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

  • C.A. Nelson
Theoretical physics


Due to the absence of hadronization effects and the large \(m_t\) 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 \(\Lambda_b\) andW 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 \(b\rightarrow l^{-}\bar{\nu}c\).


Density Matrix Relative Phasis Density Matrice Large Mass Helicity Amplitude 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • C.A. Nelson
    • 1
  1. 1.Department of Physics, State University of New York at Binghamton, Binghamton, NY 13902-6016, USA US

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