Fun with Top Spin

by Prof. Kaoru Hagiwara (KEK)

Thursday 5 Dec 2019, 15:30 → 16:30 Asia/Shanghai

East wing of Pao Yue-Kong Library/2nd-200 - 200# Meeting Room (Tsung-Dao Lee Institute (East wing of Pao Yue-Kong Library))

Abstract:

The top quark is the heaviest fundamental particle and its properties might reveal physics of the spontaneous symmetry breakdown that gives rise to all the masses of fundamental particles. The top quark has spin 1/2, and its spin polarization can be measured efficiently by using the l+ or dbar momentum in its cascade decays into b and W+, followed by W+ to l+ nu, or dbar u.  At the LHC, top or anti-top produced singly by t-channel W exchange, such as u b > d t or d bbar > u tbar, are highly polarized and their spin polarization direction is along the momentum of the down type quarks. I show all the above properties of top and anti-top spin by using a simple Fierz identity among the four spinors connected by a W propagator.

Biography:

PhD in 1979 from Tokyo Metropolitan University, Post-doc at Univ. of Wisconsin-Madison and DESY, KEK staff since 1986, emeritus since 2015