1 / 53

Physics Case For E lectron I on C ollider Abhay Deshpande

Physics Case For E lectron I on C ollider Abhay Deshpande. A. Abhay Deshpande AA Physics Capabilities of an EIC Detector Mini-Workshop at BNL September 19, 2002. http://www.bnl.gov/eic. Riken BNL Research Center. Crossing the x-Q 2 Barrier in DIS: Low-x surprises!.

ondrea
Download Presentation

Physics Case For E lectron I on C ollider Abhay Deshpande

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics Case For Electron Ion ColliderAbhay Deshpande A Abhay Deshpande AA Physics Capabilities of an EIC Detector Mini-Workshop at BNL September 19, 2002 http://www.bnl.gov/eic Riken BNL Research Center

  2. Crossing the x-Q2 Barrier in DIS: Low-x surprises! • Elastic e-p scattering (SLAC, 1950s) Q2 ~ 1 GeV2Finite Size of proton • Inelastic e-p scattering (SLAC, 1960s) Q2 > 1 GeV2Parton structure of the proton • Inelastic m-p scattering off p/d at CERN (1980s) Q2 > 1 GeV2 Unpolarized EMC effect • Inelastic e-p scattering at HERA/DESY (1990s) Q2 > 1 GeV2Unexpected rise of F2, Study of pQCD and QCD through various physics processes, diffraction… Low x What NEXT? Physics Case of EIC

  3. Physics with “Spin” full of Surprises! • Stern & Gehrlach (1921): Space quantization associated with • direction • Goudschmidt & Ulhenbeck (1926): Atomic fine structure and • electron spin magnetic moment • Stern (1933): Proton anomalous magnetic moment • Kusch (1947): Electron anomalous magnetic moment • Prescott & Yale-SLAC Collaboration (1978): EW interference • in polarized e-d DIS, parity non-conservation • EMC (1989): Proton spin crisis/puzzle Low x! • E704, AGS pp scattering, HERMES ep (1999): • ???? Transverse spin asymmetries ???? Physics Case of EIC

  4. Deep Inelastic Scattering Kinematics • Observe scattered electrons and hadrons • Observe spectator or remnant of the interaction?? Physics Case of EIC

  5. Advantages of a Collider Experiment Historically polarized & un-polarized DIS fixed target experiment However colliding beam configuration has advantages • Better angular separation between scattered lepton & nucl. Fragments • -- Better resolution for electro-magnetic probe • -- Recognition of rapidity gap events (recent history of diffraction) • Better measurement of nuclear fragments • Higher Center of Mass (CM) energies reachable • Tricky integration of beam pipe and accelerator components Physics Case of EIC

  6. The EIC w.r.t. Other Experimental Facilities • New kinematic region to be explored • EIC = eRHIC + EPIC • Kinematic Reach for DIS: • High Luminosity! Physics Case of EIC

  7. The EIC w.r.t. Other Facilities Large luminosity and high CM Energy makes EIC unique! TESLA-N Variable CM energy, ion species and polarizability of hadron beams enhances its versatility! Physics Case of EIC

  8. Scientific Frontiers Open to the EIC • Nucleon structure:  Spin structure: polarized quark and gluon distributions the nucleon  Unplarized quark and gluon distributions in the nucleon  Correlations between partons • Role of quarks and gluons in the nuclei • Hadronization in nucleons and nuclei • Partonic matter under extreme conditions Physics Case of EIC

  9. The EIC Detector  A “4p” Detector • Scattered electrons to measure kinematics of DIS • Scattered electrons at small (~zero degree) angles to tag photo-production events • Central hadronic final state for kinematics, jet measurements, quark flavor tagging, fragmentation studies…. • Central hard photon and particle/vector meson detection (DVCS) • Zero angle photon measurement to control radiative corrections and in e-A physics to tag nuclear de-excitations • Missing ET for neutrinos in final state (W physics) • Tagging forward nuclear fragments • Tagging forward particles for diffractive physics & target depedence The EI Collider will provide: • Variable energies & species of ions • Polarized beam species: p, d, He • High luminosity Physics Case of EIC

  10. 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 Physics Case of EIC

  11. 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 EIC: • 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 Physics Case of EIC

  12. Electron, Quark Kinematics q,e  5 GeV x 50 GeV p scattered electron scattered quark Physics Case of EIC

  13. Physics with Unpolarized e-p Collisions Large kinematic region already covered by HERA but additional studies at the EIC are possible & desirable! Uniqueness of EIC: High luminosity, variable Sqrt(s), deuterons, improved detector & IP • Will enable precision physics studies: • d beams  neutron structure, d/u x0, dbar(x)-ubar(x) • precision aS(Q2) • flavor separation (charm, strangeness) • slopes in dF2/dlnQ2 • precision gluon distribution x 0.001  0.5-1 • exclusive reaction measurements • transition region physics Q2=0 few GeV • nuclear fragmentation region Physics Case of EIC

