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EIC recommendation from joint QCD Town Meetings

A high luminosity Electron-Ion Collider (EIC) is the highest priority of the QCD community for new construction after

the JLab 12 GeV and RHIC II luminosity upgrades. EIC will address compelling physics questions essential for understanding the fundamental structure of matter:

- Precision imaging of sea-quarks and gluons to determine the spin, flavor and spatial structure of nucleons;

- Definitive study of the universal nature of strong gluon fields manifest in nuclei.

This goal requires that R&D resources be allocated for expeditious development of collider and detector design.

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• Substantial international interest in high luminosity (>1033cm-2s-1) polarized lepton-ion collider over decade

• Workshops Seeheim, Germany 1997 MIT, USA 2000

IUCF, USA 1999 BNL, USA 2002 BNL, USA 1999 JLab, USA 2004 Yale, USA 2000 BNL,USA 2006

• EIC received favorable review of science case in US 2001 Nuclear Physics Long Range Plan, with strong endorsement for R&D

• At BNL Workshop in March 2002, a plan was formulated to produce a conceptual design for EIC within three years

• NSAC in March 2003, declared EIC science `absolutely central’ to future of Nuclear Physics

• EIC identified in November 2003 as future priority in DOE Office of Science 20 year planning

• EIC recommended as highest new construction priority beyond Jlab 12 GeV and RHIC II luminosity upgrades by joint QCD Town Meetings

EIC Evolution

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EIC Parameter EIC SpecificationMaximum Center-of-Mass Energy 100 GeVMinimum Center-of-Mass Energy 20 GeVElectron Luminosity (ep) 1033 electron-atoms/cm2/secPositron Luminosity (ep) 1032 positron-atoms/cm2/secRange of unpolarized ions A = 1 thru A = 197Range of polarized ions Hydrogen, Deuterium or He3Number of Interaction Points (IP) At least 1, plan for 2Free Space around IP IP1: +/- 3 meter; IP2: +/-3 meter or

moreElectron/Ion Polarization >70% (Long.) / >70% (Long. and

TransverseElectron/Ion Polarimetry Precision ~1% / ~1%

Accelerator Specifications for “turn-on”

These specifications reflect what is required to realize the physics potential outlined by the various Monte Carlo simulations in the EIC White Paper, and motivate the R&D plan we will propose. The R&D will focus on how to achieve the highest possible luminosity and polarization, and refine the tools for achieving and utilizing these beams. Note that the sample of research highlights at “turn-on” shown earlier can already be achieved with luminosities of >few times 1032 electron-atoms/cm2/sec.

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Sample of Research Highlights of EIC at turn-on

= x/xIP

Syst. studies of F2(A,x,Q2):• precision measurement of G(x,Q2) • distinguish between models of shadowing

Diffractive studies in eA:• Distinguish between linear evolution and saturation models• Insight into the nature of the pomeron

Initial studies of g1(x,Q2):• Constrain unknown low-x behavior• Superb sensitivity to g at small x

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The First 5 Years (e+A only)First measurement from scaling violations of nuclear gluon distributions (for Q2 > 2

GeV2 and x < 10-2 down to 5·10-4 in 20+100 configuration). Comparison to (i) DGLAP based shadowing and (ii) saturation models. (20 weeks-year 1 measurement)

Study of centrality/A dependence of nuclear quark and gluon distributions. Comparison to model predictions. Extract A dependence of Qs in saturation framework (would require more than 1 species in year 1)

First measurement of charm distributions in cold nuclear matter- energy loss (from Au over proton, or better deuteron). Consistency check of extracted gluon distributions to that from scaling violations.

First measurement of FL in nuclei at small x (will complement e+p PRL on wide extension of measured range). Extraction of gluon distribution, test of higher twist effects, saturation,... (will require energy scan)

First measurement of diffractive structure function in nuclei F2D - study of scaling

violations of F2D with Q2. (year 1-low luminosity measurement)

Precision measurements of elastic J/ production - detailed tests of color transparency/opacity

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The luminosity drivers

• Deep exclusive physics with non-diffractive channels

Perturbatively Calculable at Large pTVanish

like 1/pT

Goal: spin/flavor structure of quark GPDsRequires: - Q2 ~ 10-20 GeV2 and L/T to facilitate interpretation

- Significantly smaller cross sections than diffractive channels (1/100) but less statistics needed than for imaging

L = 1035 assumed

• The correlation between spin and momentum of quarks

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LHeC

70 GeV e beam in LHC tunnelTake place of LHCb eA

New physics beyond the standard modele+A Operation at EIC allows to reach region competitive with LHeC (ep)

Interferes with LHC upgrades (> 2015), CLIC (2025/2030?) Realistic ?

