A search for new quarks and leptons from Z 0 decay at LEP

• Published in: Physics letters. B Vol. 236; no. 4; pp. 511 - 522
• Main Authors: Crespo, J.M., Miquel, R., Pacheco, A., Perlas, J.A., Catanesi, M.G., Farilla, A., Romano, F., Selvaggi, G., Tempesta, P., Zito, G., Hu, H., Lin, J., Wu, W., Xu, D., Blucher, E., Garrido, Ll, Grab, C., Hagelberg, R., Kasemann, M., May, J., Miotto, A., Roth, A., Rothberg, J., Rotscheidt, H., Takashima, M., Wheeler, S., Wiedenmann, W., Henrard, P., Jousset, J., Montret, J-C., Proriol, J., Simopoulou, E., Bonneaud, G., Guirlet, R., Rumpf, M., Georgiopoulos, C., Goldman, J.H., Ikeda, M., Mermikides, M., Stimpfl, G., Bencivenni, G., Picchi, P., Altoon, B., Halley, A.W., Ten Have, I., Morton, W.T., Raine, C., Brandl, B., Hanke, P., Stahl, A., Binnie, D.M., Cameron, W., Dugeay, S., Forty, R.W., Greene, A.M., Girtler, P., Rowlingson, B.S., Barczewski, T., Bonissent, A., Courvoisier, D., Etienne, F., Matsinos, E., Papalexiou, S., Cattaneo, P., Cowan, G., Dietl, H., Jahn, A., Lutz, G., Richter, R., Stierlin, U., Thomas, J., Waltermann, G., Bertin, V., Boucrot, J., Veillet, J.-J., Bradaschia, C., Ferrante, I., Fidecaro, F., Foà, L., Forti, F., Mannelli, E.B., Messineo, A., Green, M.G., Norton, P.R., Bloch-Devaux, B., Colas, P., Mirabito, L., Monnier, E., Renardy, J.-F., Combley, F., Thompson, L.F., Brandt, S., Liello, F., Rolandi, L., Cowen, D.F., Hilgart, J., Johnson, R.P., Sharma, V., Sau Lan Wu, Xue, S.T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1990
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/0370-2693(90)90392-J

A search for Z 0 decays into pairs of possible new heavy quarks (t and b′), new heavy charged leptons (L ±), stable heavy neutral leptons ( ν L) and unstable heavy neutral leptons (L 0) is performed on data collected by the ALEPH detector corresponding to 11 550 events of Z 0→hadrons. The limits on the masses of the heavy quarks are M t > 45.8 GeV and M b′ > 46.0 GeV, allowing for both charged-current and flavor-changing neutral-current decays of the b′. If an L ± decays into a stable ν L, then for M νL <42.7 GeV, the mass of L ± is excluded for all values of M L ± > M νL . Finally, while the mass of the stable ν L is excluded up to 42.7 GeV, the mass of the unstable L 0 is excluded up to 45.7 GeV with the mixing parameters | U ℓL 0 | 2 down to 10 −13 at this mass. For 25.0 GeV < M L 0 < 42.7 GeV, all values of | U ℓL 0 | 2 are excluded. All limits are given at 95% CL.