In pursuit of right-handed photons

Since the discovery of parity violation by weak interaction in 1956, this phenomenon has been studied extensively and today, maximum parity violation by weak interaction is a property of the Standard Model of particle physics. One of the consequences of this property is that, according to the Standard Model, photons emitted in transitions involving the weak interaction are of left polarization. The LHCb experiment, located at the LHC (CERN), recently studied this property for photons emitted in b → sγ type transitions. Indeed, if it turns out that these photons could also be emitted with a right polarization, this could be the sign that a new physics, beyond the Standard Model, also intervenes in these rare transitions.

Indeed, b → sγ transitions are rare: less than 1 b quark in 1,000 turns into an s quark and a photon. They have been studied for almost 30 years in numerous experiments around the world. The LHCb collaboration, using an innovative method developed by physicists from the LHCb team of IJCLab (PHE Pole), used the world's largest sample of B0 → K*0e+e- and she isolated those which come from the B0 → K*0γ decay where the (virtual) photon finally materializes into an e+e- pair, in order to identify the decays caused by the b → sγ transition. The angular distributions of the B0 → K*0e+e- decay products can be used as a polarimeter to obtain the polarization of the photon. The measurements agree well with the Standard Model, but the uncertainty is completely dominated by the sample size. An improvement in the measurement is therefore expected with all the data that will be recorded during Run3 (until 2025) and may be able to highlight a small fraction of right polarization.

More information in the preprint: arXiv :2010.06011.

2020-10-26 14:09