XXI Physics in Collision Conference Seoul Korea June Christopher M. Cormack Rutherford Appleton Laboratory High Q 2 Physics

PIC th June 2001 High Q 2 Physics - C.M. Cormack 1/35 Contents 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 A very broad range of subjects for High Q 2 and High P T - Results include Structure Functions from H1 + ZEUS Exotics Phenomena - overlap with HERA, LEP, TEVATRON

PIC th June 2001 High Q 2 Physics - C.M. Cormack 2/35 The Electron-Proton Collider e + p and e - p Introduction Luminosity Delivered

PIC th June 2001 High Q 2 Physics - C.M. Cormack 3/35 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 e +/-,Q 2

PIC th June 2001 High Q 2 Physics - C.M. Cormack 4/35 HERA KINEMATIC PLANE Accessible Kinematic Plane now almost completely covered Measurements extend to cover high y, high x and very high Q 2 Probe distances to ~ 1/1000 th of proton size

PIC th June 2001 High Q 2 Physics - C.M. Cormack 5/35 H1 Detector at HERA NC e +/- p Fine Grained Liquid Argon Calorimeter ( channels) EM section HAD section Tracking Chambers

PIC th June 2001 High Q 2 Physics - C.M. Cormack 6/35 ZEUS Detector at HERA Compensating Uranium-Scintillator Calorimeter EM section HAD section Tracking Chambers CC

PIC th June 2001 High Q 2 Physics - C.M. Cormack 7/35 L.O. QCD: Neutral Current DIS Structure Functions Longitudinal structure function Reduced cross section Photon, Z couples to all quark flavours Parity Violating term - sensitivity to valence quarks Z exchange

PIC th June 2001 High Q 2 Physics - C.M. Cormack 8/35 Standard Model shows good agreement over 6 orders of magnitude Effect of the Z 0 contribution fron xF 3 clearly seen at high Q 2 Neutral Current DIS -

PIC th June 2001 High Q 2 Physics - C.M. Cormack 9/35 Neutral Current DIS - Effect of Z 0 Exchange e - p DATA requires CONSTRUCTIVE  - Z interference e + P DATA requires DESTRUCTIVE interference

PIC th June 2001 High Q 2 Physics - C.M. Cormack 10/35 Neutral Current DIS - Reduced Cross Section SM shows good agreement with data over all Q 2 range

PIC th June 2001 High Q 2 Physics - C.M. Cormack 11/35 Neutral Current DIS - Reduced Cross Section High Precision at low to medium Q 2, x First measurements at high Q 2 and x  - Z interference seen xF 3

PIC th June 2001 High Q 2 Physics - C.M. Cormack 12/35 Neutral Current DIS - F l Extraction  Bjorken y < 0.75 First Measurement of Longitudinal Structure Function F L at High Q 2 H1 data extend to small electron energies Sign of xF 3 term depends on lepton charge y 2 F L small at high Q 2 Need high y

PIC th June 2001 High Q 2 Physics - C.M. Cormack 13/35 Neutral Current DIS - xF 3 First extraction of xF 3 on PROTON at high Q 2, x Direct Sensitivity to the valence quarks! y 2 F L small at high Q 2

PIC th June 2001 High Q 2 Physics - C.M. Cormack 14/35 Charged Current DIS Structure Functions e + p: d, s and u, c e - p: u, c and d, s `invisible`  Missing P T Q2Q2 Sensitivity to separate parton densities Effect of W mass - from propagator Probe d valence Probe u valence Reduced Cross Section W exchange L.O. CROSS SECTIONS

PIC th June 2001 High Q 2 Physics - C.M. Cormack 15/35 Charged Current DIS - Effect of different parton densities seen from lower Q 2 Factor of 10 difference in e+/e- cross section at high Q 2

PIC th June 2001 High Q 2 Physics - C.M. Cormack 16/35 Charged Current DIS Need for more d at high x ?

PIC th June 2001 High Q 2 Physics - C.M. Cormack 17/35 Charged Current DIS Possibility to extract d/u using proton as target - Higher Statistics

PIC th June 2001 High Q 2 Physics - C.M. Cormack 18/35 Charged Current DIS - Fitting M W Consistency check rather than a measurement of M W August-99 world average: M W =  GeV Q 2 dependence of CC cross section includes propagator term

PIC th June 2001 High Q 2 Physics - C.M. Cormack 19/35 Searches for New Physics The High Q 2 / P T Range Accessible at HERA allows the competitive searches in many areas for New Physics. Some of the Topics Covered W/Z production - High P T Leptons Single Top Production New Lepton-Quark Interactions Excited Fermions / Quark Substructure SuperSymmetry - Talks from U. Heintz & M. Chertok

