What is the EIC ? 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

ERL-based eRHIC DesignERL-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.

PHENIX

STAR

e-cooling (RHIC II)

Four e-beam passes

e+ storage ring 5 GeV - 1/4 RHIC circumference

Main ERL (3.9 GeV per pass)

2 different eRHIC Design options2 different eRHIC Design options

RHIC

5 – 10 GeV e-ring

e-cooling(RHIC II)

5 -10GeV full energy injector

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 LabELIC design at Jefferson Lab

30-225 GeV protons30-100 GeV/n ions 3-9 GeV electrons

3-9 GeV positrons

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

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

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

World Data on F2p Structure Function

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

World Data on F2p World Data on g1

p

4 orders of magnitude in x and Q2

< 2 orders of magnitude, precision

much worse !

World Data on F2p EIC Data on g1

p

An EIC makes it possible!Region of existing g1p data

G from scaling violations of gG from scaling violations of g1 1

G from scaling violations of gG from scaling violations of g1 1

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)

c

c

D mesons

D mesons

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

LO QCD: asymmetry in D production directly

proportional to G/G

very clean process !

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

problems:luminosity, charm cross section, background !

very demanding detector requirements !

Polarized gluon distribution via charm productionPolarized 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

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

invariant mass of K system

incl PID Background suppression:

Separation of primary andsecondary vertex absolutelyessential !

Pion/kaon separation veryhelpful !

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

Momenta of decaykaon and pion:1.5 < p < 10 (15) GeV

Angles of decay kaon and pion: 1600 < < 1770

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

Precise determination

of G/G for 0.003 < xg < 0.4

at common Q2 of 10 GeV2

howeverRHIC SPIN

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 ()

Polarized gluon distribution via charm productionPolarized gluon distribution via charm production

Precise determination

of G/G for 0.003 < xg < 0.4

at common Q2 of 10 GeV2

charm production: influence of fragmentationcharm production: influence of fragmentation

xgrec = x(shat/Q2+1)

shat = 4 Minv2

correction presently bysimple parametrisation of xg-xrec vs xg

Future: x Future: x g(x,Qg(x,Q22) from RHIC and EIC) from RHIC and EIC

EIC0.003 < x < 0.5

Statistical uncertainty in xxg g

typically < typically < 0.01 !!!0.01 !!!

EIC

Polarized gluon distribution vs QPolarized gluon distribution vs Q22

Other processes

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

• G from dijet production

Next Steps

• 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

Summary

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

gg11 and the Bjorken Sum Rule and the Bjorken Sum Rule

Bjorken Sum Rule: Γ1p - Γ1

n = 1/6 gA [1 + Ο(αs)]

• 7% (?) in unmeasured region, in future

constrained by data and lattice QCD

• 3-4% precision at various values of Q2

Needs:O(1%) Ion Polarimetry!!!

determination of s(Q2)

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