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Aaij, R.; Amhis, Y.; Barsuk, S.; Callot, O.; He, J.; Kochebina, O.; Lefrançois, J.; Machefert, F.; Martin Sanchez, A.; Nicol, M.; Robbe, P.; Schune, M.-H.; Teklishyn, M.; Viaud, B.; Vallier, A.; Ben-Haim, E.; Benayoun, M.; David, P.; del Buono, L.; Martens, A.; Milanes, D.A.; Polci, F.; Ajaltouni, Ziad Zj; Baalouch, M.; Cogneras, E.; Deschamps, O.; El Rifai, I.; Grabalosa Gándara, M.; Henrard, Pierre; Hoballah, M.; Lefèvre, R.; Li Gioi, L.; Maratas, J.; Monteil, S.; Niess, V.; Perret, Pascal; Roa Romero, Diego Alejandro; de Bonis, I.; Decamp, D.; Déléage, N.; Ghez, Ph; Hopchev, P.; Lees, J.-P.; Machikhiliyan, I.V.; Minard, M.-N.; Pietrzyk, B.; Qian, W.; t'Jampens, S.; Tisserand, V.; Tournefier, E.; Adrover, C.; Aslanides, E.; Cogan, J.; Kanso, W.; Legac, R.; Leroy, O.; Mancinelli, G.; Maurice, E.; Mordà, A.; Perrin-Terrin, M.; Sapunov, M.; Serrano, J.; Tsaregorodtsev, A.
Physical review letters, 2013, Letnik: 111Journal Article
A search for the lepton-flavour violating decays \Bsemu and \Bdemu is performed with a data sample, corresponding to an integrated luminosity of \mbox{1.0} fb$^{-1}$ of $pp$ collisions at $\sqrt{s} = 7$\, TeV, collected by the LHCb experiment. The observed number of $B^0_s \to e^{\pm} \mu^{\mp}$ and $B^0 \to e^{\pm} \mu^{mp}$ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be $BR(B^0_s \to e^{\pm} \mu^{\mp} < 1.1 \,(1.4) \times 10^{-8}$ and $BR (B^0 \to e^{\pm} \mu^{mp} < 2.8 \,(3.7) \times 10^{-9}$ at 90% (95%) confidence level (C.L.). These limits are a factor of twenty lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, $M_{\rm LQ} (B^0_s \to e^{\pm} \mu^{mp}) > 107$} TeV/c$^2$ and $M_{\rm LQ} (B^0 \to e^{\pm} \mu^{\mp}) > 126$ TeV/c$^2$ at 95% C.L., and are a factor of two higher than the previous bounds.
