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Sussex scientists close in on extremely rare decay

Likelihood contours for the disintegration probability according to the experimental data from this result (blue) and for its combination (black) with a similar result published by the same authors in 2016.

On 20 September 2018, at the international conference CKM 2018, Dr Alessandro Cerri presented on behalf of the ATLAS collaboration, the most stringent experimental constraint of the very rare decay of the B0 meson into two muon particles. The Standard Model (the best performing theory physicists have to describe the subatomic world) foresees this never observed phenomenon to happen only about 1.1 times out of ten billion decays. The new constraint gets very close to excluding probabilities as low as two times out of ten billion decays. This decay and a close relative for which Dr Cerri presented also an updated measurement, could show anomalies that would hint to theories beyond the Standard Model. 

The result has been obtained over the course of more than two years, using data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. An international group led by Dr Cerri together with the main contributor Sussex PhD student Fabio Tresoldi, and in cooperation with German, Russian and American scientists, produced and had the study publicly released by the ATLAS collaboration less than an hour before Dr Cerri's presentation. 

This new milestone surpasses what has been recently published by Large Hadron Collider experiments dedicated to the study of B mesons [LHCb Collaboration, Phys. Rev. Lett. 118 (2017)191801] as well as the result previously published on Nature [CMS and LHCb Collaborations, Nature 522 (2015) 68] in a quest spanning almost three decades.

B mesons are non-elementary particles that have been discovered in the early 80s. They are being actively investigated by scientist for their asymmetric behaviors. Excluding the Standard Model prediction for this very rare B0 meson decay with sufficient margin would be an irrefutable evidence of something new and exciting in the physics of elementary particles.

By: Justine Charles
Last updated: Tuesday, 25 September 2018