Electroweak Physics Lecture 5 Contents Top Event in the Detector Top Event Reconstruction Top Mass: Matrix Element Method

Electroweak Physics Lecture 5 Contents Top Event in the Detector Top Event Reconstruction Top Mass: Matrix Element Method www.phwiki.com

Electroweak Physics Lecture 5 Contents Top Event in the Detector Top Event Reconstruction Top Mass: Matrix Element Method

Raff, Samuel, Founding Editor has reference to this Academic Journal, PHwiki organized this Journal Electroweak Physics Lecture 5 Contents Top quark mass measurements at Tevatron Electroweak Measurements at low energy: Neutral Currents at low momentum transfer normally called low Q2 Q is the four momentum of the boson Precision measurements on muons We didn’t get to this in the lecture Slides are at the end Top Event in the Detector 2 jets from W decay 2 b-jets ± Nicest decay mode: Ws decay to lepton+jets

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Top Event Reconstruction Top Mass: Largest Systematic Effect Jet Energy Scale (JES) How well do we know the response of the calorimeters to jets In Lepton+Jets channels: 2 b-jets, 2 jets from Wqq, + Use jets from W decay (known mass) to calibrate JES Example of CDF analysis: simulation Mtop = 173.5 +2.7/-2.6 (stat) ± 2.5 (JES) ± 1.5 (syst) GeV/c2 JES = 0.10 +0.78/0.80 sigma ~16% improvement on systematic error Top Mass: Matrix Element Method

Matrix Element Method in Run II Probability as long as event to be top with given mtop: Use negative log likelihood to find best value as long as mtop: Top Mass: Template Method Dependence of reconstructed mass on true mass parameterized from fits to MC Include background templates constrained to background fraction Top Quark Mass Results

Top Quark Cross Section Test of QCD prediction: Search as long as Single Top Production Can also produce single top quarks through decay of heavy W boson Probe of Vtd Search in both s in addition to t channel Currently limit set <10.1 pb @ 95%C.L. Don’t expect a significant single until 2fb-1 of data are collected W helicity in Top Decays Top quarks decay be as long as e then can hadronise Decay products retain in as long as mation about the top spin Measure helicity of the W to test V-A structure of tWb decay F+ mb²/mW²0 Use W decays Effects in many variables: pT, cos of lepton mass of (lepton+jet) No discrepancies found, need more data as long as precision CDFII 200pb1 Tevatron Summary: mtop in addition to MW CDF in addition to DØ have extensive physics programme Most important EWK measurements are MW in addition to mtop Stated aim as long as RunII: mtop ±2.5 GeV/c2 MW to ±40 MeV/c2 Probably can do better Other EWK tests possible too! Two More Measurements as long as Our Plot Extracted from (e+eff) Afb (e+e) ALR polarisation asymmetry b in addition to c quark final states From Tevatron Tevatron + LEPII Electroweak Physics at Low Energy Low momentum transfer, Q, of the boson Test whether EWK physics works at all energy scales Møller Scattering Neutrino-Nucleon Scattering Atomic Parity Violation Plus: muon lifetime in addition to muon magnetic moment Running of sin²W The effective value of sin²eff is depend on loop effects These change as a function of Q², largest when Q²MZ, MW Want to measure sin²eff at different Q² For exchange diagram ~2.5% E158: Møller Scattering eeee scattering, first measurement at SLAC E158 in 2002 in addition to 2003 Beam of polarised electrons 90%, Ee=48.3GeV Both L in addition to R h in addition to ed electron beams Incident on liquid hydrogen target Average Q² of 0.027 (GeV/c)² (Qboson~0.16 GeV/c) Measure asymmetry between cross section as long as L in addition to R beams:

Tree Level Diagrams Photon exchange will be dominant Asymmetry between L in addition to R terms (parity violation) is from Z-exchange small asymmetry Measured Asymmetry A = 131 ± 14 (stat) ± 10 (syst) ppb sin2Weff(Q2=0.026) = 0.2397 ± 0.0010 (stat) ± 0.0008 (syst) cf 0.2381 ± 0.0006 (theory) +1.1 difference NuTeV NuTeV = neutrinos at the Tevatron Inelastic neutrino-hadron scattering Huge chunk of instrumented iron With a magnet!

NuTeV Physics Two interactions possible: Neutral Current (NC) Charged Current (CC) Pachos Wolfenstein Relationship Requires both neutrino in addition to anti-neutrino beams No interference NuTeV Beams Beam is nearly pure neutrino or anti-neutrino 98.2% 1.8% e Nu beam contamination < 10³ Anti-nu beam contamination < 2 x 10³ Events in the Detector “Event Length” used to separate CC in addition to NC interactions Raff, Samuel Computers & Operations Research Founding Editor www.phwiki.com

NuTeV Result Doesn’t agree with Z pole measurements Atomic Parity Violation Test Z in addition to interaction with nucleons at low Q² Depends on weak charge of nucleon: Large uncertainty due to nuclear effects eg nucleon spin sin²W(Q) Results Some disquiet in the St in addition to ard Model, perhaps

Low Energy Summary Important to test EWK Lagrangian at different energy scale Challenging to achieve the level of precision to compare with theory! Experimental Challenges overcome, very precise results achieved Some (small) discrepancies found between data in addition to theory End of lecture Precision measurements on muons follow Muon Lifetime The lifetime of the muon is one of the test predicted parameters in the EWK + e+ e no hadronic effects One of the most precisely measured too, use it to set GF in the Lagrangian No recent measurement of just lifetime, current investigations of decay spectrum ()=(2.19703 ± 0.00004)X106

a: Results in addition to Comparison Very precise measurement! Another hint of a problem

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