Spin Physics with an Electron-Ion-Collider

Spin Physics with an Spin Physics with an Electron-Ion-ColliderElectron-Ion-Collider

• What is the EIC ?

• Central Questions in Nucleon Structure

• The Gluon Contribution to the Nucleon Spin

• TMDs and GPDs at EIC

• Sumary

Antje Bruell, JlabRHIC&AGS Users Meeting, May 27, 2008

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

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 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

The Gluon Contribution to the The Gluon Contribution to the Nucleon Spin Nucleon Spin

Antje Bruell, Jlab

EIC meeting, MIT, April 7 2007

• Introduction

• G from scaling violations of g1(x,Q2)

• The Bjorken Sum Rule

• G from charm production

RHIC-Spin region

Precisely image the sea quarksSpin-Flavor Decomposition of the Light Quark

Sea

| p = + + + …>u

u

d

u

u

u

u

d

u

u

dd

dMany

models predict

u > 0, d < 0

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

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 !


problems:luminosity, charm cross section, background !


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 down to about 100 m• We understand the fragmentation of charm quarks ()• We can control the contributions of resolved photons• We can calculate higher order QCD corrections ()


Precise determination

of G/G for 0.003 < xg < 0.4

at common Q2 of 10 GeV2

Polarized gluon distribution vs QPolarized gluon distribution vs Q22

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!!!

Holy Grail: excellentdetermination of s(Q2)

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


Antje Bruell, Jlab


• Introduction




Exclusive Processes: Collider Exclusive Processes: Collider EnergiesEnergies

Exclusive Processes: EIC Potential and Exclusive Processes: EIC Potential and SimulationsSimulations


Antje Bruell, Jlab


• Introduction





Antje Bruell, Jlab


• Introduction




5 GeV 5 GeV 50 GeV/c 50 GeV/c

(e(e P) P)

Q2=4 GeV2

2= 0.2

P’ tagging required– Exclusivity Resolution

() ≈ 0.3GeV2 without tagging

• Transverse Imaging

Rates and coverage in different Event Topologies

-t (GeV2)

Γ d

σ/d

t (u

b/G

eV2)

-t (GeV2)

Γ d

σ/d

t (u

b/G

eV2)

Detect the neutron Missing mass reconstruction

• Neutron acceptance limits the t-coverage• The missing mass method gives full t-coverage for x<0.2

Assume dp/p=1% (pπ<5 GeV)

Ee=5 GeVEp=50 GeV

0.01<x<0.02 0.02<x<0.05 0.05<x<0.1

10<Q2<15

15<Q2<2035<Q2<40

10<Q2<1515<Q2<20

35<Q2<40

0.05<x<0.1

Assume: 100 days, Luminosity=10E34

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Unpol. DF

Helicity

Transversity

Transversity and friendsTransversity and friends

Sivers function

Boer-Mulders function

q(x)

q(x)

q(x)

⊥Tf1

⊥1h

⊥Lh1

⊥Th1

Tg1

EIC workshop, May 21th 25R.Seidl: Transversity measurements at EIC

R.Seidl: Transversity measurements at EIC 26

EIC workshop

, May 21th

First successful attempt at a global analysis for the transverse SIDIS and First successful attempt at a global analysis for the transverse SIDIS and the BELLE Collins datathe BELLE Collins data

HERMES AUT p data

COMPASS AUT d data

Belle e+ e- Collins data

Kretzer FF

First extraction of transversity (up to a sign)

Anselmino et al: hep-ex 0701006

What can ne expected at EIC?What can ne expected at EIC? Larger x range

measured b y existing experimentsCOMPASS ends at ~

0.01, go lower by almost one order of magnitude, but asymmetries become small

Have some overlap at intermediate x to test evolution of Collins function and higher twist but at higher Q2

EIC workshop, May 21th R.Seidl: Transversity measurements at EIC 27


Antje Bruell, Jlab


• Introduction





Antje Bruell, Jlab


• Introduction




Sivers effect: Kaon electroproduction

•At small x of EIC Kaon relative rates higher, making it ideal place to study the Sivers asymmetry in Kaon production (in particular K-). •Combination with CLAS12 data will provide almost complete x-range.

EIC

CLAS12

ELIC

Vanish like 1/pT (Yuan)

Correlation between Transverse Spin and Momentum of Quarks in

Unpolarized TargetAll Projected Data

Perturbatively Calculable at Large pT

Summary

EIC is the ideal machine to provide the final answers on the structure of the proton, especially in the region where ea quarks and gluons dominate

It will allow to :

• measure precisely the gluon distribution at low x and moderate Q2• determine the polarized sea quark distributions in the nucleon • map out the polarized gluon distribution in the nucleon• perform a precision test of the Bjorken Sum Rule ---> s• do gluon “tomography” via exclusive processes• determine transverse spin effects and orbital momenta• provide a understanding of the fragmentation process

• + investigate the low x phyiscs of saturation in the nucleus

World Data on F2p Structure Function

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


Antje Bruell, Jlab


• Introduction





Antje Bruell, Jlab


• Introduction




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

EIC0.003 < x < 0.5

uncertainty in xxg g typically < typically <

0.01 !!!0.01 !!!

EIC

Documents

Spin Physics with an Electron-Ion-Collider