• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 13
  • 1
  • Tagged with
  • 19
  • 19
  • 19
  • 9
  • 7
  • 6
  • 6
  • 6
  • 6
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Charge Symmetry Violation Quark Distributions via Precise Measurement of π+/π− Ratios in Semi-inclusive Deep Inelastic Scattering

Jia, Shuo January 2022 (has links)
Charge symmetry in the nucleon parton distributions assumes the distribution of quarks in the proton are related to those in the neutron. Indirect experimental evidence constrains Charge Symmetry Violation (CSV) to be less than 9%. In Quantum Chromo-Dynamics (QCD), charge symmetry is broken by the mass difference between the up and down quarks. CSV in the valence region can be extracted from precision measurements of the cross section ratio of charged pion production in semi-inclusive deep inelastic scattering (SIDIS) from deuterium. Such measurements were proposed and carried in experiment E12-09-002 at Jefferson Lab. The experiment was conducted in Hall C from fall 2018 to spring 2019 using the upgraded 10.6 GeV incident electron beam. In this SIDIS experiment, charged pions are detected in coincidence with scattered electrons covering the four-momentum transfer of the virtual photon Q^2 from 4 to 5.5 GeV^2, the Bjorken variable x for 0.35-0.65, and the fraction of energy transfer carried by the outgoing pion z from 0.4-0.7. / Physics
2

A search for supersymmetry with the ATLAS detector using kinematic shape constraints in events containing one electron or muon

Short, Daniel R. January 2012 (has links)
The ATLAS experiment is used to observe the √s=7 TeV proton-proton collisions produced by the LHC at CERN. This gives an unprecedented opportunity to search for physics beyond the Standard Model at hitherto unexplored kinematic regimes. Supersymmetry (SUSY) provides interesting solutions to a variety of theoretical problems that may be encountered in the Standard Model at high energy scales, while providing signatures that may be observed at the LHC. However, in order to produce a search that is sensitive to SUSY it is vital to understand how the physics that has been discovered to date may produce signatures that mimic those expected from SUSY. Statistical models are constructed using both Monte Carlo and data-driven predictions of various background processes. The expectations are compared to the observed data for selections containing one electron or muon, each in association with jets and missing transverse momentum. Kinematic variable shapes, in the form of histograms, are used to enhance the sensitivity of the search. Squark and gluino masses in a MSUGRA SUSY model are excluded up to 1200 GeV, while gluino masses up to 900 GeV are excluded in a simplified SUSY model. Model-independent limits are also set, excluding theoretical models with efficiency times cross section above 1 fb.
3

Phase and Intensity Monitoring of the Particle Beams at the ATLAS Experiment

Ohm, Christian January 2007 (has links)
<p>At the ATLAS experiment at CERN’s Large Hadron Collider, bunches of protons will cross paths at a rate of 40 MHz, resulting in 14 TeV head-on collisions. During these interactions, calorimeters, spectrometers and tracking detectors will look for evidence that can confirm or disprove theories about the smallest constituents of matter and the forces that hold them together. In order for these sub-detectors to sample the signals from exotic particles correctly, they rely on a constant phase between a clock signal and the bunch crossings in the experiment.</p><p>On each side of the detector, 175 m away from the interaction point, electrostatic button pick-up detectors are installed along the accelerator ring to monitor the beam. A model describing how these detectors function as beam information transducers is constructed and analyzed in order to understand the signal.</p><p>The focus of this thesis is the design, implementation and testing of a system that uses this signal to monitor the phase between the clock signal and the arrival time of the bunches in the center of the detector. In addition, the system extracts information about the proton beam structure as well as the individual bunches. Given the interaction rate and the complexity of the processes the experiment wants to study, vast amounts of data will be generated by ATLAS. To filter out well-understood phenomena, a trigger system selects only the most interesting events to be saved for further offline analysis. A proposal for how the signals from the button pick-ups can be used as input to the trigger system is therefore also presented.</p>
4

Phase and Intensity Monitoring of the Particle Beams at the ATLAS Experiment

Ohm, Christian January 2007 (has links)
At the ATLAS experiment at CERN’s Large Hadron Collider, bunches of protons will cross paths at a rate of 40 MHz, resulting in 14 TeV head-on collisions. During these interactions, calorimeters, spectrometers and tracking detectors will look for evidence that can confirm or disprove theories about the smallest constituents of matter and the forces that hold them together. In order for these sub-detectors to sample the signals from exotic particles correctly, they rely on a constant phase between a clock signal and the bunch crossings in the experiment. On each side of the detector, 175 m away from the interaction point, electrostatic button pick-up detectors are installed along the accelerator ring to monitor the beam. A model describing how these detectors function as beam information transducers is constructed and analyzed in order to understand the signal. The focus of this thesis is the design, implementation and testing of a system that uses this signal to monitor the phase between the clock signal and the arrival time of the bunches in the center of the detector. In addition, the system extracts information about the proton beam structure as well as the individual bunches. Given the interaction rate and the complexity of the processes the experiment wants to study, vast amounts of data will be generated by ATLAS. To filter out well-understood phenomena, a trigger system selects only the most interesting events to be saved for further offline analysis. A proposal for how the signals from the button pick-ups can be used as input to the trigger system is therefore also presented.
5

