1、Recent Electroweak Physics Results from ATLAS,刘建北 中国科学技术大学 (University of Science and Technology of China),2013年TeV工作组工作会议, 大连 August 21, 2013,Higgs Independent Day,July 4th 2012 at CERN,I think we have it !,Rolf-Dieter Heuer, CERN Director General,Both Peter Higgs and Boson Higgs were found. What a
2、 great day!,But what had happened before the day,We rediscovered SM by measuring the known SM processes. Majority of these processes are related to electro-weak physics. These “rediscovery” measurements are mandatory for validating the understanding of detector performance, detector and physics simu
3、lations, objects reconstruction, event selections etc. A prerequisite for Higgs searches and studies. Electro-weak physics is quite important and interesting in its own right.,I will focus on,W /Z,+,Contents,W and Z production and decays Inclusive and differential cross sections High mass Drell-Yan
4、(off Z-pole) Asymmetry measurements Polarization measurements Diboson production Inclusive and differential cross sections Anomalous triple gauge couplings (aTGC),Production rates at LHC,W and Z production,Diboson production,Calibration and Performance Precision measurements (MW, sin2w ) SM tests at
5、 TeV scale (QCD, TGCs ) Input to PDFs Probe for new physics (VV resonances ) Backgrounds for Higgs and searches,W/Z inclusive cross sections (7 TeV),Fiducial cross sections,Total cross sections,Test higher order (NNLO) QCD calculations. Minimize theoretical extrapolation uncertainties by performing
6、fiducial measurements. General agreement with predictions. Some differentiation between PDF sets already observed.,dZ/dyZ and dW/dl (7 TeV),dZ/dyZ,dW/dl,More information is extracted to constrain PDFs Broadly well described by predictions Can impact PDF central values and uncertainties. Large portio
7、n of bosons at high rapidity due to valence-sea interactions: need large detection acceptance.,dZ/d* (7 TeV),An alternative variable to Z PT , purely built on angular measurements, less sensitive to experimental systematics, much better resolution compared to Z PT in low PT domain. Therefore its an
8、optimal observable to probe low Z PT region.,High precision: typical uncertainty 1% Compared to NNLO+NNLL calculations. None calculation can describe the detailed shape in data. Very powerful in testing theories and tuning generators.,High mass Drell-Yan (7 TeV),Test pQCD calculations and EW correct
9、ions including those arising from -induced processes. Sensitive to poorly known qbar PDF at large x. Compared to NNLO QCD + NLO EW Effect due to EW corrections is not small compared to differences between PDF sets.,W lepton charge asymmetry (7 TeV),Sensitive to valence quark distributions. An import
10、ant input to PDF fit. Complementary to DIS data. Discrimination between PDF sets observed at low rapidity.,Z forward-backward asymmetry (7 TeV),Unfolded asymmetry spectra,One of the very important precision EW measurements. Important input to global eletroweak fit. Observed asymmetries consistent wi
11、th SM predictions. Extracted weak mixing angle consistent with previous measurements, and as precise as the D0 result.,W polarization (7 TeV),W helicity states in production: left-handed fraction (fL), right-handed fraction (fR) and longitudinal polarized fraction (f0). Measured the W helicity compo
12、sition in high W PT regime.,Good agreement between data and MCNLO Predictions from POWHGE somewhat smaller than data, particularly in the high PT bin., polarization (7 TeV),Study polarization of from W decays:,Using a single charged meson + decay modes,Observable adopted,Compatible with left-handed
13、hypothesis as predicted in SM,First measurement of such kind at hadron colliders.,Dibson Results,Cross section results W, Z WW WZ ZZ aTGC limits,W, Z (7 TeV),Decay modes used: Wl, Zll, Z ,Differential E measurements,Inclusive and exclusive (Njets=0) cross sections,Agreement with NLO calculation is p
14、oor for W, but improved in Njet=0.,WW (7 TeV),Decay modes used: WWee, , e,Leading lepton PT,Different cross section w.r.t. Leading lepton PT,Integrated cross sections,Measured cross sections agree with SM predictions within uncertainties (measured slightly higher than predicted).,WZ (8 TeV),Using fu
15、lly leptonic decays of WZ: WZeee, e, ee, ,Measured and predicted cross sections agree.,ZZ (7 & 8 TeV),7TeV: ZZ2l2 8TeV: ZZ4l,Good agreement between measured and predicted cross sections for 8TeV. Measured cross section slightly higher than the predicted for 7TeV (but still within uncertainties).,Tri
16、ple Gauge Couplings,Forbidden in SM,* Introduce a form factor to each parameter to ensure unitarity,TGC Analysis,Use reweighting techniques (kinematic or matrix-element based) to access the full TGC parameter space. Exploit kinematic distributions that are sensitive to anomalous TGCs (aTGC) to deriv
17、e limits on aTGCs. W,Z: transverse energy WW: leading lepton PT WZ: Z transverse PT ZZ: leading Z transverse PT NLO calculations are needed for aTGC extraction.,NLO corrections (or even EW corrections) are substantial at large energy scale,Kinematic reweighting,aTGC effects on leading lepton PT,TGC
18、Results,Conclusions,Eletroweak physics program has entered precision stage in a lot of aspects at ATLAS. 8 TeV data will largely enter the game soon. Important testing ground for SM. Valuable input to MC validation and tuning. It is impressive to see agreement with theory across orders of magnitude. No significant deviations from SM have observed yet so far. Looking forward to higher luminosity and even higher energies to test Electroweak sector in more extreme phase spaces.,
