The branching fractions of the decay $B^{+} to p bar p K^{+}$ for different intermediate states are measured using data, corresponding to an integrated luminosity of $1.0 fb^{-1}$, collected by the LHCb experiment. The total branching fraction, its c
harmless component $(M_{pbar p} <2.85 {GeV/}c^{2})$ and the branching fractions via the resonant $cbar c$ states $eta_{c}(1S)$ and $psi(2S)$ relative to the decay via a $J/psi$ intermediate state are {align*} frac{{mathcal B}(B^{+} to p bar p K^{+})_{total}}{{mathcal B}(B^{+} to J/psi K^{+} to p bar p K^{+})}=& , 4.91 pm 0.19 , {(rm stat)} pm 0.14 , {(rm syst)}, frac{{mathcal B}(B^{+} to p bar p K^{+})_{M_{pbar p} <2.85 {GeV/}c^{2}}}{{mathcal B}(B^{+} to J/psi K^{+} to p bar p K^{+})}=& , 2.02 pm 0.10 , {(rm stat)}pm 0.08 , {(rm syst)}, frac{{mathcal B} (B^{+} to eta_{c}(1S) K^{+} to p bar p K^{+})}{{mathcal B}(B^{+} to J/psi K^{+} to p bar p K^{+})} = & , 0.578 pm 0.035 , {(rm stat)} pm 0.027 , {(rm syst)}, frac{{mathcal B} (B^{+} to psi(2S) K^{+} to p bar p K^{+})}{{mathcal B}(B^{+} to J/psi K^{+} to p bar p K^{+})}=& , 0.080 pm 0.012 , {(rm stat)} pm 0.009 , {(rm syst)}. {align*} Upper limits on the $B^{+}$ branching fractions into the $eta_{c}(2S)$ meson and into the charmonium-like states X(3872) and X(3915) are also obtained.
The Ring Imaging Cherenkov detectors of the LHCb experiment at the Large Hadron Collider at CERN are equipped with Hybrid Photo-Detectors. These vacuum photo-detectors are affected by the stray magnetic field of the LHCb magnet, which degrades their
imaging properties. This effect increases the error on the Cherenkov angle measurement and would reduce the particle identification capabilities of LHCb. A system has been developed for the RICH2 Ring Imaging Cherenkov detector to perform a detailed characterisation of the magnetic distortion effects. It is described, along with the methods implemented to correct for these effects, restoring the optimal resolution.
