William Hamish Bell

University of Strathclyde · Department of Computer and Information Sciences

The reconstruction of the signal from hadrons and jets emerging from the proton–proton collisions at the Large Hadron Collider (LHC) and entering the ATLAS calorimeters is based on a three-dimensional topological clustering of individual calorimeter cell signals. The cluster formation follows cell signal-significance patterns generated by electroma...

A test of CP invariance in Higgs boson production via vector-boson fusion using the method of the Optimal Observable is presented. The analysis exploits the decay mode of the Higgs boson into a pair of \(\tau \) leptons and is based on 20.3 \(\mathrm{fb}^{-1}\) of proton–proton collision data at \(\sqrt{s}\) = 8 \(\,\mathrm{TeV}\) collected by the...

The large rate of multiple simultaneous proton– proton interactions, or pile-up, generated by the Large Hadron Collider in Run 1 required the development of many new techniques to mitigate the adverse effects of these conditions. This paper describes the methods employed in the ATLAS experiment to correct for the impact of pile-up on jet energy and...

The ATLAS measurement of the inclusive top quark pair (\(t\bar{t}\)) cross-section \(\sigma _{t\bar{t}}\) in proton–proton collisions at \(\sqrt{s}=8\) \(\,\mathrm{TeV}\) has been updated using the final 2012 luminosity calibration. The updated cross-section result is: $$\begin{aligned} \sigma _{t\bar{t}}= 242.9\pm 1.7\pm 5.5\pm 5.1\pm 4.2\,\mathrm...

Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, \(t\bar{t}\) system and event-level kinematic observables in proton–proton collisions at a centre-of-mass energy of \(\sqrt{s}=8\,\mathrm{TeV}\). The observables have been chosen to emphasize the \(t\bar{t}\) production...

The production of W boson pairs in proton-proton collisions at \( \sqrt{s}=8 \) TeV is studied using data corresponding to 20.3 fb−1 of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The W bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with rec...

A measurement of the B0 s decay parameters in the B0 s → J/ψφ channel using an integrated luminosity of 14.3 fb−1 collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase φs, the decay width Γs and the width difference between the mass eigenstates ∆Γs. The values measur...

A search for singly produced vector-like Q quarks, where Q can be either a T quark with charge \(+2/3\) or a Y quark with charge \(-4/3\), is performed in proton–proton collisions recorded with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fb\(^{-1}\) and was produced with a centre-of-mass energy of \(\s...

This paper describes a measurement of fiducial and differential cross sections of gluon-fusion Higgs boson production in the H → W W∗→ eνμν channel, using 20.3 fb−1 of proton-proton collision data. The data were produced at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV at the CERN Large Hadron Collider and recorded by the ATLAS detector in 2012....

A measurement of the Bs0 decay parameters in the Bs0 → J/ψϕ channel using an integrated luminosity of 14.3 fb−1 collected by the ATLAS detector from 8 TeV pp collisions at the LHC is presented. The measured parameters include the CP -violating phase ϕs, the decay width Γs and the width difference between the mass eigenstates ΔΓs. The values measure...

A measurement of the cross section for the inclusive production of isolated prompt photons in proton-proton collisions at a centre-of-mass energy of \( \sqrt{s}=8 \) TeV is presented. The measurement covers the pseudorapidity ranges |η γ | < 1.37 and 1.56 ≤ |η γ | < 2.37 in the transverse energy range 25 < E T γ < 1500 GeV. The results are based on...

A new search signature for excited leptons is explored. Excited muons are sought in the channel [${pp}\to \mu {\mu }^{* }\to \mu \mu \ {\rm{jet}}\;{\rm{jet}}$], assuming both the production and decay occur via a contact interaction. The analysis is based on 20.3 fb−1 of pp collision data at a centre-of-mass energy of [$\sqrt{s}\;=\;8\;{\rm{TeV}}$]...

