Browsing by Author "Järvinen, Terhi"

The neutral B_s meson consisting of \mathrm{\bar{b}} and s quarks can decay through the channel B_s → J/ψ Φ The B_s can on-flight mix with its antiparticle \mathrm{\bar{B}}_\mathrm{s} that can also decay to the J / ψΦ final state. The identification of the b quark flavour of the B_s meson at the production time is crucial for measurement of the phase Φ_s, a parameter describing the CP violation between the B_s meson eigenstates. Different types of flavour tagging methods have been developed to extract the initial flavour of decayed neutral B mesons. Since the b quarks at the LHC are produced as b\mathrm{\bar{b}} pairs, one method to identify the B_s flavour is to use muons that originate from decays of hadronised b quarks on the opposite side of the signal meson. In this work, the flavour tagging performance of muons from the opposite-side B hadron decays were studied. The flavour tagging was done for the B_s → J / ψΦ channel and the reference channel B^{+} → J / ψK^{+} with simulated B_s and B^{+} events as well as B^{+} data. This study verifies the flavour tagging performance obtained from simulated B_s events with real B^{+} data since flavour tagging cannot be directly done for B_s events reconstructed from the collision data. The tagging performances obtained from all the three samples are in agreement. The wrong tag fraction of the B^{+} data is (29 ± 0.8) %, the tagging efficiency is (4.03 ± 0.07) % and the tagging power is (0.65 ± 0.04) %. The tagging performance obtained from the B^+ data is compatible with the flavour tagging results obtained by the LHCb experiment.