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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 - PowerPoint PPT Presentation
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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 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)