Ricerc@Sapienza

The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb−1 of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B
+ → J/ψ(e
+
e
−
)K
+ decays, where one of the electrons is fully reconstructed
and paired with the kaon, while the other electron is reconstructed using only the information of
the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow
the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This
in turn allows the electron reconstruction efficiency to be measured by matching the partial track
segment found in the vertex detector to tracks found by LHCb’s regular reconstruction algorithms.
The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching
fractions involving single electrons with a systematic uncertainty below 1%.