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Summary- DIS05

Summary- DIS05. Allen Caldwell Max-Planck-Institute f. Physik. Goal of this talk. My list of the key physics topics addressed by DIS physics Where we stand - selected results Ideas for the future. The Key Topics - my opinion.

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Summary- DIS05

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  1. Summary- DIS05 Allen Caldwell Max-Planck-Institute f. Physik

  2. Goal of this talk • My list of the key physics topics addressed by DIS physics • Where we stand - selected results • Ideas for the future

  3. The Key Topics - my opinion • Hadron/nuclear structure - can we describe hadron structure to a non-expert ? Do we understand it from our theory ? • Small-x, the universal gluons - at small x, we probe the universal QCD fuzz which surrounds all particles. Test this universality. Theoretical understanding. • S - the QCD parameter. What does DIS contribute ? • Precision QCD - if we want to discover new physics, we need to know what the current physics predicts. • Spin - how is hadron spin built from constituents ? Data, theory ? I will not talk about: EW tests/parameters, searches for new physics, Pentaquarks

  4. Hadronic Structure What does a proton look like ? How would you describe it to your children. Infinite momentum frame picture ? Light-cone variables ? I think we should be able to describe the proton in its rest frame. Pick it up, turn it around, look at it from all sides. In the proton rest frame, what is the physical interpretation of Bjorken x ? x=1, infinite momentum parton in proton rest frame ?

  5. ct r * b Physics Picture in Proton Rest Frame r~ 0.2 fm/Q (0.02 – 2 fm for 100>Q2>0.01 GeV2) transverse size of probe ct ~ 0.2 fm (1/2MPx) (<1 fm to 1000‘s fm) – scale over which photon fluctuations survive. For x<0.01, ct>10 fm. No longer Proton structure - universal structure - initial conditions forgotten ? b~ 0.2 fm/sqrt(t) t=(p-p‘)2

  6. So we divide the results as follows: • x<0.01 measure universal structure of QCD radiation. x>0.1 measure hadronic structure. Non-perturbative boundary conditions. Eventually get these from the lattice ?

  7. Hadronic Structure Many results presented at this conference on the high-x pdf’s: e.g., JLAB Structure Functions of Bound Neutrons S. Kuhn F2 and FL measurements in Resonance region, and gluon distribution C. Keppel

  8. NuTeV final structure function results M. Tzanov G. Corcella Importance of large-x resummation

  9. ZEUS - NC cross sections at very high x Y. Ning xmax >0.7 Q2>5000 GeV2 New techniques with old data.

  10. Proton Structure from the lattice D. Renner Quark imaging in the proton via quantum phase space distributions A. Belitsky y x z Transverse size depends on x. m still much too high Importance of GPDs

  11. Small-x physics: the universal fuzz In this region, far from initial conditions: universal ? Check: small scales, larges scales, different sources In strong interaction, can have long chains …

  12. *P scattering cross section versus CM energy (Q2 »0). Same energy dependence observed s0.08 vs (W2)0.08 For soft scattering, small-x indeed universal

  13. What about at larger Q2 Parametrize F2 ~ x- for x<0.01

  14. The behavior of the rise with Q2 Below Q20.5 GeV2, see same energy dependence as observed in hadron-hadron interactions. Observe transition from partons to hadrons (constituent quarks) in data. Distance scale  0.3 fm ?? Is the behavior at larger Q2 universal ? Hadron-hadron scattering energy dependence (Donnachie-Landshoff)

  15. Diffraction - e Pomeron scattering Same high energy behavior as total cross section

  16. Forward neutron production - electron - pion scattering

  17. Small-x physics is (experimentally) simple The small-x data from HERA has very simple features, and has been parametrized with simple expressions. E.g., D. Haidt. Should be checked with other processes.

  18. Theory of small-x So far, the theory is very complicated. BFKL, dipole scattering, travelling waves, stochastic differential equations, chaos, biological evolution … It seems to be a wonderful theoretical playground with connections to many things. Are we getting closer ? Sometimes, I feel I understand something, but it usually doesn’t last

  19. Color Glass Condensate

  20. More exclusive data Sensitive to radiation chain

  21. Small-x physics: the gluon xg(x,Q2) a universal quantity ? The uncertainties are large at small-x. Long running discussion on xg(x,Q2)<0 at NLO. What other information do we have ?

  22. FL would be a key measurement. HERA II study by M. Klein, C. Gwenlan-Barr Jet production helps pin down the gluon at larger x. Pinning down the gluon

  23. Long held hope - Exclusive VMs C. Kiesling, M. Teubner Are we close to using also exclusive processes ?

  24. S ? Many handles: Evolution of SF, jet rates, event shapes,… Clear running seen in HERA data. New data combination with different approach to errors C. Glasman

  25. HERA data competitive. HERA II - very clear running will be observed. What is really needed is to bring down the theory uncertainties !

  26. Precision QCD tools “…The mechanic, who wishes to do his work well, must first sharpen his tools …” —Chapter15, “The Analects” attributed to Confucius, translated by James Legge. As quoted by Xiaomin Zu in her interesting contribution on making event generators more true to QCD (correct parton kinematics, e.g.) Theory: improvements in pQCD calculations Phenomenology: improved PDFs Simulations: improved event generators

  27. Example: open beauty production Agreement ? What does it take to have a significant difference ? What would be the conclusion ?

