Laboratory for Particle Properties (Phi-lab) [English | Japanese]

MTV(Mott Polarimetry for T-Violation experiment)

MTV experiment is collaboration with Murata Laboratory, Rikkyo Univ, searching time reversal symmetry violation by measuring transverse polarization of beta decay electron from 8Li.

Matter-antimatter asymmetry of the Universe implies existence of large T-Violation which is different from CKM mechanism. In atomic beta decay, T-violation arises from CKM model is much smaller than experimental sensitivity, and Observing non-zero T-violation in beta decay means discovering new physics beyond standard model.

A State of beta ray from polarized atom has an obseravable which is sensitive to T-violation. We use Polarized 8Li beam at TRIUMF Laboratory in Canada and are searching T-violation by precise measurement of beta decay.

R correlation in beta decay rate is presented with spin of parent nuclei(J),momentum of electron(p), and spin of electron(σ). Beta decay rate formula is written below \begin{align} W\propto(1+R\vec{\sigma}\cdot(\vec{J}\times \vec{p})) \end{align} The term which includes coefficient R is called R correlated term, and it's sign is inverted by time revarsal conversion. If R isn't equal to zero, Time Reversal symmetry is breaking.

In measuring R correlation, Seaching momentum and spin og electron is indispansable. So we use CDC(Cylindrical Drift Chamber) and left-right asymmetry of Mott scattering.
When an electron is scattered from an atom, scattering cross section varies with the state of electron spin. That is called Mott scattering. We can observe electoron transverse polarization as left-right asymmetry by using Mott scattering.
We can achieve a measurment of momentum and polarization of electron using Mott scattering and CDC.