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Highlights of HERA I And Prospects for HERA II

Highlights of HERA I And Prospects for HERA II. R. Yoshida Argonne National Laboratory, USA. DOE Review: 15 August 2002. Introduction:. Cannot cover everything…. HERA I (1992-2000): status of the analyses. I have chosen the following topics in areas where ANL has

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Highlights of HERA I And Prospects for HERA II

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  1. Highlights of HERA I And Prospects for HERA II R. Yoshida Argonne National Laboratory, USA DOE Review: 15 August 2002

  2. Introduction: Cannot cover everything…. HERA I (1992-2000): status of the analyses I have chosen the following topics in areas where ANL has had strong contributions. -Proton Structure Functions and DIS cross-sections (R.Y. current phys. coord. , A. Pellegrino phys. coord 2000-2001) -Jets in DIS and Photoproduction (S. Chekanov current phys. coord., J. Repond phys. coord 1997-9, S. Magill, B. Musgrave work extensively in phys. group) Potential for HERA II (2002-2006) Again I have picked a couple of topics from many possible. -High x partons -Electro-weak Physics e (27.5 GeV) p(920 GeV)

  3. Virtuality ("size" of probe) x Mom. fraction of the struck parton. HERA I results DIS NC cross-sections at low Q2 (< 500 GeV2) systematics limited. s ~ Q-4 Q2=2.7-10000 GeV2 Latest results published 2001 Very low x and Q2s Latest results published 2000 Typical uncert. 2-3% “Last word” for forseeable future.

  4. DGLAP fits to “low Q2” data Str. fcn. and parton dist.:

  5. parton dist and alpha-s: Errors and correlations of partons Extreme scaling vio. gluons ca. 10% Gluon ZEUS H. twist: QCD scale:

  6. Valence quarks determined by fixed target data

  7. HERA I results HERA I data sets: Status of high Q2 (≥ 200 GeV2) cross-section analyses: e+p 110 pb-1 e-p 16 pb-1 (statistically limited) e+ CC and NC Preliminary results 60 pb-1 CC and NC Published 1999 50 pb-1 e- CC published 2002 NC preliminary results 16 pb-1

  8. Charged Current cross-section Data shown not in fit Precision of fixed target measurements evolved with DGLAP Results ca. 50e+p and 15e-p HERA upgrade will bring x20 data by 2005-6.

  9. ZEUS data only (50 pb-1) ZEUS Only (all HERA I data)

  10. EW studies at high Q2 Charged Current cross-sections: NC EM and Weak have similar cross-sections. Vivid illustration of cross-section suppression due to the W mass CC

  11. Shape (Q2 dependence) is sensitive to the propagator mass.

  12. partons dens. SM tells us that: Combining shape and normaliz. gives strong constraint.

  13. 0.01 GeV2 < Q2 < 500 GeV2 (systematics limited) final data for HERA I published. Post HERA I PDF—on a higher level: NLO, low x gluon, high precision, uncertainties and correlations. (important for future, e.g. LHC) HERA low-x data combined with high-x fixed target gives precise as. High Q2 (> 500 GeV2, statistics limited) data: all HERA I data available. High Q2HERA I data constrains valence distributions well—independence from low Q2(higher-twist) and nuclear effects. HERA II (more later) First HERA electro-weak studies: consistency of the standard model HERA II (more later) Summary: DIS cross-section measurements from HERA I Jets at HERA I

  14. Jets in Photoproduction

  15. Angular distribution of dijets agree well with the expectations of NLO QCD Can we extract photon structure?

  16. photon structure functions Apparent sensitivity to photon structure. However:

  17. Answer: “Not as well as we’d like” QCD NLO calculations need “asymmetric” Et cuts on the dijets i.e. Et1_cut = Et2_cut At LO Et1=Et2 At NLO, (one more radiation allowed) Virtual corrections real radiation compensate each other. But not at the “point of the triangle” Asymmetric cut

  18. Parton Shower Monte Carlo describes shape of data. Probably needs resummation to have more stable results Data keeps rising Theory becomes flat as expected in NLO 25 GeV Et

  19. Jets in DIS: NLOQCD calculation this talk

  20. Importance of uncertainties and correlations in PDF’s DIS dijet Ratio Total DIS with correlations ignore correlation

  21. Theory error dominates (partially due to dijet cuts)

  22. 1%uncertaintyon jet energy scale ! 3% jet cross-section measurements! Inclusive jets (EBT> 8 GeV) Running as from single exp. Small theory error One of the most precise determinations!

