Spin Physics with eRHICSpin Physics with eRHIC

Abhay DeshpandeRIKEN BNL Research Center at BNL

Spin-2003Spin-2003XXthth Workshop on High Energy Spin Physics Workshop on High Energy Spin Physics

Dubna, September 16-20, 2003Dubna, September 16-20, 2003

Spin 2003, Dubna 2

Some spin & Low x-high QSome spin & Low x-high Q2 2 surprises…surprises…• Stern & Gehrlach (1921) Space quantization associated with direction• Goudschmidt & Ulhenbeck (1926): Atomic fine structure & electron spin magnetic moment• Stern (1933) Proton anomalous magnetic moment 2.79 N • Kusch(1947) Electron anomalous • magnetic moment 1.001190

• Prescott & Yale-SLAC Collaboration (1978) EW interference in polarized e-d DIS, parity non-conservation• European Muon Collaboration (1988/9) European Muon Collaboration (1988/9) Spin Crisis/PuzzleSpin Crisis/Puzzle• Transverse single spin asymmetries: E704, AGS pp scattering, HERMES (1990s)

RHIC Spin (2001) >> single spin neutron production(PHENIX) >> pion production (STAR) at 200 GeV Sqrt(S)

• Elastic e-p scattering at SLAC (1950s) Q2 ~ 1 GeV2 Finite size of the proton

• Inelastic e-p scattering at SLAC (1960s) Q2 > 1 GeV2 Parton structure of the proton

• Inelastic mu-p scattering off p/d/N at CERN (1980s) Q2 > 1 GeV2 Unpolarized EMC effect, nuclear shadowing?

• Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV2

Unexpected rise of F2 at low x Diffraction in e-p Saturation(??)

A facility that does both would be ideal….

Spin 2003, Dubna 3

Our knowledge of structure functionsOur knowledge of structure functions

F2

g1

Q2 (GeV2) Q2 (GeV2)10510 1021 10103

Spin 2003, Dubna 4

Deep Inelastic ScatteringDeep Inelastic Scattering

•Observe scattered electron/muon & hadrons in current jets•Observe spectator or remnant jet >> suitably designed detector…

[1]

[3]

[2]

[1]+[2]+[3] [3] exclusive [1]+[2] [2] semi-inclusive [1] [1] inclusive

Lumi

Spin 2003, Dubna 5

Why Collider in the Future?Why Collider in the Future?• Past polarized DIS experiments: in fixed target mode• Collider has distinct advantages --- Confirmed at HERA

• Better angular separation between scattered lepton & nuclear fragments

Better resolution of electromagnetic probe Recognition of rapidity gap events (recent diffractive physics)• Better measurement of nuclear fragments• Higher center of mass (CoM) energies reachable

• Tricky integration of beam pipe – interaction region -- detector

Spin 2003, Dubna 6

Proposals under considerationProposals under consideration

eRHIC at BNLeRHIC at BNLA high energy, high intensity polarized electron/positron

beam facility at BNL to collide with the existing RHIC heavy ion and polarized proton beam would

significantly enhance RHIC’s ability to probe fundamental and universal aspects of QCD

JLab Upgrade II: CEBAF II/ELICJLab Upgrade II: CEBAF II/ELICAn Electron-Light-Ion-Collider or/and a 25 GeV Fixed Target

FacilityCEBAF II/ELIC will address the question of precision

measurements of nucleon spin, including the issues related to generalized parton distributions

with its large luminosities. The collider & fixed target facility will cover complementary x-Q2 ranges

Spin 2003, Dubna 7

eRHIC vs. Other DIS Facilities (I)eRHIC vs. Other DIS Facilities (I)

eRHIC

DIS

• New kinematic region

• Ee = 5-10 GeV• Ep = 30 – 250 GeV• Sqrt(s) = ~25 – 100 GeV

• Kinematic reach of eRHIC x = 10-4 ~0.7 (Q2 > 1 GeV2) Q2 = 0 104 GeV

• Polarized e, p and light ion beams -- ~70%

• Heavy ion beams of ALL elements!

