Search for Dark Matter and Unparticles in Events with a Z Boson and Missing Transverse Momentum in Proton-proton Collisions at Sqrt(s)
Search for Dark Matter and Unparticles in Events with a Z Boson and Missing Transverse Momentum in Proton-proton Collisions at Sqrt(s)

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Published: 2017

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A search for dark matter and unparticle production at the LHC has been performed using events containing two charged leptons (electrons or muons), consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector in 2015, corresponding to an integrated luminosity of 2.3 inverse femtobarns of proton-proton collisions at the LHC, at a center-of-mass energy of 13 TeV. No excess over the standard model expectation is observed. Compared to previous searches in this topology, which exclusively relied on effective field theories, the results are interpreted in terms of a simplified model of dark matter production for both vector and axial vector couplings between a mediator and dark matter particles. The first study of this class of models using CMS data at sqrt(s)=13 TeV is presented. Additionally, effective field theories of dark matter and unparticle production are used to interpret the data.

Search for Dark Matter Particles in Proton-proton Collisions at $\sqrt{s}$
Search for Dark Matter Particles in Proton-proton Collisions at $\sqrt{s}$

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Published: 2016

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A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 inverse femtobarns, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Lambda below 1 TeV. The use of razor variables yields results that complement those previously published.

Search for Dark Matter and Unparticles Produced in Association with a Z Boson in Proton-proton Collisions at Sqrt(s)
Search for Dark Matter and Unparticles Produced in Association with a Z Boson in Proton-proton Collisions at Sqrt(s)

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Published: 2016

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A search for evidence of particle dark matter (DM) and unparticle production at the LHC has been performed using events containing two charged leptons, consistent with the decay of a Z boson, and large missing transverse momentum. This study is based on data collected with the CMS detector corresponding to an integrated luminosity of 19.7 inverse femtobarns of pp collisions at the LHC at a center-of-mass energy of 8 TeV. No significant excess of events is observed above the number expected from the standard model contributions. The results are interpreted in terms of 90% confidence level limits on the DM-nucleon scattering cross section, as a function of the DM particle mass, for both spin-dependent and spin-independent scenarios. Limits are set on the effective cutoff scale Lambda, and on the annihilation rate for DM particles, assuming that their branching fraction to quarks is 100%. Additionally, the most stringent 95% confidence level limits to date on the unparticle model parameters are obtained.

Search for Dark Matter with ATLAS
Search for Dark Matter with ATLAS

Author: Ruth Pöttgen

Publisher: Springer

Published: 2016-06-29

Total Pages: 325

ISBN-13: 3319410458

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This thesis describes in detail a search for weakly interacting massive particles as possible dark matter candidates, making use of so-called mono-jet events. It includes a detailed description of the run-1 system, important operational challenges, and the upgrade for run-2. The nature of dark matter, which accounts for roughly 25% of the energy-matter content of the universe, is one of the biggest open questions in fundamental science. The analysis is based on the full set of proton-proton collisions collected by the ATLAS experiment at the Large Hadron Collider at √s = 8 TeV. Special attention is given to the experimental challenges and analysis techniques, as well as the overall scientific context beyond particle physics. The results complement those of non-collider experiments and yield some of the strongest exclusion bounds on parameters of dark matter models by the end of the Large Hadron Collider run-1. Details of the upgrade of the ATLAS Central Trigger for run-2 are also included.

Search for Dark Matter in Final States Containing Semi-visible Jets from Proton-proton Collisions at [square Root]s
Search for Dark Matter in Final States Containing Semi-visible Jets from Proton-proton Collisions at [square Root]s

Author: Colin Terrence Fallon

Publisher:

Published: 2022

Total Pages: 0

ISBN-13:

