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W Physics at LEP Paolo Azzurri Pisa (ALEPH-CMS ) Hanoi August 7, 2004 5th Rencontres du Vietnam New Views in Particle Physics Slide 2 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Outline W-pair production at LEP2 W Gauge Couplings W Decay Couplings Other four fermion processes W mass Slide 3 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Introduction a clear evidence of the presence of Standard Model triple gauge couplings and of their SU(2) U(1) structure the first direct measurements of the W decay branching ratios, and from these: a direct test of the W lepton family and lepton-quark universality to 1% and 0.5% a test of CKM unitarity and best current determination of the Vcs amplitude an independent W mass measurement at production threshold (200 MeV accuracy) a direct measurement of the W mass and width with 40 MeV and 90 MeV accuracy The study of W-pair production at LEP2 was a nice and exciting work that provided: Slide 4 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W-pair production at LEP2 Slide 5 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W-pair production CC03 diagrams (not gauge invariant) LEP2 produced about 10000 WW events/exp. with ~700pb -1 /exp. Expect: per experiment. Slide 6 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W-pair event selection Clear event decay... sophisticated selections qq qq,We qq qq,Zee , ,ll bkg 75-80%80-90%qqqq 80-85%50-80% qq ~95%75-90% qq ~90%75-90% e qq 80-90%50-80% l purity efficiencyChannel Slide 7 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W-pair cross sections Test of the SM radiative corrections to the CC03 diagrams Clear proof of SU(2)xU(1) gauge couplings ! Precision better than 1% s (GeV) WW (pb) Slide 8 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W Gauge Couplings Slide 9 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Triple Gauge Couplings Standard electroweak theory U(1) SU(2) triple and quartic SU(2) gauge boson self couplings The signature of the non-abelian SU(2) electroweak structure ! Slide 10 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Triple Gauge Couplings The most general Lorentz Invariant WWV (V= ,Z) vertex has 7 complex couplings Slide 11 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W-pair angular distributions The WWZ and WW gauge couplings can be measured in W-pair events, fitting the W-pair event rates and the W production and decay angular distributions. Slide 12 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Triple Gauge Couplings Standard measurements of three TGC couplings that conserve C and P, U(1) em and global SU(2) L U(1) Y one dimensional fit results (LEP): Relaxing all constraints and fitting for any of the 28 WWZ and WW couplings one-dimensional fit results for the SM non-zero TGC values (ALEPH data only) all other 24 couplings are consistent with zero (within 5-20%) ! Slide 13 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W Decay Couplings Slide 14 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W leptonic couplings Direct test of W lepton universality at the 1% precision level Slide 15 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W hadronic couplings Direct test of W quark-lepton universality at the 0.6% precision level Slide 16 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Other four fermion processes Slide 17 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Z-pairs In agreement with SM within 5% precision No gauge self couplings involved in Standard Model Z-pair production Slide 18 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Single W and Z In agreement with SM within 8% precisionIn agreement with SM within 7% precision Slide 19 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W mass Slide 20 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W mass Improve the W invariant mass resolution: kinematic fit energy-momentum conservation (equal mass constraints) Direct kinematic reconstruction of the W mass in qqqq, qq l (and l l ) final states m W value extracted with different methods Breit-Wigner fit (with bias correction) Monte Carlo reweighting (with different observables M 1,M) Probability Density function P(M 1,M 2,..) Statistical power of the LEP2 data: m W (stat)=21 MeV Slide 21 5th Rencontres du VietnamP.Azzurri - W Physics at LEP W mass systematics The fully hadronic channel is de-weighted to 0.10 for possible final state interconnection effects ! m W (qqqq)= 80.420107 MeV m W (qq l )= 80.411 44 MeV (=0.18) m W (qqqq-qq l )= +2243 MeV without CR and BE errors Slide 22 5th Rencontres du VietnamP.Azzurri - W Physics at LEP Hadronic final state interactions Bose-Einstein correlations: measure two particle correlations between Ws / inside Ws full effect m W =35 MeV measured fraction m W =15 MeV Colour Reconnection effects: measure particle flow in regions between Ws / inside Ws upper limits: k i