A search is reported for excited $τ$-leptons and leptoquarks in events with two hadronically decaying $τ$-leptons and two or more jets. The search uses proton-proton ($pp$) collision data at ...$\sqrt{s}$ = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015–2018. The total integrated luminosity is 139 fb-1. The excited $τ$-lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary $τ$-lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a $τ$-lepton. No excess over the background prediction is observed. Excited $τ$-leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Λ set to 10 TeV. At the extreme limit of model validity where Λ is set equal to the excited $τ$-lepton mass, excited $τ$-leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a $τ$-lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.
A
bstract
Searches for electroweak production of wino-like chargino pairs,
χ
~
1
+
χ
~
1
−
, and of wino-like chargino and next-to-lightest neutralino,
χ
~
1
±
χ
~
2
0
, are presented. The models ...explored assume that the charginos decay into a
W
boson and the lightest neutralino,
χ
~
1
±
→
W
±
χ
~
1
0
. The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to
χ
~
1
0
and either a
Z
or a Higgs boson,
χ
~
2
0
→
Z
χ
~
1
0
or
h
χ
~
1
0
. The searches exploit the presence of a single isolated lepton and missing transverse momentum from the
W
boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying
Z
or
W
bosons or from the Higgs boson decaying into a pair of
b
-quarks. The searches use 139 fb
−
1
of
s
= 13 TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless
χ
~
1
0
in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless
χ
~
1
0
for
χ
~
2
0
→
Z
χ
~
1
0
. For decays through an on-shell Higgs boson and for mass-splitting between
χ
~
1
±
/
χ
~
2
0
and
χ
~
1
0
as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200–260 GeV and 280–470 GeV compared to previous ATLAS constraints.
A
bstract
A search is performed for a heavy particle decaying into different-flavour, dilepton final states, using 139 fb
−
1
of proton-proton collision data at
s
= 13 TeV collected in 2015–2018 by ...the ATLAS detector at the Large Hadron Collider. Final states with electrons, muons and hadronically decaying tau leptons are considered (
eμ
,
eτ
or
μτ
). No significant excess over the Standard Model predictions is observed. Upper limits on the production cross-section are set as a function of the mass of a
Z
′ boson, a supersymmetric
τ
-sneutrino, and a quantum black-hole. The observed 95% CL lower mass limits obtained on a typical benchmark model
Z
′ boson are 5.0 TeV (e
μ
), 4.0 TeV (e
τ
), and 3.9 TeV (
μτ
), respectively.
A measurement of the mass of the Higgs boson combining the H→ZZ∗→4ℓ and H→γγ decay channels is presented. The result is based on 140 fb−1 of proton-proton collision data collected by the ATLAS ...detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11 GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
A search for a new pseudoscalar a-boson produced in events with a top-quark pair, where the a-boson decays into a pair of muons, is performed using √ s =13 TeV pp collision data collected with the ...ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb −1 . The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons eμμ and μμμ . No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathit%7Bpp%7D%5Crightarrow%5Cmathit%7B%5Cbar%7Bt%7Dta%7D" data-classname="equation" /> and <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cmathit%7Bpp%7D%5Crightarrow%5Cmathit%7Bt%5Cbar%7Bt%7D%7D" data-classname="equation" /> with t → H ± b , H ± → W ± a , where a → μμ , in the mass ranges 15 GeV< m a <72 GeV and 120 GeV≤ m H ± ≤160 GeV.
This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Zγ pair in association with two jets. The analysis uses 140 fb−1 of LHC ...proton–proton collision data taken at s=13 TeV recorded by the ATLAS detector during the years 2015–2018. Events with a Z boson candidate decaying into either an e+e− or μ+μ− pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and by using the information about the centrality of the system and is measured with an observed and expected significance well above five standard deviations. The fiducial pp→Zγjj cross-section for the electroweak production is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be 16.8−1.8+2.0 fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions.
A search for Majorana neutrinos in same-sign WW scattering events is presented. The analysis uses $\sqrt{s}=13$ TeV proton–proton collision data with an integrated luminosity of 140 fb-1 recorded ...during 2015–2018 by the ATLAS detector at the Large Hadron Collider. The analysis targets final states including exactly two same-sign muons and at least two hadronic jets well separated in rapidity. The modelling of the main backgrounds, from Standard Model same-sign WW scattering and WZ production, is constrained with data in dedicated signal-depleted control regions. The distribution of the transverse momentum of the second-hardest muon is used to search for signals originating from a heavy Majorana neutrino with a mass between 50 GeV and 20 TeV. No significant excess is observed over the background expectation. The results are interpreted in a benchmark scenario of the Phenomenological Type-I Seesaw model. In addition, the sensitivity to the Weinberg operator is investigated. Upper limits at the 95% confidence level are placed on the squared muon-neutrino–heavy-neutrino mass-mixing matrix element |VμN|2 as a function of the heavy Majorana neutrino’s mass mN, and on the effective μμ Majorana neutrino mass |mμμ|.
A
bstract
A search for physics beyond the Standard Model inducing periodic signals in the dielectron and diphoton invariant mass spectra is presented using 139 fb
−
1
of
s
= 13 TeV
pp
collision data ...collected by the ATLAS experiment at the LHC. Novel search techniques based on continuous wavelet transforms are used to infer the frequency of periodic signals from the invariant mass spectra and neural network classifiers are used to enhance the sensitivity to periodic resonances. In the absence of a signal, exclusion limits are placed at the 95% confidence level in the two-dimensional parameter space of the clockwork gravity model. Model-independent searches for deviations from the background-only hypothesis are also performed.
This paper presents the observation of four-top-quark ($t$$\overline{t}$$t$$\overline{t}$) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity ...of 140 fb-1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured $t$$\overline{t}$$t$$\overline{t}$ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The $t$$\overline{t}$$t$$\overline{t}$ production cross section is measured to be ${22.5}^{+6.6}_{-5.5}$, consistent with the SM prediction of 12.0 ± 2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect $t$$\overline{t}$$t$$\overline{t}$ production.
In this chapter, we aimed at further characterizing the functional neuroanatomy of the human rapid eye movement (REM) sleep at the population level. We carried out a meta-analysis of a large dataset ...of positron emission tomography (PET) scans acquired during wakefulness, slow wave sleep and REM sleep, and focused especially on the brain areas in which the activity diminishes during REM sleep. Results show that quiescent regions are confined to the inferior and middle frontal cortex and to the inferior parietal lobule. Providing a plausible explanation for some of the features of dream reports, these findings may help in refining the concepts, which try to account for human cognition during REM sleep. In particular, we discuss the significance of these results to explain the alteration in executive processes, episodic memory retrieval and self representation during REM sleep dreaming as well as the incorporation of external stimuli into the dream narrative.
