Recent experimental data on dijet cross section in diffractive photoproduction at HERA collider are analyzed with an emphasis on QCD factorization breaking effects. The possible sources of the contradiction in conclusions of H1 and ZEUS collaborations such as different hadronization corrections and different phase space of both analysis are studied.

The LHC, with its center-of-mass energy of 7 TeV, offers the chance to investigate the fundamental constituents of matter at a higher energy scale than ever before. Using the data acquired by the ATLAS detector in the summer of 2010, two different measures of the angular distributions of dijet final states are studied and compared to Standard Model QCD expectations. Such a comparison is used to set new stringent limits on the existence of quark substructure.

The LHC, with its center-of-mass energy of 7 TeV, offers the chance to investigate the fundamental constituents of matter at a higher energy scale than ever before. Using the data acquired by the ATLAS detector in the summer of 2010, two different measures of the angular distributions of dijet final states are studied and compared to Standard Model QCD expectations. Such a comparison is used to set new stringent limits on the existence of quark substructure.

The diffractive production of two jets in deep inelastic e± p scattering is mea- sured in the kinematic region of photon virtuality 4 < Q2 < 80 GeV2 , inelasticity 0.1 < y < 0.7, momentum fraction xIP < 0.03, proton ver- tex momentum transfer |t| < 1 and mass of a dissociative baryonic system MY < 1.6 GeV. Diffractive events are identified with the large rapidity gap technique. Integrated and single differential cross sections are measured for jets of transverse momenta p∗ T1 > 5.5 GeV and p∗ T2 > 4.0 GeV and pseudora- pidities −3 < η∗ 1,2 < 0. The data were collected by the H1 experiment at the HERA collider in years 2005-2007, corresponding to an integrated luminosity of 283.7 pb−1 . The measurements are compared with NLO predictions based on the DGLAP parton evolution.

Coloured final states are ubiquitous at hadron colliders such as the Large Hadron Collider (LHC). Therefore understanding high energy perturbative quantum chromodynamics (QCD) at these experiments is essential not only as a test of the Standard Model, but also because these processes form the dominant background to many searches for new physics. One such `standard candle' is the production of a dilepton pair in association with dijets. Here we present a new description of this final state (through the production of a Z⁰ boson and γ*). This calculation adds to the fixed-order accuracy the dominant logarithms in the limit of large partonic centre-of-mass energy to all orders in the strong coupling αs. This is achieved within the framework of High Energy Jets. This calculation is made possible by extending the high energy treatment to take into account the multiple t-channel exchanges arising from Z⁰ and gamma* -emissions off several quark lines. The correct description of the interference effects from the various t-channel exchanges requires an extension of the subtraction terms in the all-order calculation. We describe this construction and compare the resulting predictions to a number of recent analyses of LHC data. The description of a wide range of observables is good, and, as expected, stands out from other approaches in particular in the regions of large dijet invariant mass and large dijet rapidity spans. In addition we also present the application of the High Energy Jets framework to two new experimental scenarios. Firstly, we show a comparison of High Energy Jets matched to the ARIADNE parton shower to an ATLAS study of gap activity in dijet events. We see that our description agrees well with the data throughout and in many distributions gives the best theoretical description. This shows the extra logarithmic corrections are essential to describe data already in LHC Run I. Secondly, we present a study of Z⁰/γ* plus dijets at 100 TeV. We compare the behaviour of the high energy logarithmic enhancements to the QCD perturbative series at 7 TeV and 100 Tev and see that at any high energy hadronic Future Circular Collider (FCC) the effects described by our resummation become significantly more important.

A search for new heavy resonances in two-jet final states is described in this thesis. The data were collected by the ATLAS detector proton-proton collisions at sqrt(s) = 7 TeV and correspond to a time-integrated luminosity of 6.1 pb−1. The background-only hypothesis was tested on the observed data using BumpHunter test statistic. Consistency was found between the observed data and the background-only prediction. No resonant features were observed. A Bayesian approach using binned maximum likelihood was used to set upper limits on the product of cross section and detector acceptance for excited-quark (q*) production as a function of q* mass. At 95% credibility level (CL), the q* mass in the interval of 0.50 TeV < mq* < 1.62 TeV is excluded, extending the reach of previous experiments.

