Showing papers by "M. Kaneda published in 2022"
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TL;DR: In this article , measurements of the production cross-sections of the Standard Model (SM) Higgs boson decaying into a pair of τ -leptons are presented, using data collected with the ATLAS detector from pp collisions produced at the Large Hadron Collider at a centre-of-mass energy of = 13 TeV.
Abstract: A bstract Measurements of the production cross-sections of the Standard Model (SM) Higgs boson ( H ) decaying into a pair of τ -leptons are presented. The measurements use data collected with the ATLAS detector from pp collisions produced at the Large Hadron Collider at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 139 fb − 1 . Leptonic ( τ → ℓν ℓ ν τ ) and hadronic ( τ → hadrons ν τ ) decays of the τ -lepton are considered. All measurements account for the branching ratio of H → ττ and are performed with a requirement |y H | < 2 . 5, where y H is the true Higgs boson rapidity. The cross-section of the pp → H → ττ process is measured to be 2 . 94 ± $$ 0.21{\left(\mathrm{stat}\right)}_{-0.32}^{+0.37} $$ 0.21 stat − 0.32 + 0.37 (syst) pb, in agreement with the SM prediction of 3 . 17 ± 0 . 09 pb. Inclusive cross-sections are determined separately for the four dominant production modes: 2 . 65 ± $$ 0.41{\left(\mathrm{stat}\right)}_{-0.67}^{+0.91} $$ 0.41 stat − 0.67 + 0.91 (syst) pb for gluon-gluon fusion, 0 . 197 ± $$ 0.028{\left(\mathrm{stat}\right)}_{-0.026}^{+0.032} $$ 0.028 stat − 0.026 + 0.032 (syst) pb for vector-boson fusion, 0 . 115 ± $$ 0.058{\left(\mathrm{stat}\right)}_{-0.040}^{+0.042} $$ 0.058 stat − 0.040 + 0.042 (syst) pb for vector-boson associated production, and 0 . 033 ± $$ 0.031{\left(\mathrm{stat}\right)}_{-0.017}^{+0.022} $$ 0.031 stat − 0.017 + 0.022 (syst) pb for top-quark pair associated production. Measurements in exclusive regions of the phase space, using the simplified template cross-section framework, are also performed. All results are in agreement with the SM predictions.
26 citations
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11 Jan 2022
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22 citations
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TL;DR: In this paper , a search for new spin-0 or spin-1 bosons using events where a Higgs boson with mass 125 GeV decays into four leptons ( ℓ = e , μ ).
Abstract: A bstract Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass 125 GeV decays into four leptons ( ℓ = e , μ ). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: H → XX/ZX → 4 ℓ , where the new boson X has a mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb − 1 at a centre-of-mass energy $$ \sqrt{s} $$ s = 13 TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into XX/ZX , improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where X is interpreted to be a dark boson.
15 citations
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TL;DR: The ATLAS Level-1 topological trigger allowed efficient data-taking by the ATLAS experiment at luminosities up to 2.1 as discussed by the authors , which exceeds the design value by a factor of two.
Abstract: Abstract During LHC Run 2 (2015–2018) the ATLAS Level-1 topological trigger allowed efficient data-taking by the ATLAS experiment at luminosities up to 2.1 $$\times $$ × 10 $$^{34}$$ 34 cm $$^{-2}$$ - 2 s $$^{-1}$$ - 1 , which exceeds the design value by a factor of two. The system was installed in 2016 and operated in 2017 and 2018. It uses Field Programmable Gate Array processors to select interesting events by placing kinematic and angular requirements on electromagnetic clusters, jets, $$\tau $$ τ -leptons, muons and the missing transverse energy. It allowed to significantly improve the background event rejection and signal event acceptance, in particular for Higgs and B -physics processes.
14 citations
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TL;DR: In this paper , the authors performed searches for nonresonant and resonant di-Higgs boson production in the bb¯γγ final state and obtained expected upper bounds on the cross-sections of diHiggs Boson production.
