Rare radiative charm decays in and beyond the standard model

Abstract

This thesis comprises a study of rare radiative |Δc| = |Δu| = 1 transitions within and beyond the standard model of particle physics. For the 18 three-body decays D → P1 P2 ɣ with 𝑃 = π, K decay amplitudes are derived using Low’s theorem, QCD factorization and heavy hadron chiral perturbation theory. Standard model predictions for branching ratios, CP asymmetries as well as forward-backward asymmetries are determined. Moreover, the effects of new physics in the coefficients of the electromagnetic dipole operators are investigated respecting the current constraints. The photon polarization in Ds→ K1(→ Kπ π) ɣ decays is studied with respect to new physics effects in the dipole coefficients. Within the standard model, the polarization parameter agrees with the SM- like partner decay 𝐷+ → 𝐾1 (→ 𝐾π π)) ɣ up to U-spin breaking corrections. The existence of partner decays allows to construct a null test which does not require precise knowledge of the hadronic K1 → Kπ π decay. Finally, different ways to test the standard model with rare radiative decays of charm baryons are discussed. Based on the approximate SU(3)𝐹 symmetry of QCD as well as its subgroups, relations between partner decays are worked out. Branching ratios, CP asymmetries as well as the photon polarizations are considered as observables and the potential of new physics effects is estimated. Methods for the extraction of the photon polarization from two-body decays Bc → B ɣ of polarized charm baryons as well as from decay chains Bc → B(→ B′ 𝑃 ) ɣ with self-analyzing hyperons 𝐵 are presented.