• High Luminosity L > (at least) 1033

up to1034 ?? cm-2 sec-1

Spin 2003, Dubna 8

eRHIC & ELIC vs. Other DIS eRHIC & ELIC vs. Other DIS FacilitiesFacilities

eRHIC:eRHIC:>> Variable beam energy>> p U hadron beams>> Light Ion polarization>> Large Luminosity>> Huge Kinematic Huge Kinematic

reachreach

ELIC:ELIC:>> Variable beam energy>> Light Ion polarization>> Huge Luminosity

TESLA-N

eRHIC

ELIC-Jlab

Spin 2003, Dubna 9

Scientific Frontiers Open to Scientific Frontiers Open to eRHICeRHIC

• Nucleon Structure: polarized & unpolarized e-p/n scattering -- Role of quarks and gluons in the nucleon >> Unpolarized quark & gluon distributions, confinement in nucleons >> Spin structure: polarized quark & gluon distributions -- Correlation between partons >> hard exclusive processes leading to Generalized Parton Distributions (GPD’s)

• Meson Structure: -- Mesons are goldstone bosons and play a fundamental role in QCD

• Nuclear structure: unpolarized e-A scattering -- Role of quarks and gluons in nuclei, confinement in nuclei -- e-p vs. e-A physics in comparison and variability of A: from dU

• Hadronization in nucleons and nuclei & effect of nuclear media -- How do partons knocked out of nucleon in DIS evolve in to colorless hadrons?

• Partonic matter under extreme conditions -- e-A vs. e-p scattering; study as a function of A

ELIC

ELIC

Spin 2003, Dubna 10

Unpolarized DIS e-p at eRHICUnpolarized DIS e-p at eRHIC• Large(r) kinematic region already covered at HERA but

additional studies at eRHIC are possible & desirable• Uniqueness of eRHIC: high luminosity, variable Sqrt(s), He3

beam, improved detector & interaction region• Will enable precision physics: -- He3 beams neutron structure d/u as x0, dbar(x)-ubar(d) -- precision measurement of S(Q2) -- precision photo-production physics -- precision gluon distribution in x=0.001 to x=0.6 -- slopes in dF2/dlnQ2

-- flavor separation (charm and strangeness) -- exclusive reaction measurements -- nuclear fragmentation region measurements

[1][1][1][1][1][2][2,3][2,3]Luminosity

Requirement

Spin 2003, Dubna 11

Polarized DIS at eRHICPolarized DIS at eRHIC• Spin structure functions g1 (p,n) at low x, high precision -- g1(p-n): Bjorken Spin sum rule better than 1% accuracy• Polarized gluon distribution function G(x,Q2) -- at least three different experimental methods• Precision measurement of S(Q2) from g1 scaling violations• Polarized s.f. of the photon from photo-production• Electroweak s. f. g5 via W+/- production• Flavor separation of PDFs through semi-inclusive DIS• Deeply Virtual Compton Scattering (DVCS) >> Gerneralized Parton Distributions (GPDs) • Transversity• Drell-Hern-Gerasimov spin sum rule test at high • Target/Current fragmentation studies• … etc….

[1]

[1]

[1][1][1,2][1][1,2][3][1][1][2,3]

LuminosityRequirement

Spin 2003, Dubna 12

Proton g1(x,Q2) low x eRHIC

eRHIC 250 x 10 GeVLuminosity = ~85 inv. pb/day

Fixed target experiments1989 – 1999 Data

10 days of eRHIC runAssume: 70% Machine Eff. 70% Detector Eff.

