Showing papers by "Brad Abbott published in 2020"
TL;DR: Combined measurements of Higgs boson production cross sections and branching fractions arc are presented in this paper, based on the analyses of the Higgs particle decay modes H -> gamma gamma, ZZ...
Abstract: Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ ...
505 citations
TL;DR: In this article, a search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented, based on 139.fb$^{-1}$ of proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider at
Abstract: A search for the electroweak production of charginos and sleptons decaying into final states with two electrons or muons is presented. The analysis is based on 139 fb$^{-1}$ of proton–proton collisions recorded by the ATLAS detector at the Large Hadron Collider at $\sqrt{s}=13$ $\text {TeV}$. Three R-parity-conserving scenarios where the lightest neutralino is the lightest supersymmetric particle are considered: the production of chargino pairs with decays via either W bosons or sleptons, and the direct production of slepton pairs. The analysis is optimised for the first of these scenarios, but the results are also interpreted in the others. No significant deviations from the Standard Model expectations are observed and limits at 95% confidence level are set on the masses of relevant supersymmetric particles in each of the scenarios. For a massless lightest neutralino, masses up to 420 $\text {Ge}\text {V}$ are excluded for the production of the lightest-chargino pairs assuming W-boson-mediated decays and up to 1 $\text {TeV}$ for slepton-mediated decays, whereas for slepton-pair production masses up to 700 $\text {Ge}\text {V}$ are excluded assuming three generations of mass-degenerate sleptons.
272 citations
TL;DR: In this paper, the trigger algorithms and selection were optimized to control the rates while retaining a high efficiency for physics analyses at the ATLAS experiment to cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), and a similar increase in the number of interactions per beam-crossing to about 60.
Abstract: Electron and photon triggers covering transverse energies from 5 GeV to several TeV are essential for the ATLAS experiment to record signals for a wide variety of physics: from Standard Model processes to searches for new phenomena in both proton–proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to 2.1×1034cm-2s-1, and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton–proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31 GeV, and rises to 96% at 60 GeV; the trigger efficiency of a 25 GeV leg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30 GeV. For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5 GeV above the corresponding trigger threshold.
180 citations
TL;DR: A search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb^{-1} of proton-proton collisions at sqrt[s]=13TeV recorded with the ATLAS detector.
Abstract: A search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb^{-1} of proton-proton collisions at sqrt[s]=13 TeV recorded with the ATLAS detector. The search for heavy resonances is performed over the mass range 0.2-2.5 TeV for the τ^{+}τ^{-} decay with at least one τ-lepton decaying into final states with hadrons. The data are in good agreement with the background prediction of the standard model. In the M_{h}^{125} scenario of the minimal supersymmetric standard model, values of tanβ>8 and tanβ>21 are excluded at the 95% confidence level for neutral Higgs boson masses of 1.0 and 1.5 TeV, respectively, where tanβ is the ratio of the vacuum expectation values of the two Higgs doublets.
178 citations
TL;DR: In this article, the results of searches for the electroweak production of supersymmetric particles in models with compressed mass spectra were presented, using 139 fb(-1) of root s = 13 TeV proton-protector.
Abstract: This paper presents results of searches for the electroweak production of supersymmetric particles in models with compressed mass spectra. The searches use 139 fb(-1) of root s = 13 TeV proton-prot ...
