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The UCLA Graduate School of Education & Information Studies (GSE&IS) includes two departments--the Department of Education and the Department of Information Studies. Together, the two departments embody the school's commitment to understand and improve educational practice, information policy, and information systems in a diverse society. Research and doctoral training programs bring together faculties committed to expanding the range of knowledge in education, information science, and associated disciplines. The professional training programs seek to develop librarians, teachers, and administrators within the enriched context of a research university.

Cover page of Search for new phenomena in final states with b-jets and missing transverse momentum in √s = 13 TeV pp collisions with the ATLAS detector

Search for new phenomena in final states with b-jets and missing transverse momentum in √s = 13 TeV pp collisions with the ATLAS detector

(2021)

The results of a search for new phenomena in final states with b-jets and missing transverse momentum using 139 fb−1 of proton-proton data collected at a centre-of-mass energy s = 13 TeV by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously. [Figure not available: see fulltext.]

Erratum to: Higgs boson production cross-section measurements and their EFT interpretation in the 4 ℓ decay channel at s = 13 TeV with the ATLAS detector (The European Physical Journal C, (2020), 80, 10, (957), 10.1140/epjc/s10052-020-8227-9)

(2021)

When quoting the final cross section result in the text of the paper (Eur. Phys. J. C 80 (2020) 957), the theory component of the uncertainty was incorrectly set to 0.04 pb while the correct value of 0.03 pb was given in Table 8 and in all other results reported in this paper.

Search for a heavy Higgs boson decaying into a Z boson and another heavy Higgs boson in the ℓℓbb and ℓℓWW final states in pp collisions at √s=13 TeV with the ATLAS detector

(2021)

A search for a heavy neutral Higgs boson, A, decaying into a Z boson and another heavy Higgs boson, H, is performed using a data sample corresponding to an integrated luminosity of 139 fb- 1 from proton–proton collisions at s=13 TeV recorded by the ATLAS detector at the LHC. The search considers the Z boson decaying into electrons or muons and the H boson into a pair of b-quarks or W bosons. The mass range considered is 230–800 GeV for the A boson and 130–700 GeV for the H boson. The data are in good agreement with the background predicted by the Standard Model, and therefore 95% confidence-level upper limits for σ×B(A→ZH)×B(H→bborH→WW) are set. The upper limits are in the range 0.0062–0.380 pb for the H→ bb channel and in the range 0.023–8.9 pb for the H→ WW channel. An interpretation of the results in the context of two-Higgs-doublet models is also given.

Search for heavy resonances decaying into a pair of Z bosons in the ℓ+ℓ-ℓ′+ℓ′- and ℓ+ℓ-νν¯ final states using 139 fb-1 of proton–proton collisions at s=13TeV with the ATLAS detector

(2021)

A search for heavy resonances decaying into a pair of Z bosons leading to ℓ+ℓ−ℓ′+ℓ′− and ℓ+ℓ−νν¯ final states, where ℓ stands for either an electron or a muon, is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV collected from 2015 to 2018 that corresponds to the integrated luminosity of 139 fb−1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Different mass ranges spanning 200 GeV to 2000 GeV for the hypothetical resonances are considered, depending on the final state and model. In the absence of a significant observed excess, the results are interpreted as upper limits on the production cross section of a spin-0 or spin-2 resonance. The upper limits for the spin-0 resonance are translated to exclusion contours in the context of Type-I and Type-II two-Higgs-doublet models, and the limits for the spin-2 resonance are used to constrain the Randall–Sundrum model with an extra dimension giving rise to spin-2 graviton excitations.

Cover page of Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in pp collisions at s√ = 13 TeV with the ATLAS detector

Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in pp collisions at s√ = 13 TeV with the ATLAS detector

(2021)

The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum are reported, using 139 fb−1 of integrated luminosity from proton-proton collisions at s√ = 13 TeV, collected by the ATLAS detector at the Large Hadron Collider during Run 2 (2015–2018). This search considers the pair production of top squarks and is sensitive across a wide range of mass differences between the top squark and the lightest neutralino. Additionally, spin-0 mediator dark-matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at 95% confidence level. The results exclude top squark masses up to about 1 TeV, and masses of the lightest neutralino up to about 500 GeV. Limits on dark-matter production are set for scalar (pseudoscalar) mediator masses up to about 250 (300) GeV.

Cover page of Optimisation of large-radius jet reconstruction for the ATLAS detector in 13 TeV proton–proton collisions

Optimisation of large-radius jet reconstruction for the ATLAS detector in 13 TeV proton–proton collisions

(2021)

Jet substructure has provided new opportunities for searches and measurements at the LHC, and has seen continuous development since the optimization of the large-radius jet definition used by ATLAS was performed during Run 1. A range of new inputs to jet reconstruction, pile-up mitigation techniques and jet grooming algorithms motivate an optimisation of large-radius jet reconstruction for ATLAS. In this paper, this optimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared. The relative performance of these jet definitions is assessed using metrics such as their pileup stability, ability to identify hadronically decaying W bosons and top quarks with large transverse momenta. A new type of jet input object, called a ‘unified flow object’ is introduced which combines calorimeter- and inner-detector-based signals in order to achieve optimal performance across a wide kinematic range. Large-radius jet definitions are identified which significantly improve on the current ATLAS baseline definition, and their modelling is studied using pp collisions recorded by the ATLAS detector at s=13TeV during 2017.

Search for pair production of scalar leptoquarks decaying into first- or second-generation leptons and top quarks in proton–proton collisions at √s = 13 TeV with the ATLAS detector

(2021)

A search for pair production of scalar leptoquarks, each decaying into either an electron or a muon and a top quark, is presented. This is the first leptoquark search using ATLAS data to investigate top-philic cross-generational couplings that could provide explanations for recently observed anomalies in B meson decays. This analysis targets high leptoquark masses which cause the decay products of each resultant top quark to be contained within a single high-pT large-radius jet. The full Run 2 dataset is exploited, consisting of 139fb-1 of data collected from proton–proton collisions at s=13TeV from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. In the absence of any significant deviation from the background expectation, lower limits on the leptoquark masses are set at 1480GeV and 1470GeV for the electron and muon channel, respectively.

Search for type-III seesaw heavy leptons in dilepton final states in pp collisions at √s=13TeV with the ATLAS detector

(2021)

A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139fb-1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.

Erratum to: Search for phenomena beyond the Standard Model in events with large b-jet multiplicity using the ATLAS detector at the LHC (The European Physical Journal C, (2021), 81, 1, (11), 10.1140/epjc/s10052-020-08730-0)

(2021)

In the original HTML version of this article, one affiliation of the author V. O. Tikhomirov was missing. He is affiliated to the following two affiliations: P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia National Research Nuclear University MEPhI, Moscow, Russia The original article has been corrected.

Cover page of Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at √s = 13 TeV with the ATLAS detector

Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at √s = 13 TeV with the ATLAS detector

(2021)

A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into b-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb−1 of pp collision data at s = 13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is 1.3 ± 1.0 times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations, compared to an expected significance of 1.0 standard deviations. [Figure not available: see fulltext.]