  23. Summary: DIS jet measurements from HERA I • Post HERA I jet studies are on a higher level: proper jet algorithms (Kt), NLO, limitations and instabilities are largely understood. • The experimental uncertainties are now extremely small—1% jet energy scale. • Photon structure from photoproduction dijets: sensitivities demonstrated and NLO instabilities understood. • Extraction of as from DIS dijets and inclusive jets—the latter results are among the most precise determinations. • Many jet measurements are now limited by the theoretical understanding: NNLO, resummations needed. • Highest scale (Et, Q2) gives most stable theoretical results more luminosity. (need to further reduce systematic errors—e.g. 3-jet/2-jet ratio.) Potential of HERA II

  24. HERAII ×5 Luminosity:  1 fb-1 by end 2006 What about really high x ?

  25. Valence distributions are not well known at very high x Botje analysis 1999 d/u ≠ 0 as x1 ? Bodek and Yang, 1998 You can get to very high x (>.65) with high luminosity 

  26. Energies and angles of the electron and the jet: 4 variables measured Need to reconstruct 2 kinematic variables: x and Q2. Jet has resolution in x but no acceptance Acceptance for electrons, but no resolution in x. 104 104 Jet Falls Into the beampipe However, not seeing a jet is a good measurement of x (Helbich and Caldwell, 2002)

  27. (Helbich and Caldwell 2002) 20 % (ish) measurement at x ≃0.8 possible: better if systematic uncertainties (hadronic energy deposit) can be brought under better control.

  28. NC DIS cross-section (polarized electrons) EW couplings Quark distributions (QCD) =0.67 at Q2=10k unpol. case =~-0.036 Sensitivity to aq already in unpolarized xF3 unpol. case

  29. Vector and Axial-vector coupling of light quarks: Gain sensitivity to vector coupling with polarization. Importance of polarization.

  30. CCFR NC/CC ratio Neutrino DIS LEP/SLC b coupling HERAII projection (u and d) LEP/SLC c coupling Neutrino DIS High precision: complimentary measurement.

  31. Sensitivity to top and Higgs mass: Higher order corrections: relates fermion masses and coupling constants Running alpha Quadratic dependence on top mass --also has logarithmic dependence on Higgs mass. Fix coupling to SM parameters: use Mz, alpha measurements Check consistency of SM by fitting for Mt and Mw:

  32. Fixing alpha and Mz : Mw to 55 MeV Precision check of EW theory when combined with precise top mass measurement from Tevatron, LHC.

  33. HERA I: Discussed results in:DIS cross-sections and DIS and photoproduction jets. In both areas HERA I has brought the pQCD studies to a qualitatively new level. Did not discuss results in: Soft physicsDIS diffraction, VM production, low x New understanding and a renewed interest (c.f. eRHIC) Heavy Flavors Charm – Study of production mechanisms in DIS and Photoproduction: another handle on gluon density of the proton Beauty - First cross-section measurements. Searches Limits complementary to Tevatron and LEP. Excited fermions, LQ, R-parity v. SUSY HERA I  Superlative QCD machine

  34. HERA II • 1 fb-1 of data  high statistics at high Q2 and Et. • Access to high-x partons at high Q2 • Jets at high Et and Q2 • pQCD studies (PDF’s, jet cross-sections) at higher scales. Further improve understanding of QCD (also important for LHC) Not covered: heavy quarks  new microvertex and forward tracking—new era in HERA heavy flavor studies Polarization (combined with large statistics)  Sensitivity to electroweak effects: a new regime of physics for HERA. HERA II: Will continue to be a superb QCD machine + provide sensitive tests of the Standard Model

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