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

PIC th June 2001 High Q 2 Physics - C.M. Cormack 21/35 Isolated High P T Leptons A class of Interesting events at HERA  Sensitivity to rare Standard Model Processes Single - W Production e e’e’  / Z 0 q q W New Physics Leptonic decay of W  events with a high energy lepton and missing transverse momentum NLO calculations are underway M. Spira e e’e’  / Z 0 q q W Stop and Sbottom production R-Parity Violating Supersymmetery Single Top production through anomalous flavour changing Neutral Current Coupling (FCNC)

PIC th June 2001 High Q 2 Physics - C.M. Cormack 22/35 Isolated High P T Leptons W  l Kinematics Expect a peak at W mass for W  l Acoplanarity Neutrino Jet Lepton

PIC th June 2001 High Q 2 Physics - C.M. Cormack 23/35 H1 Isolated High P T Leptons 0 Events found with electron running

PIC th June 2001 High Q 2 Physics - C.M. Cormack 24/35 ZEUS - Isolated High P T Leptons Search for high P T tracks in high P T CAL sample P T CAL > 25 GeV P t track > 10 GeV Check Isolation of high P t track wrt to other tracks (D track ) and Jets (D jet ) Event Rate Consistent with SM Prediction

PIC th June 2001 High Q 2 Physics - C.M. Cormack 25/35 Comparison ZEUS - H1 Selecting the same Phase Space P T X > 25 GeV SM expectations are in agreement H1 sees more events at high P T X ZEUS has the acceptance to detect events Statistical fluctuation from the SM or an indication of Physics BSM? More Data Soon

PIC th June 2001 High Q 2 Physics - C.M. Cormack 26/35 Anomalous Single Top Production Single-top production with anomalous FCNC coupling ZEUS Leptonic Channel: Final state with high P T Lepton and large P T X ZEUS D track > 0.5, D jet > 1.0 and P T X > 40 GeV ZEUS sees no events H1 Leptonic Channel: Final state with high P T (Jet) > 35 (25)Lepton and  (jet) ) 35 o M T lv > 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

PIC th June 2001 High Q 2 Physics - C.M. Cormack 27/35 ZEUS and H1 Isolated Lepton Control Plots H1 ZEUS Event rate consistent with Standard Model Observes an excess of Isolated High P T Events  sample

PIC th June 2001 High Q 2 Physics - C.M. Cormack 28/35 Search for New particles This presentation - Leptoquarks (LQ) Squarks in SUSY Excited Fermions Look for the direct production of resonances with Mass M <  s Look for deviations in SM cross section - CONTACT Interactions 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

PIC th June 2001 High Q 2 Physics - C.M. Cormack 29/35 Mass plots H1 and ZEUS + limits Resonance Hunting 1 W e e’e’  / Z 0 qq e q e q LQ NC DISSCALAR LQ: Intriguing HERA events caused excitement in past years What About New DATA ? M e / M CJ

PIC th June 2001 High Q 2 Physics - C.M. Cormack 30/35 Resonance Hunting 2 Analysis of Latest Data Excess in old data not confirmed by New DATA H1 / ZEUS  Derive Limits on LQ couplings and Masses M LQ (In BRW Model) LEP - Virtual effects to hadronic xsec Tevatron - LQ produced via strong coupling HERA - Stringent limits for intermediate mass range

PIC th June 2001 High Q 2 Physics - C.M. Cormack 31/35 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

PIC th June 2001 High Q 2 Physics - C.M. Cormack 32/35 Contact Interactions Quark form factor: R q - quark radius ZEUS R q <0.73 x cm The HERA electron microscope probing scales to 1 / 1000 th the size of the proton H1 R q <1.6 x cm

PIC th June 2001 High Q 2 Physics - C.M. Cormack 33/35 The HERA Upgrade 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 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

PIC th June 2001 High Q 2 Physics - C.M. Cormack 34/35 - The Structure Function F pb -1 x = 0.65 Q 2 = 4  10 4 Future Physics Opportunities for a discovery To complement those at the Tevatron High precision Structure Function measurements - high x constraints important for high energy processes at Tevatron and LHC

PIC th June 2001 High Q 2 Physics - C.M. Cormack 35/35 Summary - HERA High Q 2 Physics Results shown of High Q 2 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 xF 3 the last unmeasured proton structure function - Effect of  - Z interference observed High Q 2 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 - xF 3 Oportunity for discovery (LQ) More Isolated Leptons ? Outlook for HERA The HERA Upgrade

PIC th June 2001 High Q 2 Physics - C.M. Cormack 36/35 Neutral Current DIS - xF 3 Extraction Error limited by electron sample (16 pb -1 ) Positron data sample (30 pb -1 ) Extraction Method Sign of xF 3 term depends on lepton charge y 2 F L small at high Q 2