Physics & Status of eRHICPhysics & Status of eRHIC

Abhay Deshpande

Stony Brook University

RIKEN BNL Research Center

Workshop on Hadron Structure & SpectroscopyWorkshop on Hadron Structure & SpectroscopyCompass 2004, ParisCompass 2004, Paris

March 3, 2004March 3, 2004

A

Compass2004 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….

Compass2004 3

Deep Inelastic ScatteringDeep Inelastic Scattering

•Observe scattered electron/muon [1]•Observe spectator or remnant jet [1]+[2]•Obersve current jet as well [1]+[2]+[3] >> suitably designed detector…

[1]

[3]

[2]

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

Lumi

Compass2004 4

Why Collider in Future?Why Collider in Future?• Past polarized DIS experiments: in fixed target mode

– Assuming highly polarized beams…. There are no “dilution factors” as in polarized targets of fixed target experiments

• Collider has other 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

Compass2004 5

BRAHMS & PP2PP (p)

STAR (p)

PHENIX (p)

AGS

LINACBOOSTER

Pol. Proton Source500 A, 300 s

GeVs

L

50050

onPolarizati%70

cms102 2132max

<<

×= −−

Spin Rotators

Partial Siberian Snake

Siberian Snakes

200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles

RHIC pC Polarimeters

Absolute Polarimeter (H jet)

2 1011 Pol. Protons / Bunch = 20 mm mrad

RHIC accelerates heavy ions to 100 GeV/A and polarized protons to 250 GeV

RRelativistic HHeavy IIon CCollider

L. Bland, this Conferences

An ideal machine for studying QCD!

Compass2004 6

Proposal under considerationProposal 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

•10 GeV linac + e-ring + RHIC •e-ring NOT in RHIC tunnel• Other options: linac+RHIC• Nominal 10 GeV polarized electron/positron beams: -- Collisions with 5 GeV e • One IR considered so far, but plan > 1 detectors

Additional detectors and IRs not ruled out

Compass2004 7

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

eRHIC

DIS

• 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 ~70%• Polarized light ion beams: He

• Un-polarized heavy ion beams of ALL elements up to Uranium with EBIS source

• High Luminosity L ~ 1033 cm-2 sec-1

Compass2004 8

eRHIC vs. Other DIS FacilitieseRHIC vs. Other DIS Facilities

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

reachreach

ELIC at Jlab:ELIC at Jlab:(Electron-Light (Electron-Light

Ion Collider)Ion Collider)>> Variable beam energy>> p, d & He polarization>> Huge Luminosity

TESLA-N

eRHIC

ELIC-Jlab

Compass2004 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: un-polarized 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

Compass2004 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 (Transition from QCD --> pQCD) -- flavor separation (charm and strangeness) -- exclusive reaction measurements -- nuclear fragmentation region measurements

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

LuminosityRequirement

Compass2004 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 1-2% 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

Compass2004 12

Proton g1(x,Q2) low x eRHIC

eRHIC 250 x 10 GeV

Luminosity = ~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

Compass2004 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)– If HERA were to be polarized (now

hypothetical)

• 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

BNL/Stony Brook, Caltech, MIT effort for R&D on He beams near future

Compass2004 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

• Measurements at eRHIC will be complimentary with RHIC and a significant next step compared to the fixed target DIS experiments

• 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

Shape of Shape of G(x)G(x)

Compass2004 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.– (Recall: R. L. Jaffe’s talk)

• 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

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

– Factorization and renormalization scales (F & R) (G. Ridolfi’s talk)

• 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 function: (measurements to x=10-4). -- less dependence on factorization & re-normalization scale in fits as new

data is acquired

AD, V.W.Hughes, J.Lichtenstadt

Compass2004 16

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

In fixed tgt exp: scale uncertainties large

• High Sqrt(s) =100 GeV, 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

Signal: PGF

BackgroundQCD Compton

Compass2004 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 Excellent ability to gain information on gain information on the shape of gluon the 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

Compass2004 18

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

Compass2004 19

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

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

• Single and double jet asymmetries

• ZEUS acceptance

• Will resolve photon’s partonic spin contents

Direct Photon Resolved Photon

M. Stratmann, W. Vogelsang

Compass2004 20

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

Compass2004 21

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

Compass2004 22

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

Compass2004 23

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 et al.

Compass2004 24

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

Compass2004 25

DIS in Nuclei is Different! DIS in Nuclei is Different!

Regions of:• Fermi smearing• EMC effect• Enhancement• Shadowing• Saturation?

Regions of shadowing and saturation mostly around Q2 ~1 GeV2

An e-A collision at eRHIC can be at significantly higher Q2

F2D/F2A

Low Q2!

E665, NMC, SLAC Experiments

Compass2004 26

The Saturation Region…The Saturation Region…

• As parton densities grow, standard pQCD break down.

• Even though coupling is weak, physics may be non-perturbative due to high field strengths generated by large number of partons.

• A new state of matter???

An e-A collider/detector experiment with high luminosity and capability to have different species of nuclei in the same detector would be ideal… Need the eRHIC at BNL

Compass2004 27

A Color Glass Condensate??A Color Glass Condensate??

