6,029 research outputs found
Search for top quark decays t → qH with H → γγ using the ATLAS detector
No full textA search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type (c, u) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb-1 at √ = 7TeV and 20.3fb-1 at √ = 8TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to qH and the other decays to bW. Both the hadronic and the leptonic decay modes of the W boson are used. No significant signal is observed and an upper limit is set on the t → qH branching ratio of 0.79 at the 95% confidence level. The corresponding limit on the tqH coupling combination λtcH 2 + λtuH 2 is 0.17
Filtering efficiency model that includes the statistical randomness of non-woven fiber layers in facemasks
No full textFacemasks have become important tools to fight virus spread during the recent COVID-19 pandemic, but their effectiveness is still under debate. We present a computational model to predict the filtering efficiency of an N95-facemask, consisting of three non-woven fiber layers with different particle capturing mechanisms. Parameters such as fiber layer thickness, diameter distribution, and packing density are used to construct two-dimensional cross-sectional geometries. An essential and novel element is that the polydisperse fibers are positioned randomly within a simulation domain, and that the simulation is repeated with different random configurations. This strategy is thought to give a more realistic view of practical facemasks compared to existing analytical models that mostly assume homogeneous fiber beds of monodisperse fibers. The incompressible Navier-Stokes and continuity equations are used to solve the velocity field for various droplet-laden air inflow velocities. Droplet diameters are ranging from 10 nm to 1.0 μm, which covers the size range from the SARS-CoV-2 virus to the large virus-laden airborne droplets. Air inflow velocities varying between 0.1 m·s−1 to 10 m·s−1 are considered, which are typically encountered during expiratory events like breathing, talking, and coughing. The presented model elucidates the different capturing efficiencies (i.e., mechanical and electrostatic filtering) of droplets as a function of their diameter and air inflow velocity. Simulation results are compared to analytical models and particularly compare well with experimental results from literature. Our numerical approach will be helpful in finding new directions for anti-viral facemask optimization
Search for a light charged Higgs boson in t → H±b decays, with H± → cs, in pp collisions at √s = 13 TeV with the ATLAS detector
No full textA search for a light charged Higgs boson produced in decays of the top quark, t → H±b with H± → cs,
is presented. This search targets the production of top-quark
pairs tt
¯ → WbH±b, with W → ν ( = e, μ), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search
exploits b-quark and c-quark identification techniques as well
as multivariate methods to suppress the dominant tt
¯ background. The data analysed correspond to 140 fb−1 of pp
collisions at √s = 13 TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected)
95% confidence-level upper limits on the branching fraction
B(t → H±b), assuming B(t → W b) + B(t → H±(→
cs)b) = 1.0, are set between 0.066% (0.077%) and 3.6%
(2.3%) for a charged Higgs boson with a mass between 60
and 168 GeV
CP properties of Higgs boson interactions with top quarks in the tt¯H and tH processes using H→γγ with the ATLAS detector
No full textA study of the charge conjugation and parity (
C
P
) properties of the interaction between the Higgs boson and top quarks is presented. Higgs bosons are identified via the diphoton decay channel (
H
→
γ
γ
), and their production in association with a top quark pair (
t
¯
t
H
) or single top quark (
t
H
) is studied. The analysis uses
139
fb
−
1
of proton–proton collision data recorded at a center-of-mass energy of
√
s
=
13
TeV
with the ATLAS detector at the Large Hadron Collider. Assuming a
C
P
-even coupling, the
t
¯
t
H
process is observed with a significance of 5.2 standard deviations. The measured cross section times
H
→
γ
γ
branching ratio is
1.64
+
0.38
−
0.36
(
stat
)
+
0.17
−
0.14
(
sys
)
fb
, and the measured rate for
t
¯
t
H
is
1.43
+
0.33
−
0.31
(
stat
)
+
0.21
−
0.15
(
sys
)
times the Standard Model expectation. The
t
H
production process is not observed and an upper limit on its rate of 12 times the Standard Model expectation is set. A
C
P
-mixing angle greater (less) than 43
(
−
43
)
°
is excluded at 95% confidence level
Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton plus jets final state in proton-proton collisions at √s=13 TeV with the ATLAS detector
No full textA search for a charged Higgs boson, H ±, produced in top-quark decays, t → H ± b, is presented. The search targets H ± decays into a bottom and a charm quark, H ± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy s = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb −1. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions B (t → H ± b) × B(H ± → cb) for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs. [Figure not available: see fulltext.]
