2020/12/25(Fri) 11:00 -12:00 五樓第一會議室 5F, 1st Meeting Room
Title
Polarization effects in the search for dark vector boson at e^+ e^-colliders
Speaker
林貴林教授 (國立交通大學物理研究所) Prof. Guey-Lin Lin (Institute of Physics, National Chiao Tung University)Abstract
We argue that the search for dark vector boson through $e^+e^-\to Z_d\gamma$ can determine the Lorentz structure of $Z_dl^+l^-$ couplings with the detection of leptonic decays $Z_d\to l^+l^-$. We assume a general framework that the dark vector boson interacts with ordinary fermions through vector and axial-vector couplings. As a consequence of Ward-Takahashi identity, $Z_d$ is transversely polarized in the limit $m_{Z_d}\ll \sqrt{s}$. On the other hand, the fraction of longitudinal $Z_d$ is non-negligible for $m_{Z_d}$ comparable to $\sqrt{s}$. Such polarization effects can be analyzed through angular distributions of final-state particles in $Z_d$ decays.
Taking $l^{\pm}\equiv \mu^{\pm}$, we study the correlation between $Z_d$ angle relative to $e^-$ beam direction in $e^+e^-$ CM frame and $\mu^-$ angle relative to the boost direction of $Z_d$ in $Z_d$ rest frame.
This correlation is shown to be useful for probing the Lorentz structure of $Z_dl^+l^-$ couplings.
We discuss the measurement of such correlation in Belle II detector, taking into account the detector acceptance and energy resolution.
Language
演講語言 (Language): in English