  14. Spin structure function g1p/g1n with high precision and at low x Bjorken sum rule with high precision DG(x,Q2) from pQCD analysis, Di-Jet/high pT hadron events in PGF processes Precise determination of aS from g1 scaling violations alone… Polarized structure of the photon from photo-production studies Electroweak structure functions g5(+/-) from W(+/-) production in polarized ep scattering Flavor separation of PDFs through semi-inclusive DIS Transversity DVCS Contribution to GDH sum rule at very high υ Tgt/Current fragmentation Etc……. Many other measurements Topics of Interest for polarized DIS A robust program which would require a challenging detector & interaction region design Physics Case of EIC

  15. Spin Structure Function g1 at low xA. Deshpande, V. W. Hughes ~5-7 days of data 3 years of data Studies included statistical errors & detector smearing No present/future approved experiment will do as well. Physics Case of EIC

  16. Low x Measurement of g1 of the NeutronA. Deshpande, V.W.Hughes • With He+2 or Deuteron in hadron ring: g1n measurable • ~2 weeks of EIC data (only the low x data shown) • Shown is the present SMC data with various low x scenarios and uncertainties from possible HERA data in 3 years • Combined with g1p this would enable a “hyperfine” test of Bjorken sum rule which is a fundamental result of QCD (~0.5-1.0 % accuracy estimated) EIC 1 inv.fb Physics Case of EIC

  17. Polarized Gluon Distribution Polarized Gluon distribution is being pursued at various various experimental facilities as we speak…. Each has its weaknesses and strong points. At the Electron Ion Collider this will be pursued with very different physics interactions: Different Systematics/Different Kinematics Deep Inelastic Scattering Kinematics with EIC: • Perturbative QCD analysis of the g1 spin structure of the data • 2+1 Jet production in photon gluon fusion (PGF) process • 2-high pT opposite charged hadron tracks (PGF) Photoproduction (real photon) Kinematics with EIC: • Single jet production in PGF • Di-Jet production in PGF • Open charm production • …. Physics Case of EIC

  18. First Moment of the DG(x)A.Deshpande, V. W. Hughes & J. Lichtenstadt • pQCD analysis of g1 structure function at NLO gives the first moment of the polarized gluon distribution. Present value and uncertainty is: (at Q2 = 1 GeV2) 1.0 (stat) (exp.sys.) (theory/low-x) • Major source of uncertainty from low x unmeasuredregion: Theory completely unconstrained in this region. • If EIC data (~1 week) is obtained and the analysis is repeated, the theoretical uncertainties are estimated to improve by factor of ~3-5; the statistical uncertainty improves by factor ~5. Study to be repeated for 1-3yr data. +1.0 + 0.4 +1.4 - 0.4 - 0.2 - 0.5 Complimentary determination of DG to that from RHIC Spin Physics Case of EIC

  19. Photon Gluon Fusion in DIS: Di-Jet events 2-High-pT hadron events At high Sqrt(s) the theoretical interpretation is without ambiguities or uncertainties! Method already tried at HERA -- NLO calculations exist -- G(x,Q2) extracted and published (H1 & ZEUS) -- Consistent with G(x,Q2) from pQCD analysis of F2 Other “direct” methods to get DGPhoton-Gluon-Fusion (PGF) Signal: PGF Background QCD Compton Physics Case of EIC

  20. Result of Di-Jet analysis at NLOG. Radel & A. De Roeck, A. Deshpande, V. W. Hughes, J. Lichtenstadt Statistical accuracy shown for EIC for 2 luminosities Detector smearing effects studied NLO analysis for Di-Jet considered in the past • Easy to differentiate between different scenarios of DG: Improves DG by factor of ~2-3? • Combined analysis: Di-Jet + pQCD analysis of g1:DG constrained by these two together further improve the uncertainties by an additonal factor of ~3 Effectively a ~5% or better measurement of DG might be expected Physics Case of EIC

  21. DG(x)/G(x) EIC vs. Rest of the World EIC Di-Jet DATA 2fb-1 Good precision Clean measurement Range 0.01 <x< 0.3 Constrains shape!! Physics Case of EIC

