Pair Production In Final States Research Articles

A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb−1 of pp collision data collected by the ATLAS detector

This paper presents a search for top-squark pair production in final states with a top quark, a charm quark and missing transverse momentum. The data were collected with the ATLAS detector during LHC Run 2 and correspond to an integrated luminosity of 139 fb−1 of proton-proton collisions at a centre-of-mass energy of s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV. The analysis is motivated by an extended Minimal Supersymmetric Standard Model featuring a non-minimal flavour violation in the second- and third-generation squark sector. The top squark in this model has two possible decay modes, either t~1→cχ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ ilde{t}}_1\ o c{\\overset{\\sim }{\\chi}}_1^0 $$\\end{document} or t~1→tχ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ ilde{t}}_1\ o t{\\overset{\\sim }{\\chi}}_1^0 $$\\end{document}, where the χ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\overset{\\sim }{\\chi}}_1^0 $$\\end{document} is undetected. The analysis is optimised assuming that both of the decay modes are equally probable, leading to the most likely final state of tc+ETmiss\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ tc+{E}_T^{\ extrm{miss}} $$\\end{document}. Good agreement is found between the Standard Model expectation and the data in the search regions. Exclusion limits at 95% CL are obtained in the mt~1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ m\\left({\ ilde{t}}_1\\right) $$\\end{document} vs. mχ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ m\\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$\\end{document} plane and, in addition, limits on the branching ratio of the t~1→tχ~10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ ilde{t}}_1\ o t{\\overset{\\sim }{\\chi}}_1^0 $$\\end{document} decay as a function of m(t~1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\ ilde{t}}_1 $$\\end{document}) are also produced. Top-squark masses of up to 800 GeV are excluded for scenarios with light neutralinos, and top-squark masses up to 600 GeV are excluded in scenarios where the neutralino and the top squark are almost mass degenerate.

Search for chargino\u2013neutralino pair production in final states with three leptons and missing transverse momentum in sqrt{s} = 13\xa0TeV pp collisions with the ATLAS detector

A search for chargino–neutralino pair production in three-lepton final states with missing transverse momentum is presented. The study is based on a dataset of sqrt{s} = 13 TeV pp collisions recorded with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 hbox {fb}^{-1}. No significant excess relative to the Standard Model predictions is found in data. The results are interpreted in simplified models of supersymmetry, and statistically combined with results from a previous ATLAS search for compressed spectra in two-lepton final states. Various scenarios for the production and decay of charginos ({tilde{chi }}^pm _1) and neutralinos ({tilde{chi }}^0_2) are considered. For pure higgsino {tilde{chi }}^pm _1{tilde{chi }}^0_2 pair-production scenarios, exclusion limits at 95% confidence level are set on {tilde{chi }}^0_2 masses up to 210 GeV. Limits are also set for pure wino {tilde{chi }}^pm _1{tilde{chi }}^0_2 pair production, on {tilde{chi }}^0_2 masses up to 640 GeV for decays via on-shell W and Z bosons, up to 300 GeV for decays via off-shell W and Z bosons, and up to 190 GeV for decays via W and Standard Model Higgs bosons.

Search for nonresonant Higgs boson pair production in final states with two bottom quarks and two photons in proton-proton collisions at sqrt{s} = 13 TeV

A search for nonresonant production of Higgs boson pairs via gluon-gluon and vector boson fusion processes in final states with two bottom quarks and two photons is presented. The search uses data from proton-proton collisions at a center-of-mass energy of sqrt{s} = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 137 fb−1. No significant deviation from the background-only hypothesis is observed. An upper limit at 95% confidence level is set on the product of the Higgs boson pair production cross section and branching fraction into gamma gamma mathrm{b}overline{mathrm{b}} . The observed (expected) upper limit is determined to be 0.67 (0.45) fb, which corresponds to 7.7 (5.2) times the standard model prediction. This search has the highest sensitivity to Higgs boson pair production to date. Assuming all other Higgs boson couplings are equal to their values in the standard model, the observed coupling modifiers of the trilinear Higgs boson self-coupling κλ and the coupling between a pair of Higgs bosons and a pair of vector bosons c2V are constrained within the ranges −3.3 < κλ< 8.5 and −1.3 < c2V< 3.5 at 95% confidence level. Constraints on κλ are also set by combining this analysis with a search for single Higgs bosons decaying to two photons, produced in association with top quark-antiquark pairs, and by performing a simultaneous fit of κλ and the top quark Yukawa coupling modifier κt.

Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb\u22121 of sqrt{s}=13 TeV pp collision data with the ATLAS detector

The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of sqrt{s}=13 TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb−1. A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. Stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.

Search for direct top squark pair production in final states with two leptons in sqrt{s} = 13 TeV pp collisions with the ATLAS detector

The results of a search for direct pair production of top squarks in events with two opposite-charge leptons (electrons or muons) are reported, using 36.1~hbox {fb}^{-1} of integrated luminosity from proton–proton collisions at sqrt{s}=13 TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark tilde{t} and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay tilde{t} rightarrow b tilde{chi }_{1}^{pm } into a b-quark and the lightest chargino with tilde{chi }_{1}^{pm } rightarrow W tilde{chi }_{1}^{0}, the decay tilde{t} rightarrow t tilde{chi }_{1}^{0} into an on-shell top quark and the lightest neutralino, the three-body decay tilde{t} rightarrow b W tilde{chi }_{1}^{0} and the four-body decay tilde{t} rightarrow b ell nu tilde{chi }_{1}^{0}. No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the tilde{t} and tilde{chi }_{1}^{0} masses. The results exclude at 95% confidence level tilde{t} masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.

Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in [formula omitted] pp collisions with the ATLAS detector

Motivated by natural SUSY, a search for pair production of the supersymmetric partner of the top quark (stop) in final states with one isolated lepton, jets and missing transverse momentum in s=8 TeVpp collisions using 20.3 fb−1 of data from the ATLAS experiment, is presented. Five different decay scenarios for the stop are considered. As the data are in agreement with predictions from the Standard Model, the measurements are translated into 95% CL upper limits on the masses of the stop and the lightest supersymmetric particle (LSP) in various supersymmetric scenarios. The sensitivity to a limited number of pMSSM models, in which the stop can decay into heavy neutralinos and charginos, is also presented.

Search for direct top squark pair production in final states with two tau leptons in pp collisions at [Formula: see text]TeV with the ATLAS detector.

A search for direct pair production of the supersymmetric partner of the top quark, decaying via a scalar tau to a nearly massless gravitino, has been performed using 20 fb^{-1} of proton–proton collision data at sqrt{s}=8~mathrm{TeV}. The data were collected by the ATLAS experiment at the LHC in 2012. Top squark candidates are searched for in events with either two hadronically decaying tau leptons, one hadronically decaying tau and one light lepton, or two light leptons. No significant excess over the Standard Model expectation is found. Exclusion limits at 95~% confidence level are set as a function of the top squark and scalar tau masses. Depending on the scalar tau mass, ranging from the 87~mathrm{GeV} LEP limit to the top squark mass, lower limits between 490 and 650~mathrm{GeV} are placed on the top squark mass within the model considered.

Search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in s $$ \sqrt{s} $$ = 8 TeV pp collisions with the ATLAS detector

The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton--proton collision data at $\sqrt{s} = 8$ TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of $20$ fb$^{-1}$. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay modes considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a $W$ boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the $W$ bosons or the top quarks are off-shell. Decay modes involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between $210$ and $640$ GeV decaying directly to a top quark and a massless LSP is excluded at $95$ % confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at $95$ % confidence level up to a mass of $500$ GeV for an LSP mass in the range of $100$ to $150$ GeV. Stringent exclusion limits are also derived for all other stop decay modes considered, and model-independent upper limits are set on the visible cross-section for processes beyond the Standard Model.

Search for direct top-squark pair production in final states with two leptons in pp collisions at $ \sqrt{s} $ = 8 TeV with the ATLAS detector

A search is presented for direct top-squark pair production in final states with two leptons (electrons or muons) of opposite charge using 20.3fb-1 of pp collision data at sqrt(s)=8TeV, collected by the ATLAS experiment at the Large Hadron Collider in 2012. No excess over the Standard Model expectation is found. The results are interpreted under the separate assumptions (i) that the top squark decays to a b-quark in addition to an on-shell chargino whose decay occurs via a real or virtual W boson, or (ii) that the top squark decays to a t-quark and the lightest neutralino. A top squark with a mass between 150 GeV and 445 GeV decaying to a b-quark and an on-shell chargino is excluded at 95% confidence level for a top squark mass equal to the chargino mass plus 10 GeV, in the case of a 1 GeV lightest neutralino. Top squarks with masses between 215 (90) GeV and 530 (170) GeV decaying to an on-shell (off-shell) t-quark and a neutralino are excluded at 95% confidence level for a 1 GeV neutralino.

Search for direct top squark pair production in final states with one isolated lepton using 21 fb−1of data collected with the ATLAS detector

Naturalness arguments for weak-scale supersymmetry favour supersymmetric partners of the third generation quarks with masses not too far from those of their Stan- dard Model counterparts. Top or bottom scalar quarks (or squarks) with masses less than a few hundred GeV can give rise to direct pair production rates at the LHC that can be ob- served in the data sample recorded by the ATLAS detector. This proceeding summarises the latest results of a search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in √ s = 8 TeV pp collisions at the LHC, using 20. 7f b −1 of ATLAS data. Two top squark (˜) decay scenarios are considered: the decay to a top quark and a stable undetected neutral particle ( ˜ χ 0 ), and the decay to a bot- tom quark and a chargino, where the chargino decays via an on- or off-shell W boson to the ˜ χ 0 . The data are found to be consistent with Standard Model expectations and have been reinterpreted in terms of various SUSY scenarios.

