Search results for "Neutral current"
showing 10 items of 301 documents
Differential branching fractions and isospin asymmetries of B -> K ((*)) μ(+) μ(-) decays
2014
The isospin asymmetries of $B \to K\mu^+\mu^-$ and $B \to K^{*}\mu^+\mu^-$ decays and the partial branching fractions of the $B^0 \to K^0\mu^+\mu^-$, $B^+ \to K^+\mu^+\mu^-$ and $B^+ \to K^{*+}\mu^+\mu^-$ decays are measured as functions of the dimuon mass squared, $q^2$. The data used correspond to an integrated luminosity of 3$~$fb$^{-1}$ from proton-proton collisions collected with the LHCb detector at centre-of-mass energies of 7$\,$TeV and 8$\,$TeV in 2011 and 2012, respectively. The isospin asymmetries are both consistent with the Standard Model expectations. The three measured branching fractions, while individually consistent, all favour lower values than their respective Standard M…
Measurement of polarization amplitudes and CP asymmetries in B 0 → Φk *(892)0
2014
An angular analysis of the decay $B^0 \to \phi K^*(892)^0$ is reported based on a $pp$ collision data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected at a centre-of-mass energy of $\sqrt{s} = 7$ TeV with the LHCb detector. The P-wave amplitudes and phases are measured with a greater precision than by previous experiments, and confirm about equal amounts of longitudinal and transverse polarization. The S-wave $K^+ \pi^-$ and $K^+K^-$ contributions are taken into account and found to be significant. A comparison of the $B^0 \to \phi K^*(892)^0$ and $\bar{B}^0 \to \phi \bar{K}^*(892)^0$ results shows no evidence for direct CP violation in the rate asymmetry, in th…
Angular analysis of charged and neutral B → Kμ + μ − decays
2014
The angular distributions of the rare decays B → K+µ+µ- and B0 → K0 <inf>a</inf>Sμ+μ- are studied with data corresponding to 3 fb-1 of integrated luminosity, collected in proton-proton collisions at 7 and 8TeV centre-of-mass energies with the LHCb detector. The angular distribution is described by two parameters, FH and the forward-backward asymmetry of the dimuon system AFB, which are determined in bins of the dimuon mass squared. The parameter F<inf>H</inf> is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of A<inf>FB</inf> and F<inf>H</inf> reported here are the most precise to d…
Gamma(Z --> bb): A signature of hard mass terms for a heavy top
1988
Abstract We calculate analytically the weak radiative corrections to the weak neutral current gauge boson-bottom fermion vertex, keeping the mass mt of the internal fermion line for the relevant diagrams. We find, to order α, a hard mass-term dependence m t 2 M W 2 of the amplitude, for large mt values. Its origin comes from the unphysical charged Higgs coupling to fermions in the renormalizable gauge or, equivalently, from the longitudinal charged gauge boson couplings. The diagonal Z0 decay width to b-quarks decreases, due to these weak radiative corrections, by 0.6%–2.5% when the top mass mt varies from 45 to 200 GeV.
Eta-eta' Photoproduction and the axial isoscalar neutral current coupling
1995
We show that coherentη andη′ photoproduction by means of the Primakoff Effect on the proton depends on the strange component of the neutral axial current coupling. We construct polarization asymmetries that are sensitive to this coupling through theγ−Z interference. Theη′ is not a Goldstone boson of a spontaneously broken chiral symmetry, but a phenomenological analysis of theη andη′ production through chiral perturbation theory allows to calculate the observables of interest. The polarized proton or polarized photon asymmetries are predicted to be close to 10−4 for −q 2∼0.1−0.5 GeV2.
Search for flavor changing neutral currents in decays of top quarks
2011
We present a search for flavor changing neutral currents in decays of top quarks. The analysis is based on a search for ttbar -> l'null + jets (l, l' = e, mu) final states using 4.1 fb^-1 of integrated luminosity of ppbar collisions at sqrt(s) = 1.96 TeV. We extract limits on the branching ratio B(t -> Zq) (q = u, c quarks), assuming anomalous tuZ or tcZ couplings. We do not observe any sign of such anomalous coupling and set a limit of B < 3.2% at 95% C.L.
Neutral-current atmospheric neutrino flux measurement using neutrino-proton elastic scattering in Super-Kamiokande
2003
Recent results show that atmospheric $\nu_\mu$ oscillate with $\delta m^2 \simeq 3 \times 10^{-3}$ eV$^2$ and $\sin^2{2\theta_{atm}} \simeq 1$, and that conversion into $\nu_e$ is strongly disfavored. The Super-Kamiokande (SK) collaboration, using a combination of three techniques, reports that their data favor $\nu_\mu \to \nu_\tau$ over $\nu_\mu \to \nu_{sterile}$. This distinction is extremely important for both four-neutrino models and cosmology. We propose that neutrino-proton elastic scattering ($\nu + p \to \nu + p$) in water \v{C}erenkov detectors can also distinguish between active and sterile oscillations. This was not previously recognized as a useful channel since only about 2% …
Dynamical zero in ν¯e–e− scattering and the neutrino magnetic moment
2005
Abstract The Standard Model differential cross section for ν ¯ e – e − elastic scattering vanishes exactly, at lowest order, for forward electrons and incident ν ¯ e energy close to the rest energy of the electron. This dynamical zero is not induced by a fundamental symmetry of the Lagrangian but by a destructive interference between the left- and right-handed chiral couplings of the electron in the charged and neutral current amplitudes. We show that lowest-order analyses based on this favorable kinematic configuration are only mildly affected by the inclusion of the O ( α ) radiative corrections in the ν ¯ e – e − differential cross section, thus providing an excellent opportunity for the…
"Table 1" of "Measurement of the D*+- cross-section in two photon collisions at LEP"
1995
No description provided.
"Table 3" of "Precision measurement of structure function ratios for Li-6, C-12 and Ca-40"
1992
Overall normalization error of 0.5%, due to uncertainties in target thickness, not included in the table.