Software performance of the ATLAS track reconstruction for LHC run 3

Charged particle reconstruction in the presence of many simultaneous proton–proton (pp) collisions in the LHC is a challenging task for the ATLAS experiment’s reconstruction software due to the combinatorial complexity. This paper describes the major changes made to adapt the software to reconstruct high-activity collisions with an average of 50 or more simultaneous pp interactions per bunch crossing (pileup) promptly using the available computing resources. The performance of the key components of the track reconstruction chain and its dependence on pile-up are evaluated, and the improvement achieved compared to the previous software version is quantified. For events with an average of 60 pp collisions per bunch crossing, the updated track reconstruction is twice as fast as the previous version, without significant reduction in reconstruction efficiency and while reducing the rate of combinatorial fake tracks by more than a factor two

Search for heavy Majorana or Dirac neutrinos and right-handed W gauge bosons in final states with charged leptons and jets in pp collisions at √s = 13 TeV with the ATLAS detector

A search for heavy right-handed Majorana or Dirac neutrinos NR and heavy right-handed gauge bosons WR is performed in events with energetic electrons or muons, with the same or opposite electric charge, and energetic jets. The search is carried out separately for topologies of clearly separated final-state products (“resolved” channel) and topologies with boosted final states with hadronic and/or leptonic products partially overlapping and reconstructed as a large-radius jet (“boosted” channel). The events are selected from pp collision data at the LHC with an integrated luminosity of 139 fb−1 collected by the ATLAS detector at √s = 13 TeV. No significant deviations from the Standard Model predictions are observed. The results are interpreted within the theoretical framework of a left-right symmetric model, and lower limits are set on masses in the heavy righthanded WR boson and NR plane. The excluded region extends to about m(WR) = 6.4 TeV for both Majorana and Dirac NR neutrinos at m(NR) < 1 TeV. NR with masses of less than 3.5 (3.6) TeV are excluded in the electron (muon) channel at m(WR) = 4.8 TeV for the Majorana neutrinos, and limits of m(NR) up to 3.6 TeV for m(WR) = 5.2 (5.0) TeV in the electron (muon) channel are set for the Dirac neutrinos. These constitute the most stringent exclusion limits to date for the model considered

Observation of four-top-quark production in the multilepton final state with the ATLAS detector

This paper presents the observation of four-top-quark (tt¯tt¯) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 fb−1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured tt¯tt¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The tt¯tt¯ production cross section is measured to be 22.5+6.6−5.5 fb, consistent with the SM prediction of 12.0±2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect tt¯tt¯ production

Características morfológicas de cultivares de soja convencionais e Roundup ReadyTM em função da época e densidade de semeadura Morphologic characteristic of the conventional soybean genotype and Roundup ReadyTM according to the sowing season and seed densities

O trabalho tem como objetivo verificar a influência de diferentes densidades e épocas de semeadura em genótipos convencionais e Roundup ReadyTM (RR), nas características morfológicas de plantas de soja. O experimento foi conduzido em Jari, Rio Grande do Sul (RS). A primeira semeadura foi realizada dentro da época indicada para a cultura (novembro), e a segunda, após a época indicada (janeiro), com as cultivares 'CEP/CD 41', 'CD 201', 'Fundacep 39',' Fundacep 44', 'CD 205', 'BRS 133', 'Fundacep 45', 'A 6001 RG', 'Mágica', 'AL72' e 'A 8100 RG', nas densidades de 250, 400 e 550 mil sementes aptas ha-1, na safra 2005/2006. O delineamento experimental utilizado foi blocos ao acaso, com parcelas subsubdivididas e quatro repetições. Foram avaliados o ciclo das cultivares, a altura de plantas, a altura de inserção do primeiro legume, o número de ramos planta-1 e de ramos m-2, o número de nós na haste principal planta-1 e na haste principal m-2, o rendimento biológico (RB) e o índice de colheita (IC). A semeadura em janeiro ocasiona redução no ciclo da cultura, na altura de plantas, na altura de inserção do primeiro legume, no número de nós planta-1 e de RB e no atraso da semeadura. O aumento da densidade de sementes não proporcionou aumento na estatura de plantas e altura de inserção do primeiro legume, nas cultivares RR. O período do ciclo que é mais afetado com atraso da semeadura é o vegetativo. O IC foi menor na semeadura em novembro; no entanto, o RB foi maior.<br>This paper has the objective to evaluate the influence of seed densities and sowing season in conventional soybean genotype and Roundup ReadyTM (RR), in the morphological characteristic of soybean plant. The experiments were conducted in Jari-RS, Brazil. The first seeding was done within the time prescribed for the crop(November), and the second, after the time indicated (January), with the cultivars 'CEP/CD 41', 'CD 201', 'Fundacep 39', 'Fundacep 44', 'CD 205', 'BRS 133', 'Fundacep 45', 'A 6001 RG', 'Mágica, AL72' and A '8100 RG', at densities of 250, 400 and 550 thousand seed seeds suitable ha-1 in the 2005/2006 harvest. The experiment design was randomized blocks with split plots, with four replications. The cultivars cycle, plant height, height of first pod insertion, number of branches plant-1, branches m-2, nodes' number of the main stem plant-1, nodes main stem m-2, biological yield (RB) and harvest index (IC). Sowing in January causes reduction in the crop cycle, plant height, height of first pod insertion, number of nodes plant-1 and RB and the increase in seed density not increased the height of first pod insertion in RR cultivars. The period cycle that is most affected by the delayed sowing is the vegetative. The IC sowing in November was lower, but the RB was larger

Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS

Searches for long-lived particles (LLPs) are among the most promising avenues for discovering physics beyond the Standard Model at the Large Hadron Collider (LHC). However, displaced signatures are notoriously difficult to identify due to their ability to evade standard object reconstruction strategies. In particular, the ATLAS track reconstruction applies strict pointing requirements which limit sensitivity to charged particles originating far from the primary interaction point. To recover efficiency for LLPs decaying within the tracking detector volume, the ATLAS Collaboration employs a dedicated large-radius tracking (LRT) pass with loosened pointing requirements. During Run 2 of the LHC, the LRT implementation produced many incorrectly reconstructed tracks and was therefore only deployed in small subsets of events. In preparation for LHC Run 3, ATLAS has significantly improved both standard and large-radius track reconstruction performance, allowing for LRT to run in all events. This development greatly expands the potential phase-space of LLP searches and streamlines LLP analysis workflows. This paper will highlight the above achievement and report on the readiness of the ATLAS detector for track-based LLP searches in Run 3