Searches for new quarks and leptons in Z boson decays

Technical Report · Fri Jun 01 04:00:00 EDT 1990

DOI:https://doi.org/10.2172/6688415· OSTI ID:6688415

Van Kooten, R J

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: Stanford Linear Accelerator Center, Menlo Park, CA (USA)
• Sponsoring Organization: DOE/ER
• DOE Contract Number: AC03-76SF00515
• OSTI ID: 6688415
• Report Number(s): SLAC-367; ON: DE90014870
• Country of Publication: United States
• Language: English

Related Subjects

645102* -- High Energy Physics-- Particle Interactions & Properties-Experimental-- Weak Interactions & Properties
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ACCELERATOR FACILITIES
ACCELERATORS
BOSONS
DATA ACQUISITION SYSTEMS
DECAY
ELECTRON-POSITRON INTERACTIONS
ELEMENTARY PARTICLES
FERMIONS
HEAVY LEPTONS
INTERACTIONS
INTERMEDIATE BOSONS
INTERMEDIATE VECTOR BOSONS
LEPTON-LEPTON INTERACTIONS
LEPTONS
LINEAR ACCELERATORS
MASSLESS PARTICLES
MATHEMATICAL MODELS
MATHEMATICS
MATRIX ELEMENTS
MEASURING INSTRUMENTS
MONTE CARLO METHOD
NEUTRINOS
PARTICLE DECAY
PARTICLE INTERACTIONS
PARTICLE MODELS
POSTULATED PARTICLES
QUARKS
RADIATION DETECTORS
SHOWER COUNTERS
SLC DETECTORS
STANDARD MODEL
STANFORD LINEAR COLLIDER
TOP PARTICLES
TOPOLOGY
UNIFIED GAUGE MODELS
WEAK PARTICLE DECAY
Z NEUTRAL BOSONS