Upper Limit for the Decay $B^{-} \to \tau^{-}\overline{\nu}_{\tau}$ and Measurement of the $b \to \tau\overline{\nu}_{\tau}X$ Branching Ratio

• Published in: Physics letters. B 2000, Vol.496, p.43-58
• Main Authors: Abreu, P., Adam, W., Adye, T., Adzic, P., Ajinenko, I., Albrecht, Z., Alderweireld, T., Alekseev, G.D., Alemany, R., Allmendinger, T., Allport, P.P., Almehed, S., Amaldi, U., Amapane, N., Amato, S., Anassontzis, E.G., Andersson, P., Andreazza, A., Andringa, S., Antilogus, P., Apel, W.D., Arnoud, Y., Asman, B., Augustin, J.-E., Augustinus, A., Baillon, P., Bambade, P., Barao, F., Barbiellini, Guido, Barbier, R., Bardin, D.Yu, Barker, G., Baroncelli, A., Battaglia, M., Baubillier, M., Becks, K.H., Begalli, M., Behrmann, A., Beilliere, P., Belokopytov, Yu, Benekos, N.C., Benvenuti, A.C., Berat, C., Berggren, M., Bertrand, D., Besancon, M., Bigi, M., Bilenkii, M.S., Bizouard, M.A., Bloch, D., Blom, H.M., Bonesini, M., Boonekamp, M., Booth, P.S.L., Borgland, A.W., Borisov, G., Bosio, C., Botner, O., Boudinov, E., Bouquet, B., Bourdarios, C., Bowcock, T.J.V., Boyko, I., Bozovic, I., Bozzo, M., Bracko, M., Branchini, P., Brenner, R.A., Bruckman, P., Brunet, J.M., Bugge, L., Buran, T., Buschbeck, B., Buschmann, P., Cabrera, S., Caccia, M., Calvi, M., Camporesi, T., Canale, V., Carena, F., Carroll, L., Caso, C., Castillo Gimenez, M.V., Cattai, A., Cavallo, F.R., Chabaud, V., Charpentier, P., Checchia, P., Chelkov, G.A., Chierici, R., Shlyapnikov, P., Chochula, P., Chorowicz, V., Chudoba, J., Cieslik, K., Collins, P., Contri, R., Cortina, E., Cosme, G., Cossutti, F.
• Format: Article
• Language: English
• Subjects: High Energy Physics - Experiment; Physics
• ISSN: 0370-2693
• DOI: 10.1016/S0370-2693(00)01274-0

Using the data sample of hadronic $Z^0$ decays collected by the DELPHI experiment in the 1992-1995 LEP1 period, the leptonic decay of the charged $B$ mesons (\btauex) has been studied. The analysis was done in both leptonic \taulm and hadronic \tauxmm decay channels. No excess was observed in data and the upper limit BR(\btauex) $ 1.1 \times 10^{-3}$ at the 90\åonfidence level was obtained. This result is consistent with Standard Model expectations and puts a constraint on the ratio $\tan \beta / M_{H^{\pm}} 0.45$~(GeV$/c^2)^{-1} $ in the framework of models with two Higgs doublets (any type II Higgs doublet model). From the missing energy distribution, the branching ratio of \btau was measured in the hadronic channel \tauxm. The result, BR(\btau)$ = (2.19 \pm 0.24 \ (stat) \pm 0.40\; (syst)) \$, is consistent with the Standard Model prediction and with previous experimental measurements.