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Search for Dark Matter Decaying to Two Displaced Muons Produced in Proton-proton Collisions at 13 TeV with the CMS Detector, and for Dark Photons Produced in Electron-positron Fixed-target Collisions at 500 MeV with the PADME Detector

2020
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Release : 2020
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Book Synopsis Search for Dark Matter Decaying to Two Displaced Muons Produced in Proton-proton Collisions at 13 TeV with the CMS Detector, and for Dark Photons Produced in Electron-positron Fixed-target Collisions at 500 MeV with the PADME Detector by : Andre Sterenberg Frankenthal

Download or read book Search for Dark Matter Decaying to Two Displaced Muons Produced in Proton-proton Collisions at 13 TeV with the CMS Detector, and for Dark Photons Produced in Electron-positron Fixed-target Collisions at 500 MeV with the PADME Detector written by Andre Sterenberg Frankenthal. This book was released on 2020. Available in PDF, EPUB and Kindle. Book excerpt: Two novel searches for dark matter using particle accelerators are presented. The first is a search for inelastically-coupled dark matter with the CMS detector at CERN, relying on 137 inverse femtobarns of proton-proton collision data collected at 13 TeV center-of-mass energy between 2016 and 2018. The search strategy exploits the striking signature expected of inelastic dark matter: a pair of displaced, soft, and narrow muons collimated with missing transverse momentum and recoiled off an initial-state radiation jet. This is the first search for inelastic dark matter at a hadron collider. The second experiment is PADME, a small-scale detector to search for dark photons located in Frascati, Italy. PADME seeks to detect the production of dark photons in positron-electron collisions with a stationary diamond target and a 500 MeV positron beam. The missing-mass technique employed in the experiment relies on constraining all four-momenta in the system except for the dark photon and looking for a bump in the resulting invariant mass distribution corresponding to the dark photon's mass. The projected sensitivity for both experiments is compared in the context of highlighting the need for a comprehensive experimental search program for dark matter. Both analyses expect first public results by the end of 2020.

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

2019
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Release : 2019
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Book Synopsis Searching for Dark Matter with the CMS Detector in Proton-proton Collisions Containing a Single High-pT Photon and Large E^miss/t by : Brandon Leigh Allen

Download or read book Searching for Dark Matter with the CMS Detector in Proton-proton Collisions Containing a Single High-pT Photon and Large E^miss/t written by Brandon Leigh Allen. This book was released on 2019. Available in PDF, EPUB and Kindle. Book excerpt: 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 Decays of Stopped Exotic Long-lived Particles Produced in P-P Collisions at 13 TeV at CMS

2018 Large Hadron Collider (France and Switzerland)
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Release : 2018
Genre : Large Hadron Collider (France and Switzerland)
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Book Synopsis Search for the Decays of Stopped Exotic Long-lived Particles Produced in P-P Collisions at 13 TeV at CMS by : Weifeng Ji

Download or read book Search for the Decays of Stopped Exotic Long-lived Particles Produced in P-P Collisions at 13 TeV at CMS written by Weifeng Ji. This book was released on 2018. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation, I present the searches looking for decays of stopped massive long-lived exotic particles, which are pair produced in the proton-proton collisions at 13 TeV and come to rest afterwards in the CMS detector at the CERN LHC. The decays are most likely to be observed when there are no collisions. Two specific decay scenarios are studied: a long-lived particle (LLP) decaying hadronically or semi- leptonically in the calorimeter, and a LLP decaying semi-leptonically or leptonically to a pair of muons in the muon detector. The calorimeter-based search is performed using 2.7 fb-1 of 13 TeV collision run data collected in 2015 and 35.9 fb-1 of 13 TeV collision run data collected in 2016, corresponding to a total trigger livetime of 721 hours. The muon search is performed using 2.8 fb-1 of 13 TeV collision run data collected in 2015 and 36.2 fb-1 of 13 TeV collision run data collected in 2016, corresponding to a total trigger livetime of 744 hours. Search results are interpreted in a couple of simplified models. The limits on the production cross sections and masses of LLPs are calculated as a function of particle lifetimes, which vary from 100 ns to 10 days, assuming the corresponding decaying branching fractions to be 100%. The results are the most stringent ones on the stopped LLPs so far.

A Search for Long-lived Particles that Stop in the CMS Detector and Decay to Muons

2016
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Release : 2016
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Book Synopsis A Search for Long-lived Particles that Stop in the CMS Detector and Decay to Muons by :

Download or read book A Search for Long-lived Particles that Stop in the CMS Detector and Decay to Muons written by . This book was released on 2016. Available in PDF, EPUB and Kindle. Book excerpt: A search for long-lived particles that are produced in proton-proton collisions at the CERN LHC, come to rest in the CMS detector, and decay to muons is presented. The decays of the stopped particles could be observed during the intervals between LHC beam crossings, at times that are well separated from any proton-proton collisions. The analysis uses 19.7 1/fb of 8 TeV data collected by CMS in 2012, during a search interval of 293 hours of trigger livetime. Massive, long-lived particles do not exist in the Standard Model, and so any sign of them would be an indication of new physics. The results are interpreted with a model that predicts a long-lived particle that has a charge of twice the electron charge and that behaves like a lepton. Cross section limits are set for each long-lived particle mass as a function of lifetime, for lifetimes between 100 ns and 10 days. These are the first limits for long-lived stopped particles that decay to muons.

A Collider Search for Dark Matter Produced in Association with a Higgs Boson with the CMS Detector at the 13 TeV LHC

2017
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Release : 2017
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Book Synopsis A Collider Search for Dark Matter Produced in Association with a Higgs Boson with the CMS Detector at the 13 TeV LHC by : Dustin Ray Burns

Download or read book A Collider Search for Dark Matter Produced in Association with a Higgs Boson with the CMS Detector at the 13 TeV LHC written by Dustin Ray Burns. This book was released on 2017. Available in PDF, EPUB and Kindle. Book excerpt: The study presented in this dissertation is a search for dark matter produced in 13 TeV proton-proton collisions at the Large Hadron Collider (LHC) using 35.9 fb−1 of data collected in 2016 with the Compact Muon Solenoid (CMS) detector. Dark matter escapes the detector without interacting, resulting in a large imbalance of transverse momentum, which can be observed when a Higgs boson is tagged in the opposite direction. A variety of models which motivate a dark matter and Higgs interaction are discussed. The experimental signature of these models is called mono-Higgs. In this search, the Higgs is produced primarily from gluon fusion and decays to four leptons via two Z bosons (H → ZZ → 4l). In addition to observing the Higgs in the four-lepton final state, an extensive study of missing transverse energy (MET) is required to search for the mono-Higgs signature. A background model is developed for the Standard Model processes that result in the same final state as the signal, then a counting experiment is performed in an optimized signal region. There is no evidence for an excess of events in the signal region above the backgrounds, so cross section limits are set for two kinematically distinct signal models.

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