Person: Tolley, Emma
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Tolley
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Emma
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Tolley, Emma
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Publication Search for the Standard Model Higgs Boson Produced by Vector-Boson Fusion and Decaying to Bottom Quarks in S√=8 S = 8 TeV Pp Collisions With the ATLAS DetectorChan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Skottowe, Hugh Philip; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Yen, Andy; Zambito, StefanoA search with the ATLAS detector is presented for the Standard Model Higgs boson produced by vector-boson fusion and decaying to a pair of bottom quarks, using 20.2 fb−1 of LHC proton-proton collision data at √s = 8 TeV. The signal is searched for as a resonance in the invariant mass distribution of a pair of jets containing b-hadrons in vector-boson-fusion candidate events. The yield is measured to be −0.8 ± 2.3 times the Standard Model cross-section for a Higgs boson mass of 125 GeV. The upper limit on the cross-section times the branching ratio is found to be 4.4 times the Standard Model cross- section at the 95% confidence level, consistent with the expected limit value of 5.4 (5.7) in the background-only (Standard Model production) hypothesis.Publication Search for Invisible Decays of the Higgs Boson Produced in Association With a Hadronically Decaying Vector Boson in pp Collisions at √s=8(Springer Nature, 2015) Clark, Brian Lee; Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, Andy; Zambito, StefanoA search for Higgs boson decays to invisible particles is performed using 20.3 fb−1 of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V=W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain VH production followed by H decaying to invisible particles for the Higgs boson mass range 115.Publication Determination of Spin and Parity of the Higgs Boson in the WW ∗ →eνμν Decay Channel With the ATLAS Detector(Springer Nature, 2015) Clark, Brian Lee; Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, AndyStudies of the spin and parity quantum numbers of the Higgs boson in the WW ∗ →eνμν final state are presented, based on proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb −1 at a centre-of-mass energy of s √ =8 TeV. The Standard Model spin-parity J CP =0 ++ hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even ( J CP =0 ++ ) or CP-odd ( J CP =0 +− ) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.Publication Erratum To: Search for Production of WW / WZ Resonances Decaying to a Lepton, Neutrino and Jets in Pp Collisions at √s=8 TeV With the ATLAS Detector(Springer Nature, 2015) Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, AndyA search is presented for narrow diboson resonances decaying to WW or WZ in the final state where one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W/Z boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb(-1) of pp collisions at √s=8 TeV collected by the ATLAS detector at the large hadron collider. No evidence for resonant diboson production is observed, and resonance masses below 700 and 1490 GeV are excluded at 95 % confidence level for the spin-2 Randall-Sundrum bulk graviton G* with coupling constant of 1.0 and the extended gauge model W' boson respectively.Publication Search for New Phenomena in Events With at Least Three Photons Collected in Pp Collisions at √s = 8 TeV With the ATLAS Detector(Springer Nature, 2016) Clark, Brian Lee; Franklin, Melissa; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Tuna, Alexander; Yen, Andy; Zambito, StefanoResults 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 −1−1 , were collected with the ATLAS detector at the LHC. The observed data are well described by the Standard Model. Limits at the 95 % confidence level on new phenomena are presented based on the rate of events in an inclusive signal region and a restricted signal region targeting the rare decay Z→3γZ→3γ , as well as di-photon and tri-photon resonance searches. For a Standard Model Higgs boson decaying to four photons via a pair of intermediate pseudoscalar particles (a), limits are found to be σ× BR (h→aa)× BR (a→γγ)2<10−3σSMσ× BR (h→aa)× BR (a→γγ)2<10−3σSM for 10 GeV mH> 125 GeV, and for a Z′Z′ decaying to three photons via Z′→a+γ→3γZ′→a+γ→3γ . Additionally, the observed limit on the branching ratio of the Z boson decay to three photons is found to be BR (Z→3γ)<2.2×10−6(Z→3γ)<2.2×10−6 , a result five times stronger than the previous result from LEP.Publication Two-Particle Bose-Einstein Correlations in pp Collisions at √s = 0.9 and 7 TeV Measured With the ATLAS Detector(Springer Nature, 2015) Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, Andy; Zevi Della Porta, GThe paper presents studies of Bose–Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range pT > 100 MeV and |η| < 2.5 in proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb⁻¹, 190 μb⁻¹ and 12.4 nb⁻¹ for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size parameter is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.Publication Search for New Phenomena in Final States With an Energetic Jet and Large Missing Transverse Momentum in Pp Collisions at √s=8 TeV With the ATLAS Detector(Springer Nature, 2015) Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, AndyResults of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √s=8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT>120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between EmissT>150 GeV and EmissT>700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.Publication Measurement of the transverse momentum and ϕ∗η distributions of Drell–Yan lepton pairs in proton–proton collisions at √s=8 TeV with the ATLAS detector(Springer Nature, 2016) Clark, Brian Lee; Franklin, Melissa; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Tuna, Alexander; Yen, Andy; Zambito, StefanoDistributions 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 in proton–proton collisions at √ s = 7 TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the Z-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of φ ∗ η < 1 the predictions from the Monte Carlo generator ResBos are generally consistent with the data within the theoretical uncertainties. However, at larger values of φ ∗ η this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of p T while the fixed-order prediction of Dynnlo falls below the data at high values of p T . ResBos and the parton-shower Monte Carlo generators provide a much better description of the evolution of the φ ∗ η and p T distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.Publication Measurements of the Higgs boson production and decay rates and coupling strengths using pp collision data at √s=7 and 8 TeV in the ATLAS experiment(Springer Nature, 2016) Clark, Brian Lee; Franklin, Melissa; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Sun, Siyuan; Tolley, Emma; Yen, AndyCombined 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 → γγ, ZZ*, WW*, Zγ, bb̅, ττ and μμ decay modes, and the constraints on the associated production with a pair of top quarks and on the off-shell coupling strengths of the Higgs boson. The results are based on the LHC proton-proton collision datasets, with integrated luminosities of up to 4.7 fb⁻¹ at √s̅ =7 TeV and 20.3 fb⁻¹ at √s̅ = 8 TeV, recorded by the ATLAS detector in 2011 and 2012. Combining all production modes and decay channels, the measured signal yield, normalised to the Standard Model expectation, is 1.18_{-0.14} ^{+0.15}. The observed Higgs boson production and decay rates are interpreted in a leading-order coupling framework, exploring a wide range of benchmark coupling models both with and without assumptions on the Higgs boson width and on the Standard Model particle content in loop processes. The data are found to be compatible with the Standard Model expectations for a Higgs boson at a mass of 125.36 GeV for all models considered.Publication Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton–proton collisions at the LHC(Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Yen, Andy; Zambito, StefanoThis paper presents the method and performance of primary vertex reconstruction in proton-proton collision data recorded by the ATLAS experiment during Run 1 of the LHC. The studies presented focus on data taken during 2012 at a centre-of-mass energy of s√=8 TeV. The performance has been measured as a function of the number of interactions per bunch crossing over a wide range, from one to seventy. The measurement of the position and size of the luminous region and its use as a constraint to improve the primary vertex resolution are discussed. A longitudinal vertex position resolution of about 30 micrometers is achieved for events with high multiplicity of reconstructed tracks. The transverse position resolution is better than 20 micrometers and is dominated by the precision on the size of the luminous region. An analytical model is proposed to describe the primary vertex reconstruction efficiency as a function of the number of interactions per bunch crossing and of the longitudinal size of the luminous region. Agreement between the data and the predictions of this model is better than 3% up to seventy interactions per bunch crossing.