  Measurements of the differential jet cross section are presented as a
function of jet mass in dijet events, in bins of jet transverse momentum, with
and without a jet grooming algorithm. The data have been recorded by the CMS
Collaboration in proton-proton collisions at the LHC at a center-of-mass energy
of 13 TeV and correspond to an integrated luminosity of 2.3 fb$^{-1}$. The
absolute cross sections show slightly different jet transverse momentum spectra
in data and Monte Carlo event generators for the settings used. Removing this
transverse momentum dependence, the normalized cross section for ungroomed jets
is consistent with the prediction from Monte Carlo event generators for masses
below 30% of the transverse momentum. The normalized cross section for groomed
jets is measured with higher precision than the ungroomed cross section.
Semi-analytical calculations of the jet mass beyond leading logarithmic
accuracy are compared to data, as well as predictions at leading order and
next-to-leading order, which include parton showering and hadronization.
Overall, in the normalized cross section, the theoretical predictions agree
with the measured cross sections within the uncertainties for masses from 10 to
30% of the jet transverse momentum.