Abstract: Searches are performed for nonresonant and resonant di-Higgs boson production in the bb¯γγ final state. The dataset used corresponds to an integrated luminosity of 139 fb−1 of proton–proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No excess above the expected background is found and upper limits on the di-Higgs boson production cross sections are set. A 95% confidence-level upper limit of 4.2 times the cross section predicted by the Standard Model is set on pp→HH nonresonant production, where the expected limit is 5.7 times the Standard Model predicted value. The expected constraints are obtained for a background hypothesis excluding pp→HH production. The observed (expected) constraints on the Higgs boson trilinear coupling modifier κλ are determined to be [−1.5,6.7] ([−2.4,7.7]) at 95% confidence level, where the expected constraints on κλ are obtained excluding pp→HH production from the background hypothesis. For resonant production of a new hypothetical scalar particle X (X→HH→bb¯γγ), limits on the cross section for pp→X→HH are presented in the narrow-width approximation as a function of mX in the range 251 GeV≤mX≤1000 GeV. The observed (expected) limits on the cross section for pp→X→HH range from 640 fb to 44 fb (391 fb to 46 fb) over the considered mass range.8 MoreReceived 23 December 2021Accepted 1 August 2022DOI:https://doi.org/10.1103/PhysRevD.106.052001Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2022 CERN, for the ATLAS CollaborationPhysics Subject Headings (PhySH)Research AreasExtensions of Higgs sectorHadron-hadron interactionsPhysical SystemsHiggs bosonsParticles & Fields
8 citations
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TL;DR: In this article , the associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons.
Abstract: A bstract The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a b -quark pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb − 1 , were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is $$ {0.35}_{-0.34}^{+0.36} $$ 0.35 − 0.34 + 0.36 . This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
8 citations
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01 Feb 2022
TL;DR: In this paper , the authors present a measurement of the electroweak production of two jets in association with a $Z\gamma$ pair, with the $Z$ boson decaying into two neutrinos.
Abstract: This paper presents a measurement of the electroweak production of two jets in association with a $Z\gamma$ pair, with the $Z$ boson decaying into two neutrinos. It also presents a search for invisible or partially invisible decays of a Higgs boson with a mass of 125 GeV produced through vector-boson fusion with a photon in the final state. These results use data from LHC proton-proton collisions at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector and corresponding to an integrated luminosity of 139 fb$^{-1}$. The event signature, shared by all benchmark processes considered for the measurements and searches, is characterized by a significant amount of unbalanced transverse momentum and a photon in the final state, in addition to a pair of forward jets. Electroweak $Z\gamma$ production in association with two jets is observed in this final state with a significance of 5.2 (5.1 expected) standard deviations. The measured fiducial cross-section for this process is 1.31$\pm$0.29 fb. An observed (expected) upper limit of 0.37 ($0.34^{+0.15}_{-0.10}$) at 95% confidence level is set on the branching ratio of a 125 GeV Higgs boson to invisible particles, assuming the Standard Model production cross-section. The signature is also interpreted in the context of decays of a Higgs boson into a photon and a dark photon. An observed (expected) 95% CL upper limit on the branching ratio for this decay is set at 0.018 ($0.017^{+0.007}_{-0.005}$), assuming the Standard Model production cross-section for a 125 GeV Higgs boson.
8 citations
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TL;DR: In this article , a search for resonant Higgs boson pair production in the $b\bar{b}b \bar{ b}$ final state is presented. But the analysis is divided into two channels, targeting Higgs particle decays which are reconstructed as pairs of small-radius jets or as individual large-radius jet.
