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Division of Nuclear Physics American Physical Society October 23-26, 2013 Newport News, VA. Studies of e+A physics at an Electron-Ion Collider. Liang Zheng On behalf of the BNL EIC Science Task Force Brookhaven National Lab - PowerPoint PPT Presentation
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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)