Physics & Status of eRHIC

1. Physics & Status of eRHIC A Abhay Deshpande Stony Brook University RIKEN BNL Research Center Workshop on Hadron Structure & Spectroscopy Compass 2004, Paris March 3, 2004

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

4. 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

5. L. Bland, this Conferences BRAHMS & PP2PP (p) PHENIX (p) STAR (p) Relativistic Heavy Ion Collider RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Spin Rotators 2  1011 Pol. Protons / Bunch e = 20 p mm mrad Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles An ideal machine for studying QCD! RHIC accelerates heavy ions to 100 GeV/A and polarized protons to 250 GeV

6. Proposal 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 • 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

7. eRHIC vs. Other DIS Facilities (I) • 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 ~ 1033cm-2 sec-1 eRHIC DIS

8. eRHIC vs. Other DIS Facilities eRHIC: >> Variable beam energy >> p  U hadron beams >> Light Ion polarization >> Large Luminosity >> Huge Kinematic reach ELIC at Jlab: (Electron-Light Ion Collider) >> Variable beam energy >> p, d & He 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: 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 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

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 (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] 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 1-2% 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) • If HERA were to be polarized (now hypothetical) • 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 BNL/Stony Brook, Caltech, MIT effort for R&D on He beams near future

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 • 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 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 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. • (Recall: R. L. Jaffe’s talk) • 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 • unknown shape of the PDFs in unmeasured low x region where eRHIC data will play a crucial role • Factorization and renormalization scales (mF & mR) (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

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

19. M. Stratmann, W. Vogelsang Photon 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

20. 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

21. 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

22. 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.

23. 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 et al.

24. 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

25. E665, NMC, SLAC Experiments 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!

26. 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

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

28. Interaction Region Design….early ideas… Budker/MIT Proposal B. Parker’s (BNL) Proposal

29. 10GeV e 5-10 GeV IP12 p IP10 IP2 RHIC IP8 IP4 IP6 A Possible Lay Out of the Collider at BNL • 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 candidates for collision points • Two detector designs under consideration e-cooling R&D needed & started OTHER :Ring with 6 IPS, Linac-Ring, Linac-Re-circulating ring

30. Where do electrons and quarks go? q,e  p 10 GeV x 250 GeV 1770 1600 100 10 GeV 5 GeV 5 GeV 900 scattered electron scattered quark

31. Electron kinematics… some details… 10 GeV x 250 GeV • At HERA: • Electron method: Dx/x ~DE/(y.E) Limited by calorimeter resolution Hadron method: Limited by noise in calorimeter (E_noise/E_beam) At eRHIC: • Measure electron energy with tracker (< 20 GeV, large kin. region) Dp/p ~ 0.005-0.0001 (2-4T Magnet) Design low noise calorimeter Crystal or SPACAL scattered electron

32. Electron, Quark Kinematics q,e  5 GeV x 50 GeV p scattered electron scattered quark

33. 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 • 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

34. Whitepaper 2001/2 Detector Design (I)… others expected

35. Whitepaper 2001/2 Detector Design (I)… others expected

36. Detector Design II --- HERA like… Hadronic Calorimeter Outer trackers 5m 2.5m Inner trackers EM Calorimeter Nearest beam elements 1m

37. A. Deshpande, N. Smirnov Detector Design II: HERA like…+ PID HCAL EMCal Solenoid AEROGEL TOF A HERA like Detector with dedicated PID: >>Time of flight >>Aerogel Ckov Beam elements 7m P/A e Inner trackers 5m Outer trackers

38. 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 accelerator physicists… Recent interest from HERA (low x, low Q2 physics) • 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!

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)

40. 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) • 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)???