Standard Model predictions for rare K and B decays without new physics infection

Andrzej J. Buras

doi:10.1140/epjc/s10052-023-11222-6

2021 Impact factor 4.991

Particles and Fields

Open Access

Eur. Phys. J. C (2023) 83: 66
https://doi.org/10.1140/epjc/s10052-023-11222-6

Regular Article - Theoretical Physics

Standard Model predictions for rare K and B decays without new physics infection

Andrzej J. Buras¹^,2^a

¹ TUM Institute for Advanced Study, Lichtenbergstr. 2a, 85747, Garching, Germany
² Physik Department, TU München, James-Franck-Straße, 85748, Garching, Germany

^a aburas@ph.tum.de

Received: 17 November 2022
Accepted: 12 January 2023
Published online: 24 January 2023

Abstract

The Standard Model (SM) does not contain by definition any new physics (NP) contributions to any observable but contains four CKM parameters which are not predicted by this model. We point out that if these four parameters are determined in a global fit which includes processes that are infected by NP and therefore by sources outside the SM, the resulting so-called SM contributions to rare decay branching ratios cannot be considered as genuine SM contributions to the latter. On the other hand genuine SM predictions, that are free from the CKM dependence, can be obtained for suitable ratios of the K and B rare decay branching ratios to , and , all calculated within the SM. These three observables contain by now only small hadronic uncertainties and are already well measured so that rather precise SM predictions for the ratios in question can be obtained. In this context the rapid test of NP infection in the sector is provided by a plot that involves , , , and the mixing induced CP-asymmetry . As with the present hadronic matrix elements this test turns out to be negative, assuming negligible NP infection in the sector and setting the values of these four observables to the experimental ones, allows to obtain SM predictions for all K and B rare decay branching ratios that are most accurate to date and as a byproduct to obtain the full CKM matrix on the basis of transitions alone. Using this strategy we obtain SM predictions for 26 branching ratios for rare semileptonic and leptonic K and B decays with the pair or the pair in the final state. Most interesting turn out to be the anomalies in the low bin in () and ().

© The Author(s) 2023

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