Using a measure of the jet energy resolution that relies on momentum balance in direct photon events, a correction to the modelled detector resolution is developed. The correction is produced by iteratively unfolding the model from the measured data. Jets in the model are then smeared using this correction, and the result is compared to the data using a χ2 test. This method is shown to be effective at improving the agreement between the data and the model, even when the model initially shows poor agreement to the data. / Graduate / 0798 / bmoir@ualberta.net

Universiẗat, Diss., 2007--Frankfurt (Main).

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, August 1999. / Includes bibliographical references. Also available on the Internet.

Techn. Hochsch., Diss., 2003--Aachen.

Universiẗat, Diss., 1993--Frankfurt (Main).

One of the primary goals of the CERN Large Hadron Collider is to search for new physics. Many such searches have been carried out, in particular searches for supersymmetry, yet no new physics beyond the Standard Model has been found. With a large number of free parameters introduced by frameworks such as supersymmetry, it can be difficult to interpret the null results of searches. The first analysis presented in this thesis attempts to tackle this difficulty head-on, and gives a summary of the constraints from the Run-1 ATLAS searches. A combination of 22 searches were used, with integrated luminosities of up to 20.3 inverse femtobarns of 7 and 8 TeV data. The results are interpreted in the context of the 19-dimensional phenomenological MSSM, and are presented in terms of the masses of supersymmetric particles. Constraints from dark matter, heavy flavour and precision electroweak measurements were incorporated, and results are also interpreted in terms of these observables. Properties of models missed by the Run-1 searches are also shown. The second analysis presented in this thesis documents a direct search for new physics, using 18.2 inverse femtobarns of 13 TeV data collected during 2015 and 2016 by the ATLAS detector. The search targets final states with large jet multiplicity (at least 7 to at least 10 jets), which can arise from the pair production of gluinos decaying via a cascade. Further requirements are imposed on the sum of masses of reclustered large-radius jets. No evidence for new physics is found, and the results are interpreted in both a model-independent way and in terms of two simplified supersymmetric models, one of which was inspired by the results of the first study. Limits on the gluino mass of up to 1600 GeV are set at the 95 % confidence level, extending previous limits.

The Standard Model of particle physics describes all known elementary particles and their interactions. Despite its great experimental success, we know that the Standard Model is not a complete description of Nature and therefore new phenomena should be observed at higher energies. In the coming years the Large Hadron Collider will test the Standard Model by colliding protons with center of mass energies of up to 14 TeV providing some of the most stringent tests on the Standard Model. Experimental searches for Dark Matter provide a complementary program to test physics at the weak scale. In the near future new experimental data coming from direct detection experiments, and from satellites and telescopes will drastically improve our sensitivity to weak scale dark matter. This could lead to the first direct observation of dark matter, and thus of physics beyond the Standard Model. In this thesis I propose different extensions of the Standard Model and discuss their experimental consequences. I first discuss models for Axigluons, which are spin one particles in the adjoint representation of the SU(3) color gauge group. These models were motivated by the measurement of higher than predicted forward-backward asymmetry in top quark pair production at the Tevatron. I study different scenarios for Axigluon models that can explain the Tevatron result and explore their signatures at the Large Hadron Collider. Second I discuss the implications of ultraviolet scale invariance for the Standard Model, which has been advocated as a solution to the hierarchy problem. I show that in order to solve the hierarchy problem with scale invariance, new physics is required not far from the weak scale. In the last part of this thesis I propose a new model for dark matter, in which dark matter is charged under a hidden non-Abelian gauge group. This leads to modifications in the sensitivity of the usual experimental searches for dark matter in addition to distinct signatures in the Cosmic Microwave Background and in Large Scale Structure data.

Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The Standard Model of particle physics provides an accurate description of all experimental data to date. The only unobserved piece of the Standard Model is the Higgs boson, a consequence of the spontaneous breaking of electroweak symmetry by the Higgs mechanism. An alternative to the Higgs mechanism is proposed by Technicolor theories which break electroweak symmetry dynamically through a new force. Technicolor predicts many new particles, called Technihadrons, that could be observed by experiments at hadron colliders. This thesis presents a search for two of the lightest Technihadrons, the ρT and ωT . The Low-Scale Technicolor model predicts the phenomenology of these new states. The ρT and ωT are produced through qq annihilation and couple to Standard Model fermions through the Drell-Yan process, which can result in the dimuon final state. The ρT and ω T preferentially decay to the πT and a Standard Model gauge boson if kinematically allowed. Changing the mass of the πT relative to that of the ρT and ωT affects the cross section times branching fraction to dimuons. The ρT and ωT are expected to have masses below about 1 TeV. The Large Hadron Collider (LHC) at CERN outside of Geneva, Switzerland, produces proton-proton collisions with a center of mass energy of 7 TeV. A general purpose high energy physics detector ATLAS has been used in this analysis to search for Technihadrons decaying to two muons. We use the ATLAS detector to reconstruct the tracks of muons with high transverse momentum coming from these proton-proton collisions. The dimuon invariant mass spectrum is analyzed above 130 GeV to test the consistency of the observed data with the Standard Model prediction. We observe excellent agreement between our data and the background only hypothesis, and proceed to set limits on the cross section times branching ratio of the ρT and ωT as a function of their mass using the Low-Scale Technicolor model. We combine the dielectron and dimuon channels to exclude masses of the ρT and ωT between 130 GeV - 480 GeV at 95% Confidence Level for masses of the πT between 50 GeV - 480 GeV. In addition for the parameter choice of m(π T ) = m(ρT /ω T )- 100 GeV, 95% Confidence Level limits are set excluding masses of the ρT and ωT below 470 GeV. This analysis represents the current world's best limit on this model. / 2031-01-01