Supersymmetry searches at the LHC and their interpretations

Fawcett, William James January 2017 (has links)
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 &percnt; confidence level, extending previous limits.
6

Development and Performance of Detectors for the Cryogenic Dark Matter Search Experiment with an Increased Sensitivity Based on a Maximum Likelihood Analysis of Beta Contamination

Driscoll, Donald D., Jr. 14 January 2004 (has links)
No description available.
7

Measurement of CP violation in B→DK* decays with the LHCb experiment

Smith, Edmund Robert Henry January 2014 (has links)
This thesis reports an analysis of 3.0fb<sup>-1</sup> of pp collision data collected by the LHCb experiment in 2011 and 2012. Decays of neutral B mesons to neutral D mesons and excited neutral kaons are reconstructed, because of their sensitivity to the CP-violating phase of the CKM matrix, γ.
8

Standard model and exotic physics with the top quark at ATLAS

Bernard, Clare Sullivan 12 March 2016 (has links)
The top quark is the most massive fundamental particle in the Standard Model of particle physics. Only experimentally observed in 1995, it can be used as a precise test of Standard Model predictions, and it could lend insight to the problem of what lies beyond the Standard Model. This thesis presents a measurement of top-quark pair production using data collected at a center-of-mass energy √s=7 TeV in 2011, and a search for production of vector-like quarks using data collected at √s=8 TeV in 2012. Both datasets were recorded by the ATLAS detector, a multipurpose proton-proton collider located at the CERN LHC outside of Geneva Switzerland. The top-quark pair production cross-section is measured as a function of four different variables and the results are presented as normalized, differential spectra. The variables considered are the transverse momentum of the top quark, and the mass, rapidity, and transverse momentum of the top-quark pair system. Events are selected in the lepton+jets channel, and the measured spectra are corrected for detector resolution and efficiency. The final results are compared with predictions from various Monte Carlo generators, theoretical calculations and proton parton distribution functions and found to be in reasonable agreement. Data is found to be softer than all predictions, particularly for high values of top-quark transverse momentum and the top-quark pair invariant mass. The search for vector-like quarks focuses on new heavy quarks that decay with a large branching ratio to a Z boson and a third generation Standard Model quark. Events are selected with at least two leptons (electrons or muons), and two of the leptons are required to reconstruct a Z boson with high transverse momentum. No significant excess of events is observed above the Standard Model prediction. Upper limits on the masses of vector-like T and B quarks are derived for various branching ratio hypotheses.
9

The cosmic muon flux in the ATLAS Detector at the Large Hadron Collider

Hill, Ewan Chin 01 September 2011 (has links)
Many ATLAS analyses study events with muons in them including those searching for the Higgs boson and new physics. Cosmics muons, however, can also occasionally enter the detector and mimic the trajectory of a muon from one of the collisions produced by CERN’s Large Hadron Collider. By understanding the different ways ATLAS triggers on, collects, reconstructs, and analyses data from cosmic rays and collisions, the flux of cosmic muons with transverse momenta above 20 GeV in the central region of the detector was measured to be 1.34 ± 0.06 (stat.) s^−1 m^−2 . At the same time the cosmic muon charge ratio has been measured to be 1.3 ± 0.1 (stat.). This measurement of the cosmic muon flux in ATLAS is the first step in quantifying the sizes of the cosmic muon backgrounds to various physics analyses that look for events with muons. / Graduate
10

Search for new spin-0 particles near π⁰ mass produced in association with τ pairs at BABAR

Beaulieu, Alexandre 29 August 2013 (has links)
This research project searches for new physics in the τ sector that would resolve the tension between BABAR measurement for the pion-photon transition form factor Fπ0(Q^2)and the standard model asymptotic prediction. This behaviour could be explained by a new light pseudo-scalar state that mixes with the π 0 and enhances its coupling to the c and b quarks or the τ lepton, or by a new spin-0 particle with mass very close to the π 0 . We examine one channel to test for existence of such objects: their creation in association with τ pairs in e+ e− collisions. The analysis uses a typical cut-based approach as the large predicted cross-sections and the kinematics of the final states allow for a direct selection of signal events and background suppression. Current simulation studies predict a 90% CL limit on the production cross-section on the order of 100 fb in case of no signal, while the theory predicts production cross-sections on the order of 1 pb to 100 pb depending on the model. / Graduate / 0798 / beaa@uvic.ca

Page generated in 0.1132 seconds