Alladi Ramakrishnan Hall

A U-spin puzzle in B decays

Suman Kumbhakar

University of Montreal

We impose U-spin symmetry [$SU(2)_{\rm Uspin}$] on the Hamiltonian for B decays. As expected, we find the equality of amplitudes related by the exchange $d \leftrightarrow s$. We also find that the amplitudes for the $\Delta S=0$ processes $B_d \to \pi^+\pi^-$, $B^0_s \to \pi^+K^-$ and $B^0_d \to K^+K^-$ form a U-spin triangle relation. The amplitudes for $B_s \to K^+K^-$, $B_d \to \pi^-K^+$ and $B^0_s \to \pi^+\pi^-$ form a similar $\Delta S=1$ triangle relation. And these two triangles are related to one another by $d \leftrightarrow s$. We perform fits to the observables for these six decays. If perfect U-spin is assumed, the fit is very poor. If U-spin-breaking contributions are added, we find many scenarios that can explain the data. However, in all cases, 100\% U-spin breaking is required, considerably larger than the naive expectation of $\sim 20\%$. This is the U-spin puzzle; it may be strongly hinting at the presence of new physics.

Reference: B.~Bhattacharya, S.~Kumbhakar, D.~London and N.~Payot, " U-spin puzzle in B decays", Phys. Rev. D 107 (2023) no. 1, L011505 [arXiv:2211.06994 [hep-ph]]