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What is the EIC ?

- Electron Ion Collider as the ultimate QCD machine
- Variable center of mass energy between 20 and 100 GeV
- High luminosity
- Polarized electron and proton (deuteron, 3He) beams
- Ion beams up to A=208

Explore the new QCD frontier:

strong color fields in nuclei

Precisely image the sea-quarks

and gluons in the nucleon

5 – 10 GeV e-ring

5 -10GeV full energy injector

RHIC

PHENIX

Main ERL (3.9 GeV per pass)

STAR

e+ storage ring

5 GeV - 1/4 RHIC circumference

e-cooling

(RHIC II)

Four e-beam passes

2 different eRHIC Design options

ERL-based eRHIC Design- Electron energy range from 3 to 20 GeV
- Peak luminosity of 2.6 1033 cm-2s-
- high electron beam polarization (~80%)
- full polarization transparency at all energies
- multiple electron-hadron interaction points
- 5 meter “element-free” straight section(s)
- ability to take full advantage of electron cooling of the hadron beams;
- easy variation of the electron bunch frequency to match the ion bunch frequency at different ion energies.

- Based on existing technology
- Collisions at 12 o’clock interaction region
- 10 GeV, 0.5 A e-ring with 1/3 of RHIC circumference (similar to PEP II HER)
- Inject at full energy 5 – 10 GeV
- Polarized electrons and positrons

ELIC design at Jefferson Lab

30-225 GeV protons

30-100 GeV/n ions

3-9 GeV electrons

3-9 GeV positrons

- Polarized H, D, 3He,
- Ions up to A = 208

- Average Luminosity from 1033to 1035 cm-2 sec-1 per Interaction Point

Green-field design of ion complex directly aimed at full exploitation of science program.

World Data on F2p Structure Function

Next-to-Leading-Order (NLO) perturbative QCD (DGLAP) fits

World Data on g1p

4 orders of magnitude in x and Q2

< 2 orders of magnitude, precision much worse !

G from scaling violations of g1

G from scaling violations of g1

- EIC will allow precision determination of g1(x,Q2) over very large kinematic range
- and thus will:
- precisely determine the integral of G
- allow to distinguish between different functional forms of g(x)

- Measurement of G is likely to be limited by systematic uncertainty in polarization measurement
- ---- needs careful investigation (similar for existing global fits)

D mesons

c

D mesons

Polarized gluon distribution via charm productionvery clean process !

LO QCD: asymmetry in D production directly

proportional to G/G

Polarized gluon distribution via charm production

problems:luminosity, charm cross section, background !

Polarized gluon distribution via charm production

- starting assumptions for EIC:
- vertex separation of better than 100m
- full angular coverage (3<<177 degrees)
- perfect particle identification for pions and kaons
- (over full momentum range)

- detection of low momenta particles (p>0.5 GeV)
- measurement of scattered electron
- (even at very small scattering angles)

- 100% efficiency

very demanding detector requirements !

invariant mass of K system

Polarized gluon distribution via charm productionBackground suppression:

Separation of primary and

secondary vertex absolutely

essential !

Pion/kaon separation very

helpful !

Polarized gluon distribution via charm production

Momenta of decay

kaon and pion:

1.5 < p < 10 (15) GeV

Angles of decay kaon

and pion:

1600 < < 1770

Polarized gluon distribution via charm production

Precise determination

of G/G for

0.003 < xg < 0.4

at common Q2 of 10 GeV2

however

RHIC SPIN

of G/G for

0.003 < xg < 0.4

at common Q2 of 10 GeV2

Polarized gluon distribution via charm production- If:
- We can measure the scattered electron even at angles close to 00 (determination of photon kinematics)
- We can separate the primary and secondary vertex to better than 100 m ()
- We understand the fragmentation of charm quarks ()
- We can control the contributions of resolved photons
- We can calculate higher order QCD corrections ()

charm production: influence of fragmentation

xgrec = x(shat/Q2+1)

shat = 4 Minv2

correction presently by

simple parametrisation

of xg-xrec vs xg

Future: x g(x,Q2) from RHIC and EIC

EIC

0.003 < x < 0.5

Statistical uncertainty in xg typically < 0.01 !!!

EIC

- G from dijet production

- promising channel for determination of G
- needs more detailed study !

- determine sensitivity of g1 to different “realistic” models for G (including different functional forms !)
- generate pseudo EIC data and include in full QCD fit procedure (including estimates of systematic uncertainties !)
- study fragmentation in charm production
- include other charm decay channels (including D* tagging)
- understand the possibility to determine the charm mass from charm cross section measurements

- EIC is the ideal machine to finally determine the contribution of the gluons to the nucleon spin!
- measurements of g1 will allow
- a precise determination of G from its scaling violation
- systematics due to uncertainty in proton beam polarization ?

- measurements of charm cross section asymmetries will provide a precise determination of G/G for 0.003<x<0.5 at a fixed value of Q2 of ~10 GeV2
- ……. provided we can
- measure the scattered electron at extremely small angles
- separate the primary and secondary vertex with sufficient precision
- control the contribution of resolved photons
- understand NLO corrections and the mass of the charm quark

g1 and the Bjorken Sum Rule

Bjorken Sum Rule: Γ1p - Γ1n = 1/6 gA [1 + Ο(αs)]

Needs:

O(1%) Ion Polarimetry!!!

determination of as(Q2)

- Sub-1% statistical precision at ELIC
- (averaged over all Q2)

- 7% (?) in unmeasured region, in future
- constrained by data and lattice QCD

- 3-4% precision at various values of Q2

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