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The EIC and the LHeCLHeC: L = 1.1x1033 cm-

2s-1 Ecm = 1.4 TeV

EIC: L > 1x1033 cm-2s-1

Ecm = 20-100+ GeV

• Add 70-100 GeV electron ring to interact with LHC ion beam• Use LHC-B interaction region• High luminosity mainly due to large ’s (= E/m) of beams

• Variable energy range• Polarized and heavy ion beams• High luminosity in energy region of interest for nuclear scienceNuclear science goals:• Explore the new QCD frontier: strong color fields in nuclei• Precisely image the sea-quarks and gluons to determine the spin, flavor and spatial structure of the nucleon.

High-Energy physics goals:• Parton dynamics at the TeV scale - physics beyond the

Standard Model - physics of high parton

densities (low x)

Important cross fertilization of ideas:• Significant European interest in an EIC• EIC collaborators on LHeC Science Advisory Committee

(with Research Directors of CERN, FNAL, DESY)

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Geometrical Scaling from DGLAP ?

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Systematic in FL Measurements

Estimated Systematic errors are for the self-generated set of measurements at EIC Ldt = 5/A fb-1 (10+100) GeV = 5/A fb-1 (10+50) GeV = 2/A fb-1 (5+50) GeV

Errors blow up where NMC + JLAB upgrade data will kick in

Also: possibility to run EIC at lower energies to easily overcome large sys. errors

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Experimental Aspects

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Centrality & Nuclear Fragments – How ? Many reason to study nuclear effects

such as shadowing as a function of centrality.

In e+A this was never attempted Studying diffractive events also implies

measuring the nuclear fragments (or better their absence)

Both require the measurement of “wounded” nucleons and fragments

studies and R&D Need reliable generators that include

good descripton of nuclear breakup dynamics

Study (using VENUS):Chwastowski,hep-ex/0206043

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Vector Meson Production

HERA: Survival prob. of qq pair of d=0.32 fm scattering off a proton from elastic vector meson production (here ).Strong gluon fields in center of p at HERA (Q2

s ~ 0.5 GeV2)?

b profile of nuclei more uniform and Q2

s ~ 2 GeV2

Surv

ival

Pro

babi

lity color opacity color transparency

“color dipole” picture

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Further Research Highlights of EIC

RHICLHC

Unique access to sea quarks and gluons!

g/g

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World Data on F2p Structure Function

Next-to-Leading-Order (NLO) perturbative QCD (DGLAP) fits do a good job of reproducing the data over the full measurement range.

Gluons rule at small-x!

xf(

x)

50% of momentum carried by gluons

F2 = q eq2 xfq(x,Q2)

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The Gluon Contribution to the Proton Spin

RHIC-Spin

x

g

g/g

Open Charm Production Dijet Production

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Total Photon Cross Sections

At large Ecm: total cross sections rise as W. Associated with two-gluon or Pomeron exchange mechanism

Two-gluon (Pomeron) exchange dominant for J/, , production at large energies

LO factorization ~ dipole picture sensitive to gluon distribution squared!

L

R

Spin-Orbit Effects and Transverse Spin

Observed Large“Single-Spin Asymmetry”

Now confirmed at much higher energies at STAR (and Brahms)

Fermilab E704:p p X at 400 GeV

Must be due to spin-orbit

effects in the proton itself

and/or in the fragmentation

process

19gives transverse size of quark (parton) with longitud. momentum fraction x

Fourier transform in momentum transfer

x = 0.01 x = 0.40 x = 0.70

Wigner function: Probability to find a u(x) quark with a certain polarization at position r and with momentum k

Wu(x,k,r)

GPDu(x,,t) Hu, Eu, Hu, Eu

~~

p

m

BGPD

d2k

T

u(x)u, u

F1u(t)

F2u,GA

u,GPu

f1(x)g1, h1

PartonDistributions

Form Factors

d2k

T

dx

= 0, t = 0

Link to Orbital

Momentum

Towards a 3D spin-flavor landscape

Want PT > but not too large!

Link to Orbital

Momentum

p

m

xTMD

d3 r

TMDu(x,kT) f1,g1,f1T ,g1T

h1, h1T ,h1L ,h1

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Most of the mass of ordinary matter is concentrated in protons and neutrons. It arises from …[a]… profound, and beautiful, source.

Numerical simulation of QCD shows that if we built protons and neutrons in an imaginary world with no Higgs mechanism - purely out of quarks and gluons with zero mass - their masses would not be very different from what they actually are. Their mass arises from pure energy, associated with the dynamics of confinement in QCD, according to the relation m=E/c2. This profound account of the origin of mass is a crown jewel in our Theory of Matter.’’

Frank Wilczek CERN October 11, 2000

The Origin of Mass in the Universe

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Proton = u + u + d

Mproton >> 2Mu + Md

~ 0.02 x Mproton

Most of the mass in the world around us arises from QCD, predominantly from the gluons. • QCD tells us that the proton

consists of spin-½ quarks that interact via exchange of spin-1 gluons.

• This is a highly relativistic system described by a non-Abelian gauge theory, completely unlike an atom or nucleus.

• The quark model has had great success in predicting the spins of baryons: this is a direct consequence of symmetry.

• We have learned that the quark model breaks down in understanding proton structure from scattering experiments.

• The gluons have been shown to play a far more dominant role than previously assumed.