The subject of the study is the measurement of the properties of the jets selected by the CMS detector in 2016 at a collision energy of 13 TeV with an integrated luminosity of 36 fb^-1. The jets were selected in events with two oppositely directed jets (dijet channel). Three samples of jets were used in the study: from events without additional jets, from events with one or two additional jets, and from events with more than two additional jets. The samples are divided into subsamples of the jets in bins according to the transverse momentum of the jet in the range from 30 to 1000 GeV. The bin size is 30 GeV.
The goal of the study is to measure the average charged-particle multiplicity and the fraction of gluon jets in the samples, depending on the average transverse momentum of the jet.
In the work, the average charged-particle multiplicity was measured for jets with cutting off low-energy tracks (less than 500 MeV). The corrections were made: (1) the contribution of the pile up jets was subtracted, (2) the correction for low-energy tracks and tracks outside the tracker, (3) jet energy correction, (4) the correction for lost and fake tracks.
The second measurement performed in the work is the measurement of the gluon jet fractions in the same samples. The quark-gluon discriminator (QGL) developed for CMS is used for this measurement. The measurement was performed by fitting the QGL distribution of jets in the data by a linear combination of QGL distributions for quark and gluon jets with one parameter — the gluon jet fraction. For fitting, the method of weighted least squares is used. Quark and gluon QGL distributions were obtained using a combination of MadGraph5 + Pythia8 generators. In this study, it was shown that independent measurements of the average charged-particle multiplicities in the jet and the gluon jet fractions are in qualitative agreement with each other for the studied jet samples.