Abstract
In high energy exclusive processes involving leptons, QED corrections can be sensitive to infrared scales like the lepton mass and the soft photon energy cut, resulting in large logarithms that need to be resummed to all order in $\ensuremath{\alpha}$. When considering the ratio of the exclusive processes between two different lepton flavors, the ratio $R$ can be expressed in terms of factorized functions in the decoupled leptonic sectors. While some of the functional terms cancel, there remain the large logarithms due to the lepton mass difference and the energy cut. This factorization process can be universally applied to the exclusive processes such as $Z\ensuremath{\rightarrow}{l}^{+}{l}^{\ensuremath{-}}$ and ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{l}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{l}$, where the resummed result in the ratio gives significant deviations from the naive expectation from lepton universality.
Highlights
In high energy exclusive processes involving leptons, QED corrections can be sensitive to infrared scales like the lepton mass and the soft photon energy cut, resulting in large logarithms that need to be resummed to all order in α
Lepton universality has been tested in B decays, where flavor transitions are highly entangled. (We refer to Ref. [3] for the recent review.) Since the masses of electrons and muons are negligible compared to the b quark mass, it is natural to expect that the decay modes with the electron and with the muon are almost identical in the Standard Model (SM)
Unlike for inclusive processes, in exclusive processes rather large differences in QED corrections can be expected between lepton flavors even though the lepton masses are much smaller than the relevant decay or scattering hard scale
Summary
In high energy exclusive processes involving leptons, QED corrections can be sensitive to infrared scales like the lepton mass and the soft photon energy cut, resulting in large logarithms that need to be resummed to all order in α. When considering the ratio of the exclusive processes between two different lepton flavors, the ratio R can be expressed in terms of factorized functions in the decoupled leptonic sectors. While some of the functional terms cancel, there remain the large logarithms due to the lepton mass difference and the energy cut. This factorization process can be universally applied to the exclusive processes such as Z → lþl− and B− → l−νl, where the resummed result in the ratio gives significant deviations from the naive expectation from lepton universality. With the decay ratios between two different lepton flavors defined by
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
