scholarly journals Search for $$ t\overline{t} $$ resonances in fully hadronic final states in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

2020 ◽  
Vol 2020 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Production Cross ◽  
Hadron Collider ◽  
Top Quarks ◽  
Atlas Detector ◽  
Proton Collision ◽  
Large Radius ◽  
Final States ◽  
Jet Substructure ◽  
High Transverse Momentum ◽  
Hadronic Final States

Abstract This paper presents a search for new heavy particles decaying into a pair of top quarks using 139 fb−1 of proton-proton collision data recorded at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search is performed using events consistent with pair production of high-transverse-momentum top quarks and their subsequent decays into the fully hadronic final states. The analysis is optimized for resonances decaying into a $$ t\overline{t} $$ t t ¯ pair with mass above 1.4 TeV, exploiting a dedicated multivariate technique with jet substructure to identify hadronically decaying top quarks using large-radius jets and evaluating the background expectation from data. No significant deviation from the background prediction is observed. Limits are set on the production cross-section times branching fraction for the new Z′ boson in a topcolor-assisted-technicolor model. The Z′ boson masses below 3.9 and 4.7 TeV are excluded at 95% confidence level for the decay widths of 1% and 3%, respectively.

scholarly journals Search for heavy resonances decaying into a pair of Z bosons in the $$\ell ^+\ell ^-\ell '^+\ell '^-$$ and $$\ell ^+\ell ^-\nu {{\bar{\nu }}}$$ final states using 139 $$\mathrm {fb}^{-1}$$ of proton–proton collisions at $$\sqrt{s} = 13\,$$TeV with the ATLAS detector

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Production Cross ◽  
Hadron Collider ◽  
Higgs Doublet ◽  
Atlas Detector ◽  
Proton Collision ◽  
Type I ◽  
Final States ◽  
Proton Proton ◽  
Upper Limits ◽  
Heavy Resonances

AbstractA search for heavy resonances decaying into a pair of Z bosons leading to $$\ell ^+\ell ^-\ell '^+\ell '^-$$ ℓ + ℓ - ℓ ′ + ℓ ′ - and $$\ell ^+\ell ^-\nu {{\bar{\nu }}}$$ ℓ + ℓ - ν ν ¯ final states, where $$\ell $$ 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 $$\mathrm {fb}^{-1}$$ 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.

scholarly journals Search for heavy diboson resonances in semileptonic final states in pp collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Cross Sections ◽  
Production Cross ◽  
Vector Boson ◽  
Hadron Collider ◽  
Gluon Fusion ◽  
Mass Range ◽  
Atlas Detector ◽  
Proton Collision ◽  
Final States ◽  
Heavy Resonances

AbstractThis paper reports on a search for heavy resonances decaying into WW, ZZ or WZ using proton–proton collision data at a centre-of-mass energy of $$\sqrt{s}=13$$ s = 13  TeV. The data, corresponding to an integrated luminosity of 139 $$\mathrm{fb}^{1}$$ fb 1 , were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one W or Z boson decays leptonically, and the other W boson or Z boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300–5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. Production through gluon–gluon fusion, Drell–Yan or vector-boson fusion are considered, depending on the assumed model.

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

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
W Bosons ◽  
Top Quarks ◽  
Atlas Detector ◽  
Large Radius ◽  
Jet Substructure ◽  
Proton Proton ◽  
Proton Collisions ◽  
Wide Range ◽  
New Type ◽  
Proton Proton Collisions

AbstractJet 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 $$\sqrt{s}=13~\text {TeV}$$ s = 13 TeV during 2017.

scholarly journals Search for excited electrons singly produced in proton–proton collisions at $$\sqrt{s} ~=~13~\text {Te}\text {V}$$ with the ATLAS experiment at the LHC

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
M. Aaboud ◽  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
...  
Keyword(s):  
Cross Sections ◽  
Production Cross ◽  
Hadron Collider ◽  
Excited Electron ◽  
Electron Mass ◽  
Large Radius ◽  
Final States ◽  
Hadronic Jets ◽  
Proton Proton ◽  
Atlas Experiment

Abstract A search for excited electrons produced in pp collisions at $$\sqrt{s}$$s  = 13 $$\text {Te}\text {V}$$Te via a contact interaction $$q{\bar{q}}\rightarrow ee^*$$qq¯→ee∗ is presented. The search uses 36.1 fb$$^{-1}$$-1 of data collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider. Decays of the excited electron into an electron and a pair of quarks ($$eq{\bar{q}}$$eqq¯) are targeted in final states with two electrons and two hadronic jets, and decays via a gauge interaction into a neutrino and a $$W$$W boson ($$\nu W$$νW) are probed in final states with an electron, missing transverse momentum, and a large-radius jet consistent with a hadronically decaying $$W$$W boson. No significant excess is observed over the expected backgrounds. Upper limits are calculated for the $$pp \rightarrow ee^*\rightarrow eeq{\bar{q}} $$pp→ee∗→eeqq¯ and $$pp \rightarrow ee^*\rightarrow e\nu W $$pp→ee∗→eνW production cross sections as a function of the excited electron mass $$m_{e^*}$$me∗ at 95% confidence level. The limits are translated into lower bounds on the compositeness scale parameter $$\Lambda $$Λ of the model as a function of $$m_{e^*}$$me∗. For $$m_{e^*} <0.5$$me∗<0.5 $$\text {Te}\text {V}$$Te, the lower bound for $$\Lambda $$Λ is 11 $$\text {Te}\text {V}$$Te. In the special case of $$m_{e^*} =\Lambda $$me∗=Λ, the values of $$m_{e^*} <4.8$$me∗<4.8 $$\text {Te}\text {V}$$Te are excluded. The presented limits on $$\Lambda $$Λ are more stringent than those obtained in previous searches.

