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Studies of Proton Structure at HERA

New results on. Studies of Proton Structure at HERA. I. Tsurin. on behalf of ZEUS and H1. Neutral current (NC) Charged current (CC) Structure functions F 2 , xF 3 , F L Parton distribution functions (PDF) The strong coupling constant α S. 12 th International QCD Conference.

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Studies of Proton Structure at HERA

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  1. New results on Studies of Proton Structure at HERA I. Tsurin on behalf of ZEUS and H1 • Neutral current (NC) • Charged current (CC) • Structure functions F2, xF3 , FL • Parton distribution functions (PDF) • The strong coupling constant αS 12th International QCD Conference Montpellier July 4-9, 2005

  2. p-energy: 920 GeV e-energy: 27.6 GeV ep-Collider HERA HERA II: longitudinal e± beam polarisation ZEUS H1 Detectors instrumentation: • Liquid argon calorimeter (H1) • and compensated uranium • calorimeter (ZEUS) • Tracking and vertex detectors • Silicon micro-strip detectors • Muon barrels and endcaps

  3. Deeply Inelastic Scattering high x, low Q2 NC event low Q2 NC event e p high Q2 NC event CC event e p H1 ZEUS

  4. HERA I Neutral Current Charged Current NC and CC Cross-sections NC cross-section (ץ*, Z0): CC cross-section (W±): Reduced cross sections:

  5. e- e+ Neutral Current QPM (FL=0): Z exchange increases electron proton cross section and reduces positron proton cross section at large Q2 HERA I:

  6. Z0 Contribution at High Q2 Measurements of xF3 provide a constraint on u, d valence quark densities at large x

  7. Proton Structure at Low x Steep rise towards low x driven by: - sea quark densities - gluon densities δF2/ δ(lnQ2) at low x reflects the gluon mo- mentum distributions. at low x gluon density dominates !

  8. Structure Function FL Decreasing of the NC cross section at low x (high y) is due to FL Extrapolation:

  9. e- e+ Charged Current CC processes provide flavor information at high x: measurements of uV and dV densities

  10. HERA II Electron Beam Positron Beam CC with Polarised e± Beams Linear dependence of CC cross section on the longitudinal polarisation of the electron and positron beams

  11. Parton Distribution Functions and αS Determination of PDFs by H1 and ZEUS using NC and CC events measurements only Strong coupling constant αS as measured from jet rates and from jets and NLO QCD fits to structure functions.

  12. Contribution from Heavy Quarks Classical method: reconstruct D* New measurement: a c-quark lifetime tagging using the silicon detectors. The first measurement of 75 pb-1 The contribution of c and b quarks up to 30% and 3% respect.

  13. Outlook H1 and ZEUS collect data with high luminosity and e± polarized beams. Physics of HERA II has begun. More statistics will lead to higher precision in structure analyses. Acknowledgments • H1 Collaboration • ZEUS Collaboration • DESY directorate

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