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Particles and Fields


Eur. Phys. J. C 19, 323-337
DOI: 10.1007/s100520100609

Use of $\Lambda_b$ polarimetry in top quark spin-correlation functions

C.A. Nelson

Department of Physics, State University of New York at Binghamton, Binghamton, NY 13902-6016, USA

(Received: 26 January 2001 / Published online: 15 March 2001 -© Springer-Verlag 2001)

Abstract
Due to the absence of hadronization effects and the large mt mass, top quark decay will be uniquely sensitive to fundamental electroweak physics at the Tevatron, at the LHC, and at a future linear collider. A "complete measurement" of the four helicity amplitudes in $t \rightarrow W^+ b$ decay is possible by the combined use of $\Lambda_b$ and W polarimetry in stage-two spin-correlation functions (S2SC). In this paper, the most general Lorentz-invariant decay density matrix is obtained for the decay sequence $t \rightarrow W^+ b$ where $b\rightarrow
l^{-}\bar{\nu}c$ and $W^{+}\rightarrow l^{+}\nu _{l}$ [ or $W^{+}\rightarrow j\overline{_{d}}j_{u}$] , and likewise for $\bar{t} \rightarrow W^- \bar{b}$. These density matrices are expressed in terms of b-polarimetry helicity parameters which enable a unique determination of the relative phases among the $A(\lambda_{W^+},\lambda_b)$ amplitudes. Thereby, S2SC distributions and single-sided b-W-interference distributions are expressed in terms of these parameters. The four b-polarimetry helicity parameters involving the A(-1,-1/2) amplitude are considered in detail. $\Lambda_b$ polarimetry signatures will not be suppressed in top quark analyses when final $\bar{\nu}$ angles-and-energy variables are used for $b\rightarrow
l^{-}\bar{\nu}c$.



© Società Italiana di Fisica, Springer-Verlag 2001