Abstract: A search for resonant Higgs boson pair production in the $b\bar{b}b\bar{b}$ final state is presented. The analysis uses 126-139 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}$ = 13 TeV collected with the ATLAS detector at the Large Hadron Collider. The analysis is divided into two channels, targeting Higgs boson decays which are reconstructed as pairs of small-radius jets or as individual large-radius jets. Spin-0 and spin-2 benchmark signal models are considered, both of which correspond to resonant $HH$ production via gluon$-$gluon fusion. The data are consistent with Standard Model predictions. Upper limits are set on the production cross-section times branching ratio to Higgs boson pairs of a new resonance in the mass range from 251 GeV to 5 TeV.
7 citations
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01 Jan 2022
TL;DR: In this paper , a technique is presented to measure the efficiency with which c-jets are mistagged as b-Jets (mistagging efficiency) using $$t\bar{t}$$.
Abstract: Abstract A technique is presented to measure the efficiency with which c -jets are mistagged as b -jets (mistagging efficiency) using $$t\bar{t}$$ t t ¯ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known $$W\rightarrow cs$$ W → c s branching ratio, which allows a measurement to be made in an inclusive c -jet sample. The data sample used was collected by the ATLAS detector at $$\sqrt{s} = 13$$ s = 13 $$\text {TeV}$$ TeV and corresponds to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and $$t\bar{t}$$ t t ¯ decay products that yields the highest likelihood value. The distribution of the b -tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b -jet tagging requirement.
7 citations
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31 Jan 2022
TL;DR: In this article , a technique is presented to measure the efficiency with which c-jets are mistagged as b-Jets (mistagging efficiency) using $$t\bar{t}$$.
Abstract: Abstract A technique is presented to measure the efficiency with which c -jets are mistagged as b -jets (mistagging efficiency) using $$t\bar{t}$$ t t ¯ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known $$W\rightarrow cs$$ W → c s branching ratio, which allows a measurement to be made in an inclusive c -jet sample. The data sample used was collected by the ATLAS detector at $$\sqrt{s} = 13$$ s = 13 $$\text {TeV}$$ TeV and corresponds to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and $$t\bar{t}$$ t t ¯ decay products that yields the highest likelihood value. The distribution of the b -tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b -jet tagging requirement.
7 citations
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TL;DR: The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events as discussed by the authors .
Abstract: The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with GEANT4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation -- the calorimeter shower simulation -- with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges and simulation needs of the ATLAS experiment. With highly accurate performance and a new ability to model substructure within jets, AtlFast3 is designed to be used to simulate large numbers of events for a wide range of physics processes.
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TL;DR: In this article , a measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and $pp$ collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented.
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TL;DR: In this paper , a new method to account for these additional interactions in the simulation chain is described, instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the interactions are presampled, independent of the hard scatter, and stored as combined events.
Abstract: Abstract The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
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01 Jul 2022
TL;DR: In this paper , a search for long-lived charginos produced either directly or in the cascade decay of heavy prompt gluino states is presented, based on proton-proton collision data collected at a centre-of-mass energy of 13 TeV between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb$^{-1}$.
Abstract: A search for long-lived charginos produced either directly or in the cascade decay of heavy prompt gluino states is presented. The search is based on proton-proton collision data collected at a centre-of-mass energy of $\sqrt{s}$ = 13 TeV between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb$^{-1}$. Long-lived charginos are characterised by a distinct signature of a short and then disappearing track, and are reconstructed using at least four measurements in the ATLAS pixel detector, with no subsequent measurements in the silicon-microstrip tracking volume nor any associated energy deposits in the calorimeter. The final state is complemented by a large missing transverse-momentum requirement for triggering purposes and at least one high-transverse-momentum jet. No excess above the expected backgrounds is observed. Exclusion limits are set at 95% confidence level on the masses of the chargino and gluino for different chargino lifetimes. Chargino masses up to 660 (210) GeV are excluded in scenarios where the chargino is a pure wino (higgsino). For charginos produced during the cascade decay of a heavy gluino, gluinos with masses below 2.1 TeV are excluded for a chargino mass of 300 GeV and a lifetime of 0.2 ns.
