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

2. Compass20042 Some spin & Low x-high Q 2 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 1.00119  0 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/Puzzle 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. Compass20043 Deep 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

4. Compass20044 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. Compass20045 BRAHMS & PP2PP (p) STAR (p) PHENIX (p) AGS LINAC BOOSTER Pol. Proton Source 500  A, 300  s Spin Rotators Partial Siberian Snake Siberian Snakes 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipoles RHIC pC Polarimeters Absolute Polarimeter (H jet) 2  10 11 Pol. Protons / Bunch  = 20  mm mrad RHIC accelerates heavy ions to 100 GeV/A and polarized protons to 250 GeV RHIC Relativistic Heavy Ion Collider L. Bland, this Conferences An ideal machine for studying QCD!

6. Compass20046 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. Compass20047 eRHIC vs. Other DIS Facilities (I) eRHIC DIS E e = 5-10 GeV E p = 30 – 250 GeV Sqrt(s) = ~25 – 100 GeV Kinematic reach of eRHIC x = 10 -4  ~0.7 (Q 2 > 1 GeV 2 ) Q 2 = 0  10 4 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 ~ 10 33 cm -2 sec -1

8. Compass20048 eRHIC vs. Other DIS Facilities eRHIC: >> Variable beam energy >> p  U hadron beams >> Light Ion polarization >> Large Luminosity Huge Kinematic reach >> Huge Kinematic reach ELIC at Jlab: (Electron-Light Ion Collider) >> Variable beam energy >> p, d & He polarization >> Huge Luminosity TESLA-N eRHIC ELIC-Jlab

9. Compass20049 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. Compass200410 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  S (Q 2 ) -- precision photo-production physics -- precision gluon distribution in x=0.001 to x=0.6 -- slopes in dF 2 /dlnQ 2 (Transition from QCD --> pQCD) -- flavor separation (charm and strangeness) -- exclusive reaction measurements -- nuclear fragmentation region measurements [1] [2] [2,3] Luminosity Requirement

11. Compass200411 Polarized DIS at eRHIC Spin structure functions g 1 (p,n) at low x, high precision -- g 1 (p-n): Bjorken Spin sum rule better than 1-2% accuracy Polarized gluon distribution function  G(x,Q 2 ) -- at least three different experimental methods Precision measurement of  S (Q 2 ) from g 1 scaling violations Polarized s.f. of the photon from photo-production Electroweak s. f. g 5 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] [1,2] [1] [1,2] [3] [1] [2,3] Luminosity Requirement

12. Compass200412 Proton g 1 (x,Q 2 ) low x eRHIC eRHIC 250 x 10 GeV Luminosity = ~85 inv. pb/day Fixed target experiments 1989 – 1999 Data 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 AD, V.W.Hughes

13. Compass200413 Low x measurement of g 1 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 runningIf 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 AD, V.W.Hughes BNL/Stony Brook, Caltech, MIT effort for R&D on He beams near future

14. Compass200414 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 First moment of  G -- Scaling violations (pQCD analysis at NLO) of g 1  First moment of  G -- (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  G(x)

15. Compass200415  G from Scaling Violations of g 1 World data (today) allows a NLO pQCD fit to the scaling violations in g 1 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

16. Compass200416 Photon 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 F 2 results on G Signal: PGF Background QCD Compton

17. Compass200417 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 distributionExcellent ability to gain information on the shape of gluon distribution Easy to differentiate different  G scenarios: factor 3 improvements in ~2 weeks If combined with scaling violations of g 1 : 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

18. Compass200418 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 PhotonResolved Photon

19. Compass200419 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 M. Stratmann, W. Vogelsang

20. Compass200420 Parity Violating Structure Function g 5 This is also a test For eRHIC kinematics Experimental signature is a huge asymmetry in detector (neutrino) Unique measurement Unpolarized xF 3 measurements at HERA in progress Will access heavy quark distribution in polarized DIS

21. Compass200421 Measurement Accuracy PV g 5 at eRHIC Assumes: 1.Input GS Pol. PDfs 2.xF 3 measured by then 3.4 fb -1 luminosity Positrons & Electrons in eRHIC  g 5 (+) >> reason for keeping the option of positrons in eRHIC J. Contreras, A. De Roeck

22. Compass200422 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 A 1 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

23. Compass200423 DVCS/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.

24. Compass200424 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 &  -A experiments including target fragmentation QCD in: x > [1/(2m N R N ) ] ~ 0.1 (high x) QCD in: [1/(2m N R A )] < x < [1/(2m N R N )] ~ 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/(2m N R A )] ~ 0.01 (low x) See: www.bnl.gov/eic for further detailswww.bnl.gov/eic

25. Compass200425 DIS in Nuclei is Different! Regions of: Fermi smearing EMC effect Enhancement Shadowing Saturation? Regions of shadowing and saturation mostly around Q 2 ~1 GeV 2 An e-A collision at eRHIC can be at significantly higher Q 2 F 2 D/F 2 A Low Q 2 ! E665, NMC, SLAC Experiments

26. Compass200426 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. Compass200427 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.

28. Compass200428 Interaction Region Design….early ideas… B. Parker’s (BNL) Proposal Budker/MIT Proposal

29. Compass200429 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 pointsIP12, IP2 and IP4 are possible candidates for collision points Two detector designs under considerationTwo detector designs under consideration p e 10GeV 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

30. Compass200430 Where do electrons and quarks go?  p q,e 10 GeV x 250 GeV 177 0 160 0 scattered electronscattered quark 10 GeV 5 GeV 90 0 5 GeV 10 0

31. Compass200431 Electron kinematics… some details… scattered electron 10 GeV x 250 GeV At HERA:  Electron method:  x/x ~  E/(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)  p/p ~ 0.005-0.0001  (2-4T Magnet)  Design low noise calorimeter  Crystal or SPACAL

32. Compass200432 Electron, Quark Kinematics scattered electronscattered quark 5 GeV x 50 GeV  p q,e

33. Compass200433 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 E T 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. Compass200434 Detector Design (I)… others expected Whitepaper 2001/2

35. Compass200435 Detector Design (I)… others expected Whitepaper 2001/2

36. Compass200436 Detector Design II --- HERA like… Hadronic Calorimeter EM Calorimeter Outer trackers Inner trackers 5m Nearest beam elements 1m 2.5m

37. Compass200437 Detector Design II: HERA like…+ PID AEROGEL HCAL P/A e A. Deshpande, N. Smirnov EMCal TOF Outer trackers Inner trackers Beam elements Solenoid A HERA like Detector with dedicated PID: >>Time of flight >>Aerogel Ckov 5m 7m

38. Compass200438 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)~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 WGSubgroups: Accelerator WG, Physics WG + Detector WG E-mails: BNL based self-registered email servers… list yourselves!

39. Compass200439 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 Q 2, 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. Compass200440 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)???