Measurement of $R_{b}$ and $BR(b \to \ell \nu X)$ at LEP Using Double-Tag Methods

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2000, Vol.13, p.47-61
• Main Authors: Acciarri, M., Achard, P., Adriani, O., Aguilar-Benitez, M., Alcaraz, J., Alemanni, G., Allaby, J., Aloisio, A., Alviggi, M G., Ambrosi, G., Anderhub, H., Andreev, V P., Angelescu, T., Anselmo, F., Arefev, A., Azemoon, T., Aziz, T., Bagnaia, P., Baksay, L., Balandras, A., Ball, R C., Banerjee, S., Banerjee, Sw, Barczyk, A., Barillere, R., Barone, L., Bartalini, P., Basile, M., Battiston, R., Bay, A., Becattini, F., Becker, U., Behner, F., Bellucci, L., Berdugo, J., Berges, P., Bertucci, B., Betev, B L., Bhattacharya, S., Biasini, M., Biland, A., Blaising, J J., Blyth, S C., Bobbink, G J., Boehm, A., Boldizsar, L., Borgia, B., Bourilkov, D., Bourquin, M., Braccini, S., Branson, J G., Brigljevic, V., Brochu, F., Buffini, A., Buijs, A., Burger, J D., Burger, W J., Busenitz, J., Button, A., Cai, X D., Campanelli, M., Capell, M., Cara Romeo, G., Carlino, G., Cartacci, a M., Casaus, J., Castellini, G., Cavallari, F., Cavallo, N., Cecchi, C., Cerrada, M., Cesaroni, F., Chamizo, M., Chang, y H., Chaturvedi, U K., Chemarin, M., Chen, A., Chen, G., Chen, G M., Chen, H F., Chen, H S., Chereau, X., Chiefari, G., Cifarelli, L., Cindolo, F., Civinini, C., Clare, I., Clare, R., Coignet, G., Colijn, a P., Colino, N., Costantini, S., Cotorobai, F., Cozzoni, B., de La Cruz, B., Csilling, A., Cucciarelli, S., Dai, T S., van Dalen, J A., d'Alessandro, R.
• Format: Article
• Language: English
• Subjects: High Energy Physics - Experiment; Physics
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1007/s100520100612

We present a combined measurement of $\Rb = \Gamma(\mathrm{Z \rightarrow b\overline{b}}) / \Gamma(\mathrm{Z} \rightarrow\mbox{hadro ns})$ and the semileptonic branching ratio of b quarks in Z decays, $\Brbl$, using double-tag methods. Two analyses are performed on one million hadronic Z decays collected in 1994 and 1995. The first analysis exploits the capabilities of the silicon microvertex detector. The tagging of b-events is based on the large impact parameter of tracks from weak b-decays with respect to the $\mathrm{e^+e^-}$ collision point. In the second analysis, a high-$p_t$ lepton tag is used to enhance the b-component in the sample and its momentum spectrum is used to constrain the model dependent uncertainties in the semileptonic b-decay. The analyses are combined in order to provide precise determinations of $\Rb$ and $\Brbl$: Rb = 0.2174 \pm 0.0015\mbox{(stat.)} \pm 0.0028\mbox{(sys.)}; $\Brbl = (10.16 \pm 0.13\mbox{(stat.)} \pm 0.30\mbox{(sys.)})\%.