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TL;DR: In this paper , a 3D two-way FSI scheme for simultaneous collision/contact of multiple flexible fibers is developed, which is successfully validated in experimental benchmarks of flexible fiber collision and contact behaviors induced by airflows.
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01 Jul 2022
TL;DR: In this article , the results of two studies of Higgs boson properties using the final state were presented, based on a dataset corresponding to 36.1/fb collisions recorded by the ATLAS experiment at the Large Hadron Collider.
Abstract: This article presents the results of two studies of Higgs boson properties using the $WW^*(\rightarrow e
u\mu
u)jj$ final state, based on a dataset corresponding to 36.1/fb of $\sqrt{s}$=13 TeV proton$-$proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study targets Higgs boson production via gluon$-$gluon fusion and constrains the CP properties of the effective Higgs$-$gluon interaction. Using angular distributions and the overall rate, a value of $\tan(\alpha) = 0.0 \pm 0.4$ stat. $ \pm 0.3$ syst is obtained for the tangent of the mixing angle for CP-even and CP-odd contributions. The second study exploits the vector-boson fusion production mechanism to probe the Higgs boson couplings to longitudinally and transversely polarised $W$ and $Z$ bosons in both the production and the decay of the Higgs boson; these couplings have not been directly constrained previously. The polarisation-dependent coupling-strength scale factors are defined as the ratios of the measured polarisation-dependent coupling strengths to those predicted by the Standard Model, and are determined using rate and kinematic information to be $a_L=0.91^{+0.10}_{-0.18}$(stat.)$^{+0.09}_{-0.17}$(syst.) and $a_{T}=1.2 \pm 0.4 $(stat.)$ ^{+0.2}_{-0.3} $(syst.). These coupling strengths are translated into pseudo-observables, resulting in $\kappa_{VV}= 0.91^{+0.10}_{-0.18}$(stat.)$^{+0.09}_{-0.17}$(syst.) and $\epsilon_{VV} =0.13^{+0.28}_{-0.20}$ (stat.)$^{+0.08}_{-0.10}$(syst.). All results are consistent with the Standard Model predictions.
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TL;DR: In this article , the energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range $10
Abstract: The energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range $10
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TL;DR: The ATLAS Level-1 topological trigger allowed efficient data-taking by the ATLAS experiment at luminosities up to 2.1 as discussed by the authors , which exceeds the design value by a factor of two.
Abstract: Abstract During LHC Run 2 (2015–2018) the ATLAS Level-1 topological trigger allowed efficient data-taking by the ATLAS experiment at luminosities up to 2.1 $$\times $$ × 10 $$^{34}$$ 34 cm $$^{-2}$$ - 2 s $$^{-1}$$ - 1 , which exceeds the design value by a factor of two. The system was installed in 2016 and operated in 2017 and 2018. It uses Field Programmable Gate Array processors to select interesting events by placing kinematic and angular requirements on electromagnetic clusters, jets, $$\tau $$ τ -leptons, muons and the missing transverse energy. It allowed to significantly improve the background event rejection and signal event acceptance, in particular for Higgs and B -physics processes.
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TL;DR: In this paper , the trajectories of b-hadron trajectories were obtained from a sample of dileptonic tt¯ events, and the associated set of charged-particle tracks was separated into those from the primary pp interaction vertex and those from displaced b-decay secondary vertex, which were then used to construct observables that characterize the longitudinal and transverse momentum distributions of the b hadron within the jet.
