Searches for new quarks and leptons in Z boson decays
Searches for the decay of Z bosons into pairs of new quarks and leptons in a data sample including 455 hadronic Z decays are presented. The Z bosons were produced in electon-positron annihilations at the SLAC Linear Collider operating in the center-of-mass energy range from 89.2 to 93.0 GeV. The Standard Model provides no prediction for fermion masses and does not exclude new generations of fermions. The existence and masses of these new particles may provide valuable information to help understand the pattern of fermion masses, and physics beyond the Standard Model. Specific searches for top quarks and sequential fourth generation charge--1/3(b{prime}) quarks are made considering a variety of possible standard and non-standard decay modes. In addition, searches for sequential fourth generation massive neutrinos {nu}{sub 4} and their charged lepton partners L{sup {minus}} are pursued. The {nu}{sub 4} may be stable or decay through mixing to the lighter generations. The data sample is examined for new particle topologies of events with high-momentum isolated tracks, high-energy isolated photons, spherical event shapes, and detached vertices. No evidence is observed for the production of new quarks and leptons. 95% confidence lower mass limits of 40.7 GeV/c{sup 2} for the top quark and 42.0 GeV/c{sup 2} for the b{prime}-quark mass are obtained regardless of the branching fractions to the considered decay modes. A significant range of mixing matrix elements of {nu}{sub 4} to other generation neutrinos for a {nu}{sub 4} mass from 1 GeV/c{sup 2} to 43 GeV/c{sup 2} is excluded at 95% confidence level. Measurements of the upper limit of the invisible width of the Z exclude additional values of the {nu}{sub 4} mass and mixing matrix elements, and also permit the exclusion of a region in the L{sup {minus}} mass versus {nu}{sub 4} mass plane.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- AC03-76SF00515
- OSTI ID:
- 6688415
- Report Number(s):
- SLAC-367; ON: DE90014870; TRN: 90-027603
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Z NEUTRAL BOSONS
WEAK PARTICLE DECAY
DATA ACQUISITION SYSTEMS
ELECTRON-POSITRON INTERACTIONS
HEAVY LEPTONS
MATRIX ELEMENTS
MONTE CARLO METHOD
NEUTRINOS
QUARKS
SHOWER COUNTERS
SLC DETECTORS
STANDARD MODEL
STANFORD LINEAR COLLIDER
TOP PARTICLES
TOPOLOGY
ACCELERATOR FACILITIES
ACCELERATORS
BOSONS
DECAY
ELEMENTARY PARTICLES
FERMIONS
INTERACTIONS
INTERMEDIATE BOSONS
INTERMEDIATE VECTOR BOSONS
LEPTON-LEPTON INTERACTIONS
LEPTONS
LINEAR ACCELERATORS
MASSLESS PARTICLES
MATHEMATICAL MODELS
MATHEMATICS
MEASURING INSTRUMENTS
PARTICLE DECAY
PARTICLE INTERACTIONS
PARTICLE MODELS
POSTULATED PARTICLES
RADIATION DETECTORS
UNIFIED GAUGE MODELS
645102* - High Energy Physics- Particle Interactions & Properties-Experimental- Weak Interactions & Properties