E2 strength in the radiative charmed baryon decay ∑c∗ → Λcγ

The radiative decay ∑Q∗ → ΛQγ can have both magnetic dipole (M1) and electric quadrupole (E2) components. In the heavy quark limit MQ → ∞ the transition arises from the spin of the light degrees of freedom changing from sl = 1 to sl = 0 and hence the E2 contribution vanishes. We compute the leading contribution to the E2 strength in chiral perturbation theory and find that the amplitude is enhanced by a small energy denominator in the chiral limit. This enhancement essentially compensates for the 1Mc suppression that is present in the charm system. We find a mixing ratio of order a few percent dependent upon the ∑c-∑c∗ spin symmetry breaking mass difference. The analogous quantity in the b-baryon sector is smaller by a factor of ∼ McMb.