  22. Polarized Parton Distribution of the Photon • Photoproduction studies with single and di-jet and one and 2 high pT opposite charged hadrons. • At high enough energies the photon can resolve itself into its parton content • With polarized protons asymmetries related to the spin structure of the photon can be extracted! A UNIQUE measurement! • Asymmetries sensitive to the gluon structure as well! Direct Photon Resolved Photon Physics Case of EIC

  23. Statistical uncertainty with 1 inv.fb. ~2wks running for EIC Single and double jet asymmetries ZEUS Acceptance cuts Will resolve the photon pdfs easily! Spin structure of polarized photon!M. Stratmann & W. Vogelsang Direct Photon Resolved Photon Physics Case of EIC

  24. Unique measurement with EIC polarized HERA Experimental Signature: missing (neutrino) momentum: huge asymmetry in detector Complementary measurement to RHIC SPIN Parity Violating Structure Functions g5 For EIC kinematics Physics Case of EIC

  25. Measurement Accuracy PV g5 with EICJ. Contreras & A. De Roeck Assume: 1) Input GS Polarized PDFs 2) xF3 is measured well by that time 3) 4fb-1 luminosity If e+ and e- possible then one can have g5(+) as well. Separate flavors Delta u, Delta d etc. Physics Case of EIC

  26. DGH sum rule: At EIC n range: GeV-few TeV range Although contribution to integral is small: explore energy dependence of cross-section. Complementary to JLAB, MAMI Experimental effort Drell-Hearn-Gerasimov Sum RuleS. Bass, A. De Roeck, A. Deshpande Electron Tagger: Inclusive Photoproduction measurement Physics Case of EIC

  27. DVCS/Vector meson production • Hard exclusive DIS process • g (default) but also pions, vector • mesons…. • Remove a parton & put another one • back in  Microsurgery of Baryons! Claim: Possible access to skewed/off forward PDFs Polarized structure: Access to quark orbital angular momentum(??) ?? ?? ? H(x,,t), E(x,,t)  Jq =q+Lq ? • An ongoing debate….R. Jaffe/X.Ji …… • Will need a large kinematic coverage in the data  EIC’s variable energy • scheme should help Physics Case of EIC

  28. DVCS has been observed at HERA (ZEUS,H1), recently by HERMES and later by Jlab Potential for getting to Nucleon Angular Momentum??? Reflection of processes in the nucleon Could be measured with EIC with considerable x,Q2 range.  Extrapolations and generalizations involved may become clearer by then? Deeply Virtual Compton Scattering at EICD. Hasell,R. Milner et al. EIC: 5 GeV e on 50 GeV proton: Much large range possible…. Physics Case of EIC

  29. DVCS at EIC (preliminary) A. Sandacz Acceptance enhanced ZEUS-like detector Add Roman pots a la PP2PP at RHIC 10 x 250 GeV Full curve: all events Dashed curve: accepted events Q2>1 GeV2: 50K events/fb-1 Q2> 1 GeV2 20<W<95 GeV 0.1<|t|<1.0 GeV2 Physics Case of EIC

  30. Target & Current Fragmentation RegionT. Londergan & P. Moulders • Target and current fragments separated naturally in a collider mode compared to the fixed target experiment • Exclusive/Semi-Inclusive measurements need high luminosity • EIC will have both capabilities • Numerous measurements leading to detailed study of different fragmentation functions using the different species of beams at EIC both in polarized and unpolarized DIS. Physics Case of EIC

  31. Polarized & Unpolarized Strange Quark Distribution Measurements E. Kinney, U. Stoesslein • Assuming that u and d quark • distributions are measured by the • time EIC comes along…. • A detector with a good particle ID • for pion/kaon… separation could • access strange quark distribution • Upper left plot shows statistical • accuracy for Asymmetries measured • for events with Kaons with 1fb-1 • luminosity at EIC • Lower left plot shows the accuracy • on strange quark distribution • possible Physics Case of EIC

  32. Collider helps: Target Fragmentation StudiesD. De Florian, G. M. Shore & G. Veneziano Experimetal Measurement: Different targets,Forward detectors, Detect positive & negative hadrons, Provide good PID Physics Case of EIC

  33. …and extend into a novel high parton density region: Color Glass Condensate Study e-A in a collider mode for the first time! QCD in a different environment! Clarify & reinforce the physics studied so far from e-A/m-A in fixed target experiments including target fragmentation region….. Low x Physics with e-A Collider • Physics to be explored can be broadly categorized into three x regions • 1) High x • 2) Intermediate x • 3) Low x Physics Case of EIC