Studies included statistical error & detector smearing to confirm that asymmetries are measurable. No present or future approved

experiment will be able to make this measurement

AD, V.W.Hughes

Spin 2003, Dubna 13

Low x measurement of gLow x measurement of g11 of of NeutronNeutron

• With polarized He3

• ~ 2 weeks of data at eRHIC

• Compared with SMC(past) & possible HERA data

• If combined with g1 of proton If combined with g1 of proton results in Bjorken sum rule results in Bjorken sum rule test of better than 1-2% within test of better than 1-2% within a couple of months of runninga couple of months of running

EIC 1 inv.fb

AD, V.W.Hughes

Spin 2003, Dubna 14

Polarized Gluon Measurement at Polarized Gluon Measurement at eRHICeRHIC

• This is the hottest of the experimental measurements being pursued at various experimental facilities:

-- HERMES/DESY, COMPASS/CERN, RHIC-Spin/BNL & E159/E160 at SLAC -- Reliability from applicability of pQCD without doubt leaves only RHIC• Measurements at eRHIC will be complimentary with RHIC

• Deep Inelastic Scattering kinematics at eRHIC -- Scaling violations (pQCD analysis at NLO) of g1 First moment of First moment of GG -- (2+1) jet production in photon-gluon-fusion process -- 2-high pT hadron production in PGF • Photo-production (real photon) kinematics at eRHIC -- Single and di-jet production in PGF -- Open charm production in PGF

• ELIC measurements possible but in limited kinematic range and would result in considerable scale dependences in interpretation.

Shape of DG(x)Shape of DG(x)

Spin 2003, Dubna 15

G from Scaling Violations of gG from Scaling Violations of g11

• World data (today) allows a NLO pQCD fit to the scaling violations in g1 resulting in the polarized gluon distribution and its first moment.

• SM collaboration, B. Adeva et al. PRD (1998) 112002 G = 1.0 +/- 1.0 (stat) +/- 0.4 (exp. Syst.) +/- 1.4 (theory)• Theory uncertainty dominated by the lack of knowledge

of the shape of the PDFs in unmeasured low x region where eRHIC data will play a crucial role.

lack of knowledge of the functional form or shape of the gluon pdf

• With approx. 1 week of eRHIC statistical and theoretical uncertainties can be reduced by a factor of 3

-- coupled to better low x knowledge of spin structure -- less dependence on factorization & re-normalization scale in

fits as new data is acquired

AD, V.W.Hughes, J.Lichtenstadt

Spin 2003, Dubna 16

Photon Gluon Fusion at eRHICPhoton Gluon Fusion at eRHIC• “Direct” determination of G -- Di-Jet events: (2+1)-jet events -- High pT hadrons

• High Sqrt(s) at eRHIC -- no theoretical ambiguities

regarding interpretation of data

• Both methods tried at HERA in un-polarized gluon determination & both are successful!

-- NLO calculations exist -- H1 and ZEUS results -- Consistent with scaling violation

F2 results on G

• Scale uncertainties at ELIC large

Signal: PGF

BackgroundQCD Compton

Spin 2003, Dubna 17

Di-Jet events at eRHIC: Analysis at Di-Jet events at eRHIC: Analysis at NLONLO

• Stat. Accuracy for two luminosities

• Detector smearing effects considered

• NLO analysis

• Excellent ability to gain Excellent ability to gain information on the information on the shape of gluon shape of gluon distributiondistribution

• Easy to differentiate different G scenarios: factor 3 improvements in ~2 weeks• If combined with scaling violations of g1: factors of 5 improvements in uncertainties observed in the same time.• Better than 3-5% uncertainty can be expected from eRHIC G program

G. Radel & A. De Roeck,AD, V.W.Hughes,J.Lichtenstadt

Spin 2003, Dubna 18

Di-Jet at eRHIC vs. World Data for Di-Jet at eRHIC vs. World Data for G/GG/G

Good precisionClean measurement in x

range 0.01< x < 0.3Constrains shape of G(x)Polarization in HERA much

more difficult than RHIC.

eRHIC Di-Jet DATA 2fb-1

G from scaling violations > xmin~ 10-5 at HERA > xmin~ 10-4 at eRHIC

G. Radel, A. De Roeck,AD

ELIC

Spin 2003, Dubna 19

Polarized PDFs of the PhotonsPolarized PDFs of the Photons• Photo-production studies with single and di-jet

• Photon Gluon Fusion or Gluon Gluon Fusion (Photon resolves in to its partonic contents)

• Resolved photon asymmetries result in measurements of spin structure of the photon

• Asymmetries sensitive to gluon polarization as well… but we will consider the gluon polarization “a known” quantity!