A search for new heavy resonances in two-jet final states is described in this thesis. The data were collected by the ATLAS detector proton-proton collisions at sqrt(s) = 7 TeV and correspond to a time-integrated luminosity of 6.1 pb−1. The background-only hypothesis was tested on the observed data using BumpHunter test statistic. Consistency was found between the observed data and the background-only prediction. No resonant features were observed. A Bayesian approach using binned maximum likelihood was used to set upper limits on the product of cross section and detector acceptance for excited-quark (q*) production as a function of q* mass. At 95% credibility level (CL), the q* mass in the interval of 0.50 TeV < mq* < 1.62 TeV is excluded, extending the reach of previous experiments.

Title: Analysis of dijet events in diffractive ep interactions with tagged leading proton at the H1 experiment Author: Richard Polifka Department: Institute of Particle and Nuclear Physics Supervisor: RNDr. Alice Valkárová, DrSc. Supervisor's e-mail address: avalkar@mail.desy.de Abstract: An inclusive dijet production in diffractive deep-inelastic scattering is measured. The diffractive selection is based on tagging of the leading proton in the Forward Proton Spectrometer. The statistics of events obtained during the HERA II running period (integrated luminosity of 156.7 pb−1 ) enables the measurement of jet final states with leading proton for the first time. The data cover the phase space of xIP < 0.1, |t| <= 1.0 GeV2 and 4 <= Q2 <= 110 GeV2 . The dijet data are compared with the next to leading order predictions of the quantum chromodynamics (QCD). The phase space of diffractive dijets is in this analysis by factor of 3 in xIP larger than in previous measurements. The QCD predictions based on the DGLAP parton evolution describe the measured data well even in a non-DGLAP enriched phase space where one on the jets goes into the region close to the direction of the outgoing proton. The measured single-differential cross sections are compared to several Monte Carlo models with different treatment of...

The Large Hadron Collider (LHC) has provided, and will continue to provide, data for collisions at the highest energies ever seen in a particle accelerator. A strong knowledge of the properties of amplitudes for Quantum Chromodynamics in the High Energy Limit is therefore important to interpret this data. We study this limit in the context of the High Energy Jets (HEJ) formalism. This formalism resums terms in the perturbative expansion of the cross-section that behave like αn/s log (s/-t)ⁿ¯¹, which are enhanced in this limit. Understanding this region is particularly important in certain key analyses at the LHC: for example, Higgs-boson- plus-dijet analyses where cuts are applied to pick out events with a large mjj and in many searches for new physics. In this thesis, we discuss two directions in which HEJ's accuracy has been improved. Firstly, we look at adding descriptions of partonic subprocesses which are formally sub-leading in the jet cross-section but Leading Logarithmic (LL) in the particular subprocess itself. This required the derivation of new effective vertices that describe the emission of a quark/anti-quark pair in a way that is consistent with the resummation procedure. The inclusion of such processes reduces HEJ's dependence on fixed-order calculations and marks an important step towards full Next-to-Leading Logarithmic (NLL) accuracy in the inclusive dijet cross-section. The second extension was to improve our description of events involving the emission of a Higgs boson along with jets. Specifically, we derive new effective vertices which keep the full dependence on the quark mass that appears in the loops that naturally arise in such amplitudes. The formalism is also simple enough to allow for any number of extra nal state jets in the process. Therefore, HEJ is unique in its ability to provide predictions for high-multiplicity Higgs-plus-jets processes with full nite quark mass e ects. Such a calculation is far beyond the reach of any xed order approach.

