DNP 2013, Liang Zheng

Dihadron correlation

Xiao, Dominguez, Yuan 2011/2012

- Back to back hadron pairs decorrelate
- Strong suppression at away side predicted by saturation
- Probe nuclei in kT space.

trigger

y=0.7

zh1 = zh2 = 0.3

p1T>2GeV

1GeV < p2T < p1T

transverse plane

Df

associate

DNP 2013, Liang Zheng

Dihadron correlation: non-saturation

ep/eAu 20x100 GeV

0.6<y<0.8

1 <Q2<2 GeV2

pt1>2 GeV, 1 GeV<pt2<pt1

0.2<z1,z2<0.4

2559 < ν < 3412 GeV

<xbj>=2.59x10-4

<xg>=3.42x10-2

Charged particles

- Nuclear effect:
- nPDF EPS09
- Cold nuclear medium energy loss

DNP 2013, Liang Zheng

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.

DNP 2013, Liang Zheng

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

DNP 2013, Liang Zheng

Structure functions

Sensitive to gluons

eAu:

5x50 2 fb-1

5x75 4 fb-1

5x100 4 fb-1

Running combined 6 months total (50% eff)

Systematics-error dominated

DNP 2013, Liang Zheng

Diffraction

Exclusive Vector meson production

Coherent: nuclei intact

Incoherent: break up

Finding the source

DNP 2013, Liang Zheng

Dihadron correlation at an EIC

10x100 GeV

Lc = z0.35(1-z) ν

y = 0.3, z = 0.3, ν= 640 GeV, Lc = 420 fm

y = 0.7, z = 0.3, ν = 1492 GeV, Lc = 979fm

charged pion

z>0.1, ν>6 GeV, xFeynman>0, pT>0.1 GeV

Where we are

eic-tf-meeting

Kinematics coverage in the Dihadron correlation at an EIC

10x100

20x100

Black box:0.6<y<0.8

Red box:0.25<y<0.35

Qs2 for Au

Qs2 for Ca

Qs2 for proton

eic-tf-meeting

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