Emily Nurse W production and properties at CDF0

Emily Nurse W production and properties at CDF1 The electron and muon channels are used to measure W properties, due to their clean experimental signature. The large mass (~80 GeV ) of W bosons gives their decay products large p T. W events can be used to: constrain the QCD part of the production mechanism: W charge asymmetry. measure W properties: W mass (see talk by Oliver Steltzer-Chilton) and W width. W production at the Tevatron C.O.M energy = 1.96 TeV

Emily Nurse W production and properties at CDF2 e  Detecting W decay particles at CDF SILICONSILICON DRIFT CHAMBER SOLENOIDSOLENOID EM HADRONIC MUON CHAMBERS Electrons: detected in central trackers (p measurement) and EM calorimeter (E measurement). Muons: detected in central trackers (p measurement), calorimeter (MIP signal) and muon chambers. Neutrinos : not detected! Vector sum the total transverse energy (E T =Esin  ) in calorimeters. “Missing E T ” inferred as neutrino p T. TRACKERSCALORIMETERS

Emily Nurse W production and properties at CDF3 W charge asymmetry: introduction xf(x,Q 2 ) x Q 2 = 100 GeV 2 MRST2004NLO u p W+W+ ud uu u d p e+e+ e d W-W- W+W+ y protonantiproton Parton Distribution Functions describe the momentum distribution of partons in the (anti-)proton. They are constrained by fits to data. Fraction of proton momentum carried by quark W production and properties at CDF (helps constrain PDFs!)

Emily Nurse W production and properties at CDF4 W charge asymmetry: from e +(-) asymmetry Since p L is not known the W  rapidity cannot be reconstructed  traditionally the electron charge asymmetry is measured. The V-A structure of the W +(-) decay favours a backward (forward) e +(-) “diluting” the W charge asymmetry.

Emily Nurse W production and properties at CDF5 W charge asymmetry: direct measurement This CDF measurement (performed in W  e channel): p L determined by constraining M W = 80.4 GeV  two possible y W solutions. Each solution receives a weight probability according to: a)V-A decay structure b)W cross-section:  (y W ) (Process iterated since  (y W ) depends on asymmetry)

Emily Nurse W production and properties at CDF6 W width : introduction Predicted very precisely within the Standard Model by summing the leptonic and hadronic partial widths:  W SM = 2091 ± 2 MeV [PDG: J. Phys. G 33, 1] Deviations from this prediction suggest non-SM decay modes.  W is an input to the W mass measurement:  M W ~  W / 7 WW Ideally we would reconstruct the invariant mass of the decay products to measure  W, since isn’t detected we reconstruct the transverse mass: MWMW

Emily Nurse W production and properties at CDF7 W width : Analysis strategy Simulate m T distribution with a dedicated fast parameterised MC (using a Breit-Wigner lineshape). MC simulates QCD (RESBOS Balazs et.al. PRD56, 5558 ) and QED (Berends & Kleiss Berends et.al. ZPhys. C27, 155 ) corrections. Utilise Z  ll (and W  l ) data to calibrate the detector to a high precision. Fit m T templates (with  W varying) to the data, fit range: GeV optimised to reduce total uncertainty

Emily Nurse W production and properties at CDF8 W width : Lepton p T   momentum measured in central tracker - scale and resolution calibrated using Z  resonance. e  energy measured in EM calorimeter - scale and resolution calibrated using Z  ee resonance and E/p in W  e data.

Emily Nurse W production and properties at CDF9 W width : Neutrino p T p T inferred from E T miss U=(U x, U y )=  towers Esin  ( cos , sin  ) vector sum over calorimeter towers Excluding those surrounding lepton p T = E T miss = -(U + p T lep )p T = E T miss = -(U + p T lep ) U mostly comes from gluon radiation from incoming quarks (also Underlying Event (UE), photons from bremsstrahlung). Accurate predictions of U (QCD radiation, UE, hadronisation and detector response to hadrons) is difficult (and slow) from first principles. Devise an ad-hoc parameterised model of the recoil in terms of the boson p T, tuned to the recoil in Z  ll events (where the Z p T can be reconstructed).

Emily Nurse W production and properties at CDF10 W width: results  W = 2032  71 (stat + syst) MeV

Emily Nurse W production and properties at CDF11 W width: systematic uncertainties

Emily Nurse W production and properties at CDF12 W width: world average Central value decreases by 44 MeV: 2139  2095 MeV Uncertainty reduced by 22%: 60  47 MeV World’s most precise single measurement!

Emily Nurse W production and properties at CDF13 Indirect Width Measurement R = WW ZZ  (Z  ll)  (W  l )  (W)  (Z) XX R exp =   BR (W  l )   BR (Z  ll) Precision LEP Measurements SM Calculation NNLO Calculation CDF Run II INDIRECT width (72 pb -1 ): 2092 ± 42 MeV PRL 94, CDF Run II DIRECT width (350 pb -1 ): 2032 ± 71 MeV preliminary

Emily Nurse W production and properties at CDF14 Summary W charge asymmetry measurement - will help constrain PDFs (due to be updated this summer). W width measurement (world’s most precise measurement!) - consistent with the Standard Model prediction and indirect measurement.

Emily Nurse W production and properties at CDF15 Back-up slides

Emily Nurse W production and properties at CDF16 e asymmetry |||| ||||

Emily Nurse W production and properties at CDF17 Hadronic Recoil: U U1U1 U2U2 Accurate predictions of U is difficult (and slow) from first principles. U simulated with ad-hoc parameterised model, tuned on Z  ll data. U split into components parallel (U 1 ) and perpendicular (U 2 ) to Z p T 7 parameter model describes the response and resolution in the U 1 and U 2 directions as a function of the Z p T. Systematic comes from parameter uncertainties (limited Z stats). Z  ee responseresolution Data MC

Emily Nurse W production and properties at CDF18 W  e Hadronic Recoil: U (p T ) U || U U U split into components parallel (U || ) and perpendicular (U  ) to charged lepton. Many distributions used to cross check the model in W  l data: Data MC W  e

Emily Nurse W production and properties at CDF19 multijet muon channel only: Jet fakes/contains a lepton E T miss from misconstruction electron and muon channel: Backgrounds Z  ll One lepton lost E T miss from missing lepton WW  decays to e/  intrinsic E T miss Decay In-Flight x x x x x x x x K,  fake high-p T track Kaon/pion decays “In-Flight” to a . Kink in track gives high-p T measurement. E T miss from mis-measured track p T. Need the m T distributions and the normalisations!

Emily Nurse W production and properties at CDF20 Backgrounds