22-29 July 2015
Europe/Vienna timezone

B to K* l+l- decays in the Standard Model: a theoretical reappraisal

Jul 23, 2015, 9:30 AM


talk Flavour Physics and Fundamental Symmetries Flavour Physics and Fundamental Symmetries


Ayan Paul (INFN, Sezione di Roma)


The rare semileptonic B_d → K∗μ+μ− decay has been extensively studied within the Standard Model (SM) and beyond. In the last two releases, measurements provided by the LHCb experiment suggested a discrepancy found between the theoretical SM prediction and the experimental value of the angular observable P′5 at low q^2. We critically reassess the theoretical uncertainties in the Standard Model calculation of the B_d → K∗l+l− angular observables, focusing on this kinematic region. We point out that even optimized observables are affected by sizable uncertainties coming from several sources. First, departures from the infinite mass limit are numerically sizable and cannot be reduced by redefining the soft functions. Second, hadronic contributions generated by current-current operators with charm are difficult to estimate, especially for q^2 ~ 4 mc^2. Finally, charmonium contributions are not power suppressed and are expected to increase the uncertainties close to the hadronic resonances. Taking these uncertainties into account, we perform a detailed numerical analysis and present both predictions and fit results obtained using different sets of data, showing agreement between theory and experiment.

Primary author

Ayan Paul (INFN, Sezione di Roma)

Presentation materials