Abstract: Several observables sensitive to the fragmentation of b quarks into b hadrons are measured using 36 fb−1 of s=13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Jets containing b hadrons are obtained from a sample of dileptonic tt¯ events, and the associated set of charged-particle tracks is separated into those from the primary pp interaction vertex and those from the displaced b-decay secondary vertex. This division is used to construct observables that characterize the longitudinal and transverse momentum distributions of the b hadron within the jet. The measurements have been corrected for detector effects and provide a test of heavy-quark-fragmentation modeling at the LHC in a system where the top-quark decay products are color connected to the proton beam remnants. The unfolded distributions are compared with the predictions of several modern Monte Carlo parton-shower generators and generator tunes, and a wide range of agreement with the data is observed, with p values varying from 5×10−4 to 0.98. These measurements complement similar measurements from e+e− collider experiments in which the b quarks originate from a color singlet Z/γ*.3 MoreReceived 1 March 2022Accepted 8 July 2022DOI:https://doi.org/10.1103/PhysRevD.106.032008Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.© 2022 CERN, for the ATLAS CollaborationPhysics Subject Headings (PhySH)Research AreasQuark & gluon jetsPhysical SystemsTop quarkTechniquesMulti-purpose particle detectorsPrecision measurementsParticles & Fields
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TL;DR: In this paper , the energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range $10
Abstract: The energy response of the ATLAS calorimeter is measured for single charged pions with transverse momentum in the range $10
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01 Apr 2022
TL;DR: In this paper , a search for the production of a single top quark via left-handed flavour-changing neutral-current (FCNC) interactions of a top particle, a gluon and an up or charm quark is presented.
Abstract: Abstract A search is presented for the production of a single top quark via left-handed flavour-changing neutral-current (FCNC) interactions of a top quark, a gluon and an up or charm quark. Two production processes are considered: $$u+g\rightarrow t$$ u + g → t and $$c+g\rightarrow t$$ c + g → t . The analysis is based on proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events with exactly one electron or muon, exactly one b -tagged jet and missing transverse momentum are selected, resembling the decay products of a singly produced top quark. Neural networks based on kinematic variables differentiate between events from the two signal processes and events from background processes. The measured data are consistent with the background-only hypothesis, and limits are set on the production cross-sections of the signal processes: $$\sigma (u+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell
u )<3.0\,$$ σ ( u + g → t ) × B ( t → W b ) × B ( W → ℓ ν ) < 3.0 pb and $$\sigma (c+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell
u )<4.7\,$$ σ ( c + g → t ) × B ( t → W b ) × B ( W → ℓ ν ) < 4.7 pb at the 95% confidence level, with $$\mathcal {B}(W\rightarrow \ell
u )=0.325$$ B ( W → ℓ ν ) = 0.325 being the sum of branching ratios of all three leptonic decay modes of the W boson. Based on the framework of an effective field theory, the cross-section limits are translated into limits on the strengths of the tug and tcg couplings occurring in the theory: $$|C^{\,ut}_{uG}|/\Lambda ^2 < 0.057\,$$ | C uG u t | / Λ 2 < 0.057 TeV $$^{-2}$$ - 2 and $$|C^{\,ct}_{uG}|/\Lambda ^2 < 0.14\,$$ | C uG c t | / Λ 2 < 0.14 TeV $$^{-2}$$ - 2 . These bounds correspond to limits on the branching ratios of FCNC-induced top-quark decays: $$\mathcal {B}(t\rightarrow u+g)< 0.61\times 10^{-4}$$ B ( t → u + g ) < 0.61 × 10 - 4 and $$\mathcal {B}(t\rightarrow c+g)< 3.7\times 10^{-4}$$ B ( t → c + g ) < 3.7 × 10 - 4 .
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TL;DR: In this paper , a new method to account for these additional interactions in the simulation chain is described, instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the interactions are presampled, independent of the hard scatter, and stored as combined events.
Abstract: Abstract The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
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TL;DR: In this paper , a simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in single-topquark production is presented, based on data from proton-proton collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb$-1.