151 citations
Aix-Marseille University1, University of Oklahoma2, University of Massachusetts Amherst3, University of Pavia4, University of Göttingen5, Royal Holloway, University of London6, University of Toronto7, Niels Bohr Institute8, University of Sussex9, Tel Aviv University10, Technion – Israel Institute of Technology11, Argonne National Laboratory12, King's College London13, International Centre for Theoretical Physics14, University of Tokyo15, University of Mainz16, University of Savoy17, AGH University of Science and Technology18, Northern Illinois University19, Ludwig Maximilian University of Munich20, Boğaziçi University21, University of Geneva22, Rutherford Appleton Laboratory23, Santa Cruz Institute for Particle Physics24, Université Paris-Saclay25, University of Auvergne26, Radboud University Nijmegen27, Alexandru Ioan Cuza University28, University of Granada29, Spanish National Research Council30, Joint Institute for Nuclear Research31, McGill University32, Lawrence Berkeley National Laboratory33, University of Rome Tor Vergata34, Kyoto University35, Russian Academy of Sciences36, University of Bologna37, University of Victoria38, CERN39, National Technical University of Athens40, University of Amsterdam41, Czech Technical University in Prague42, Tomsk State University43, University of Washington44, University of Oregon45, University of Birmingham46, University of Copenhagen47, National University of La Plata48, University of Glasgow49, Autonomous University of Madrid50, Federal University of Rio de Janeiro51, University of Oxford52, Brandeis University53, University of Michigan54, Iowa State University55, University of Sheffield56, University of Texas at Austin57, Heidelberg University58, University of Bern59, University of Milan60, Columbia University61, Novosibirsk State University62, Budker Institute of Nuclear Physics63, Oklahoma State University–Stillwater64, University of California, Irvine65, KEK66, Chinese Academy of Sciences67
TL;DR: In this article, a search for new resonances decaying into a pair of jets is reported using the dataset of proton-proton collisions recorded at s = 13 TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018.
Abstract: A search for new resonances decaying into a pair of jets is reported using the dataset of proton-proton collisions recorded at s = 13 TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the Standard Model background. In addition to an inclusive dijet search, events with jets identified as containing b-hadrons are examined specifically. No significant excess of events above the smoothly falling background spectra is observed. The results are used to set cross-section upper limits at 95% confidence level on a range of new physics scenarios. Model-independent limits on Gaussian-shaped signals are also reported. The analysis looking at jets containing b-hadrons benefits from improvements in the jet flavour identification at high transverse momentum, which increases its sensitivity relative to the previous analysis beyond that expected from the higher integrated luminosity.
138 citations
University of Oklahoma1, University of Massachusetts Amherst2, CERN3, University of Göttingen4, Royal Holloway, University of London5, University of Toronto6, University of Copenhagen7, University of Sussex8, Tel Aviv University9, University of Oslo10, Federal University of Rio de Janeiro11, McGill University12, Technion – Israel Institute of Technology13, United States Department of Energy14, International Centre for Theoretical Physics15, University of Tokyo16, University of Mainz17, University of Victoria18, AGH University of Science and Technology19, Northern Illinois University20, Ludwig Maximilian University of Munich21, Boğaziçi University22, University of Geneva23, Rutherford Appleton Laboratory24, University of California, Santa Cruz25
TL;DR: The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz.
Abstract: The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015–2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at √s=13 TeV certified for physics analysis.
131 citations
TL;DR: In this paper, a search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented, where leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels.
Abstract: A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in pp collisions at $ \sqrt{s} $ = 13 TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb$^{−1}$, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of c- or b-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass.[graphic not available: see fulltext]
101 citations
TL;DR: A search for narrowly resonant new physics using a machine-learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection and results are complementary to the dedicated searches for the case that B and C are standard model bosons.
Abstract: This Letter describes a search for narrowly resonant new physics using a machine-learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search A→BC, for m_{A}∼O(TeV), m_{B},m_{C}∼O(100 GeV) and B, C are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full run 2 sqrt[s]=13 TeV pp collision dataset of 139 fb^{-1} recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV. Cross-section limits for narrow-width A, B, and C particles vary with m_{A}, m_{B}, and m_{C}. For example, when m_{A}=3 TeV and m_{B}≳200 GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on m_{C}. For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search. These results are complementary to the dedicated searches for the case that B and C are standard model bosons.
89 citations
TL;DR: In this article, a search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell bosons is presented for a three-lepton final state.
Abstract: A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell
W
and
Z
bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of
√
s
=
13
TeV
were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of
139
fb
−
1
. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV.
80 citations
TL;DR: In this article, the performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015-2018 at the Large Hadron Collider.
