Measurement of Forward Energy Flow at 13 TeV with the CMS Experiment

The measurement of the energy flow is performed with the forward (HF: $3.15 <\mid \eta \mid) < 5.2$) and very-forward (CASTOR: $-6.6 < \eta < -5.2$) calorimeters of CMS at the centre-of-mass energy of 13 TeV. The data were taken during the several periods of low luminosity operation in 2015. The results are compared to Monte Carlo (MC) model predictions as well as the earlier proton-proton data taken at $\sqrt{s} = 0.9$ TeV and 7 TeV. Furthermore, the beam fragmentation which provides valuable input for tuning of MC models used to describe high energy hadronic interactions is also studied at the regions close to the beam rapidities.