UC Riverside

In this analysis we present the first results of the measurement of the shape parameter rb in the Lund-Bowler fragmentation function for the b quark in a ttbar environment. The analysis uses charmed mesons produced in the leptonic decays of ttbar at sqrt(s)=13 TeV in the CMS detector using the full 2016 dataset with an integrated luminosity of 35.9 fb^-1. The charged particle decays of J/Psi -> mu^+ mu^- and D^0 -> K pi are used as proxies for the parent b quark via the ratio xB (the pT of the charmed meson divided by the sum of the transverse momentum of all charged particles in the jet containing the meson) to measure the shape parameter rb. The shape parameter rb is measured to be rb = 0.841 +/- 0.014 (stat) +/- 0.031 (syst).