Narrow Results

This review presents the world's most precise measurement of the W-boson mass m_W using data corresponding to ≈ 2.2 fb^-1 integrated luminosity collected with the CDF II detector at Fermi National Accelerator Laboratory (Fermilab). With samples of 470,126 W → eν candidates and 624,708 W → μν candidates, m_W is measured to be 80387±12_stat ± 15_syst = 80387 ± 19 MeV [Phys. Rev. Lett.108, 151803 (2012)]. This result significantly exceeds the precision of all previous measurements and improves the world averaged precision by 30%.

Electroweak data from the high energy electron–positron and proton–antiproton colliders are reviewed. On the whole the data is consistent with and supports the predictions of the electroweak theory. However, a crucial prediction of the theory remains to be verified: the existence of the Higgs boson and its light mass, less than 193 GeV, obtained from a fit to all the data within the electroweak framework. The lower limit on its mass from direct searches being 114 GeV, the mass of the Higgs is fixed within a narrow range which is expected to be explored at the Fermilab Tevatron experiments or later at the Large Hadron Collider at CERN.

The anomalous $WW\gamma$ coupling is probed through $e\gamma \to \nu W$ at the ILC. With a spectacular single lepton final state, this process is well suited to study the above coupling. Cross-section measurements can probe $\delta {\kappa }_{\gamma }$ to about $\pm 0.004$ for a luminosity of 100 fb${}^{-1}$ at 500 GeV center-of-mass energy with unpolarized electron beam. The limits derivable on ${\lambda }_{\gamma }$ from the total cross-section are comparatively more relaxed. Exploiting the energy-angle double distribution of the secondary muons, kinematic regions sensitive to these couplings are identified. The derivable limit on ${\lambda }_{\gamma }<0$ could be improved to a few per-mil, focusing on such regions. More importantly, the angular distributions at fixed energy values, and energy distribution at fixed angles present very interesting possibility of distinguishing the case of ${\lambda }_{\gamma }<0$ and ${\lambda }_{\gamma }\ge 0$.

We have updated theoretical studies of heavy vector quarkonium production, including $J/\mathrm{\Psi }$, ${\mathrm{\Psi }}^{\prime }$ and $\mathrm{\Upsilon }$, in the exclusive W-boson decays. Particularly, in the standard model the branching fraction of $W^{-}\to J/\mathrm{\Psi }{\ell }^{-}{\bar{\nu }}_{\ell }$ ($\ell =e$ or $\mu$) has been predicted to be about $8.5\times 10^{-7}$, which is substantially larger than those of two-body hadronic radiative W decays. Thus in the future high-luminosity experimental facilities, this rare channel could be very useful to search for the exclusive W-boson decays containing the hadronic final state. Furthermore, the surprisingly large decay rate can be explained by an electromagnetic fragmentation formalism. We have analyzed the lepton fragmentation and the photon fragmentation processes, and calculated their contributions to the differential decay rate of $W^{-}\to J/\mathrm{\Psi }{\ell }^{-}{\bar{\nu }}_{\ell }$ in the fragmentation limit. It is found that the fragmentation contribution agrees well with the result from the full calculation.

We have updated theoretical studies of heavy vector quarkonium production, including J/Ψ, Ψ′ and ϒ, in the exclusive W-boson decays. Particularly, in the standard model the branching fraction of $W^{-}\to J/\text{Ψ}{\ell }^{-}{\overline{\nu }}_{\ell }(\ell =e \text{or} \mu )$ has been predicted to be about 8.5 × 10⁻⁷, which is substantially larger than those of two-body hadronic radiative W decays. Thus in the future high-luminosity experimental facilities, this rare channel could be very useful to search for the exclusive W-boson decays containing the hadronicfinal state. Furthermore, the surprisingly large decay rate can be explained by an electromagnetic fragmentation formalism. We have analyzed the lepton fragmentation and the photon fragmentation processes, and calculated their contributions to the differential decay rate of $W^{-}\to J/\text{Ψ}{\ell }^{-}{\overline{\nu }}_{\ell }$ in the fragmentation limit. It is found that the fragmentation contribution agrees well with the result from the full calculation.