Abstract
Reconstruction of the B0→ D∗−τ+ντ angular distribution is complicated by the strongly biasing effect of losing the neutrino information from both the B and τ decays. In this work, a novel method for making unbiased measurements of the angular coefficients while preserving the model independence of the angular technique is demonstrated. The twelve angular functions that describe the signal decay, in addition to background terms, are modelled in a multidimensional fit, using template probability density functions that encapsulate all resolution and acceptance effects. Sensitivities at the LHCb and Belle II experiments are estimated, and sources of systematic uncertainty are discussed, notably in the extrapolation to a measurement of R(D∗).
Highlights
In order to further characterise the underlying physics in b → cτ ντ transitions, it is necessary to study the kinematics of semitauonic B decays in addition to their rates
Results for 50 ab−1 of e+e− data (Nsig = 7000): the four-dimensional template fit to the B-factory sample is performed in ((cos θD, cos θL, χ)Reco, boosted decision tree (BDT)) variable space, where the decay angles are calculated using the true B meson four-vector to mimic the benefit of the hadronic tagging
Smaller variations in the angular coefficient measurements are seen when the number of bins in the weighting procedure is varied from the default 303 binning
Summary
Monte Carlo (MC) signal samples of B0 → D∗−τ +ντ decays are generated using the RapidSim package [33]. RapidSim is a fast MC generator for simulating heavy-quark hadron decays. The three-prong τ + → π+π+π−ντ decay, rather than the more abundant muonic τ decay, is the focus of this study. This is because the presence of a τ decay vertex results in lower backgrounds, and with only two neutrinos in the final state, this mode has the best decay angle resolution. Detector acceptance effects are modelled by restricting generated B0 mesons to the momentum range [0, 100] GeV/c and the pseudorapidity range [1, 6], which is similar to the geometrical acceptance of the LHCb detector
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