  34. Highest energy fixed target experiment (NMC @ CERN, E665 @ FNAL) used secondary muon beams and achieved Beam intensities: Target thinkness: 600 gm/cm2 Luminosity: Electron DIS experiments at SLAC & DESY: Large beam currents but limited beam energies: Why e-A in Collider Mode? An e-A Collider with appropriately chosen beam energies can overcome all these limitations! Ee ~5-10 GeV, EA~100 GeV/nucleon Luminosity > per e-N This corresponds to approx. 85pb-1 per day! • Thick targets do not allow a good measurement of the target fragments! ONLY INCLUSIVE MEASUREMENTS Physics Case of EIC

  35. Experimental Hints of the Unusual in NucleiM. L. Leicht et al. for FNAL E866 • 800 GeV Proton-fixed target A collisions: Comparison of Drell-Yan di-muon production vs production and then decay of J/Y and Upsilon • Nuclear medium enhances high parton density effects! Also more recent results from RHIC… Physics Case of EIC

  36. Fermi motion EMC effect Enhancement Shadowing Saturation? DIS on Nuclei is Different!E665, NMC & SLAC Collaborations F2D/F2A Region of Shadowing and saturation hardly have data with Q2> 1 GeV2 Low Q2! An e-A Collider will measure these regions! Physics Case of EIC

  37. Statistical Precision possible with EICT. Sloan • Statistical Precision Possible with EIC: • NMC data F2(Ca/D) • EIC data with L=1 pb-1 • Recall expected rates at • EIC are ~85 pb-1/day • Also extends the measurements in to the low x region keeping the Q2>1 GeV2! • Region of saturation? T. Sloan EIC 1 inv. pb Physics Case of EIC

  38. Why high Q2 important at low x? • Before HERA: for Although low x, the coupling constant too large to make predictions and extract information in this region from theory. Lack of high Q2 a stumbling block for understanding QCD. • HERA: Ep = 820-925 GeV, Ee=27.6 GeV, = 300 GeV For • At HERA in good portion of low x region of interest. Coupling weak: computations in conventional pQCD possible & tested with data but interpretation is ambiguous. • Hard (BFKL) Pomeron: In QCD it comes from gluon ladder diagrams 1) LO BFKL predicts cross sections rising faster than the HERA data 2) NLO corrections large and negative: Resummations necessary! Confusion! Interest! Formulate QCD at small x: High Parton Density Physics Physics Case of EIC

  39. Lessons from HERA: Hints of something new? • At high Q2 (>>10 GeV2), the rise of gluon structure function at small x is well understood in pQCD framework. • extracted reliably! • However this is not extremely low x! • In region Q2 (1-10) GeV2 issues less clear: Although fits accommodate data well, the interpretation problematic! Gluon too small, and sea quark distribution more than glue! Is the pQCD approach breaking down? If so Why? Physics Case of EIC

  40. What could be wrong with the low Q2 evaluations of HERA pQCD fits? Coupling strength is still weak in 1-10 GeV2 region! Screening effects due to large parton densities need to be considered specially! Phenomenological models that take these into account Explain inclusive and diffractive data together! Evidence of possible high parton density phenomena Physics Case of EIC

  41. In Summary…. • As parton densities become too high, standard pQCD breaks down. • Even though the coupling is weak, the physics may be non-perturbative due to high field strengths generated by large number of partons • A novel state of matter? To experimentally explore this novel state of matter an e-A collider with LARGE luminosity and HIGH energy beams is essential! Physics Case of EIC

  42. High Parton Density Matter(HPDM) • For a fixed external probe the number of partons per unit area grows rapidly with increasing energy (decreasing x) • QCD field strengths grow as Small coupling implies large field strengths… non-linearities of theory are manifest and significantly change the properties of distributions in high energy collisions. • Calculations indicate that the rapid rise of gluon distributions (as seen at HERA) will saturate.. i.e. grow slowly….. perhaps as slowly as ~ln(1/x). Will form a “Color Glass Condensate! ” Physics Case of EIC

  43. ColorGlassCondensate….(CGC)L. McLerran, R. Venugopalan et al. • Why Glass? At small x, partons are rapidly fluctuating gluons interacting weakly with each other, but strongly coupled to the high x parton color charges which act as random-static-sources of color charge. Analogous to a spin glass system of condensed matter: a disordered state of spins is coupled to random magnetic impurities. • Why Condensate? Gluon occupation number very large. They form a condensate. Being bosons large numbers can occupy the same state. A Bose-Einstein condensate leads to a huge overpopulation of the ground states A new state of matter at high energies would display dramatically different, yet simple, property of glassy condensates. Physics Case of EIC