Direct Photon Resolved Photon

Spin 2003, Dubna 20

Photon Spin Structure at eRHICPhoton Spin Structure at eRHIC• Stat. Accuracy

estimated for 1 fb-1 running (2 weeks at EIC)

• Single and double jet asymmetries

• ZEUS acceptance

• Will resolve photon’s partonic spin contents

Direct Photon Resolved Photon

M. Stratmann, W. VogelsangeRHIC

Spin 2003, Dubna 21

Parity Violating Structure Parity Violating Structure Function gFunction g55

• This is also a test

For eRHIC kinematics

• Experimental signature is a huge asymmetry in detector (neutrino)• Unique measurement• Unpolarized xF3 measurements at HERA in progress• Will access heavy quark distribution in polarized DIS

Spin 2003, Dubna 22

Measurement Accuracy PV gMeasurement Accuracy PV g55 at at eRHICeRHIC

Assumes:1. Input GS Pol. PDfs2. xF3 measured by

then3. 4 fb-1 luminosity

Positrons & Electrons in eRHIC g5(+)

>> reason for keeping the option of positrons in eRHIC

J. Contreras, A. De Roeck

Spin 2003, Dubna 23

Drell Hern Gerasimov Spin Sum Drell Hern Gerasimov Spin Sum RuleRule

• DHG Sum rule:

• At eRHIC range: GeV few TeV

• Although contribution from to

the this sum rule is small, the high n behavior is completely unknown and hence theoretically biased in any present measurements at:

Jefferson Lab., MAMI, BNL

• Inclusive Photo-production measurement

• Using electron tagger in RHIC ring Q2 ~ 10-6 10-2 GeV2 Sqrt(s) ~ 25 85 GeV

S.D.Bass, A. De Roeck,AD

Spin 2003, Dubna 24

DVCS/Vector Meson ProductionDVCS/Vector Meson Production• Hard Exclusive DIS process

• (default) but also vector mesons possible

• Remove a parton & put another back in!

Microsurgery of Baryons!

•Claim: Possible access to skewed or off forward PDFs? Polarized structure: Access to quark orbital angular momentum?

On going theoretical debate… experimental effort just beginning…--A. Sandacz & AD

Spin 2003, Dubna 25

Strange Quark Distributions at Strange Quark Distributions at eRHICeRHIC

• After measuring u & d quark polarized distributions…. Turn to s quark (polarized & otherwise)

• Detector with good Particle ID: pion/kaon separation

• Upper Left: statistical errors for kaon related asymmetries shown with A1 inclusive

• Left: Accuracy of strange quark distribution function measurements possible with eRHIC and HERMES (2003-05) and some theoretical curves on expectations.

U. Stoesslein, E. Kinney

Spin 2003, Dubna 26

Highlights of e-A Physics at Highlights of e-A Physics at eRHICeRHIC

• Study of e-A physics in Collider mode for the first time• QCD in a different environment

• Clarify & reinforce physics studied so far in fixed target e-A & -A experiments including target fragmentation

QCD in: x > [1/(2mNRN) ] ~ 0.1 (high x) QCD in: [1/(2mNRA)] < x < [1/(2mNRN)] ~ 0.1 (medium x) Quark/Gluon shadowing Nuclear medium dependence of hadronization

• …. And extend in to a very low x region to explore: saturation effects or high density partonic matter also called the