Event-shape observables measured using charged particles in inclusive Z-boson events are presented, using the electron and muon decay modes of the Z bosons. The measurements are based on an integrated luminosity of \(1.1~\mathrm{fb}^{-1}\) of proton–proton collisions recorded by the ATLAS detector at the LHC at a centre-of-mass energy \(\sqrt{s}=7\...

This paper presents measurements of distributions of charged particles which are produced in proton–proton collisions at a centre-of-mass energy of \(\sqrt{s} = 8 \mathrm {\, TeV}\) and recorded by the ATLAS detector at the LHC. A special dataset recorded in 2012 with a small number of interactions per beam crossing (below 0.004) and corresponding...

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with pT > 500 MeV inside high-momentum j...

The production of D*±, D± and Ds± charmed mesons has been measured with the ATLAS detector in pp collisions at s=7 TeV at the LHC, using data corresponding to an integrated luminosity of 280 nb-1. The charmed mesons have been reconstructed in the range of transverse momentum 3.5<pT(D)<100 GeV and pseudorapidity |η(D)|<2.1. The differential cross se...

A search for the pair production of top squarks, each with R-parity-violating decays into two Standard Model quarks, is performed using 17.4 fb−1 of √s = 8 TeV proton-proton collision data recorded by the ATLAS experiment at the LHC. Each top squark is assumed to decay to a b- and an s-quark, leading to four quarks in the final state. Background di...

The number of charged particles inside jets is a widely used discriminant for identifying the quark or gluon nature of the initiating parton and is sensitive to both the perturbative and non-perturbative components of fragmentation. This paper presents a measurement of the average number of charged particles with >500 pT> 500 {\mathrm{MeV}} MeV ins...

This paper presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other qu...

A search for the standard model Higgs boson produced in association with a vector boson with the decay H→ττ is presented. The data correspond to 20.3 fb-1 of integrated luminosity from proton-proton collisions at s=8 TeV recorded by the ATLAS experiment at the LHC during 2012. The data agree with the background expectation, and 95% confidence-level...

This paper presents measurements of W±Z production in pp collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb-1. The measu...

A search is performed for the process , predicted in composite Higgs scenarios, where is a heavy colour octet vector resonance and a vector-like quark of charge . The data were obtained from pp collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of , recorded by the ATLAS detector at the LHC. The largest backgro...

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of tau -> 3 mu. A method utilising the production of t leptons via W -> tau nu decays is used. This method is applied to the sample of 20.3 fb(-1) of pp collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC...

The distribution of particles inside hadronic jets produced in the decay of boosted W and Z bosons can be used to discriminate such jets from the continuum background. Given that a jet has been identified as likely resulting from the hadronic decay of a boosted W or Z boson, this paper presents a technique for further differentiating Z bosons from...

The production rates of prompt and non-prompt J/psi and psi(2S) mesons in their dimuon decay modes are measured using 2.1 and 11.4 fb(-1) of data collected with the ATLAS experiment at the Large Hadron Collider, in proton-proton collisions at root s = 7 and 8 respectively. Production cross-sections for prompt as well as non-prompt sources, ratios o...

Distributions of transverse momentum pTℓℓ and the related angular variable ϕη∗ of Drell–Yan lepton pairs are measured in 20.3fb-1 of proton–proton collisions at √ s = 8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements i...

This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the e...

Distributions of transverse momentum p T and the related angular variable φ∗ η of Drell–Yan lepton pairs are measured in 20.3 fb−1 of proton–proton collisions at √s = 8 TeV with the ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements i...

ATLAS has measured two-particle correlations as a function of the relative azimuthal angle, Δϕ, and pseudorapidity, Δη, in sqrt[s]=13 and 2.76 TeV pp collisions at the LHC using charged particles measured in the pseudorapidity interval |η|<2.5. The correlation functions evaluated in different intervals of measured charged-particle multiplicity show...

Charged-particle distributions are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 μb−1, recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transver...

