Measurement of track reconstruction inefficiencies in the core of jets via pixel dE/dx with the ATLAS experiment using $\sqrt{s}=13$ TeV $\textit{pp}$ collision data

The inefficiency of the ATLAS charged particle reconstruction in the core of jets is studied as a function of the transverse momentum of the jet between 200 GeV and 1600 GeV, using proton-proton data collected by the ATLAS experiment from the LHC in 2015 at a center-of-mass energy of $\sqrt{s}=13$ TeV. Quantifying such an inefficiency is important for numerous performance studies and physics analyses, including calibration of the jet energy scale and mass. A fully data driven method to measure the fraction of lost tracks using the energy loss, dE/dx, of charged particles in the pixel detector is presented. The fraction of lost tracks is at most $5\%$ as a function of jet transverse momentum. The fraction of lost tracks estimated from Monte Carlo simulation samples are compared to the results and found to agree within $25\%$.