What is the eic
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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

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What is the EIC ?

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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 design

e-cooling (RHIC II)

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

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.


What is the eic

World Data on F2p Structure Function

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


What is the eic

World Data on F2p

World Data on g1p

4 orders of magnitude in x and Q2

< 2 orders of magnitude, precision much worse !


What is the eic

Region of existing g1p data

World Data on F2p

EIC Data on g1p

An EIC makes it possible!


G from scaling violations of g 1

G from scaling violations of g1


G from scaling violations of g 11

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)


Polarized gluon distribution via charm production

c

D mesons

c

D mesons

Polarized gluon distribution via charm production

very clean process !

LO QCD: asymmetry in D production directly

proportional to G/G


Polarized gluon distribution via charm production1

Polarized gluon distribution via charm production

problems:luminosity, charm cross section, background !


Polarized gluon distribution via charm production2

Polarized gluon distribution via charm production

  • starting assumptions for EIC:

  • vertex separation of better than 100m

  • 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 !


Polarized gluon distribution via charm production3

incl PID

invariant mass of K  system

Polarized gluon distribution via charm production

Background suppression:

Separation of primary and

secondary vertex absolutely

essential !

Pion/kaon separation very

helpful !


Polarized gluon distribution via charm production4

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 production5

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


Polarized gluon distribution via charm production6

Precise determination

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

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 q 2 from rhic and eic

Future: x g(x,Q2) from RHIC and EIC

EIC

0.003 < x < 0.5

Statistical uncertainty in xg typically < 0.01 !!!

EIC


Polarized gluon distribution vs q 2

Polarized gluon distribution vs Q2


What is the eic

Other processes

  • G from dijet production

  • promising channel for determination of G

  • needs more detailed study !


What is the eic

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


What is the eic

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


G 1 and the bjorken sum rule

g1 and the Bjorken Sum Rule


What is the eic

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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