Measurement of the ratio. sigma. ter dot B. tau. (W sup + yields ell sup +. nu. )/. sigma. ter dot B. tau. (Z sup 0 yields ell sup + ell sup minus ) and interpretation at the CERN proton-antiproton collider
The cross-section times branching ratio {sigma}{center dot}B{tau} for the leptonic decays W{sup {plus minus}} {yields} {ell}{sup {plus minus}}{nu} and Z{sup 0} {yields} {ell}{sup +}{ell}{sup {minus}} is measured with the UA1 detector at the CERN proton-antiproton collider. Averaging between electron and muon channels gives {sigma}{center dot}B{tau}(W{sup {plus minus}} {yields} {ell}{sup {plus minus}}{nu}) = 0.63 {plus minus} 0.11 nb and {sigma}{center dot}B{tau}(Z{sup 0} {yields} {ell}{sup +}{ell}{sup {minus}}) = 0.071 {sub {minus}0.013}{sup +0.016} nb at {radical}s = 630 GeV. The {sigma}{center dot}B{tau} for individual electron, muon, and tau channels imply g{sup {mu}}/g{sub e} = 1.00{sub {minus}0.006}{sup +0.09}, g{sub {tau}}/g{sub e} = 1.01{sub {minus}0.09}{sup +0.15}, and k{sup {mu}}/k{sub e} = 1.00{sub {minus}0.10}{sup +0.19}, where g and k are the W and Z leptonic coupling strengths, respectively. These ratios verify lepton universality at q{sup 2} {approx equal} m{sub W}{sup 2} to about 10%. The ratio R {identical to} {sigma}{center dot}B{tau}(W{sup {plus minus}} {yields} {ell}{sup {plus minus}}{nu})/{sigma}{center dot}B{tau}(Z{sup 0} {yields} {ell}{sup +}{ell}{sup {minus}}) is used to constrain the number of light neutrino types, N{sub {nu}}. The measured value R = 9.1{sub {minus}1.0}{sup +1.9} is combined with the equivalent result of UA2 to give R = 8.4{sub {minus}0.8}{sup +1.3}. The upper limit is then R < 10.1 at 90% confidence, which implies that for a top quark heavier than 44 GeV/c{sup 2} (the current lower bound), N{sub {mu}} < 4.6. Imposing the physical constraining N{sub {mu}} {ge} 3 and allowing only integral values of N{sub {nu}} gives N{sub {nu}} {le} 5 at 91% confidence. The sensitivity of R to nonstandard physics is explored. The ratio and hence limit for N{sub {nu}} are found to be insensitive to sequential leptons, sleptons, light technipions, and charged Higgs bosons.
- Research Organization:
- Harvard Univ., Boston, MA (USA)
- OSTI ID:
- 5011685
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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