Person: Ippolito, Valerio
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Ippolito
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Valerio
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Ippolito, Valerio
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Publication Measurement of the Centrality and Pseudorapidity Dependence of the Integrated Elliptic Flow in Lead–lead Collisions at √sNN=2.76TeV With the ATLAS Detector(Springer Nature, 2014) Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Morii, Masahiro; Spearman, William; Yen, Andy; Zevi Della Porta, GThe integrated elliptic flow of charged particles produced in Pb+Pb collisions at sNN=2.76 TeV has been measured with the ATLAS detector using data collected at the Large Hadron Collider. The anisotropy parameter, v2, was measured in the pseudorapidity range |η|≤2.5 with the event-plane method. In order to include tracks with very low transverse momentum pT, thus reducing the uncertainty in v2 integrated over pT, a 1~ b-1 data sample recorded without a magnetic field in the tracking detectors is used. The centrality dependence of the integrated v2 is compared to other measurements obtained with higher pT thresholds. The integrated elliptic flow is weakly decreasing with |η|. The integrated v2 transformed to the rest frame of one of the colliding nuclei is compared to the lower-energy RHIC data.Publication Measurement of the Top-Quark Mass in the Fully Hadronic Decay Channel From ATLAS Data at √s= 7TeV(Springer Nature, 2015) Franklin, Melissa; Huth, John; Ippolito, Valerio; Lopez Mateos, David; Mercurio, Kevin; Spearman, William; Sun, Siyuan; Yen, Andy; Zevi Della Porta, GThe mass of the top quark is measured in a data set corresponding to 4.6 fb-1 of proton–proton collisions with centre-of-mass energy √ = 7TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top–antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified b-quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the W boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of mt = 175.1 ± 1.4 (stat.) ± 1.2 (syst.) GeV.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 Erratum To: 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, WilliamPublication 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.