On measurement of photon polarization in radiative penguin $B$ decays to baryons

TL;DR

This paper proposes a novel, model-independent method to measure photon polarization in radiative $B$ decays to baryons, using the decay $B^- o \Lambdaar{p} \gamma$, which can test the Standard Model and probe New Physics.

Contribution

The paper introduces a new technique leveraging $\Lambda$ hyperon decay to measure photon polarization in $B$ decays, enabling tests of the Standard Model with existing and future data.

Findings

The $B^- o \Lambdaar{p} \\gamma$ decay has a large branching fraction.

The method allows for model-independent measurement of photon polarization.

Upcoming high-luminosity experiments can apply this method for stringent tests.

Abstract

A measurement of the photon polarization in radiative penguin $B$ decays provides a test of the Standard Model and a probe for New Physics, that can lead to a deviation from the Standard Model prediction of left-handed photons in $b\to s \gamma$. We propose a new method to measure the photon polarization using the baryonic decay $B^- \to \Lambda\bar{p} \gamma$. The $P$-violating $\Lambda$-hyperon decay allows a measurement of the $\Lambda$ helicity to be performed, which can be uniquely related to the photon polarization in a model-independent way. The $B^- \to \Lambda\bar{p} \gamma$ decay was recently measured to have a large branching fraction providing a possibility to get meaningful results with the data already available at LHC and B-factory experiments. An increase of the $B$-meson sample at high luminosity LHC experiments and Belle II should provide a really stringent test by using this method already in the near future.