Abstract: The performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015-2018 at the Large Hadron Collider. It is prima ...
TL;DR: In this article, a search for the direct production of the supersymmetric partners of staus (staus) in final states with two hadronically decaying leptons is presented.
Abstract: A search for the direct production of the supersymmetric partners of
τ
-leptons (staus) in final states with two hadronically decaying
τ
-leptons is presented. The analysis uses a dataset of
p
p
collisions corresponding to an integrated luminosity of
139
fb
−
1
, recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of 13 TeV. No significant deviation from the expected Standard Model background is observed. Limits are derived in scenarios of direct production of stau pairs with each stau decaying into the stable lightest neutralino and one
τ
-lepton in simplified models where the two stau mass eigenstates are degenerate. Stau masses from 120 GeV to 390 GeV are excluded at 95% confidence level for a massless lightest neutralino.
TL;DR: A study of the charge conjugation and parity (CP) properties of the interaction between the Higgs boson and top quarks is presented.
Abstract: A study of the charge conjugation and parity (CP) properties of the interaction between the Higgs boson and top quarks is presented. Higgs bosons are identified via the diphoton decay channel (H→γγ), and their production in association with a top quark pair (tt[over ¯]H) or single top quark (tH) is studied. The analysis uses 139 fb^{-1} of proton-proton collision data recorded at a center-of-mass energy of sqrt[s]=13 TeV with the ATLAS detector at the Large Hadron Collider. Assuming a CP-even coupling, the tt[over ¯]H process is observed with a significance of 5.2 standard deviations. The measured cross section times H→γγ branching ratio is 1.64_{-0.36}^{+0.38}(stat)_{-0.14}^{+0.17}(sys) fb, and the measured rate for tt[over ¯]H is 1.43_{-0.31}^{+0.33}(stat)_{-0.15}^{+0.21}(sys) times the Standard Model expectation. The tH production process is not observed and an upper limit on its rate of 12 times the Standard Model expectation is set. A CP-mixing angle greater (less) than 43 (-43)° is excluded at 95% confidence level.
TL;DR: The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate.
Abstract: The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate ...
TL;DR: In this article, the authors present direct searches for lepton flavour violation in Higgs boson decays, H→eτ and H→μτ, performed with the ATLAS detector at the LHC.
TL;DR: In this article, a search for heavy neutral Higgs bosons produced in association with one or two b-quarks and decaying to bquark pairs is presented using 27.8 fb(-1) of root s=13 TeV proton-proton collision data.
Abstract: A search for heavy neutral Higgs bosons produced in association with one or two b-quarks and decaying to b-quark pairs is presented using 27.8 fb(-1) of root s=13 TeV proton-proton collision data r ...
TL;DR: The results of a search for electroweakino pair production were given in this paper, in which the chargino ((chi) over tilde (+/-)(1)) decays into a W boson and the...
Abstract: The results of a search for electroweakino pair production pp -> (chi) over tilde (+/-)(1) (chi) over tilde (0)(2) in which the chargino ((chi) over tilde (+/-)(1)) decays into a W boson and the ...
TL;DR: In this paper, the first search for non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV was presented. But the search was restricted to the case of dielectric dielectrons.
Abstract: A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton fi ...
TL;DR: In this article, a search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge.
Abstract: A search for supersymmetric partners of gluons and quarks is presented, involving signatures with jets and either two isolated leptons (electrons or muons) with the same electric charge, or at leas ...
TL;DR: In this paper, a search for long-lived particles decaying into an oppositely charged lepton pair, mu mu, ee, or e mu, is presented using 32.8 fb(-1) of pp collision data collected at root s = 13 TeV by the ATLAS.
TL;DR: In this article, a study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of > 98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.
Abstract: The factor of four increase in the LHC luminosity, from 0.5 × 1034 cm−2s−1 to 2.0 × 1034cm−2s−1, and the corresponding increase in pile-up collisions during the 2015–2018 data-taking period, presented a challenge for the ATLAS trigger, particularly for those algorithms that select events with missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of > 98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.
