Abstract
Many of the precise measurements expected from LHCb will be based on the observation of time-dependent CP asymmetries, which rely on flavour tagging. This article shows that the high precisions aimed for at LHCb impose stringent conditions on both flavour tagging performance and its calibration. The algorithms that have been developed for flavour tagging at LHCb are described, as well as the procedure for obtaining the required level of calibration by using control channels.
Highlights
Flavour tagging algorithms aim for the determination of the flavour of reconstructed B mesons at their production
Opposite side tagging Tagging information from the other B meson in the event is obtained from the charge of the lepton from a semileptonic decay, from the charge of a kaon from the b → c → s decay chain, or from the charge of the tracks from a secondary vertex reconstructed in the event
A wrong tag probability ωi is computed for each of the tagging candidates present. This is done by means of a neural network that has as input several of the properties of the tagger and that has been trained on independent Monte Carlo (MC) samples
Summary
Flavour tagging algorithms aim for the determination of the flavour of reconstructed B mesons at their production. SS algorithms exploit the correlation of the charge of mesons produced in the fragmentation chain with the original flavour of the signal B, i.e., the B decay of interest. OS algorithms exploit the perfect anti-correlation between the flavours of the two B hadrons produced in the event, via the partial reconstruction of a flavour-specific final state of the other B hadron in the event (the tagging B). The performance of tagging algorithms is characterized by their efficiency ( tag) and the probability of the tagging assignment to be wrong (ω).
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