1,727 research outputs found
Search for the Higgs boson decaying to bottom quarks and W boson tagging techniques at the ATLAS experiment at the LHC
No full textThe Standard Model of particle physics is currently the most complete theory of
subatomic particles. The discovery of the Higgs boson with a mass of 125 GeV
in 2012 further validated the Standard Model, providing evidence for the theory
that vector bosons obtain non-zero masses through the Higgs mechanism. Studies
are ongoing to determine the exact nature and properties of the Higgs boson. A
Higgs boson of this mass is predicted to decay to a pair of b-b quarks with a
branching ratio of 58%, however this decay mode has not yet been observed.
This thesis presents a search for the associated production of a Higgs boson with
a leptonically decaying W boson, WH → ℓvb-b, using 20.3 fb-1 of Run 1 data
collected by ATLAS at the LHC from pp collisions at a centre-of-mass energy
of ps = 8 TeV. The observed (expected) significance of a Higgs boson with a
mass of 125 GeV for the WH → ℓvb-b process is found to be 2:7σ (1:3σ). The
measured cross section in units of the expected Standard Model cross section has
a best-fit value of μ = μ/μSM = 2:2+0:67-0:64(stat:)+0:7-0:59(syst:) = 2:2+0:97-0:87. The results
are combined with the search for ZH → v-vb-b and ZH → ℓ+ℓ-b-b to provide a
best-fit value of μ = μ/μSM = 1:1+0:61-0:56. The start of Run 2 of the LHC in 2015 saw the collision energy being raised
to √s = 13 TeV, increasing the probability of particles being produced with
a large momentum boost. At these high energies there is also a possibility to
discover new particles and interactions. An extension of the Standard Model, the
Heavy Vector Triplet (HVT) model, describes new heavy vector bosons W¹ and
Z¹, which can decay to pairs of heavy bosons (W, Z or Higgs bosons). If the
W0 and Z0 bosons are sufficiently heavy, the hadronic decays of the diboson final
states produce boosted jets. In this thesis, methods for identifying hadronically
decaying boosted bosons are developed, based on techniques that examine the
internal substructure of the jet. Multiple substructure variables are combined into a single discriminant using two
machine learning techniques: boosted decision trees and deep neural networks.
Simulated events of W¹→WZ → q-qq-q are used to develop these boosted W boson
taggers. An improvement in the background rejection power, whilst keeping 50% of the signal, over previous boosted W boson taggers of up to 13%-when using
deep neural networks-and 36%-when using boosted decision trees-is obtained.
The performance of the new boosted W boson taggers are evaluated in a search
for a narrow WW resonances from the decay of a Z¹ with boson-tagged jets in
3.2 fb-1 of pp collisions at √s = 13 TeV collected with the ATLAS detector
Collecting Rooms: Objects, Identities and Domestic Spaces
No full textThis practice-based enquiry into United Kingdom based collecting rooms reveals five participants’ motivations, frustrations and satisfactions manifested in the creation of their spaces. Through the examination of theorists and commentators in the distinct but related fields of cultural theory, sociology and art, the thesis proposes that a collector’s past can be witnessed through memories generated by and within the space. The thesis also advances the idea that part of the experience of the space takes place in the present but simultaneously imagines the future. I have constructed spatial portraits using semi-structured interviews, photography and video, which explore the environment of each collector thus gaining insights into individual circumstances and personal situations.
Narrative within this enquiry takes three intersecting forms: firstly the account of the construction of each collecting room, which divests objects of their historical origins, replacing these with personal associations or meanings devised by each collector. Secondly, each participants’ re-telling of their narratives and thirdly through the re-presentation of the collectors’ narratives to an audience. The latter brings my agency as an artist into focus. Uniting all three narrative forms, the creative practice intends to produce a metanarrative of each collecting room that further investigates the temporality of the space through the combined use of still photography, video and sound.
Constructed from a symbiotic relationship between theory and practice, the research uses a methodology that combines Sensory Ethnography with Interpretive Phenomenological Analysis. This methodology explores the idiosyncrasies of each collector, engendering an extensive investigation of the individual collecting spaces. This detailed approach formed and eventually determined the number of participants, resulting in the production of a developmental case study and four original re-presentations that respond to ideas and debates on collecting, material culture and domestic space. These artworks that have been informed by combining existing research methods and constitute my contribution to new knowledge, disclosing ideas and observations which combine narrative and experience not necessarily discernable from theoretical arguments alone
Jets & Substructure: experiment
No full textRecent developments and status of tools to determine jet substructure at the LHC are presented
Evidence for Electroweak Production of W(+/-)W(+/-)jj in pp Collisions at root s=8 TeV with the ATLAS Detector
No full textFurther distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.This Letter presents the first study of W±W±jj, same-electric-charge diboson production in association with two jets, using 20.3 fb-1 of proton-proton collision data at √s=8 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons (e±e±, e±μ±, and μ±μ±) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for W±W±jj production and electroweak-only W±W±jj production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings
Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at √<span style="text-decoration:overline">s</span>=7 TeV with the ATLAS experiment
No full textContains fulltext :
93952.pdf (Publisher’s version ) (Open Access
Measurement of the production cross section for W-bosons in association with jets in pp collisions at s=7 TeV with the ATLAS detector
No full textThis Letter reports on a first measurement of the inclusive W + jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W-boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma (W + >= n)/sigma(W + >= n - 1) for inclusive jet multiplicities n = 1-4. The results, based on an integrated luminosity of 1.3 pb(-1), have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n <= 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicitie
Measurement of total and differential production cross sections in proton-proton collisions at 8 TeV with the ATLAS detector and limits on anomalous triple-gauge-boson couplings
No full textSee paper for full list of authors - 60 pages plus author list (77 pages total), 16 figures, 36 tables, submitted to JHEP, all figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2013-07/International audienceThe production of boson pairs in proton-proton collisions at 8 TeV is studied using data corresponding to 20.3 fb of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the branching fractions to leptons in order to obtain the total production cross section, which is found to be 71.1(stat)(syst) pb. This agrees with the next-to-next-to-leading-order Standard Model prediction of 63.2(scale)(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings
Measurement of and -boson production cross sections in collisions at TeV with the ATLAS detector
No full textSee paper for full list of authors - 17 pages plus author list + cover pages (34 pages total), 5 figures, 3 tables, submitted to Phys. Lett. B, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2015-03/International audienceMeasurements of the and production cross sections (where ) in proton-proton collisions at TeV are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb. The total inclusive -boson production cross sections times the single-lepton-flavour branching ratios are nb and nb for and , respectively. The total inclusive -boson production cross section times leptonic branching ratio, within the invariant mass window GeV, is nb. The , , and -boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The cross-section ratios benefit from significant cancellation of experimental uncertainties, resulting in and . Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements
- …
