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XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001

XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001. High Q 2 Physics. Christopher M. Cormack Rutherford Appleton Laboratory. Contents.

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XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001

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  1. XXI Physics in Collision Conference Seoul Korea June 28 - 30 2001 High Q2 Physics Christopher M. Cormack Rutherford Appleton Laboratory

  2. Contents A very broad range of subjects for High Q2 and High PT - Results include Structure Functions from H1 + ZEUS Exotics Phenomena - overlap with HERA, LEP, TEVATRON • Introduction • HERA • DATA • H1 / ZEUS Detectors • Neutral Current • Z Exchange • Charged Current • W Exchange • New Physics ? • LQ Resonances • Isolated Leptons • Top Searches • The Future • Summary + Outlook High Q2 Physics - C.M. Cormack

  3. Introduction The Electron-Proton Collider 1998-2000 e+p and e-p 1994-1997 Luminosity Delivered High Q2 Physics - C.M. Cormack

  4. e+/- ,Q2 HERA Deep Inelastic Scattering Kinematics Kinematic Variables Resolving power Negative of the four-momentum transfer between lepton and proton “Momentum fraction of proton carried by the struck quark” Inelasticity Momentum fraction of the lepton carried by the exchange High Q2 Physics - C.M. Cormack

  5. HERA KINEMATIC PLANE • Accessible Kinematic Plane now almost completely covered • Measurements extend to cover high y, high x and very high Q2 • Probe distances to ~ 1/1000th of proton size High Q2 Physics - C.M. Cormack

  6. e+/- p NC H1 Detector at HERA Fine Grained Liquid Argon Calorimeter (45 000 channels) EM section HAD section Tracking Chambers High Q2 Physics - C.M. Cormack

  7. CC ZEUS Detector at HERA Compensating Uranium-Scintillator Calorimeter EM section HAD section Tracking Chambers High Q2 Physics - C.M. Cormack

  8. Photon, Z couples to all quark flavours Z exchange Parity Violating term - sensitivity to valence quarks Neutral Current DIS Structure Functions Longitudinal structure function L.O. QCD: Reduced cross section High Q2 Physics - C.M. Cormack

  9. Neutral Current DIS - • Standard Model shows good agreement over 6 orders of magnitude • Effect of the Z0 contribution fron xF3 clearly seen at high Q2 High Q2 Physics - C.M. Cormack

  10. Neutral Current DIS - Effect of Z0 Exchange • e - pDATA requiresCONSTRUCTIVE - Z interference • e +P DATA requires DESTRUCTIVE interference High Q2 Physics - C.M. Cormack

  11. Neutral Current DIS - Reduced Cross Section • SM shows good agreement with data over all Q2 range High Q2 Physics - C.M. Cormack

  12. High Precision at low to medium Q2, x • First measurements at high Q2 and x •  - Z interference seen xF3 Neutral Current DIS - Reduced Cross Section High Q2 Physics - C.M. Cormack

  13. y2 FL small at high Q2 Need high y Neutral Current DIS - Fl Extraction H1 data extend to small electron energies  Bjorken y < 0.75 Sign of xF3 term depends on lepton charge First Measurement of Longitudinal Structure Function FL at High Q2 High Q2 Physics - C.M. Cormack

  14. Neutral Current DIS - xF3 y2 FL small at high Q2 • First extraction of xF3 on PROTONat high Q2, x Direct Sensitivity to the valence quarks! High Q2 Physics - C.M. Cormack

  15. e+p:d, s and u, c e-p:u, c and d, s Charged Current DIS Structure Functions `invisible`Missing PT Q2 W exchange L.O. CROSS SECTIONS Probed valence Probeu valence • Sensitivity to separate parton densities • Effect of W mass - from propagator Reduced Cross Section High Q2 Physics - C.M. Cormack

  16. Charged Current DIS - • Effect of different parton densities seen from lower Q2 • Factor of 10 difference in e+/e- cross section at high Q2 High Q2 Physics - C.M. Cormack

  17. Charged Current DIS • Need for more d at high x ? High Q2 Physics - C.M. Cormack

  18. Charged Current DIS • Possibility to extract d/u using proton as target - Higher Statistics High Q2 Physics - C.M. Cormack

  19. Charged Current DIS - Fitting MW Q2 dependence of CC cross section includes propagator term Consistency check rather than a measurement of MW August-99 world average: MW = 80.376  0.039 GeV High Q2 Physics - C.M. Cormack

  20. Searches for New Physics The High Q2 / PT Range Accessible at HERA allows the competitive searches in many areas for New Physics. • Some of the Topics Covered • W/Z production - High PT Leptons • Single Top Production • New Lepton-Quark Interactions • Excited Fermions / Quark Substructure • SuperSymmetry - Talks from U. Heintz & M. Chertok High Q2 Physics - C.M. Cormack

  21. H1 Since 1994 Both Experiments Have observed a strange type of Event Produced at High PT With Isolated Leptons and Missing PT Observation of Events at High PT with Isolated Muons ZEUS

  22. e e’  / Z0 q e e’ W q  / Z0 q W q Isolated High PT Leptons • A class of Interesting events at HERA • Sensitivity to rare Standard Model Processes Single - W Production Leptonic decay of W  events with a high energy lepton and missing transverse momentum NLO calculations are underway M. Spira New Physics Stop and Sbottom production R-Parity Violating Supersymmetery Single Top production through anomalous flavour changing Neutral Current Coupling (FCNC) High Q2 Physics - C.M. Cormack

  23. Neutrino Jet Acoplanarity Lepton Isolated High PT Leptons W l  Kinematics Expect a peak at W mass for W l  High Q2 Physics - C.M. Cormack