  28. Example: Jet Rates Data and calculations becoming more accurate. Still need to understand what a significant deviation would be. Big issue: PDFs and their uncertainties.

  29. PDFs Big progress in recent years - uncertainties on PDF’s. New developments, e.g., NN pdf extraction. What the NN says about small-x with pre-HERA data. Error bands reasonable.

  30. The error bars The shift Central values This prompted me to think of Rumsfeld’s words: • Known knowns • known unknowns • unknown unknowns • what about unknown knowns ???

  31. Techniques for reducing the unknowns ? S. Glazov combined the HERA data using known correlations between systematics.

  32. Spin of the proton Open question: how do we understand the spin of the proton ? Quark model, Ang Momentum from quarks only 0.3 h/2 Rest in gluons ? Orbital ang mom ? What we measure: New techniques being developed. Will eventually need small-x.

  33. D. Ryckbosch

  34. Very nice ! I’ve wanted to see something like this for some time. From C. Keppel talk Visualization of Sivers effect

  35. Ideas for the Future • Key measurements: • Hadron structure - JLAB, MINERA, COMPASS+ fixed target at CERN. Require large statistics - need subtle correlations, differences of cross sections, multiply differential cross sections  wavefunctions ! • Small-x physics - LHC, eRHIC (eLIC), ILC, eLHC. Luminosity requirement modest. However, need optimized (forward) detectors, high energies. • Spin - eRHIC (eLIC). Requires large luminosity, high energy to reach small-x glue.

  36. 6 GeV CEBAF add Hall D (and beam line) 12 Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls

  37. Milestones and Timelines for 12 GeV • 1994-2002 Development of Science Case and Exp.Equiment • April 2002 Recommendation by NSAC Long Range Planning • April 2004 DOE Approval of Mission Need (CD-0) • 2004-2005 Development of Conceptual Design Report • Oct 2004 GlueX Detector Review • Jan 2005 Review of Spectrometer Options • April 2005 DOE Science Review of the 12 GeV Upgrade (very positive response ! ) • Sept 2005 Critical Decision on Prel. Baseline Range (CD-1) • 2007-2008 Engineering and Design • 2008-2011 Construction • 2012 Beam on Target

  38. Summary CEBAF operation @ 6 GeV has provided results with unprecedented precision on structure functions and form factors (including strangeness) Upcoming years will highlight precision hypernuclear studies, standard model tests and . . . • The Upgrade to 12 GeV is essential to provide access • to new kinematic regions and will: • determine with extreme precision the spin and flavour structure • of the nucleon in the valence region • provide a totally new and complete view of the nucleon structure • access to quark angular momentum • finally (after > 30 years) determine the origin of the EMC effect • test our understanding of quark confinement • and much much more . . .

  39. e’ DVCS Bethe-Heitler e g 2 e’ g p p g e’ e e + g p GPD’s p p p ) ( s a 3 d x y 2 2 + + + * * = T T T T T T B BH DVCS BH DVCS DVCS BH f dx dydtd p + e 3 2 2 8 e Q 1 B Beam Spin Asymmetry Beam Spin Asymmetry ~

  40. Forward physics at the LHC Higgs discovery channel ? Hard & soft diffraction - gluon collider.

  41. H. Kowalski - event rates, background levels look promising

  42. eRHIC vs. Other DIS Facilities • New kinematic region for polarized DIS • Ee = 10 GeV (~5-12 GeV variable) • Ep = 250 GeV (~50-250 GeV variable) • EA= 100 GeV/nucleon • Sqrt[Sep] = 30-100 GeV • Kinematic reach of eRHIC: • X = 10-4 --> 0.7 (Q2 > 1 GeV2) • Q2 = 0 --> 104 GeV2 • Polarization of e,p and He beams at least ~ 70% or better • Heavy ions of ALL species at RHIC • Luminosity Goal: • L(ep) ~1033-34 cm-2 sec-1 eRHIC DIS Key step: NSAC review 2005/2006.

  43. ELIC-Jlab • eRHIC • Variable beam energy • P-U ion beams • Light ion poalrization • Huge luminosity TESLA-N Optimized detector design will make a big difference in the physics which can be accessed. Towards Bjorken’s FAD.

  44. Precision eA measurements • Enhancement of possible nonlinear effects (saturation) r b At small x, the scattering is coherent over nucleus, so the diquark sees much larger # of partons: xg(xeff,Q2) = A1/3 xg(x,Q2), at small-x, xg  x- , so xeff- = A1/3x-  so xeff  xA-1/3  = xA-3 (Q2< 1 GeV2) = xA-1 (Q2  100 GeV2)

  45. ILC: • high energy, so in principle e+e- gives access to small-x. However, low rates, need forward detectors. Better is e , but likely staged because of cost pressure. • eLHC: • extends HERA physics by 1 order of magnitude in x. Time scale and cost acceptable ?

  46. Action: the last recourse of those who do not know how to dream. Oscar Wilde There are many ideas being discussed for the future. Decide which physics is important Decide which option is feasible in a reasonable time-scale Don’t let the perfect be the enemy of the good

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