Color Glass Condensate (CGC) QCD in: x < [1/(2mNRA)] ~ 0.01 (low x)

See: www.bnl.gov/eic for further details

Spin 2003, Dubna 27

Using Nuclei to Increase the Gluon Density

• Parton density at low x rises as• Unitarity saturation at some• In a nucleus, there is a large enhancement of the parton densities / unit area

compared to a nucleon

•

ExampleQ2=4 (GeV/c)2

< 0.3 A = 200

XXepep=10=10-7-7 for for X XeAeA = 10 = 10-4-4

1x2

sQ

2 1 13 3

2

//

6 for 200

A A A

N N N

G R GA AG r AG

A

22

11

343

eA sep s

X Qx Q

A

Spin 2003, Dubna 28

A Detector for eRHIC A 4 Detector• Scattered electrons to measure kinematics of DIS• Scattered electrons at small (~zero degrees) to tag photo production• Central hadronic final state for kinematics, jet measurements, quark

flavor tagging, fragmentation studies, particle ID• Central hard photon and particle/vector detection (DVCS)• ~Zero angle photon measurement to control radiative corrections

and in e-A physics to tag nuclear de-excitations• Missing ET for neutrino final states (W decays)• Forward tagging for 1) nuclear fragments, 2) diffractive physics

• “At least one” second detector could be “rolled” in from time to time….

…under consideration

• eRHIC will provide: 1) Variable beam energies 2) different hadronic species, some of them polarization, 3) high luminosity

Spin 2003, Dubna 29

Moving Towards eRHIC….Moving Towards eRHIC….• September 2001: EIC grew out of joining of two communities: 1) polarized eRHIC (ep and eA at RHIC) BNL, UCLA, YALE and people from DESY & CERN 2) Electron Poliarized Ion Collider (EPIC) 3-5 GeV e X 30-50 GeV polarized light ions Colorado, IUCF, MIT/Bates, HERMES collaborators

• February 2002: White paper submitted to NSAC Long Range Planning Review Received enthusiastic support as a next R&D project

• Steering Committee: 8 members, one each from BNL, IUCF, LANL, LBL, MIT, UIUC, Caltech, JLAB, Kyoto U.+ Contact person (AD)

• ~20 (~13 US + ~7 non-US) Institutes, ~100 physicists + ~40 ~20 (~13 US + ~7 non-US) Institutes, ~100 physicists + ~40 accelerator physicists… accelerator physicists… Recent interest from HERARecent interest from HERA

• See for more details: EIC/eRHIC Web-page at “http://www.bnl.gov/eic”

• Subgroups: Accelerator WG, Physics WG + Detector WGSubgroups: Accelerator WG, Physics WG + Detector WG • E-mails: BNL based self-registered email servers… list yourselves!

Spin 2003, Dubna 30

Present Lay Out of the Collider at Present Lay Out of the Collider at BNLBNL• Proposed by BINP & MIT/Bates + BNL with input from DESY• E-ring is ¼ of RHIC ring• Collisions in one interaction region >> Multiple detectors under >> Multiple detectors under

considerationconsideration• Collision energies Ee=5-10 GeV• Injection linac 2-10 GeV• Lattice based on “superbend” magnets• Self polarization using Sokolov Ternov Effect:

(14-16 min pol. Time)• IP12, IP2 and IP4 are possible IP12, IP2 and IP4 are possible

candidates for collision pointscandidates for collision points

p

e2GeV (10GeV)

2-10 GeV

IP12

IP2

IP4

IP6

IP8

IP10

RHIC

OTHER : Ring with 6 IPS, Linac-Ring, Linac-Re-circulating ring

e-cooling

NSAC Subcommittee Evaluation March 03: 1 Science, 2 for ReadinessNSAC Subcommittee Evaluation March 03: 1 Science, 2 for Readiness