  24. H1 Isolated High PT Leptons 0 Events found with electron running High Q2 Physics - C.M. Cormack

  25. ZEUS - Isolated High PT Leptons • Search for high PT tracks in high PTCAL sample • PTCAL > 25 GeV • Pttrack > 10 GeV Check Isolation of high Pttrack wrt to other tracks (Dtrack) and Jets (Djet) Event Rate Consistent with SM Prediction High Q2 Physics - C.M. Cormack

  26. Comparison ZEUS - H1 Selecting the same Phase Space PTX > 25 GeV • SM expectations are in agreement • H1 sees more events at high PTX • ZEUS has the acceptance to detect events • Statistical fluctuation from the SM or an indication of Physics BSM? More Data Soon High Q2 Physics - C.M. Cormack

  27. Anomalous Single Top Production Single-top production with anomalous FCNC coupling • ZEUS Leptonic Channel: • Final state with high PT Lepton and large PTX • ZEUS Dtrack > 0.5, Djet> 1.0 and PTX > 40 GeV • ZEUS sees no events • H1 Leptonic Channel: • Final state with high PT (Jet) > 35 (25)Lepton and (jet) < (>) 35o • MTlv > 10 GeV (Reject -ve leptons) • H1 sees 5 events(3e+2) for 1.4  0.5 expected Limits for Anomalous FCNC couplings  coupling LEP e+ e- tc,tu TEVATRON RARE TOP DECAY High Q2 Physics - C.M. Cormack

  28. ZEUS and H1 Isolated Lepton Control Plots H1 Observes an excess of Isolated High PT Events ZEUS  sample Event rate consistent with Standard Model High Q2 Physics - C.M. Cormack

  29. Search for New particles Look for the direct production of resonances with Mass M < s Look for deviations in SM cross section - CONTACT Interactions • This presentation - Leptoquarks (LQ) • Squarks in SUSY • Excited Fermions • Leptoquarks (LQ) • Scalar and Vector, colour triplet bosons • Carry Fermion number F=3B+L=0,2 • Decays - Look for Resonances in e q system • Generic Models LQ  l q • LQ   q High Q2 Physics - C.M. Cormack

  30. e SCALAR LQ: e’  / Z0 q q e e LQ q q Resonance Hunting 1 Mass plots H1 and ZEUS + limits NC DIS Me / MCJ W Intriguing HERA events caused excitement in past years What About New DATA ? High Q2 Physics - C.M. Cormack

  31. Resonance Hunting 2 Analysis of Latest 1999 -2000 Data Excess in old data not confirmed by New DATA H1 / ZEUS  Derive Limits on LQ couplings  and Masses MLQ (In BRW Model) LEP -Virtual effects to hadronic xsec Tevatron - LQ produced via strong coupling HERA - Stringent limits for intermediate mass range High Q2 Physics - C.M. Cormack

  32. Limits from New Data • Quick look at Contact Interactions • Large Mass Leptoquarks - See Previous • Large Extra Dimensions - Kaluza-Klein Gravitons • Compositness - Quark Radius Kaluza-Klein Graviton Exchange - Effective contact interaction H1 M-S > 0.93 TeV M+S > 0.63 TeV ZEUS M-S > 0.82 TeV M+S > 0.81 TeV High Q2 Physics - C.M. Cormack

  33. Contact Interactions Quark form factor: Rq - quark radius ZEUS Rq <0.73 x 10-16 cm H1 Rq <1.6 x 10-16 cm The HERA electron microscope probing scales to 1/1000th the size of the proton High Q2 Physics - C.M. Cormack

  34. The HERA Upgrade • Luminosity Upgrade: • Large increase on present luminosity • Running Programme: • Five years of running • starting in September 2001 •  1000 pb-1 for both H1 / ZEUS • Polarisation for Collider Experiments: • Longitudinally Polarised electron/positron beams •  60% (design goal) • Measurements of NC and CC DIS using high luminosity and • upgraded detectors will constrain: • Singlet, non-singlet quark densities • u, d, s (CC DIS) • c, b, g (NC DIS) • i.e. COMPLETE study of proton structure Measurements of NC and CC DIS using high luminosity and upgraded detectors will constrain: Singlet, non-singlet quark densities u, d, s (CC DIS) c, b, g (NC DIS) i.e. COMPLETE study of proton structure High Q2 Physics - C.M. Cormack

  35. x = 0.65 Q2 = 4  104 1000 pb-1 Future Physics - The Structure Function F2 1000 pb-1 High precision Structure Function measurements - high x constraints important for high energy processes at Tevatron and LHC Opportunities for a discovery To complement those at the Tevatron High Q2 Physics - C.M. Cormack

  36. Outlook for HERA Summary - HERA High Q2 Physics • Results shown of High Q2 NC + CC cross sections - with high statistics data sets (e- & e+) • Wealth of Data + measurements allowing tests of QCD and Electroweak parameters • The recent 16 pb-1 electron data has allowed the first extraction of xF3 the last unmeasured proton structure function - Effect of - Z interference observed • High Q2 cross sections are well described by the Standard model - a triumph for QCD • Opportunity to constrain pdfs (d/u ratio) at high x possible with clean proton target • Need for forth coming higher statistics to improve Charged Current xsec and better constraint on the high x valence pdfs - xF3 • Oportunity for discovery (LQ) • More Isolated Leptons ? The HERA Upgrade High Q2 Physics - C.M. Cormack

  37. Sign of xF3 term depends on lepton charge y2 FL small at high Q2 Neutral Current DIS - xF3 Extraction Extraction Method • Error limited by electron sample (16 pb-1) • Positron data sample (30 pb-1) High Q2 Physics - C.M. Cormack

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