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Register a new userNew algorithms for identifying the flavour of $B^0$ mesons using pions and protons
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Two new algorithms for use in the analysis of $pp$ collision are developed to identify the flavour of $B^0$ mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using $B^0 rightarrow D^- pi^+$ decays from $pp$ collision data collected by LHCb at centre-of-mass energies of 7 and 8 TeV. The tagging power of the new pion algorithm is 60 % greater than the previously available one; the algorithm using protons to identify the flavour of a $B^0$ meson is the first of its kind.
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A new algorithm for the determination of the initial flavour of $B_s^0$ mesons is presented. The algorithm is based on two neural networks and exploits the $b$ hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the $B_s^0$ meson. The second network combines the kaon charges to assign the $B_s^0$ flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the $B_s^0$-$bar{B}_s^0$ flavour oscillations in $B_s^0 to D_s^- pi^+$ decays, and by analysing flavour-specific $B_{s 2}^{*}(5840)^0 to B^+ K^-$ decays. The tagging power measured in $B_s^0 to D_s^- pi^+$ decays is found to be $(1.80 pm 0.19({rm stat}) pm 0.18({rm syst}))$%, which is an improvement of about 50% compared to a similar algorithm previously used in the LHCb experiment.
Decays of the Y(5S) resonance to channels with B^+ and B^0 mesons are studied using a 23.6 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e^+ e^- collider. Fully reconstructed B^+ -> J/psi K^+, B^0 -> J/psi K^{*0}, B^+ -> bar{D}^0 pi^+ and B^0 -> D^- pi^+ decays are used to obtain the charged and neutral B production rates per bbar{b} event, f(B^+) = (72.1 ^{+3.9}_{-3.8} pm 5.0)% and f(B^0) = (77.0 ^{+5.8}_{-5.6} pm 6.1)%. Assuming equal rates to B^+ and B^0 mesons in all channels produced at the Y(5S) energy, we measure the fractions for transitions to two-body and three-body channels with B meson pairs, f(Bbar{B}) = (5.5 ^{+1.0}_{-0.9} pm 0.4)%, f(Bbar{B}^* + B^*bar{B}) = (13.7 pm 1.3 pm 1.1)%, f(B^*bar{B}^*) = (37.5 ^{+2.1}_{-1.9} pm 3.0)%, f(Bbar{B}pi) = (0.0 pm 1.2 pm 0.3)%, f(Bbar{B}^*pi + B^*bar{B}pi) = (7.3 ^{+2.3}_{-2.1} pm 0.8)%, and f(B^*bar{B}^*pi) = (1.0 ^{+1.4}_{-1.3} pm 0.4)%. The latter three fractions are obtained assuming isospin conservation.
The decay of the narrow resonance $overline{B}{}_{s2}^{*0}!rightarrow B^- K^+$ can be used to determine the $B^-$ momentum in partially reconstructed decays without any assumptions on the decay products of the $B^-$ meson. This technique is employed for the first time to distinguish contributions from $D^0$, $D^{*0}$, and higher-mass charmed states ($D^{**0}$) in semileptonic $B^-$ decays by using the missing-mass distribution. The measurement is performed using a data sample corresponding to an integrated luminosity of 3.0 fb${}^{-1}$ collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 and 8 TeV. The resulting branching fractions relative to the inclusive $B^- !rightarrow D^0 X mu^- overline{ u}_mu$ are $f_{D^0} = mathcal{B}( B^- rightarrow D^0mu^-overline{ u}_mu )/mathcal{B}( B^- rightarrow D^0 X mu^- overline{ u}_mu ) = 0.25 pm 0.06$, $f_{D^{**0}} = mathcal{B}( B^- rightarrow ( D^{**0} rightarrow D^0 X)mu^-overline{ u}_mu )/mathcal{B}( B^- rightarrow D^0 X mu^- overline{ u}_mu ) = 0.21 pm 0.07$, with $f_{D^{*0}} = 1 - f_{D^0} - f_{D^{**0}}$ making up the remainder.
The calibration and performance of the opposite-side flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been developed using simulated events and optimized and calibrated with B+ -> J/psi K+, B0 -> J/psi K*0 and B0 -> D*- mu+ nu_mu decay modes with 0.37 fb^-1 of data collected in pp collisions at sqrt(s) = 7 TeV during the 2011 physics run. The opposite-side tagging power is determined in the B+ -> J/psi K+ channel to be (2.10 +- 0.08 +- 0.24) %, where the first uncertainty is statistical and the second is systematic.
A search for $B^{0}_{s}totau^{pm}mu^{mp}$ and $B^{0}totau^{pm}mu^{mp}$ decays is performed using data corresponding to an integrated luminosity of 3 fb$^{-1}$ of proton-proton collisions, recorded with the LHCb detector in 2011 and 2012. For this search, the $tau$ lepton is reconstructed in the $tau^{-}topi^{-}pi^{+}pi^{-} u_{tau}$ channel. No significant signal is observed. Assuming no contribution from $B^{0}totau^{pm}mu^{mp}$ decays, an upper limit is set on the $B^{0}_{s}totau^{pm}mu^{mp}$ branching fraction of $mathcal{B}left( B^{0}_{s}totau^{pm}mu^{mp}right) < 4.2times 10^{-5}$ at $95%$ confidence level. If instead no contribution from $B^{0}_{s}totau^{pm}mu^{mp}$ decays is assumed, a limit of $mathcal{B}left( B^{0}totau^{pm}mu^{mp}right) < 1.4times 10^{-5}$ is obtained at $95%$ confidence level. These are the first limit on $mathcal{B}left( B^{0}_{s}totau^{pm}mu^{mp}right)$ and the worlds best limit on $mathcal{B}left( B^{0}totau^{pm}mu^{mp}right)$.
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