TL;DR: A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic t (t) over bar plus missing transverse momen was conducted in this paper.
Abstract: A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic t (t) over bar plus missing transverse momen
TL;DR: In this paper, a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions is presented.
Abstract: Several models of physics beyond the Standard Model predict the existence of dark photons, light neutral particles decaying into collimated leptons or light hadrons. This paper presents a search for long-lived dark photons produced from the decay of a Higgs boson or a heavy scalar boson and decaying into displaced collimated Standard Model fermions. The search uses data corresponding to an integrated luminosity of 36.1 fb- 1 collected in proton–proton collisions at s=13 Te recorded in 2015–2016 with the ATLAS detector at the Large Hadron Collider. The observed number of events is consistent with the expected background, and limits on the production cross section times branching fraction as a function of the proper decay length of the dark photon are reported. A cross section times branching fraction above 4 pb is excluded for a Higgs boson decaying into two dark photons for dark-photon decay lengths between 1.5 mm and 307 mm.
University of Oklahoma1, University of Massachusetts Amherst2, CERN3, University of Göttingen4, Royal Holloway, University of London5, University of Toronto6, University of Copenhagen7, University of Sussex8, Tel Aviv University9, Federal University of Rio de Janeiro10, McGill University11, Andrés Bello National University12, Technion – Israel Institute of Technology13, Politehnica University of Bucharest14, United States Department of Energy15, International Centre for Theoretical Physics16, University of Tokyo17, University of Mainz18, University of Victoria19, AGH University of Science and Technology20, Northern Illinois University21, Ludwig Maximilian University of Munich22, Boğaziçi University23, University of Geneva24, Rutherford Appleton Laboratory25, University of California, Santa Cruz26
TL;DR: In this paper, the authors measured jet substructure quantities using jets groomed with the soft-drop grooming procedure in dijet events from 32.9 fb-1 of pp collisions collected with the ATLAS detector at s=13 -TeV.
Abstract: Jet substructure quantities are measured using jets groomed with the soft-drop grooming procedure in dijet events from 32.9 fb-1 of pp collisions collected with the ATLAS detector at s=13 TeV. These observables are sensitive to a wide range of QCD phenomena. Some observables, such as the jet mass and opening angle between the two subjets which pass the soft-drop condition, can be described by a high-order (resummed) series in the strong coupling constant αS. Other observables, such as the momentum sharing between the two subjets, are nearly independent of αS. These observables can be constructed using all interacting particles or using only charged particles reconstructed in the inner tracking detectors. Track-based versions of these observables are not collinear safe, but are measured more precisely, and universal nonperturbative functions can absorb the collinear singularities. The unfolded data are directly compared with QCD calculations and hadron-level Monte Carlo simulations. The measurements are performed in different pseudorapidity regions, which are then used to extract quark and gluon jet shapes using the predicted quark and gluon fractions in each region. All of the parton shower and analytical calculations provide an excellent description of the data in most regions of phase space.
Aix-Marseille University1, University of Oklahoma2, University of Massachusetts Amherst3, University of Pavia4, University of Göttingen5, Royal Holloway, University of London6, University of Toronto7, University of Copenhagen8, University of Sussex9, Tel Aviv University10, University of Oslo11, University of Bergen12, McGill University13, Technion – Israel Institute of Technology14, Argonne National Laboratory15, International Centre for Theoretical Physics16, University of Tokyo17, University of Mainz18, University of Victoria19, AGH University of Science and Technology20, Northern Illinois University21, Ludwig Maximilian University of Munich22, Boğaziçi University23, University of Geneva24, Rutherford Appleton Laboratory25, Santa Cruz Institute for Particle Physics26
TL;DR: In this article, the authors measured the top quark pair production cross-section with an opposite-charge pair and b-tagged jets at the LHC and derived the double ratio of the cross-sections at different energies.