scholarly journals Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 $$\text {TeV}$$

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
G. Aad ◽  
◽  
B. Abbott ◽  
D. C. Abbott ◽  
O. Abdinov ◽  
...  
Keyword(s):  
Top Quark ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Higgs Bosons ◽  
Proton Collision ◽  
Jet Substructure ◽  
Proton Proton ◽  
Quark Pairs ◽  
Systematic Uncertainties ◽  
B Quark

Abstract This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, $$H \rightarrow b\bar{b}$$H→bb¯, for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy $$\sqrt{s}=13$$s=13 $$\text {TeV}$$TeV. These decays are reconstructed from calorimeter jets found with the anti-$$k_{t}$$kt$$R = 1.0$$R=1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of $$R = 0.2$$R=0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb$$^{-1}$$-1 of data collected in 2015 and 2016 using $$g\rightarrow b\bar{b}$$g→bb¯ and $$Z(\rightarrow b\bar{b})\gamma $$Z(→bb¯)γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties.

scholarly journals Search for Heavy Higgs Bosons with the ATLAS Detector

2018 ◽  
Vol 46 ◽  
pp. 1860056
Author(s):  
Jana Schaarschmidt
Keyword(s):  
Large Hadron Collider ◽  
Cross Section ◽  
Production Cross Section ◽  
Production Cross ◽  
Hadron Collider ◽  
New Physics ◽  
Atlas Detector ◽  
Higgs Bosons ◽  
Final States ◽  
Atlas Experiment

The ATLAS experiment at the Large Hadron Collider performed searches for heavy Higgs bosons, whose presence would establish the existance of new physics. Searches for charged and neutral Higgs bosons are carried out using 8 or 13 TeV data for various production modes and in many different final states. No deviations from Standard Model expectations are observed. Exclusions limits are set on the production cross section and on parameters in various benchmark models.

scholarly journals Measurements of the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson at $$\sqrt{s} = 13$$ TeV with the ATLAS detector

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Top Quark ◽  
Production Cross ◽  
Hadron Collider ◽  
Inclusive Cross Section ◽  
Atlas Detector ◽  
Proton Collision ◽  
Proton Proton ◽  
Theoretical Predictions

AbstractMeasurements of both the inclusive and differential production cross sections of a top-quark–antiquark pair in association with a Z boson ($$t{\bar{t}}Z$$ t t ¯ Z ) are presented. The measurements are performed by targeting final states with three or four isolated leptons (electrons or muons) and are based on $$\sqrt{s} = 13$$ s = 13  TeV proton–proton collision data with an integrated luminosity of 139 $$\hbox {fb}^{-1}$$ fb - 1 , recorded from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. The inclusive cross section is measured to be $$\sigma _{t{\bar{t}}Z} = 0.99 \pm 0.05$$ σ t t ¯ Z = 0.99 ± 0.05  (stat.) $$\pm \, 0.08$$ ± 0.08  (syst.) pb, in agreement with the most precise theoretical predictions. The differential measurements are presented as a function of a number of kinematic variables which probe the kinematics of the $$t{\bar{t}}Z$$ t t ¯ Z system. Both absolute and normalised differential cross-section measurements are performed at particle and parton levels for specific fiducial volumes and are compared with theoretical predictions at different levels of precision, based on a $$\chi ^{2}/$$ χ 2 / ndf and p value computation. Overall, good agreement is observed between the unfolded data and the predictions.

scholarly journals Highlights of top quark measurements in hadronic final states at ATLAS

2018 ◽  
Vol 172 ◽  
pp. 04001
Author(s):  
Serena Palazzo
Keyword(s):  
Top Quark ◽  
Theoretical Calculations ◽  
Production Cross ◽  
Hadron Collider ◽  
Center Of Mass ◽  
Inclusive Cross Section ◽  
Final States ◽  
Top Quark Production ◽  
Quark Production ◽  
Hadronic Final States

Measurements of inclusive and differential top quark production cross sections in hadronic final states, including hadronic τ decays, in proton-proton collisions with the ATLAS detector at the Large Hadron Collider are presented at center-of-mass energies of 7, 8 and 13 TeV. The inclusive cross section measurements reach high precision and are compared to other decay modes and the best available theoretical calculations. Differential measurements of the kinematic properties of top quark events are also discussed. These measurements use boosted top quarks, probing our understanding of top quark production in the TeV regime.

scholarly journals Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

2021 ◽  
Vol 2021 (6) ◽  
Author(s):  
◽  
G. Aad ◽  
B. Abbott ◽  
D. C. Abbott ◽  
A. Abed Abud ◽  
...  
Keyword(s):  
Pair Production ◽  
Top Quark ◽  
Production Cross ◽  
Branching Fraction ◽  
Hadron Collider ◽  
Atlas Detector ◽  
Third Generation ◽  
Final State ◽  
Generation Scalar ◽  
Scalar Leptoquarks

Abstract A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton is presented. The search is based on a dataset of pp collisions at $$ \sqrt{s} $$ s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ-lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν. Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into tτ, the lower mass limit is 1.22 TeV.

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