This article presents the sensitivity of the ATLAS experiment to the lepton-flavour-violating decays of τ → 3μ. A method utilising the production of τ leptons via W → τ ν decays is used. This method is applied to the sample of 20.3 fb−1 of pp collision data at a centre-of-mass energy of 8 TeV collected by the ATLAS experiment at the LHC in 2012. No...

This article reports on a search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks, using data from 20.3 fb-1 of pp collisions at a center-of-mass energy of 8 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum bb system with either a pa...

The electroweak production and subsequent decay of single top quarks is determined by the properties of the Wtb vertex. This vertex can be described by the complex parameters of an effective Lagrangian. An analysis of angular distributions of the decay products of single top quarks produced in the t -channel constrains these parameters simultaneous...

Results of a search for new phenomena in events with at least three photons are reported. Data from proton–proton collisions at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 20.3 fb (Formula presented.) , were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. L...

Prompt photon production in sNN=2.76-TeV Pb+Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb-1. Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum...

A search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 7.0 fb-1. A customized trigger significantly increases the sensitivity, permitting a search for such partic...

The ZZ production cross section in proton-proton collisions at 13 TeV center-of-mass energy is measured using 3.2 fb^{-1} of data recorded with the ATLAS detector at the Large Hadron Collider. The considered Z boson candidates decay to an electron or muon pair of mass 66-116 GeV. The cross section is measured in a fiducial phase space reflecting th...

This Letter presents evidence for single top-quark production in the s-channel using proton–proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS detector at the CERN Large Hadron Collider. The analysis is performed on events containing one isolated electron or muon, large missing transverse momentum and exactly two b-tagged jets in...

The ATLAS experiment has performed extensive searches for the electroweak production of charginos, neutralinos, and staus. This article summarizes and extends the search for electroweak supersymmetry with new analyses targeting scenarios not covered by previously published searches. New searches use vector-boson fusion production, initial-state rad...

The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum-weighted sums, called jet charge, in dijet events using 20.3 fb-1 of data recorded with the ATLAS detector at s=8 TeV in pp collisions at the LHC. The j...

In the pp→tt process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is perform...

The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb−1 of pp collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pse...

A search is conducted for new physics in multijet final states using 3.6 inverse femtobarns of data from proton-proton collisions at \( \sqrt{s}=13 \) TeV taken at the CERN Large Hadron Collider with the ATLAS detector. Events are selected containing at least three jets with scalar sum of jet transverse momenta (H T) greater than 1 TeV. No excess i...

A search is performed for the production of high-mass resonances decaying into a photon and a jet in 3.2 fb−1 of proton-proton collisions at a centre-of-mass energy of \( \sqrt{s}=13 \) TeV collected by the ATLAS detector at the Large Hadron Collider. Selected events have an isolated photon and a jet, each with transverse momentum above 150 GeV. No...

This paper reports a detailed study of techniques for identifying boosted, hadronically decaying W bosons using 20.3 fb (Formula presented.) of proton–proton collision data collected by the ATLAS detector at the LHC at a centre-of-mass energy (Formula presented.). A range of techniques for optimising the signal jet mass resolution are combined with...

Charged Higgs bosons heavier than the top quark and decaying via H ± → tb are searched for in proton-proton collisions measured with the ATLAS experiment at \( \sqrt{s}=8 \) TeV corresponding to an integrated luminosity of 20.3fb−1. The production of a charged Higgs boson in association with a top quark, gb → tH ±, is explored in the mass range 200...

Eur. Phys. J. C (2016) 76:152 DOI 10.1140/epjc/s10052-016-3934-y Publisher’s Erratum Erratum to: Study of the spin and parity of the Higgs boson in diboson decays with the ATLAS detector ATLAS Collaboration CERN, 1211 Geneva 23, Switzerland Published online: 17 March 2016 © CERN for the benefit of the ATLAS collaboration 2016. This article is publi...