Abstract: The inclusive top quark pair (
$$t\bar{t}$$
) production cross-section $$\sigma _{t\bar{t}}$$
has been measured in proton–proton collisions at $$\sqrt{s}=13\,\text {TeV}$$
, using 36.1 fb
$$^{-1}$$
of data collected in 2015–2016 by the ATLAS experiment at the LHC. Using events with an opposite-charge $$e\mu $$
pair and b-tagged jets, the cross-section is measured to be: $$\begin{aligned} \sigma _{t\bar{t}} = 826.4 \pm 3.6\,\mathrm {(stat)}\ \pm 11.5\,\mathrm {(syst)}\ \pm 15.7\,\mathrm {(lumi)}\ \pm 1.9\,\mathrm {(beam)}\,\mathrm {pb}, \end{aligned}$$
where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 2.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. It is used to determine the top quark pole mass via the dependence of the predicted cross-section on $$m_t^{\mathrm{pole}}$$
, giving $$m_t^{\mathrm{pole}}=173.1^{+2.0}_{-2.1}\,\text {GeV}$$
. It is also combined with measurements at $$\sqrt{s}=7\,\text {TeV}$$
and $$\sqrt{s}=8\,\text {TeV}$$
to derive ratios and double ratios of $$t\bar{t}$$
and Z cross-sections at different energies. The same event sample is used to measure absolute and normalised differential cross-sections as functions of single-lepton and dilepton kinematic variables, and the results are compared with predictions from various Monte Carlo event generators.
TL;DR: In this article, a search for the Z gamma decay of the Higgs boson, with Z boson decays into pairs of electrons or muons, was presented, using proton-proton collision data at root s = 13 TeV corresponding...
University of Oklahoma1, University of Massachusetts Amherst2, CERN3, University of Göttingen4, Royal Holloway, University of London5, University of Toronto6, University of Copenhagen7, University of Sussex8, Tel Aviv University9, Federal University of Rio de Janeiro10, McGill University11, Technion – Israel Institute of Technology12, United States Department of Energy13, International Centre for Theoretical Physics14, University of Tokyo15, University of Mainz16, University of Victoria17, AGH University of Science and Technology18, Northern Illinois University19, Nova Southeastern University20, Andrés Bello National University21, Ludwig Maximilian University of Munich22, Boğaziçi University23, University of Geneva24, Rutherford Appleton Laboratory25, University of California, Santa Cruz26
TL;DR: In this paper, a search for pair production of long-lived neutral particles using proton-proton collision data was presented, where limits were placed on scalar boson propagators with masses from 125 GeV to 1000 GeV decaying into pairs of longlived hidden-sector scalars with masses between 8 GeV and 400 GeV.
Abstract: A search is presented for pair production of long-lived neutral particles using
33
fb
−
1
of
√
s
=
13
TeV
proton–proton collision data, collected during 2016 by the ATLAS detector at the LHC. This search focuses on a topology in which one long-lived particle decays in the ATLAS inner detector and the other decays in the muon spectrometer. Special techniques are employed to reconstruct the displaced tracks and vertices in the inner detector and in the muon spectrometer. One event is observed that passes the full event selection, which is consistent with the estimated background. Limits are placed on scalar boson propagators with masses from 125 GeV to 1000 GeV decaying into pairs of long-lived hidden-sector scalars with masses from 8 GeV to 400 GeV. The limits placed on several low-mass scalars extend previous exclusion limits in the range of proper lifetimes
c
τ
from 5 cm to 1 m.
TL;DR: In this paper, a measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider.
Abstract: A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the tt¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
TL;DR: In this article, a test of CP invariance in Higgs boson production via vector-boson fusion is performed in the H →======ττ decay channel using the Optimal Observable method.
TL;DR: A search for Higgs boson pair production via vector-boson fusion (VBF) in the bbbb final state is carried out with the ATLAS experiment using 126 fb(-1) of proton-proton collision data delivered a...
Abstract: A search for Higgs boson pair production via vector-boson fusion (VBF) in the bbbb final state is carried out with the ATLAS experiment using 126 fb(-1) of proton- proton collision data delivered a ...