The highly celebrated discovery of a new particle with a mass of 125 GeV in proton-proton collisions by the ATLAS and CMS experiments at the CERN Large Hadron Collider in 2012 has been shown to be compatible with the Standard Model description of the Higgs boson. However, in order to fully verify the Standard Model nature of the Higgs boson, most of its properties still remain to be measured. Such measurements include differential cross section measurements, which are shown here for the H→WW decay channel and the coupling of the Higgs boson to bottom quarks, for which a study of future prospects is presented. Differential fiducial cross section measurements of the Higgs boson were performed in the H → WW*→lvlv channel at the ATLAS detector with 20 fb−1 of √s = 8 TeV collision data. For Higgs bosons produced by gluon-gluon fusion, the cross section is measured as a function of kinematic variables, including transverse momentum and rapidity of the Higgs boson, as well as the number of jets associated with the Higgs event. The obtained distributions are unfolded to a fiducial volume using a two-dimensional iterative Bayesian algorithm. The measured fiducial differential cross sections are compared to predictions from Monte Carlo generators. The total cross section measured in the fiducial volume defined by the charged lepton and neutrino kinematic properties is 36.0 ± 9.7 fb. Additionally the jet-veto efficiency in the fiducial volume is extracted from the differential cross sections. An analysis is presented of Higgs boson production and decay into bottom quarks in association with a vector boson at the ATLAS detector for the future high-luminosity LHC with proton-proton collisions at √s = 14 TeV. The vector bosons are reconstructed from Z→l+l− or W→lv final states, where l is an electron or muon. The analysis uses generator-level Monte Carlo samples to which efficiency and resolution smearing functions are applied. These reproduce the expected resolution of the upgraded ATLAS detector for the foreseen amount of pile-up due to multiple overlapping proton-proton collisions. The analysis of the ZH(→ l+l−b¯b) channel is presented and results are combined with the WH(→lvb¯b) channel from a corresponding study. For an integrated luminosity of 300 fb−1 using an average pile-up of 60, the expected significance is 3.9 σ with an expected error on the signal strength of 25%. Likewise, for 3000 fb−1 using an average pileup of 140 the expected significance is 8.8 σ , and the error on the signal strength is expected to be about 15%.

La production des états charmonia (par exemple le J/ψ et le ψ(2S)) est l’une des sondes étudiées pour comprendre les propriétés du Plasma de Quarks et de Gluons (PQG) formé dans les collisions d’ions lourds à très haute énergie. En effet, la présence d’un milieu déconfiné est susceptible de modifier le taux de production des charmonia par effet d’écrantage de couleur de la paire de quarks charme-anti-charme. Une telle suppression fut déjà observée dans les collisions d’ions lourds aux énergies du SPS et du RHIC. Dans les collisions Pb-Pb à √sNN = 2.76 TeV au LHC, une suppression relative du taux de production du J/ψ par rapport à celui mesuré dans les collisions pp normalisé aux nombres de collisions binaires proton-proton (facteur de modification nucléaire RAA) fut aussi mesurée. Cette suppression est cependant moins importante que ce qui fut observé à plus petites énergies dans le centre de masse. Ceci peut s’expliquer par la présence d’un nouveau mécanisme de production, la recombinaison de quarks charme et anticharme déconfinés au moment de l’expansion hydrodynamique du PQG ou durant la phase d’hadronisation. Dans cette thèse, nous présentons les résultats de la production de J/ψ dans les collisions pp et Pb-Pb, mesurée par le détecteur ALICE à √sNN = 5.02 TeV à rapidité avant dans le canal de décroissance dimuonique. La section efficace de production mesurée dans les collisions pp est comparée à différents modèles théoriques et est utilisée pour calculer le RAA en collisions Pb-Pb, lui-même comparé à différentes prédictions théoriques ainsi qu’aux précédentes mesures. / The production of charmonium states (for instance J/ψ and ψ(2S)) is one of the probes studied to investigate the properties of the Quark-Gluon Plasma (QGP) formed in high-energy heavy-ion collisions. Indeed, the presence of a deconfined medium should modify the charmonium production yield, due to the color screening of the charm quark anti-quark potential. Such a suppression was already observed in heavy-ion collisions at SPS and RHIC energies. In Pb-Pb collisions at √sNN = 2.76 TeV at the LHC, a clear suppression of the J/ψ yield with respect to the one measured in binary-scaled pp collisions (nuclear modification factor RAA) was observed, but much smaller than that at lower collision energies. This observation can be explained by the presence of a new production mechanism, the (re)combination of deconfined charm and anti-charm quarks during the hydrodynamical expansion of the QGP or at the hadronization stage. In this thesis, we report on the results of the J/ψ production in pp and Pb-Pb collisions measured with the ALICE detector √sNN = 5.02 TeV at forward rapidity in the dimuon channel. The cross-section in pp collisions is compared to various model calculations, and is used to compute the RAA in Pb-Pb collisions, which is also compared to theoretical predictions as well as to previous measurements.