Abstract: A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in $t$-channel single-top-quark production is presented. This analysis is based on data from proton--proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb$^{-1}$, collected with the ATLAS detector at the LHC. Selected events contain exactly one isolated electron or muon, large missing transverse momentum and exactly two jets, one being $b$-tagged. Stringent selection requirements are applied to discriminate $t$-channel single-top-quark events from the background contributions. The top-quark and top-antiquark polarisation vectors are measured from the distributions of the direction cosines of the charged-lepton momentum in the top-quark rest frame. The three components of the polarisation vector for the selected top-quark event sample are $P_{x'} =0.01\pm0.18$, $P_{y'} = -0.029\pm0.027$, $P_{z'} =0.91\pm0.10$ and for the top-antiquark event sample they are $P_{x'} = -0.02\pm0.20$, $P_{y'} = -0.007\pm0.051$, $P_{z'} = -0.79\pm 0.16$. Normalised differential cross-sections corrected to a fiducial region at the stable-particle level are presented as a function of the charged-lepton angles for top-quark and top-antiquark events inclusively and separately. These measurements are in agreement with Standard Model predictions. The angular differential cross-sections are used to derive bounds on the complex Wilson coefficient of the dimension-six $\mathcal{O}_{tW}$ operator in the framework of an effective field theory. The obtained bounds are $C_{tW} \in\ [-0.9,1.4]$ and $C_{itW} \in [-0.8,0.2]$, both at 95\% confidence level.
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TL;DR: In this article , a study of 13 TeV pp collisions at the LHC is presented, where the ratios of the branching fractions of the two decays to the branching fraction of the $$ {B}_c^{+} $$
Abstract: A bstract A study of $$ {B}_c^{+}\to J/\psi {D}_s^{+} $$ B c + → J / ψ D s + and $$ {B}_c^{+}\to J/\psi {D}_s^{\ast +} $$ B c + → J / ψ D s ∗ + decays using 139 fb − 1 of integrated luminosity collected with the ATLAS detector from $$ \sqrt{s} $$ s = 13 TeV pp collisions at the LHC is presented. The ratios of the branching fractions of the two decays to the branching fraction of the $$ {B}_c^{+} $$ B c + → J/ψπ + decay are measured: $$ \mathcal{B}\left({B}_c^{+}\to J/\psi {D}_s^{+}\right)/\mathcal{B}\left({B}_c^{+}\to J/{\psi \pi}^{+}\right) $$ B B c + → J / ψ D s + / B B c + → J / ψπ + = 2 . 76 ± 0 . 47 and $$ \mathcal{B}\left({B}_c^{+}\to J/\psi {D}_s^{\ast +}\right)/\mathcal{B}\left({B}_c^{+}\to J/{\psi \pi}^{+}\right) $$ B B c + → J / ψ D s ∗ + / B B c + → J / ψπ + = 5 . 33 ± 0 . 96. The ratio of the branching fractions of the two decays is found to be $$ \mathcal{B}\left({B}_c^{+}\to J/\psi {D}_s^{\ast +}\right)/\mathcal{B}\left({B}_c^{+}\to J/\psi {D}_s^{\ast +}\right) $$ B B c + → J / ψ D s ∗ + / B B c + → J / ψ D s ∗ + = 1 . 93 ± 0 . 26. For the $$ {B}_c^{+}\to J/\psi {D}_s^{\ast +} $$ B c + → J / ψ D s ∗ + decay, the transverse polarization fraction, Γ ±± / Γ, is measured to be 0 . 70 ± 0 . 11. The reported uncertainties include both the statistical and systematic components added in quadrature. The precision of the measurements exceeds that in all previous studies of these decays. These results supersede those obtained in the earlier ATLAS study of the same decays with $$ \sqrt{s} $$ s = 7 and 8 TeV pp collision data. A comparison with available theoretical predictions for the measured quantities is presented.
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09 Aug 2022
TL;DR: In this article , a search for events with two displaced vertices from long-lived particles (LLP) pairs using data collected by the ATLAS detector at the LHC is presented.