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"This dissertation presents a novel search for new physics using the full Run 2 dataset of 137.6 fb-1 collected by the Compact Muon Solenoid during proton-proton runs of the Large Hadron Collider. The new physics in question is dark matter production in a unique signature called semi-visible jets. Semi-visible jets are produced when a new massive mediator particle emerges from the proton-proton interaction. This mediator then decays to unstable dark matter particles which hadronize and produce a mixture of standard model particles and stable dark matter particles. The stable dark particles are only detectable as missing transverse momentum, and the standard particles are detectable as jets. This produces a signature where two jets are produced, one of which is aligned with the total missing transverse momentum. The search is presented in two phases: a classical cut-based search which uses a series of cuts based on event kinematics to select events which look like the signal signature, and a machine learning based search which uses a technique called boosted decision trees to identify semi-visible jets in a more powerful but model-dependent way. No evidence for Physics Beyond the Standard Model is observed in either search. The classical search excludes the possibility that the mediator could have a mass between 1.5 TeV and 3.98 TeV, while the model-dependent search excludes mediators with masses between 1.5 TeV and 5.08 TeV. Additionally, ranges of other signal parameters are excluded"--Page viii.

Searching for Dark Matter with the CMS Detector in Proton-proton Collisions Containing a Single High-pT Photon and Large E^miss/t
Searching for Dark Matter with the CMS Detector in Proton-proton Collisions Containing a Single High-pT Photon and Large E^miss/t

Author: Brandon Leigh Allen

Publisher:

Published: 2019

Total Pages: 165

ISBN-13:

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In this thesis, we present a search for dark matter in final states containing a high- PT photon and large missing transverse momentum in proton-proton collisions at [square root of s] = 13 TeV using data collected by the Compact Muon Solenoid.(CMS) experiment at the CERN Large Hadron Collider (LHC) corresponding to an integrated luminosity of 35.9 inverse femtobarns. The main advances in experimental technique compared to previous searches in this final state are the use of data-driven control regions to constrain the main irreducible backgrounds from Z( --> vv̄ + [gamma] and W( --> [iota]v)+ [gamma] production and an in-depth study of the unique anomolous detector signatures that result in backgrounds due to non-collision processes. With these improvements, we have the most robust analysis of this kind presented to date. No deviations from the predictions of the standard model are observed. The results are interpreted in the context of dark matter production and limits on new physics parameters are calculated at 95% confidence level. We focus on two simplified dark matter production models where new vector and axial mediators couple a new dark dirac fermion to the Standard Model quarks. These models are chosen as they cover a large class of WIMP-like dark matter particles that show up in many types of more complete new physics models. For the two models considered, the observed (expected) lower limits on the masses of the new mediators are 950 (1150) GeV for a dark matter particle of a mass of 1 GeV.

Search for the Production of Dark Matter in Association with Top-Quark Pairs in the Single-Lepton Final State in Proton-Proton Collisions at $\sqrt{s}$
Search for the Production of Dark Matter in Association with Top-Quark Pairs in the Single-Lepton Final State in Proton-Proton Collisions at $\sqrt{s}$

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Publisher:

Published: 2015

Total Pages: 35

ISBN-13:

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A search is presented for particle dark matter produced in association with a pair of top quarks in pp collisions at a centre-of-mass energy of s√=8 TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 19.7 fb-1. This search requires the presence of one lepton, multiple jets, and large missing transverse energy. No excess of events is found above the SM expectation, and upper limits are derived on the production cross section. Interpreting the findings in the context of a scalar contact interaction between fermionic dark matter particles and top quarks, lower limits on the interaction scale are set. These limits are also interpreted in terms of the dark matter-nucleon scattering cross sections for the spin-independent scalar operator and they complement direct searches for dark matter particles in the low mass region.

Search for W' {u2192} Tb in Proton-proton Collisions at $ \sqrt{s}
Search for W' {u2192} Tb in Proton-proton Collisions at $ \sqrt{s}

Author:

Publisher:

Published: 2016

Total Pages:

ISBN-13:

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A search for dark matter particles directly produced in proton-proton collisions recorded by the CMS experiment at the LHC is presented. The data correspond to an integrated luminosity of 18.8 inverse femtobarns, at a center-of-mass energy of 8 TeV. The event selection requires at least two jets and no isolated leptons. The razor variables are used to quantify the transverse momentum balance in the jet momenta. The study is performed separately for events with and without jets originating from b quarks. The observed yields are consistent with the expected backgrounds and, depending on the nature of the production mechanism, dark matter production at the LHC is excluded at 90% confidence level for a mediator mass scale Lambda below 1 TeV. The use of razor variables yields results that complement those previously published.