A
bstract
A determination of the top-quark mass is presented using 20.2 fb
−
1
of 8 TeV proton-proton collision data produced by the Large Hadron Collider and collected by the ATLAS experiment. The ...normalised differential cross section of top-quark pair production in association with an energetic jet is measured in the lepton+jets final state and unfolded to parton and particle levels. The unfolded distribution at parton level can be described using next-to-leading-order QCD predictions in terms of either the top-quark pole mass or the running mass as defined in the (modified) minimal subtraction scheme. A comparison between the experimental distribution and the theoretical prediction allows the top-quark mass to be extracted in the two schemes. The value obtained for the pole-mass scheme is:
m
t
pole
=
171.1
±
0.4
stat
±
0.9
syst
−
0.3
+
0.7
theo
GeV
The extracted value in the running-mass scheme is:
m
t
m
t
=
162.9
±
0.5
stat
±
1.0
syst
−
1.2
+
2.1
theo
GeV
.
The results for the top-quark mass using the two schemes are consistent, when translated from one scheme to the other.
This paper presents studies of Bose–Einstein correlations (BEC) in proton–proton collisions at a centre-of-mass energy of 13 TeV, using data from the ATLAS detector at the CERN Large Hadron Collider. ...Data were collected in a special low-luminosity configuration with a minimum-bias trigger and a high-multiplicity track trigger, accumulating integrated luminosities of 151
μ
b
-
1
and 8.4 nb
-
1
, respectively. The BEC are measured for pairs of like-sign charged particles, each with
|
η
|
<
2.5
, for two kinematic ranges: the first with particle
p
T
>
100
MeV and the second with particle
p
T
>
500
MeV. The BEC parameters, characterizing the source radius and particle correlation strength, are investigated as functions of charged-particle multiplicity (up to 300) and average transverse momentum of the pair (up to 1.5 GeV). The double-differential dependence on charged-particle multiplicity and average transverse momentum of the pair is also studied. The BEC radius is found to be independent of the charged-particle multiplicity for high charged-particle multiplicity (above 100), confirming a previous observation at lower energy. This saturation occurs independent of the transverse momentum of the pair.
Lanthanum carbide is considered as a potential target for generation of radioactive ion beams by means of the ISOL (Isotope Separation On Line) technique. This method requires the use of porous ...refractories as targets, in order to work in extreme conditions (more than 2000°C in high vacuum) to enhance the release of the generated isotopes. Several techniques can be used to generate open interconnected porosity in lanthanum carbide. The use of polymeric (nylon and polypropylene) fibers as sacrificial fillers was successfully tested in a previous work. Here, the effect of the fibers length is reported and discussed in terms of porosity and permeability.
This article presents the results of two studies of Higgs boson properties using the
W
W
∗
(
→
e
ν
μ
ν
)
j
j
final state, based on a dataset corresponding to
36.1
fb
-
1
of
s
=
13
TeV proton–proton ...collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study targets Higgs boson production via gluon–gluon fusion and constrains the CP properties of the effective Higgs–gluon interaction. Using angular distributions and the overall rate, a value of
tan
(
α
)
=
0.0
±
0.4
(
stat
.
)
±
0.3
(
syst
.
)
is obtained for the tangent of the mixing angle for CP-even and CP-odd contributions. The second study exploits the vector-boson fusion production mechanism to probe the Higgs boson couplings to longitudinally and transversely polarised
W
and
Z
bosons in both the production and the decay of the Higgs boson; these couplings have not been directly constrained previously. The polarisation-dependent coupling-strength scale factors are defined as the ratios of the measured polarisation-dependent coupling strengths to those predicted by the Standard Model, and are determined using rate and kinematic information to be
a
L
=
0
.
91
-
0.18
+
0.10
(stat.)
-
0.17
+
0.09
(syst.) and
a
T
=
1.2
±
0.4
(stat.)
-
0.3
+
0.2
(syst.). These coupling strengths are translated into pseudo-observables, resulting in
κ
VV
=
0
.
91
-
0.18
+
0.10
(stat.)
-
0.17
+
0.09
(syst.) and
ϵ
VV
=
0
.
13
-
0.20
+
0.28
(stat.)
-
0.10
+
0.08
(syst.). All results are consistent with the Standard Model predictions.
A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb-1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, ...recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH+ → tbtb, is explored in the H+ mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b-tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass; they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and $$ {M}_h^{125} $$ M h 125 scenarios.
A search for charged Higgs bosons decaying into W±W± or W±Z bosons is performed, involving experimental signatures with two leptons of the same charge, or three or four leptons with a variety of ...charge combinations, missing transverse momentum and jets. A data sample of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb-1. The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged H±± bosons, or the associated production of a doubly charged H±± boson and a singly charged H± boson. No significant deviations from the Standard Model predictions are observed. H±± bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively.
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.
The production cross-section of a top quark in association with a W boson is measured using proton–proton collisions at √s = 8TeV. The dataset corresponds to an integrated luminosity of 20.2 fb–1, ...and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant tt¯ background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured cross-section is σtW = 26 ± 7pb, in good agreement with the Standard Model expectation.
A measurement of the B$_s^0$→J/ψϕ decay parameters using 80.5 fb-1 of integrated luminosity collected with the ATLAS detector from 13 Te proton–proton collisions at the LHC is presented. ...The measured parameters include the CP-violating phase ϕs, the width difference Δ Γs between the B$_s^0$ meson mass eigenstates and the average decay width Γs. The values measured for the physical parameters are combined with those from 19.2fb-1 of 7 and 8 Te data, leading to the following: ϕs=-0.087±0.036(stat.)±0.021(syst.)radΔΓs=0.0657±0.0043(stat.)±0.0037(syst.)ps-1Γs=0.6703±0.0014(stat.)±0.0018(syst.)ps-1Results for ϕs and Δ Γs are also presented as 68% confidence level contours in the ϕs–Δ Γs plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. ϕs and Δ Γs measurements are in agreement with the Standard Model predictions.
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