Eur. Phys. J. C (2016) 76:153 DOI 10.1140/epjc/s10052-016-3935-x Publisher’s Erratum Erratum to: ATLAS Run 1 searches for direct pair production of third-generation squarks at the Large Hadron Collider ATLAS Collaboration CERN, 1211 Geneva 23, Switzerland Published online: 17 March 2016 © CERN for the benefit of the ATLAS collaboration 2016. This a...

The differential cross-section for pair production of top quarks with high transverse momentum is measured in 20.3 fb-1 of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for tt¯ events in the lepton+jets channel. The cross-section is reported as a function of the hadronically decaying top quark transverse...

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb−1 of pp collision data at s=8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances...

The strength and tensor structure of the Higgs boson's interactions are investigated using an effective Lagrangian, which introduces additional CP-even and CP-odd interactions that lead to changes in the kinematic properties of the Higgs boson and associated jet spectra with respect to the Standard Model. The parameters of the effective Lagrangian...

A search for the flavour-changing neutral-current decay \(t\rightarrow qZ\) is presented. Data collected by the ATLAS detector during 2012 from proton–proton collisions at the Large Hadron Collider at a centre-of-mass energy of \(\sqrt{s}=8\) TeV, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\), are analysed. Top-quark pair-production...

A search for single top-quark production via flavour-changing neutral current processes from gluon plus up- or charm-quark initial states in proton-proton collisions at the LHC is presented. Data collected with the ATLAS detector in 2012 at a centre-of-mass energy of 8 TeV and corresponding to an integrated luminosity of 20.3 fb[Formula: see text]...

A search is presented for a new, light boson with a mass of about 1 GeV and decaying promptly to jets of collimated electrons and/or muons (lepton-jets). The analysis is performed with 20.3 fb−1 of data collected by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a centre-of-mass energy of 8 TeV. Events are required t...

A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb\(^{-1}\) of proton–proton collision data at \(\sqrt{s}=8~\mathrm{TeV}\). The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched f...

This paper reports inclusive and differential measurements of the \(t\bar{t}\) charge asymmetry \(A_{\text {C}}\) in \(20.3~{\mathrm{fb}^{-1}}\) of \(\sqrt{s} = 8~\mathrm TeV{}\) \(pp\) collisions recorded by the ATLAS experiment at the Large Hadron Collider at CERN. Three differential measurements are performed as a function of the invariant mass,...

A search for vector-like quarks and excited quarks in events containing a top quark and a W boson in the final state is reported here. The search is based on 20.3 fb−1 of proton-proton collision data taken at the LHC at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector. Events with one or two leptons, and one, two or three jets are se...

A search for a Higgs boson produced via vector-boson fusion and decaying into invisible particles is presented, using 20.3 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the LHC. For a Higgs boson with a mass of 125 GeV, assuming the Standard Model production cross section, an upper bound...

This Letter describes a model-agnostic search for pairs of jets (dijets) produced by resonant and non-resonant phenomena beyond the Standard Model in 3.6 of proton–proton collisions with a centre-of-mass energy of TeV recorded by the ATLAS detector at the Large Hadron Collider. The distribution of the invariant mass of the two leading jets is exami...

Combined analyses of the Higgs boson production and decay rates as well as its coupling strengths to vector bosons and fermions are presented. The combinations include the results of the analyses of the \(H\rightarrow \gamma \gamma ,\, ZZ^*,\, WW^*,\, Z\gamma ,\, b\bar{b},\, \tau \tau \) and \(\mu \mu \) decay modes, and the constraints on the asso...

Fiducial cross-sections for \(t\bar{t} \) production with one or two additional b-jets are reported, using an integrated luminosity of 20.3 fb\(^{-1}\) of proton–proton collisions at a centre-of-mass energy of 8 TeV at the Large Hadron Collider, collected with the ATLAS detector. The cross-section times branching ratio for \(t\bar{t} \) events with...