We have measured the tau lifetime using three different techniques. The results from the three methods are consistent with one another. The decay length method is independent from the other two techniques since it uses a completely separate set of events. The impact parameter and impact parameter difference methods share about 70%of the events. However, because they make use of different information, they are not totally correlated. We have determined the correlation between the two techniques using Monte Carlo and following the procedure described in Ref. [19]. For the events that are common to the IP and IPD methods, we obtain a correlation factor of 53%. This results in an overall correlation of 37%between the two measurements. In this evaluation, common systematic effects are also taken into account.
A combined result of
is derived from
the IP and IPD measurements. With the inclusion of the DL measurement, we
obtain:
This result is in agreement with the present world average
value[20]. Our measurement is currently limited by the relatively
small size of our data sample; we expect a significant improvement in the
future as we anticipate a substantial increase in statistics, together with an
associated decrease in the systematic error. A precise measurement of the
tau lifetime at SLD, performed in a different environment relative to other
experiments because of the small beam size and three-dimensional
high-resolution vertexing, will represent an important contribution.
This work was supported by Department of Energy contracts: DE-FG02-91ER40676 (BU), DE-FG03-92ER40701 (CIT), DE-FG03-91ER40618 (UCSB), DE-FG03-92ER40689 (UCSC), DE-FG03-93ER40788 (CSU), DE-FG02-91ER40672 (Colorado), DE-FG02-91ER40677 (Illinois), DE-AC03-76SF00098 (LBL), DE-FG02-92ER40715 (Massachusetts), DE-AC02-76ER03069 (MIT), DE-FG06-85ER40224 (Oregon), DE-AC03-76SF00515 (SLAC), DE-FG05-91ER40627 (Tennessee), DE-AC02-76ER00881 (Wisconsin), DE-FG02-92ER40704 (Yale); National Science Foundation grants: PHY-91-13428 (UCSC), PHY-89-21320 (Columbia), PHY-92-04239 (Cincinnati), PHY-88-17930 (Rutgers), PHY-88-19316 (Vanderbilt), PHY-92-03212 (Washington); the UK Science and Engineering Research Council (Brunel and RAL); the Istituto Nazionale di Fisica Nucleare of Italy (Bologna, Ferrara, Frascati, Pisa, Padova, Perugia); and the Japan-US Cooperative Research Project on High Energy Physics (Nagoya, Tohoku).