Abstract: A search for events with two displaced vertices from long-lived particles (LLP) pairs using data collected by the ATLAS detector at the LHC is presented. This analysis uses 139~fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded in 2015-2018. The search employs techniques for reconstructing vertices of LLPs decaying to jets in the muon spectrometer displaced between 3 m and 14 m with respect to the primary interaction vertex. The observed numbers of events are consistent with the expected background and limits for several benchmark signals are determined. For the Higgs boson with a mass of 125 GeV, the paper reports the first exclusion limits for branching fractions into neutral long-lived particles below 0.1%, while branching fractions above 10% are excluded at 95% confidence level for LLP proper lifetimes ranging from 4 cm to 72.4 m. In addition, the paper present the first results for the decay of LLPs into into $t\bar{t}$ in the ATLAS muon spectrometer.
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11 May 2022
TL;DR: In this paper , the authors reported constraints on Higgs boson production with transverse momentum above 1 TeV, which corresponds to an integrated luminosity of 136 fb$^{-1} .
Abstract: This paper reports constraints on Higgs boson production with transverse momentum above 1 TeV. The analyzed data from proton-proton collisions at a center-of-mass energy of 13 TeV were recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018 and correspond to an integrated luminosity of 136 fb$^{-1}$. Higgs bosons decaying into $b\bar{b}$ are reconstructed as single large-radius jets recoiling against a hadronic system and identified by the experimental signature of two $b$-hadron decays. The experimental techniques are validated in the same kinematic regime using the $Z\rightarrow b\bar{b}$ process. The 95% confidence-level upper limit on the cross section for Higgs boson production with transverse momentum above 450 GeV is 115 fb, and above 1 TeV it is 9.6 fb. The Standard Model predictions in the same kinematic regions are 18.4 fb and 0.13 fb, respectively.
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TL;DR: In this paper , the phase-field lattice Boltzmann method was used to obtain the flow and wetting characteristics of a single-layered rod array with different rod gaps.
Abstract: Stator coils of automobiles in operation generate heat and are cooled by coolant poured from above. The flow characteristic of the coolant depends on the coil structure, flow condition, solid–fluid interaction, and fluid property, which has not been clarified due to its complexities. Since straight coils are aligned and layered with an angle at the coolant-touchdown region, the coil structure is simplified to a horizontal square rod array referring to an actual coil size. To obtain the flow and wetting characteristics, two-phase fluid flow simulations are conducted by using the phase-field lattice Boltzmann method. First, the flow onto the single-layered rod array is discussed. The wetting area is affected both by the rod gap and the wettability, which is normalized by the gap and the averaged boundary layer thickness. Then, the flow onto the multi-layered rod arrays is investigated with different rod gaps. The top layer wetting becomes longitudinal due to the reduction of the flow advection by the second layer. The wetting area jumps up at the second layer and increases proportionally to the below layers. These become remarkable at the narrow rod gap case, and finally, the dimensionless wetting area is discussed at each layer.
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TL;DR: In this paper , a comparison of the production cross sections for e+μ− and e−μ+ pairs was performed at the LHC to constrain physics processes beyond the Standard Model.
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TL;DR: The semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector as discussed by the authors , and it consists of 4088 silicon strip sensor modules, which achieved a data-quality efficiency of 99.85%.
Abstract: The semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector. It consists of 4088 silicon strip sensor modules. During Run 2 (2015–2018) the Large Hadron Collider delivered an integrated luminosity of 156 fb-1 to the ATLAS experiment at a centre-of-mass proton-proton collision energy of 13 TeV. The instantaneous luminosity and pile-up conditions were far in excess of those assumed in the original design of the SCT detector. Due to improvements to the data acquisition system, the SCT operated stably throughout Run 2. It was available for 99.9% of the integrated luminosity and achieved a data-quality efficiency of 99.85%. Detailed studies have been made of the leakage current in SCT modules and the evolution of the full depletion voltage, which are used to study the impact of radiation damage to the modules.