Search for direct third-generation squark pair production in final states with missing transverse momentum and two b-jets in $ \sqrt{s}=8 $ TeV pp collisions with the ATLAS detector

AbstractThe results of a search for pair production of supersymmetric partners of the Standard Model third-generation quarks are reported. This search uses 20.1 fb−1ofppcollisions at$ \sqrt{s}=8 $TeV collected by the ATLAS experiment at the Large Hadron Collider. The lightest bottom and top squarks ($ {{\widetilde{b}}_1} $and$ {{\widetilde{t}}_1} $respectively) are searched for in a final state with large missing transverse momentum and two jets identified as originating fromb-quarks. No excess of events above the expected level of Standard Model background is found. The results are used to set upper limits on the visible cross section for processes beyond the Standard Model. Exclusion limits at the 95 % confidence level on the masses of the third-generation squarks are derived in phenomenological supersymmetricR-parity-conserving models in which either the bottom or the top squark is the lightest squark. The$ {{\widetilde{b}}_1} $is assumed to decay via$ {{\widetilde{b}}_1}\to b_{{\chi 1}}^{{\sim 0}} $and the$ {{\widetilde{t}}_1} $via$ {{\widetilde{t}}_1}\to b_{{\chi 1}}^{{\sim \pm }} $, with undetectable products of the subsequent decay of the$ _{{\chi 1}}^{{\sim \pm }} $due to the small mass splitting between the$ _{{\chi 1}}^{{\sim \pm }} $and the$ _{{\chi 1}}^{{\sim 0}} $.

Search for light top squark pair production in final states with leptons and b-jets with the ATLAS detector in [formula omitted] proton–proton collisions

The results of a search for pair production of light top squarks are presented, using 4.7 fb−1 of s=7 TeV proton–proton collisions collected with the ATLAS detector at the Large Hadron Collider. This search targets top squarks with masses similar to, or lighter than, the top quark mass. Final states containing exclusively one or two leptons (e,μ), large missing transverse momentum, light-flavour jets and b-jets are used to reconstruct the top squark pair system. Event-based mass scale variables are used to separate the signal from a large tt¯ background. No excess over the Standard Model expectations is found. The results are interpreted in the framework of the Minimal Supersymmetric Standard Model, assuming the top squark decays exclusively to a chargino and a b-quark, while requiring different mass relationships between the Supersymmetric particles in the decay chain. Light top squarks with masses between 123–167 GeV are excluded for neutralino masses around 55 GeV.

Search for direct top squark pair production in final states with one electron or muon using 21 fb−1of ATLAS data

This article presents latest results of the search for top squark pair production in final states with one isolated lepton, jets, and missing transverse momentum in √ s = 8TeV pp collisions using L=21 fb −1 of data recorded with the ATLAS detector at the LHC. Two top squark decay scenarios are considered: (a) to a top quark and a long-lived undetected neutral particle (LSP), (b) to a bottom quark and a chargino, where the chargino decays via an on- or off-shell W boson to the LSP. The analysis also employs a new dedicated shape-fit method to target the challenging parameter region where m(˜ t) is close to the kinematic boundary m(t) +m(LSP).

Searches for direct supersymmetric gaugino and slepton pair production in final states with leptons with the ATLAS detector

A search for direct production of supersymmetric gauginos and sleptons in final states with two and three leptons is presented. The two lepton analysis uses 4.7 fb(-1) of proton-proton collision data at root s = 7 TeV, while the three lepton analysis uses 13 fb(-1) at root s = 8 TeV. All data were recorded by the ATLAS detector at the Large Hadron Collider. The results are interpreted in the phenomenological minimal supersymmetric Standard Model, as well as simplified models. No significant excess above the Standard Model expectation is observed. Limits on the particle masses are placed at the 95% confidence level. In simplified models, chargino masses are excluded up to 580 GeV.

Search for Direct Top Squark Pair Production in Final States with One Isolated Lepton, Jets, and Missing Transverse Momentum ins=7 TeVppCollisions Using4.7 fb−1of ATLAS Data

A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at sqrt[s] = 7 TeV. The measurement is based on 4.7 fb(-1) of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230 GeV and 440 GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400 GeV are excluded for LSP masses up to 125 GeV.

Search for light scalar top-quark pair production in final states with two leptons with the ATLAS detector in $\sqrt{s}=7\ \mathrm{TeV}$ proton–proton collisions

A search is presented for the pair production of light scalar top quarks in sqrt(s) = 7 TeV proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider. This analysis uses the full data sample collected during 2011 that corresponds to a total integrated luminosity of 4.7 fb-1. Light scalar top quarks are searched for in events with two opposite-sign leptons (e, mu), large missing transverse momentum and at least one jet in the final state. No excess over Standard Model expectations is found, and the results are interpreted under the assumption that the light scalar top decays to a b-quark in addition to an on-shell chargino whose decay occurs through a virtual W boson. If the chargino mass is 106 GeV, light scalar top quark masses up to 130 GeV are excluded for neutralino masses below 70 GeV.

Search for top and bottom squarks from gluino pair production in final states with missing transverse energy and at least three b-jets with the ATLAS detector

This letter reports the results of a search for top and bottom squarks from gluino pair production in 4.7 fb^-1 of pp collisions at sqrt(s) = 7 TeV using the ATLAS detector at the LHC. The search is performed in events with large missing transverse momentum and at least three jets identified as originating from a b-quark. Exclusion limits are presented for a variety of gluino-mediated models with gluino masses up to 1 TeV excluded.