Abstract
The search for exclusive hadronic vector boson decays is an ongoing part of the LHC programme where, to date, no such decays have been observed. In addition to the intrinsic interest in the branching ratios, there is potential for a measurement of the W boson mass quite distinct from the usual methods. The radiative decay modes offer good potential channels for this search; however, we highlight three issues with it not previously discussed: particle misidentification, partial reconstruction and the impact of interference with QCD. These issues cause shifts in the peak position of tens or hundreds of MeV/c2.
Highlights
Introduction ce an us criExclusive decays of W and Z bosons to hadronic final states have never been observed
It may be possible to record exclusive fully-hadronic events using either a J/ψ decaying to muons or a modified tau-pair trigger at first level, with a tight selection on the mass in charged particles at high level, but we focus on the radiative decay topology here
Radiative W boson decays are predicted by PYTHIA and Sherpa for three-body and four-body final states, with branching ratios of a few in 10−8
Summary
The signature studied here is that of a W boson decaying to a photon recoiling against a low-multiplicity jet. (c) shows the pT distribution of the final state particles when requiring a photon and exactly three additional particles, generated using the Sherpa-EW-Lund configuration. The distributions of the W + →ud particle multiplicities produced by these generators when requiring at least one photon in the final state are shown in figure 2 (a). One interesting feature is that Sherpa, using its default cluster fragmentation, has the highest probability of producing fewer than five charged particles in Z decay, while it has the lowest probability of giving fewer than five total particles in radiative W decay. This remains true when the requirement for at least one photon is removed.
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