Recent progress in decays of $b$ and $c$ hadrons

TL;DR

The paper addresses the persistent anomalies in $b\to s$ and $b\to c$ transitions and the exclusive-inclusive tensions in the CKM elements $|V_{ub}|$ and $|V_{cb}|$. It surveys the theoretical framework (form factors, Wilson coefficients) and the experimental landscape, highlighting advances in Lattice QCD and LCSR form factors, NNLL RG running, and lepton-universality tests such as $R_{K^{(\ast)}}$ and $R_{D^{(\ast)}}$. It also surveys inclusive and exclusive determinations of CKM elements and the status of radiative and neutrino channels, along with global fits to Wilson coefficients that favor possible new-physics contributions. Finally, it highlights the upcoming Belle II and LHCb Upgrade II data as critical to resolving these tensions and clarifying the flavor structure of any new physics.

Abstract

In the last ten years there has been great progress in calculations of decays of $B$ and $D$ mesons, and baryons containing a heavy $b$ or $c$ quark. One propelling factor has been the measurement of several anomalies in $b\to s$ and $b\to c$ transitions, these are one of the only signs of physics beyond the Standard Model. The deviations included measurements of branching ratios, angular observables and lepton universality ratios. Another factor is the exclusive-inclusive discrepancy in the determination of the CKM elements $V_{ub}$ and $V_{cb}$. We will first review recent calculations involving $b\to s$ and $c\to u$ transitions that could shed light on the neutral current anomalies. We will then summarise the progress the determination of the CKM elements, $V_{ub}$ and $V_{cb}$. Finally we will discuss the current theoretical status and experimental prospects for the lepton universality ratios in $b\to s$ and $b\to c$ semileptonic decays.

Figures (3)

• Figure 1: We summarise the most recent determinations for inclusive $V_{cb}$ (left) (GS'13 Gambino:2013rza, AGHN '14 Alberti:2016fba, GHT'16 Gambino:2016fdy, BCG'21 Bordone:2021oof, HST'22 Hayashi:2022hjk and BFOPvT'22 Bernlochner:2022ucr) and compare this to the HFLAV experimental average from 2016 HFLAV:2016hnz and for exclusive $V_{cb}$ (right), from $B\to D$ (HPQCD'17 Harrison:2017fmw, GJS'19 Gambino:2019sif and BJvD'19 Bordone:2019vic), from $B\to D$ (FNAL/MILC'15 MILC:2015uhg, HPQCD'15 Na:2015kha and BJvD'19 Bordone:2019vic), and from $B_s\to D_s$ (HPQCD'21 Harrison:2021tol)
• Figure 2: We summarise the most recent determinations for inclusive $V_{ub}$ (left), from BaBar'16 BaBar:2016rxh, Belle'21 Belle:2021ymg, (where DN, BLNP, GGOU, DGE and ADFR are different theoretical methods described in the text) and GHM'16 Gambino:2016fdy and for exclusive $V_{ub}$ (right), from $B\to\pi\ell\nu$ (IKMvD'14 Imsong:2014oqa, FNAL/MILC'15 FermilabLattice:2015mwy, RBC/UKQCD'15 Flynn:2015mha, HFLAV'16 HFLAV:2016hnz, LMvD'21 Leljak:2021vte and JLQCD'21 Colquhoun:2022atw), from $B\to\rho\ell\nu$ and $B\to\omega\ell\nu$ (BSZ'15 Straub:2015ica and BPR'21 Bernlochner:2021rel).
• Figure 3: We summarise the most recent determinations for the ratio of exclusive $V_{ub}/V_{cb}$ (left) measured at LHCb LHCb:2020istLHCb:2015eia. For the determination from $B_s$ decays, the form factor for the $B_s\to D_s$ transition is taken from the 2020 HPQCD result McLean:2019qcx, and for the $B_s\to K$ from FNAL/MILC'19 FermilabLattice:2019ikx and LCSR KR'17 Khodjamirian:2017fxg as indicated. For the determination from $\Lambda_b$ decays the form factors are from DM'15 Detmold:2015aaa. These are compared to the ratio of the HFLAV experimental averages for $V_{ub}^{\rm excl}$ and $V_{cb}^{\rm excl}$Amhis:2022mac. We further present the most recent theory predictions for $R_D$ (right) (HPQCD'15 Na:2015kha, FNAL/MILC'15 MILC:2015uhg, BLPR'17 Bernlochner:2017jka, BJvD'19 Bordone:2019vic) and for $R_{D*}$(BLPR'17 Bernlochner:2017jka, GJS'19 Gambino:2019sif, BJvD'19 Bordone:2019vic, JNK'20 Jaiswal:2020wer, FNAL/MILC'21 FermilabLattice:2021cdg).