The LHC particle accelerator at CERN probes the elementary building blocks of matter by colliding protons at a center-of-mass energy of √s = 13 TeV. Collimated sprays of particles arise when quarks and gluons are produced at high energies, that are reconstructed from measured data and clustered together into jets. Accurate measurements of the energy of jets are paramount for sensitive particle physics analyses at the CMS experiment. Jet energy corrections are for that reason used to map measurements towards Monte Carlo simulated truth values, which are independent of detector response. The aim of this thesis is to improve upon the standard jet energy corrections by utilizing deep learning. Recent advancements on learning from point clouds in the machine learning community have been adopted in particle physics studies to improve jet flavor classification accuracy. This includes representing jet constituents as an unordered set, or a so-called “particle cloud”. Two highly performant models suitable for such data are the set-based Particle Flow Network and the graph-based ParticleNet. A natural next step in the advancement of jet energy corrections is to adopt a similar methodology, only changing the problem statement from classification to regression. The deep learning models developed in this work provide energy corrections that are generically applicable to differently flavored jets. Their performance is presented in the form of jet energy response resolution and reduction in flavor dependence. The models achieve state of the art performance for both metrics, significantly surpassing the standard corrections benchmark.

The production of a Z boson, decaying to two charged leptons, in association with jets in proton- proton collisions at a centre- of- mass energy of 13 TeV is measured. Data recorded with the CMS detector at the LHC are used that correspond to an integrated luminosity of 2.19 fb - 1. The cross section is measured as a function of the jet multiplicity and its dependence on the transverse momentum of the Z boson, the jet kinematic variables ( transverse momentum and rapidity), the scalar sum of the jet momenta, which quantifies the hadronic activity, and the balance in transverse momentum between the reconstructed jet recoil and the Z boson. The measurements are compared with predictions from four different calculations. The first two merge matrix elements with different parton multiplicities in the final state and parton showering, one of which includes oneloop corrections. The third is a fixed- order calculation with next- to- next- to- leading order accuracy for the process with a Z boson and one parton in the final state. The fourth combines the fully differential next- to- next- to- leading order calculation of the process with no parton in the final state with next- to- next- to- leading logarithm resummation and parton showering.

Measurements of differential cross sections for inclusive very forward jet production in proton-lead collisions as a function of jet energy are presented. The data were collected with the CMS experiment at the LHC in the laboratory pseudorapidity range 6 : 6 < < 5 : 2. Asymmetric beam energies of 4TeV for protons and 1.58TeV per nucleon for Pb nuclei were used, corresponding to a center-of-mass energy per nucleon pair of p sNN = 5 : 02TeV. Collisions with either the proton (p+ Pb) or the ion (Pb+ p) traveling towards the negative hemisphere are studied. The jet cross sections are unfolded to stable-particle level cross sections with pT & 3 GeV, and compared to predictions from various Monte Carlo event generators. In addition, the cross section ratio of p+ Pb and Pb+ p data is presented. The results are discussed in terms of the saturation of gluon densities at low fractional parton momenta. None of the models under consideration describes all the data over the full jet-energy range and for all beam con fi gurations. Discrepancies between the di ff erential cross sections in data and model predictions of more than two orders of magnitude are observed.

Searches for resonances decaying into pairs of jets are performed using proton-proton collision data collected at root s = 13 TeV corresponding to an integrated luminosity of up to 36 fb(-1). A low-mass search, for resonances with masses between 0.6 and 1.6 TeV, is performed based on events with dijets reconstructed at the trigger level from calorimeter information. A high-mass search, for resonances with masses above 1.6 TeV, is performed using dijets reconstructed offline with a particle-flow algorithm. The dijet mass spectrum is well described by a smooth parameterization and no evidence for the production of new particles is observed. Upper limits at 95% confidence level are reported on the production cross section for narrow resonances with masses above 0.6 TeV. In the context of specific models, the limits exclude string resonances with masses below 7.7 TeV, scalar diquarks below 7.2 TeV, axigluons and colorons below 6.1 TeV, excited quarks below 6.0 TeV, color-octet scalars below 3.4 TeV, W' bosons below 3.3 TeV, Z' bosons below 2.7 TeV, Randall-Sundrum gravitons below 1.8 TeV and in the range 1.9 to 2.5 TeV, and dark matter mediators below 2.6 TeV. The limits on both vector and axial-vector mediators, in a simplified model of interactions between quarks and dark matter particles, are presented as functions of dark matter particle mass and coupling to quarks. Searches are also presented for broad resonances, including for the first time spin-1 resonances with intrinsic widths as large as 30% of the resonance mass. The broad resonance search improves and extends the exclusions of a dark matter mediator to larger values of its mass and coupling to quarks.

Double-parton scattering is investigated using events with a Z boson and jets. The Z boson is reconstructed using only the dimuon channel. The measurements are performed with proton-proton collision data recorded by the CMS experiment at the LHC at root s = 13TeV, corresponding to an integrated luminosity of 35.9 fb(-1) collected in the year 2016. Differential cross sections of Z+ >= 1 jet and Z+ >= 2 jets are measured with transverse momentum of the jets above 20 GeV and pseudorapidity vertical bar eta vertical bar < 2.4. Several distributions with sensitivity to double-parton scattering effects are measured as functions of the angle and the transverse momentum imbalance between the Z boson and the jets. The measured distributions are compared with predictions from several event generators with different hadronization models and different parameter settings for multiparton interactions. The measured distributions show a dependence on the hadronization and multiparton interaction simulation parameters, and are important input for future improvements of the simulations.