PoS - Proceedings of Science
Volume 411 - 11th International Workshop on the CKM Unitarity Triangle (CKM2021) - Wg2&3
On the $ R_{K} $ theory error
S. Nabeebaccus* and R. Zwicky
Full text: pdf
Pre-published on: January 13, 2023
Published on: June 16, 2023
Abstract
We compute the double differential rate of $ \bar{B}\to \bar{K}\ell^{+}\ell^- $ at $ {\cal O}( \alpha ) $ in QED, using a mesonic effective theory framework. While soft and soft collinear logarithms cancel at the differential level in any set of kinematic variables, the cancellation of hard collinear logarithms $\ln m_\ell$ depends on the choice of differential variables even in the photon-inclusive case.
Crucially, using gauge invariance, we show that structure-dependent QED corrections do not lead to additional hard collinear logs.
Using photon energy cuts, emulating the LHCb procedure, we report a correction to $ R_{K} $ of $ \approx1.7\% $ due to QED. This correction is accidentally small due to the cuts and is expected to be largely captured by PHOTOS. Finally, the effect of migration of radiation is discussed, whereby QED corrections at larger $ q^2 $ (lepton pair momentum squared) can ``leak" into lower values. This effect could be relevant in view of charmonium resonances and is deserving of further attention.
DOI: https://doi.org/10.22323/1.411.0071
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