Time & Place: May 15, Wednesday, 4:00 pm, Room 9409

Speaker: Prof. Ka Ma (马凯), Shanxi University of Technology

Title: Asymmetry Observables for Measuring Spin Correlations in
Top-Quark Pair Production

Abstract: Spin correlations between top-quark and anti-top-quark in pair
production are sensitive to physics beyond the standard model. A
complete set of observables, that can be used to measure all independent
parameters of the production spin density matrix, is necessary to search
for anomalous interactions in the production dynamics. In this paper, we
provide a set of asymmetry observables for measuring all the density
matrix elements. These observables are defined regardless of the
production mechanism, and can be specified in any desired reference
frame, particularly the laboratory frame in which the first evidence of
spin correlation was observed experimentally. Our method can be used to
find an optimal Lorentz frame in which the sensitivity to the density
matrices is high for given production process and experimental
environment, or to test possible correlations among the matrix elements.
Here we show the results when our method is applied for Probing
CP-Violating Yukawa Interaction of Top-Quark. One can see the advantages
of our method clearly. Most importantly, we find an enhancement effect
in the rest frame of Higgs boson for both CP-odd and CP-even observables.