R&D needed & started

Spin 2003, Dubna 31

ELIC vs. Other DIS Facilities (I)ELIC vs. Other DIS Facilities (I)• Jlab: ELIC High luminosity

measurements: EXCLUSIVE measurements and associated physics at intermediate x & Q2

• Ee = 3-5 (7) GeV• Ep = 30 – 100 (150) GeV• Sqrt(s) = ~20 – 45 (65 ??) GeV

• Kinematic reach of ELIC x = 10-3 ~0.8 (Q2 > 1 GeV2) Q2 = 0 6 x102 GeV

• Polarized e, p, light ion beams -- 70% polarization

• High Luminosity L > 1033 up to1035 cm-2 sec-1

DIS

ELICeRHIC

Spin 2003, Dubna 32

JLAB/ELIC LayoutIon Source RFQDTL CCL

IR IR

Beam Dump

Snake

Snake

CEBAF with Energy Recovery

5 GeV electrons 50-100 GeV light ions

Solenoid

Injector

One accelerating & one decelerating pass through CEBAFNSAC Subcommittee Evaluation March 03: 1 Science, 3 for ReadinessNSAC Subcommittee Evaluation March 03: 1 Science, 3 for Readiness

L. Merminga/R. Ent

Spin 2003, Dubna 33

JLAB/ELIC Aggressive R& D Launched• Conceptual development: >> Circulator ring to reduce the high current polarized photo-

injector and ERL requirement >> Highest luminosity limits• Analysis and simulations: >> electron cooling and short bunches >> beam-beam physics >> energy recovery linac physics

• Experimental research effort: >> CEBAF-ERL to address ERL issues in large scale systems >> JLAB FEL (10mA), Cornell/JLAB Prototypes (100 mA), BNL BNL

Cooling Prototype (100mA) to address high current ERL Cooling Prototype (100mA) to address high current ERL issuesissues.

L. Merminga

Spin 2003, Dubna 34

A possible time line for eRHIC…A possible time line for eRHIC…“Predictions are very difficult to make, especially when they are about the

future” --- Albert E.

• “Absolutely Central to the field…” NSAC 2001-2 Long Range Planning document summary; high on R&D recommendation projects.• Highest possible scientific recommendation from NSAC Subcommittee February/March 2003, Readiness Index 2 ( JLAB-ELIC 3)

• eRHIC: Zero-th Design Report (Physics + Accelerator Lattice) Requested by BNL Management: January 2004 e-cooling R&D money started (with RHIC II) some DOE+some BNL internalFOLLOWING THIS TIME LINE FOR GETTING READY: (FUTURE)FOLLOWING THIS TIME LINE FOR GETTING READY: (FUTURE)• Expected “formal” approval 2005-6 Long Range Review (Ready CD0)• Detector R&D money could start for hardware 2007 (CD1)• Ring, IR, Detector design(s) 2008(CD2)• Final Design Ready 2009 (CD3) begin construction • ~3/5 years for staged detector and IR construction without

interfering with the RHIC running• First collisions (2011)???

Spin 2003, Dubna 35

Luminosity Comparison TableL. Merminga(Jlab)) & V. Ptiitsyn(BNL)

Parameter

Units Design

e- IonsEnergy GeV 5 50/10

0ElectronCooling

- - Yes

Circulator Ring

- Yes -

Luminosity

cm-2 sec-1

6x1034 / 1x1035

Iave A 2.5 2.5fc MHz 1500

Parameters e-ring

ion ring

p Au

C, m 1022 3833

E, GeV 5–10 250 100/u

nb 96 360

Nb 11011 11011 1109

I, Arms,mmrad*, cm*, mm

0.4545–25100.07–0.050.05

0.4517–9

270.07–0.05

0.005L, cm-2 s-1   (0.5-

0.9)1033(0.5-

0.9)1031

JLAB/ELIC eRHIC

Spin 2003, Dubna 36

Scale Dependence: NLO/LO K factorM. Stratmann & W. Vogelsang