Measurement of charm production in CMS and total charm cross section with non-universal charm fragmentation

This thesis presents differential and total charm cross section measurements at various center-of-mass energies in pp collisions. For the purpose of measuring the total charm cross section, the D${}^{\text{∗}+}$ differential cross sections are measured at $\sqrt{s}$ = 7, 0.9 and 13 TeV in the CMS detector by covering the largest possible phase space, resulting in the smallest extrapolation factor ever introduced at the LHC. The measured fiducial cross sections are extrapolated to the total cross section using a data-driven parametrization which is introduced for the first time to be applied to all the weakly-decaying ground states in pp collisions with non-universal charm fragmentation. Also adding other LHC measurements, the total charm-pair cross sections are measured at $\sqrt{s}$ = 0.9, 5, 7, and 13 TeV to be 1.83${}_{-0.37}^{+0.35}$, 8.43${}_{-1.16}^{+1.05}$, 9.39${}_{-1.49}^{+1.35}$, and 17.43${}_{-2.57}^{+2.10}$ mb, respectively. These measurements supersede all the earlier LHC measurements which were derived under the fragmentation universality assumption, and show consistency with NNLO QCD theory predictions. The measurement of the total charm cross section as a function of the center-of-mass energy can be used to constrain QCD parameters. The very first example is shown to constrain the charm mass and the parton distribution functions particularly in thelow-x region.