Measuring polarizations of bottom, charm, strange, up and down quarks in top decays

摘要

Standard Model $t\bar t$ samples in ATLAS and CMS provide an opportunity toconduct measurements of the polarization of quarks produced in top-quarkdecays. The bottom quarks from the $t \to W^+ b$ decays, as well as the charm,strange, up and down quarks from the subsequent $W^+ \to c\bar s, u\bar d$decays, are polarized. When a polarized quark hadronizes to a baryon, itspolarization is partly preserved, and is reflected in the angular distributionsof the baryon decay products. For the strange and bottom quarks, this effecthas already been seen in hadronic $Z$ decays at LEP. In Run 2 of the LHC,$t\bar t$ samples will have comparable statistics and several advantages fromthe point of view of flavor tagging. We propose strategies for suchmeasurements in ATLAS and CMS. We estimate that precision of order $10\%$ isattainable for the polarizations of the strange, charm and bottom quarks. Infuture higher-statistics runs, polarizations of up and down quarks might bemeasurable as well.