Search for charginos and neutralinos in final states with two boosted hadronically decaying bosons and missing transverse momentum in pp collisions at √s=13 TeV with the ATLAS detector

A search for charginos and neutralinos at the Large Hadron Collider using fully hadronic final states and missing transverse momentum is reported. Pair-produced charginos or neutralinos are explored, each decaying into a high-pT Standard Model weak boson. Fully hadronic final states are studied to exploit the advantage of the large branching ratio, and the efficient rejection of backgrounds by identifying the high-pT bosons using large-radius jets and jet substructure information. An integrated luminosity of 139  fb−1 of proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 13 TeV is used. No significant excess is found beyond the Standard Model expectation. Exclusion limits at the 95% confidence level are set on wino or higgsino production with various assumptions about the decay branching ratios and the type of lightest supersymmetric particle. A wino (higgsino) mass up to 1060 (900) GeV is excluded when the lightest supersymmetry particle mass is below 400 (240) GeV and the mass splitting is larger than 400 (450) GeV. The sensitivity to high-mass winos and higgsinos is significantly extended relative to previous LHC searches using other final states.publishedVersio

Measurement of the production cross section of pairs of isolated photons in pp collisions at 13 TeV with the ATLAS detector

A measurement of prompt photon-pair production in proton-proton collisions at √s = 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb−1. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of pT,γ1(2) > 40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.publishedVersio

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Machine learning techniques for cross-section measurements for the vector-boson fusion production of the Higgs boson in the H→WW∗→eνμν H\rightarrow WW^* \rightarrow e\nu\mu\nu\ decay channel with the ATLAS detector

This article reports on the measurements of the fiducial and differential production cross section of Higgs bosons with an electron, a muon, and two energetic neutrinos from the decay of $W$ bosons in the final state. The understanding of the fundamental properties of the Higgs boson is one of the main goals of the physics programme of the Large Hadron Collider. The analysis of 139 fb$^{-1}$ of proton--proton collision data at a centre-of-mass energy of $\sqrt s$ = 13 TeV recorded by the ATLAS experiment unlocks the study of the Higgs boson’s properties with unprecedented precision. While the first differential and fiducial production cross section measurements had been reported in the diphoton and four-lepton final states, the exploration of secondary production mechanisms in extreme kinematic regions has been heavily anticipated. Cutting-edge machine- learning-based methodologies are exploited for maximising the signal sensitivity while minimising the model- dependency of the results. The results are compared with state-of-the-art theoretical predictions. Furthermore, the measurements are used to constrain the presence of new phenomena in the framework of Effective Field Theories

Higgs differential cross-sections and CP Higgs couplings results with the ATLAS experiment

With the pp collision dataset collected at 13 TeV, detailed measurements of Higgs boson properties can be performed. The Higgs kinematics and CP properties can be measured with various production and decay modes and interpreted to constrain beyond-the-Standard-Model phenomena. This talk presents the measurements of Higgs boson differential and fiducial cross-sections as well as their combination and interpretations, and limits on the mixing of CP-even and CP-odd Higgs states are set by exploiting the properties of diverse final state

Search for charginos and neutralinos in final states with two boosted hadronically decaying bosons and missing transverse momentum in pp collisions at √s=13 TeV with the ATLAS detector

A search for charginos and neutralinos at the Large Hadron Collider using fully hadronic final states and missing transverse momentum is reported. Pair-produced charginos or neutralinos are explored, each decaying into a high-pT Standard Model weak boson. Fully hadronic final states are studied to exploit the advantage of the large branching ratio, and the efficient rejection of backgrounds by identifying the high-pT bosons using large-radius jets and jet substructure information. An integrated luminosity of 139  fb−1 of proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 13 TeV is used. No significant excess is found beyond the Standard Model expectation. Exclusion limits at the 95% confidence level are set on wino or higgsino production with various assumptions about the decay branching ratios and the type of lightest supersymmetric particle. A wino (higgsino) mass up to 1060 (900) GeV is excluded when the lightest supersymmetry particle mass is below 400 (240) GeV and the mass splitting is larger than 400 (450) GeV. The sensitivity to high-mass winos and higgsinos is significantly extended relative to previous LHC searches using other final states

Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in pp collisions at √s=13 TeV

A search for events with two displaced vertices from long-lived particle (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 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 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 tt¯ in the ATLAS muon spectrometer.publishedVersio

Measurement of the production cross section of pairs of isolated photons in pp collisions at 13 TeV with the ATLAS detector

A measurement of prompt photon-pair production in proton-proton collisions at √s = 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb−1. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of pT,γ1(2) > 40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system

Study of B+c→J/ψD+s and B+c→J/ψD∗+s decays in pp collisions at √s = 13 TeV with the ATLAS detector

A study of B+c→J/ψD+sBc+→J/ψDs+ and B+c→J/ψD∗+sBc+→J/ψDs∗+ decays using 139 fb−1 of integrated luminosity collected with the ATLAS detector from 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+cBc+ → J/ψπ+ decay are measured: B(B+c→J/ψD+s)/B(B+c→J/ψπ+)B(Bc+→J/ψDs+)/B(Bc+→J/ψπ+) = 2.76 ± 0.47 and B(B+c→J/ψD∗+s)/B(B+c→J/ψπ+)B(Bc+→J/ψDs∗+)/B(Bc+→J/ψπ+) = 5.33 ± 0.96. The ratio of the branching fractions of the two decays is found to be B(B+c→J/ψD∗+s)/B(B+c→J/ψD∗+s)B(Bc+→J/ψDs∗+)/B(Bc+→J/ψDs∗+) = 1.93 ± 0.26. For the B+c→J/ψD∗+sBc+→J/ψDs∗+ 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 s√s = 7 and 8 TeV pp collision data. A comparison with available theoretical predictions for the measured quantities is presented.publishedVersio

Search for invisible Higgs-boson decays in events with vector-boson fusion signatures using 139 fb−1 of proton-proton data recorded by the ATLAS experiment

A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb−1 of pp collision data at a centre-of-mass energy of s√ = 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0.145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0.103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1.0 pb for a scalar boson mass of 50 GeV to 0.1 pb at a mass of 2 TeV.publishedVersio