• At small x, partons are rapidly fluctuating gluons interacting weakly with each other, but still strongly coupled to the high x parton color charges which act as random static sources of COLOR charge

Analogous to spin GLASS systems in condensed matter: a disordered spin state coupled to random magnetic impurities

• Gluon occupation number large; being bosons they can occupy the same state to form a CONDENSATE

Bose Einstein condensate leads to a huge over population of ground states

• A new “state matter”(??): Color Glass Condensate (CGC) at high energy density would display dramatically different, yet simple properties of glassy condensates

E. Iancu, L. McLerran,R. Venugopalan, et al.

Compass2004 28

Interaction Region Design….early ideas…Interaction Region Design….early ideas…

B. Parker’s (BNL) ProposalBudker/MIT Proposal

Compass2004 29

A Possible Lay Out of the Collider at A Possible Lay Out of the Collider at BNLBNL• Proposed by BNL, MIT/Bates + BNL +

DESY• E-ring is 1/3 the size of RHIC ring• Collision energies Ee=5-10 GeV• Injection linac 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• Two detector designs under Two detector designs under

considerationconsideration

p

e10GeV

5-10 GeV

IP12

IP2

IP4

IP6

IP8

IP10

RHIC

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

e-cooling R&D needed & started

Compass2004 30

Where do electrons and quarks go?

pq,e

10 GeV x 250 GeV1770 1600

scattered electron scattered quark

10 GeV

5 GeV900

5 GeV

100

Compass2004 31

Electron kinematics… some details…

scattered electron

10 GeV x 250 GeV

At HERA:Electron method: x/x ~E/(y.E) Limited by calorimeter resolutionHadron method: Limited by noise in calorimeter (E_noise/E_beam)

At eRHIC:Measure electron energy with tracker (< 20 GeV, large kin. region) p/p ~ 0.005-0.0001 (2-4T Magnet)Design low noise calorimeter Crystal or SPACAL

Compass2004 32

Electron, Quark Kinematics

scattered electron scattered quark

5 GeV x 50 GeVpq,e

Compass2004 33

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

• Presently interest in at least one other specialized detector … how to?– under consideration

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

Compass2004 34

Detector Design (I)… others expectedDetector Design (I)… others expected

Whitepaper 2001/2

Compass2004 35

Detector Design (I)… others expectedDetector Design (I)… others expected

Whitepaper 2001/2

Compass2004 36

Detector Design II --- HERA like…Hadronic Calorimeter

EM Calorimeter

Outer trackers

Inner trackers

5m

Nearest beam elements 1m

2.5m

Compass2004 37

Detector Design II: HERA like…+ PID

AEROGEL

HCAL

P/Ae

A. Deshpande, N. Smirnov

EMCal

TOF

Outer trackers

Innertrackers

Beam elements

Solenoid

A HERA likeDetector with dedicated PID:>>Time of flight>>Aerogel Ckov

5m

7m

Compass2004 38

Moving Towards eRHIC….Moving Towards eRHIC….• September 2001: eRHIC 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, US-HERMES collaborators

• Steering Committee: 8 members, one each from BNL, IUCF, LANL,MIT, UIUC, Caltech, JLAB, Kyoto U.+ Stony Brook

• ~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 HERA (low x, Recent interest from HERA (low x, low Q2 physics)low Q2 physics)

• 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!

Compass2004 39

Present Activities• Accelerator & IR Design WG:

– BNL-MIT/Bates collaboration on e-ring design

– BNL-JLAB collaboration on linac design

– Weekly meetings, monthly video meetings

– Synchroton radiation in IR: focus group BNL, Iowa State U.

– ZDR Ready by February 2004: External Review March04

• Physics & MC WG:– BNL, Colorado U., Jlab, LBL, MIT, UIUC (scientists/faculty+students)

– Meet every three months

– Setup MC generators start studies of physics processes including detector acceptances

– Will iterate with the detector/IR design and provide guidance on the final detector design

• Detector Design: Will be taken up in detail in the coming year– Basic functionality of ZEUS/H1 detectors adjusted for different energy

– Additional acceptances in forward & backward region (low Q2, low x)

– Specialized particle ID for lower center of mass energy physics

– Integration of electron beam polarimetry in the IR

– Selection of detector technology: coupled to the interests of various institutions

Meetings 2004: January (BNL), March 15-17 at Jlab (EIC2004), Fall 2004(?), December(BNL)

Compass2004 40

A possible time line for eRHIC…A possible time line for eRHIC…

• “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• One of the 28 must-do science projects by US DoE in the next 20

years

• eRHIC: Zero-th Design Report (Physics + Accelerator Lattice) Requested by BNL Management: Ready February 2004. e-cooling R&D money started (with RHIC II) some DOE+some BNL internal

FOLLOWING 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 design studies could start for hardware 2008 (CD1) (DoE: now?)• Ring, IR, Detector design(s) ready: 2009(CD2)• Final Design Ready 2010 (CD3) begin construction • ~2--> 5 years for staged detector and IR construction without

interfering with the RHIC running• First collisions with limited detector (2012/13)???