Combined SLD Measurement of Ab at the Z0 Resonance using Various Techniques Page: 2 of 9
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This note provides a brief overview of four separate analyses performed by the SLD
Collaboration to measure the parity-violation parameter Ab in polarized Z0 decays, and a
description of how the analyses are combined to form a overall SLD result. The reader is
referred to the detailed notes available for each analysis for specific information on how each
analysis is performed.
The most statistically powerful analysis selects bb events using an inclusive topological
vertexing technique and forms the momentum-weighted jet charge of all selected events
to identify the quark direction. This analysis was most recently updated at Moriond '99
to include the full 1993-8 SLD dataset. The updated systematic errors are reproduced in
Table 1. The combined jet-charge result is:
Ab = 0.882 0.020(stat) 0.029(syst) (jet-charge). (1)
The next analysis uses identified high-momentum muons and electrons to tag heavy
flavor (b, c) events and then employs a number of kinematic and vertexing variables to
try to distinguish leptons arising from b-hadron decays from those arising from c-hadron
decays. The lepton sign is used to sign the quark direction and Ab and A, are measured
simulataneously. This analysis was most recently updated at Moriond '99 to include the
full 1993-8 SLD dataset. The updated systematic errors are reproduced in Tables 2 (
tag) and 3 (e tag). The combined lepton-tag result is:
Ab = 0.924 0.032(stat) 0.026(syst) (leptons). (2)
Another analysis uses identified K associated with separated topological vertices to sign
the quark direction, exploiting the dominant b -+ c -+ s decay chain. In the original version
of this analysis, the error in the result was dominated by the experimental uncertainty in
the relative rates of B -+ K+X vs. B -+ K-X decay. This analysis has been updated at this
conference to include data from the 1997-8 data run and now employs a self-calibration
technique which removes the reliance on relative production rates of K in B decays. The
combined K -tag result is:
Ab = 0.960 0.040(stat) 0.056(syst) (kaons). (3)
The last analysis uses the charge of the separated topological vertices themselves to assign
the quark direction. The vertex charge is weighted in the analysis based on the mass of the
reconstructed vertex, which gives an indication of the fraction of the B decay tracks which
have been correctly assigned to the vertex. This analysis, which has been first presented at
this conference, includes data from the 1996-8 data run and also employs a self-calibration
technique to determine the correct-sign probability directly from the data. The vertex-charge
Ab = 0.897 0.027(stat)ji0 (syst) (vertex-charge). (4)
We have combined these four results as follows. The statistical overlap between the
analyses was determined by explicitly tabulating events used by the four analyses for a
subset of the total data which is common to all four and was marked by stable detector
performance. Each event in this dataset used by a given analysis was assigned a weight
by that analysis based on its estimated b-hadron purity, correct-signing probability, and
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Crawford, Glen D. Combined SLD Measurement of Ab at the Z0 Resonance using Various Techniques, report, July 27, 1999; Menlo Park, California. (https://digital.library.unt.edu/ark:/67531/metadc620132/m1/2/: accessed April 26, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.