Le Modèle standard de la physique de particules explique avec beaucoup de succès comment les particules fondamentales interagissent entre elles. Néanmoins, ce modèle n’est pas capable d’expliquer certains défis contemporains du domaine, comme la grande quantité de paramètres libres, le problème de la hiérarchie ou l’identité de la matière sombre. Pour expliquer ces phénomènes, il faut chercher la physique au-delà du Modèle standard. De sorte à satisfaire les contraintes provenant des mesures expérimentales, on peut considérer l’addition d’une seule nouvelle particule au Modèle standard qui se couple à deux quarks, le diquark. Sa contribution aux processus hadroniques offre une opportunité d’obtenir des limites dans ses paramètres à partir des données expérimentales contemporaines. Ceci nous permettrait d’évaluer son potentiel et d’identifier les processus auxquels cette particule peut contribuer. Parmi les états de diquarks possibles, on trouve les diquarks scalaires Dᵘ et Dᵈ, qui possèdent un couplage antisymétrique à des paires de quarks droitiers du type up ou du type down, respectivement. L’obtention des contraintes sur les valeurs de leur masse Mᴰ et leurs couplages aux quarks (x^q, y^q), où q = u, d, est l’objectif central de ce travail. Pour cela, on considère tout d’abord des recherches directes dans la production de dijet, la signature expérimentale des désintégrations de ces particules. Ensuite, on sonde l’influence indirecte du diquark Dᵘ dans les mesures expérimentales de la section efficace de production d’un seul quark top. Les données expérimentales obtenues dans le Grand collisionneur d’hadrons (LHC) pour ces processus à haute énergie sont utilisées pour comparer les prédictions théoriques de ces modèles et quantifier leur viabilité en fournissant de nouvelles contraintes sur ses paramètres. On est capable d’améliorer les contraintes trouvées dans la littérature de |xᵘ| ≤ 14,4 à |xᵘ| ≤ 0,13–0,15 pour Dᵘ et de |xᵈyᵈ| ≤ 0,022 avec |yᵈ| ≤ 0,17 à |xᵈ| ≤ 0,15–0,17 pour Dᵈ, les deux avec une masse de Mᴰ = 600 GeV. De plus, l’analyse des données pour la production d’un seul quark top montre que la réduction de l’espace de phase des pᵀ peut améliorer encore plus ces contraintes. / The Standard Model of particle physics explains with great success how fundamental particles interact. However, this model cannot explain some contemporary challenges of the domain, such as the large number of free parameters, the hierarchy problem or the identity of dark matter. To explain these phenomena, we need to search for physics beyond the Standard Model. In order to satisfy the existing constraints from experimental measurements, we can consider the addition of a single new particle to the Standard Model that couples to two quarks, a diquark. Its contribution to hadronic processes offers an opportunity to set limits on its parameters from contemporary experimental data. This would allow us to evaluate their potential and identify processes to which they can contribute. Among the possible diquark states, we find the scalar diquarks Dᵘ and Dᵈ, which have an antisymmetric coupling to pairs of right-handed up-type or down-type quarks, respectively. To obtain constraints on their mass Mᴰ and on their couplings to quarks (x^q, y^q), where q = u, d, is the main goal of this work. In order to do so, we start by considering direct searches in the production of dijet, the experimental signature of the decay of these particles. Afterwards, we probe the indirect influence of the Dᵘ diquark to the experimental measurements of the single-top-production cross section. Recent data for both of these processes from the Large Hadron Collider (LHC) is used to compare the theoretical predictions of these models and quantify their viability by providing new constraints on its parameters. We are able to improve the constraints found in the literature from |xᵘ| ≤ 14.4 to |xᵘ| ≤ 0.13–0.15 for Dᵘ and from |xᵈyᵈ| ≤ 0.022 to |yᵈ| ≤ 0.17 to |xᵈ| ≤ 0.15–0.17 for Dᵈ, both with masses of Mᴰ = 600 GeV. Other than that, the analysis of the data from single top production shows that the reduction of the pᵀ space can further improve these constraints.