50 research outputs found
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Measurement of the W-pair cross section in collisions at 172 GeV
The e+e- --> W+W- cross section is measured in a data sample collected by ALEPH at a mean centre--of--mass energy of 172.09 GEV, corresponding to an integrated luminosity of 10.65 pb-1. Cross sections are given for the three topologies, fully leptonic, semi-leptonic and hadronic of a W-pair decay. Under the assumption that no other decay modes are present, the W-pair cross section is measured to be 11.7 +- 1.2 (stat.) +- 0.3 (syst.) pb. The existence of the triple gauge boson vertex of the Standard Model is clearly preferred by the data. The decay branching ratio of the W boson into hadrons is measured to be B(W --> hadrons) = 67.7 +- 3.1 (stat.) +- 0.7 (syst.)%, allowing a determination of the CKM matrix element |Vcs|= 0.98 +- 0.14 (stat.) +- 0.03 (syst.)
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.
A new method is presented for the measurement of the mean lepton lifetime using events in which 's are pair-produced and both 's decay to hadrons and . Based on the correlation between the two 's produced at a symmetric collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a lifetime of \fs is obtained from the sample in which both 's decay to one charged track, and \fs from the sample in which one decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting lifetime is \fs
Searches for Charginos and Neutralinos in Collisions at = 161 and 172 GeV
The data recorded by the ALEPH detector at centre-of-mass energies of 161, 170, and 172 GeV are analysed for signals of chargino and neutralino production. No evidence of a signal is found, although candidate events consistent with the expectations from Standard Model processes are observed. Limits at 95% C.L. on the production cross sections are derived and bounds on the parameters of the Minimal Supersymmetric Standard Model are set. The lower limit on the mass of the lightest chargino is 85.5 GeV/c^2 for gaugino-like charginos (mu = -500 GeV/c^2), and 85.0 GeV/c^2 for Higgsino-like charginos (M_2 = 500 GeV/c^2), for heavy sneutrinos (M(snu) 200 GeV/c^2) and tanb = sqrt(2). The effect of light sleptons on chargino and neutralino limits is investigated. The assumptions of a universal slepton mass and a universal gaugino mass are relaxed, allowing less model-dependent limits to be obtained