814 research outputs found
Search for boosted diphoton resonances in the 10 to 70 GeV mass range using 138 fbā1 of 13 TeV pp collisions with the ATLAS detector
A search for diphoton resonances in the mass range between 10 and 70 GeV with the ATLAS experiment at the Large Hadron Collider (LHC) is presented. The analysis is based on pp collision data corresponding to an integrated luminosity of 138 fbā1 at a centre-of-mass energy of 13 TeV recorded from 2015 to 2018. Previous searches for diphoton resonances at the LHC have explored masses down to 65 GeV, finding no evidence of new particles. This search exploits the particular kinematics of events with pairs of closely spaced photons reconstructed in the detector, allowing examination of invariant masses down to 10 GeV. The presented strategy covers a region previously unexplored at hadron colliders because of the experimental challenges of recording low-energy photons and estimating the backgrounds. No significant excess is observed and the reported limits provide the strongest bound on promptly decaying axion-like particles coupling to gluons and photons for masses between 10 and 70 GeV
Measurement of the total and differential Higgs boson production cross-sections at s = 13 TeV with the ATLAS detector by combining the H ā ZZ * ā 4 ā and H ā Ī³Ī³ decay channels
The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H ā ZZ* ā 4ā and H ā Ī³Ī³ decay channels. The results are based on a dataset of 139 fbā1 of protonāproton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is 55.5ā3.8+4.0 pb, consistent with the Standard Model prediction of 55.6 Ā± 2.5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H ābbĀÆ and ccĀÆ decay channels
Measurement of the properties of Higgs boson production at sā = 13 TeV in the H ā Ī³Ī³ channel using 139 fbā1 of pp collision data with the ATLAS experiment
Measurements of Higgs boson production cross-sections are carried out in the diphoton decay channel using 139 fbā1 of pp collision data at sā
= 13 TeV collected by the ATLAS experiment at the LHC. The analysis is based on the definition of 101 distinct signal regions using machine-learning techniques. The inclusive Higgs boson signal strength in the diphoton channel is measured to be 1.04+0.10ā0.09
. Cross-sections for gluon-gluon fusion, vector-boson fusion, associated production with a W or Z boson, and top associated production processes are reported. An upper limit of 10 times the Standard Model prediction is set for the associated production process of a Higgs boson with a single top quark, which has a unique sensitivity to the sign of the top quark Yukawa coupling. Higgs boson production is further characterized through measurements of Simplified Template Cross-Sections (STXS). In total, cross-sections of 28 STXS regions are measured. The measured STXS cross-sections are compatible with their Standard Model predictions, with a p-value of 93%. The measurements are also used to set constraints on Higgs boson coupling strengths, as well as on new interactions beyond the Standard Model in an effective field theory approach. No significant deviations from the Standard Model predictions are observed in these measurements, which provide significant sensitivity improvements compared to the previous ATLAS results
Measurement of the Higgs boson mass in the HāÆāāÆZZāāÆāāÆ4ā decay channel using 139 fbā1 of TeV pp collisions recorded by the ATLAS detector at the LHC
The mass of the Higgs boson is measured in the
ā
decay channel. The analysis uses protonāproton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fbā1. The measured value of the Higgs boson mass is
GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of
GeV
Search for a new Zā² gauge boson in 4Ī¼ events with the ATLAS experiment
This paper presents a search for a new Zā² vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at sā
= 13 TeV, corresponding to an integrated luminosity of 139 fbā1. The new gauge boson Zā² is predicted by LĪ¼ ā LĻ models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4Ī¼) final state, using a deep learning neural network classifier to separate the Zā² signal from the Standard Model background events. The di-muon invariant masses in the 4Ī¼ events are used to extract the Zā² resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Zā² production cross-section times the decay branching fraction of pp ā Zā²Ī¼Ī¼ ā 4Ī¼ are set from 0.31 to 4.3 fb for the Zā² mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, gZā², of the Zā² boson to the second and third generation leptons above 0.003 ā 0.2 have been excluded
Observation of gauge boson joint-polarisation states in WĀ±Z production from pp collisions at ās = 13 TeV with the ATLAS detector
Measurements of joint-polarisation states of W and Z gauge bosons in
production are presented. The data set used corresponds to an integrated luminosity of 139 fbā1 of protonāproton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. The
candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The simultaneous pair-production of longitudinally polarised vector bosons is measured for the first time with a significance of 7.1 standard deviations. The measured joint helicity fractions integrated over the fiducial region are
,
,
and
, in agreement with the next-to-leading-order Standard Model predictions. Individual helicity fractions of the W and Z bosons are also measured and found to be consistent with joint helicity fractions within the expected amounts of correlation. Both the joint and individual helicity fractions are also measured separately in
and
events. Inclusive and differential cross sections for several kinematic observables sensitive to polarisation are presented
Probing the CP nature of the topāHiggs Yukawa coupling in ttĀÆH and tH events with H ā bbĀÆ decays using the ATLAS detector at the LHC
The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fbā1 of protonāproton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of ās = 13 TeV. The CP structure of the top quarkāHiggs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, ttH , or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in ttH and tH events, where dedicated CP -sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP -odd admixture in the topāHiggs Yukawa coupling, the mixing angle between CP -even and CP -odd couplings is measured to be Ī± = 11 Ā°+52Ā° ā73Ā°, compatible with the SM prediction corresponding to Ī± = 0
Search for heavy resonances decaying into a Z or W boson and a Higgs boson in final states with leptons and b-jets in 139 fbā1 of pp collisions at sā = 13 TeV with the ATLAS detector
This article presents a search for new resonances decaying into a Z or W boson and a 125 GeV Higgs boson h, and it targets the Ī½Ī½ĀÆĀÆĀÆbbĀÆĀÆ
, ā+āābbĀÆĀÆ
, or āĀ±Ī½bbĀÆĀÆ
final states, where ā = e or Ī¼, in proton-proton collisions at sā
= 13 TeV. The data used correspond to a total integrated luminosity of 139 fbā1 collected by the ATLAS detector during Run 2 of the LHC at CERN. The search is conducted by examining the reconstructed invariant or transverse mass distributions of Zh or Wh candidates for evidence of a localised excess in the mass range from 220 GeV to 5 TeV. No significant excess is observed and 95% confidence-level upper limits between 1.3 pb and 0.3 fb are placed on the production cross section times branching fraction of neutral and charged spin-1 resonances and CP-odd scalar bosons. These limits are converted into constraints on the parameter space of the Heavy Vector Triplet model and the two-Higgs-doublet model
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