Daniel Savoiu

A selection of recent experimental results on jet measurements in proton-proton collisions at $\sqrt{s}$ = 13 TeV from the CMS Collaboration is presented. Differential measurements of the inclusive jet and dijet production cross sections are performed as a function of transverse momentum ($p_{\rm T}$) and absolute rapidity, and the impact of these data on determinations of the strong coupling constant and the parton distribution functions is presented. In addition, a measurement of jet multiplicity and $p_{\rm T}$ in multijet events is outlined and compared to predictions obtained for different parton shower models and with various Monte Carlo (MC) event generators. Finally, a measurement of the Lund jet plane density, which represents the phase space of emissions inside jets, is described, and the results are compared to predictions obtained from MC generators with different tunes, parton showers and hadronization models.

Inclusive jet cross section measurements from the ATLAS, CDF, CMS, D0, H1, STAR, and ZEUS experiments are explored for determinations of the strong coupling constant $$\alpha _{\text {s}} (M_{\text {Z}})$$ . Various jet cross section data sets are reviewed, their consistency is examined, and the benefit of their simultaneous inclusion in the $$\alpha _{\text {s}} (M_{\text {Z}})$$ determination is demonstrated. Different methods for the statistical analysis of these data are compared and one method is proposed for a coherent treatment of all data sets. While the presented studies are based on next-to-leading order in perturbative quantum chromodynamics (pQCD), they lay the groundwork for determinations of $$\alpha _{\text {s}} (M_{\text {Z}})$$ at next-to-next-to-leading order.

Fast interpolation-grid frameworks facilitate an efficient and flexible evaluation of higher-order predictions for any choice of parton distribution functions or value of the strong coupling αs . They constitute an essential tool for the extraction of parton distribution functions and Standard Model parameters, as well as studies of the dependence of cross sections on the renormalisation and factorisation scales. The APPLfast project provides a generic interface between the parton-level Monte Carlo generator and both the APPLgrid and the fastNLO libraries for the grid interpolation. The extension of the project to include hadron-hadron collider processes at next-to-next-to-leading order in perturbative QCD is presented, together with an application for jet production at the LHC.

Inclusive jet cross section measurements from the ATLAS, CDF, CMS, D0, H1, STAR, and ZEUS experiments are explored for determinations of the strong coupling constant $α_{\text{s}}(M_{\text{Z}})$. Various jet cross section data sets are reviewed, their consistency is examined, and the benefit of their simultaneous inclusion in the $α_{\text{s}}(M_{\text{Z}})$ determination is demonstrated. Different methods for the statistical analysis of these data are compared and one method is proposed for a coherent treatment of all data sets. While the presented studies are based on next-to-leading order in perturbative quantum chromodynamics (pQCD), they lay the groundwork for determinations of $α_{\text{s}}(M_{\text{Z}})$ at next-to-next-to-leading order.

Fitting models to measured data is one of the standard tasks in the natural sciences, typically addressed early on in physics education in the context of laboratory courses, in which statistical methods play a central role in analysing and interpreting experimental results. The increased emphasis placed on such methods in modern school curricula, together with the availability of powerful free and open-source software tools geared towards scientific data analysis, form an excellent premise for the development of new teaching concepts for these methods at the university level. In this article, we present kafe2, a new tool developed at the Faculty of Physics at the Karlsruhe Institute of Technology, which has been used in physics laboratory courses for several years. Written in the {\it Python} programming language and making extensive use of established numerical and optimization libraries, {\it kafe2} provides simple but powerful interfaces for numerically fitting model functions to data. The tools provided allow for fine-grained control over many aspects of the fitting procedure, including the specification of the input data and of arbitrarily complex model functions, the construction of complex uncertainty models, and the visualization of the resulting confidence intervals of the model parameters.

In light of the large quantity of data collected during the second operational run of the Large Hadron Collider (LHC) at CERN, which has made it possible to perform measurements at unprecedented energies with a high degree of statistical precision, the necessity of understanding and constraining the systematic effects on such measurements has become increasingly important. Precision measurements of jet observables in proton-induced collisions have proven instrumental in constraining the parton distribution functions (PDFs) which describe the internal structure of protons, and which remain one of the largest sources of uncertainty in many analyses performed at hadron colliders. This thesis presents the first triple-differential measurement of the dijet production cross section performed in proton-proton collisions at a center-of-mass energy of 13 TeV, based on a data sample of 35.9 fb$^{-1}$ recorded by the CMS experiment at the Large Hadron Collider at CERN. The cross section is measured using anti-$k_\text{T}$ jets with radius parameters of R = 0.4 and R = 0.8 as a function of the dijet rapidity separation $y^{*}$ , the total boost of the dijet system $y_\text{b}$ , and either the average transverse momentum $\langle p_\text{T}\rangle_{1,2}$ or the invariant mass $m_\text{jj}$ of the dijet system as the third variable. This choice of rapidity variables exploits the topology of the dijet system to achieve an increased sensitivity to the proton PDFs. After accounting for detector-induced systematic effects in a three-dimensional unfolding procedure, the measured spectra are compared to fixed-order theory predictions at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics, obtained using several recent PDF sets. While the data are observed to be described by the theory within the experimental and theoretical uncertainties across a large portion of the phase space, potentially significant deviations are observed in areas where a heightened sensitivity to the PDFs is expected.