  44. Inclusive Signatures Of CGC/HDPM The structure function F2(x,Q2), dF2/dlnQ2, dF2/dlnx. dF2/dlnQ2 at fixed x @ high Q2 is the Gluon Distribution. Predictions from saturation models VERY DIFFERENT from those in conventional pQCD EIC: Large luminosity and substantial x-Q2 coverage: Precise measurements possible! Longitudinal structure function FL = F2 –2xF1 Needs variable beam energies Possible @ EIC/eRHIC – Provides independent measurement of the gluon distribution Measurement of Nuclear Shadowing Quark Shadowing (F2A/A*F2N) in fixed tgt experiments: Observed Gluon Shadowing (GA/A*GN) indirect evidence through pQCD fits but are at low Q2! Gluon shadowing expected to be VERY LARGE at low x and perturbatively reliable Q2s. EIC with high energy can do precise measurements! In addition, direct measurements possible using semi-inclusive channels (see next slide) Relation between Shadowing and Diffraction Relation between diffraction off nucleons and shadowing in nuclei will be very different in high parton density environment.EIC with different hadron beams will explore this. Physics Case of EIC

  45. Semi-Inclusive Signatures of CGC • Hard Diffraction: Large rapidity gap between fragmentation region of electron and that of the target. At HERA 7-10% of the cross section corresponds to hard diffraction! Models with Saturation effects can explain this. These models predict that in eA scattering, the hard diffractive cross section could be huge! (~30-40%). EIC will clearly see this! • Coherent & Inclusive vector meson production: For light vector mesons, the diffractive cross-section is ~1/2 inclusive cross-section. For heavier vector mesons, this factor decreases (finally to 1/ln(Q2)). EIC will measure (for different A) r,w,f,J/y,U cross sections • Gluon distribution measurements using jets and other semi-inclusive probes • Large multiplicity fluctuations on event-by-event basis Physics Case of EIC

  46. Implications of EIC for A-A and p-A Collisions • Goal of RHIC is to discover and study properties of QGP Possible scenario: QGP formed when CGC “shatters”! • Bottom line: gluon distribution in nuclei important for initial conditions for QGP formation in A-A collisions. • Physics of p-A complementary to that of e-A Consequences of the absence of evidence of CGC Should we be probing even deeper? We learnt something already! A) What was it that we saw hints of at HERA? B) Is there a possibility that such a state of matter indeed does not exist? What does this mean for QCD at high energies? Physics Case of EIC

  47. A Case for the EIC • Explore a new regime of QCD:An e-A collider will provide a unique opportunity to explore fundamental and universal aspects of QCD. • Measurements would be essential to fully understand the QGP already being pursued at RHIC now, and that would be studied at RHIC later…. And in future at LHC. • An e-A collider will allow us to explore with great precision inclusive measurements that have not been pursued beyond the fixed target experimental era. It would also enable, for the first time, a wide range of semi-inclusive and exclusive measurements in the nuclear environment . Physics Case of EIC

  48. A Case for the EIC (Continued)… • A polarized e-p scattering facility with variable sqrt(s) will allow • a) at high sqrt(s) a new region in the x-Q2 to be explored for the pol. DIS. It will address issues that no other present or future approved facility will address b) in the already measured x-Q2 range the high luminosity of EIC will allow us to settle lots of yet uncertain issues regarding the nucleon spin related to semi-inclusive and exclusive measurements… DETECTOR DESIGN SHOULD BEGIN IN EARNEST http://www.bnl.gov/eic Physics Case of EIC

  49. Time Line for EIC (past) • September 2000: Electron Ion Collider grew out of a joining of forces from two communities: 1) Polarized eRHIC (ep and eA at RHIC) -- BNL, DESY, UCLA, Yale & CERN fixed target & HERA Collider Experiment Community 2) Electron Polarized Ion Collider (EPIC) (3-5 GeV e X 30-50 GeV polarized light ions.) -- Colorado, IUCF, MIT/Bates, IUCF & HERMES Community • February 2002: A white paper was submitted to NSAC Long Range Planning Review  Received enthusiastic support as a next R&D project beyond RHIC II at BNL ** Steering Committee 7 prominent scientists from DoE labs and DoE supported university groups & 1 contact person ** Physics Working Group, Accelerator Working Group (BNL-MIT-Budker Institute)  Detector simulations about to begin with various detector concepts in mind Physics Case of EIC

  50. EIC Time Line… (future)…. “Predictions are very difficult to make, especially when they are about the future…..” - Albert E. • Expected presentation & approval in next LRP (2006) • R&D money for detector could start (2007) • Construction of IR and Detector components (2008) • 3 yrs for construction of IR & Detector (??) without interfering • with the on going RHIC program • First collisions (2011) ?? If you know how to get it done earlier… -- I am listening…. Physics Case of EIC

More Related