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Spin Physics with eRHIC

Spin Physics with eRHIC. Abhay Deshpande RIKEN BNL Research Center at BNL. Spin-2003 X th Workshop on High Energy Spin Physics Dubna, September 16-20, 2003. Some spin & Low x-high Q 2 surprises…. Stern & Gehrlach (1921) Space quantization associated with direction

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Spin Physics with eRHIC

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  1. Spin Physics with eRHIC Abhay Deshpande RIKEN BNL Research Center at BNL Spin-2003 Xth Workshop on High Energy Spin Physics Dubna, September 16-20, 2003

  2. Some spin & Low x-high Q2 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 mN • Kusch(1947) Electron anomalous • magnetic moment 1.00119m0 • Prescott & Yale-SLAC Collaboration (1978) EW interference in polarized e-d DIS, parity non-conservation • European Muon Collaboration (1988/9) Spin 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….

  3. Our knowledge of structure functions g1 F2 105 10 103 10 1 102 Q2 (GeV2) Q2 (GeV2)

  4. Deep Inelastic Scattering [1] [2] [3] • Observe scattered electron/muon & hadrons in current jets • Observe spectator or remnant jet • >> suitably designed detector… Lumi [1]+[2]+[3]  [3] exclusive [1]+[2]  [2] semi-inclusive [1]  [1] inclusive

  5. 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

  6. Proposals under consideration eRHIC at BNL A 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/ELIC An Electron-Light-Ion-Collider or/and a 25 GeV Fixed Target Facility CEBAF 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

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

  8. eRHIC & ELIC vs. Other DIS Facilities eRHIC: >> Variable beam energy >> p  U hadron beams >> Light Ion polarization >> Large Luminosity >> Huge Kinematic reach ELIC: >> Variable beam energy >> Light Ion polarization >> Huge Luminosity ELIC-Jlab TESLA-N eRHIC

  9. Scientific Frontiers Open to eRHIC • 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 dU • 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

  10. Unpolarized 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 x0, dbar(x)-ubar(d) -- precision measurement of aS(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

  11. Polarized DIS at eRHIC [1] [1] [1] [1] [1,2] [1] [1,2] [3] [1] [1] [2,3] • 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 DG(x,Q2) -- at least three different experimental methods • Precision measurement of aS(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 n • Target/Current fragmentation studies • … etc…. Luminosity Requirement

  12. AD, V.W.Hughes Proton g1(x,Q2) low x eRHIC Fixed target experiments 1989 – 1999 Data eRHIC 250 x 10 GeV Luminosity = ~85 inv. pb/day 10 days of eRHIC run Assume: 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

  13. AD, V.W.Hughes Low x measurement of g1 of Neutron • With polarized He3 • ~ 2 weeks of data at eRHIC • Compared with SMC(past) & possible HERA data • If combined with g1 of proton results in Bjorken sum rule test of better than 1-2% within a couple of months of running EIC 1 inv.fb

  14. Polarized Gluon Measurement at eRHIC • 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 DG -- (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)

  15. AD, V.W.Hughes, J.Lichtenstadt DG from Scaling Violations of g1 • 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 DG = 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

  16. Photon Gluon Fusion at eRHIC • “Direct” determination of DG -- 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 Background QCD Compton

  17. G. Radel & A. De Roeck, AD, V.W.Hughes,J.Lichtenstadt Di-Jet events at eRHIC: Analysis at NLO • Stat. Accuracy for two luminosities • Detector smearing effects considered • NLO analysis • Excellent ability to gain information on the shape of gluon distribution • Easy to differentiate different DG 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 DG program

  18. G. Radel, A. De Roeck,AD Di-Jet at eRHIC vs. World Data for DG/G Good precision Clean measurement in x range 0.01< x < 0.3 Constrains shape of DG(x) Polarization in HERA much more difficult than RHIC. eRHIC Di-Jet DATA 2fb-1 ELIC DG from scaling violations > xmin~ 10-5 at HERA > xmin~ 10-4 at eRHIC

  19. Polarized 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

  20. eRHIC M. Stratmann, W. Vogelsang Photon 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

  21. Parity Violating Structure Function g5 • This is also a test • 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 For eRHIC kinematics

  22. J. Contreras, A. De Roeck Measurement Accuracy PV g5 at eRHIC Assumes: • Input GS Pol. PDfs • xF3 measured by then • 4 fb-1 luminosity Positrons & Electrons in eRHIC  g5(+) >> reason for keeping the option of positrons in eRHIC

  23. S.D.Bass, A. De Roeck,AD Drell Hern Gerasimov Spin Sum Rule • 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

  24. DVCS/Vector Meson Production • Hard Exclusive DIS process • g (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

  25. U. Stoesslein, E. Kinney Strange Quark Distributions at eRHIC • 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.

  26. Highlights of e-A Physics at eRHIC • 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 & m-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

  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 Example Q2=4 (GeV/c)2 < 0.3 A = 200 Xep=10-7 for  XeA = 10-4

  28. A Detector for eRHIC  A 4p 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

  29. 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 accelerator physicists… Recent interest from HERA • See for more details: EIC/eRHIC Web-page at“http://www.bnl.gov/eic” • Subgroups: Accelerator WG, Physics WG + Detector WG • E-mails: BNL based self-registered email servers… list yourselves!

  30. 2GeV (10GeV) e 2-10 GeV IP12 p IP10 IP2 RHIC IP8 IP4 IP6 Present Lay Out of the Collider at BNL • 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 consideration • 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 candidates for collision points e-cooling R&D needed & started OTHER :Ring with 6 IPS, Linac-Ring, Linac-Re-circulating ring NSAC Subcommittee Evaluation March 03: 1 Science, 2 for Readiness

  31. 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 to1035cm-2 sec-1 eRHIC ELIC DIS

  32. L. Merminga/R. Ent Ion Source RFQ DTL Snake CCL IR IR Snake Solenoid 5 GeVelectrons 50-100 GeV light ions Injector CEBAF with Energy Recovery Beam Dump JLAB/ELIC Layout One accelerating & one decelerating pass through CEBAF NSAC Subcommittee Evaluation March 03: 1 Science, 3 for Readiness

  33. L. Merminga 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 Cooling Prototype (100mA) to address high current ERL issues.

  34. 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 internal 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)???

  35. Parameters e-ring ion ring p Au C, m 1022 3833 E, GeV 5–10 250 100/u nb 96 360 Nb 11011 11011 1109 I, A erms,mmrad b*, cm s*, mm x 0.45 45–25 10 0.07–0.05 0.05 0.45 17–9 27 0.07–0.05 0.005 L, cm-2 s-1 (0.5-0.9)1033 (0.5-0.9)1031 L. Merminga(Jlab)) & V. Ptiitsyn(BNL) Luminosity Comparison Table JLAB/ELIC eRHIC

  36. M. Stratmann & W. Vogelsang Scale Dependence: NLO/LO K factor

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