Measurement of the and production cross sections in multilepton final states using 3.2 fb of collisions at = 13 TeV with the ATLAS detector
No full textSee paper for full list of authors - 22 pages plus author list + cover page (40 pages total), 8 figures, 5 tables. Submitted to Eur. Phys. J. C. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2015-22/International audienceA measurement of the and production cross sections in final states with either two same-charge muons, or three or four leptons (electrons or muons) is presented. The analysis uses a data sample of proton-proton collisions at TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015, corresponding to a total integrated luminosity of 3.2 fb. The inclusive cross sections are extracted using likelihood fits to signal and control regions, resulting in pb and pb, in agreement with the Standard Model predictions
Search for a light charged Higgs boson in the decay channel H+→cs¯ in tt¯ events using pp collisions at s√=7 TeV with the ATLAS detector
No full textA search for a charged Higgs boson (H +) in tt¯ decays is presented, where one of the top quarks decays via t→H + b, followed by H +→ two jets ( cs¯ ). The other top quark decays to Wb, where the W boson then decays into a lepton (e/μ) and a neutrino. The data were recorded in pp collisions at s√=7 TeV by the ATLAS detector at the LHC in 2011, and correspond to an integrated luminosity of 4.7 fb−1. With no observation of a signal, 95 % confidence level (CL) upper limits are set on the decay branching ratio of top quarks to charged Higgs bosons varying between 5 % and 1 % for H + masses between 90 GeV and 150 GeV, assuming B(H+→cs¯)=100 %
Search for a light charged Higgs boson in decays, with , in the lepton+jets final state in proton-proton collisions at TeV with the ATLAS detector
No full textA search for a charged Higgs boson, , produced in top-quark decays, , is presented. The search targets decays into a bottom and a charm quark, . The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing -hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy TeV between 2015 and 2018 with the ATLAS detector at CERN's Large Hadron Collider, amounting to an integrated luminosity of 139 fb. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.A search for a charged Higgs boson, H, produced in top-quark decays, t → Hb, is presented. The search targets H decays into a bottom and a charm quark, H → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions (t → Hb) × B(H → cb) for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.[graphic not available: see fulltext]A search for a charged Higgs boson, , produced in top-quark decays, , is presented. The search targets decays into a bottom and a charm quark, . The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing -hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy TeV between 2015 and 2018 with the ATLAS detector at CERN's Large Hadron Collider, amounting to an integrated luminosity of 139 fb. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs
Search for Heavy Higgs Bosons A/H Decaying to a Top Quark Pair in pp Collisions at root s=8 TeV with the ATLAS Detector
No full textA search for heavy pseudoscalar (A) and scalar (H) Higgs bosons decaying into a top quark pair (t¯t)
has been performed with 20.3 fb−1 of proton-proton collision data collected by the ATLAS experiment
at the Large Hadron Collider at a center-of-mass energy ffiffi
s p ¼ 8 TeV. Interference effects between the
signal process and standard model t¯t production, which are expected to distort the signal shape from a
single peak to a peak-dip structure, are taken into account. No significant deviation from the standard
model prediction is observed in the t¯t invariant mass spectrum in final states with an electron or muon,
large missing transverse momentum, and at least four jets. The results are interpreted within the context
of a type-II two-Higgs-doublet model. Exclusion limits on the signal strength are derived as a function
of the mass mA=H and the ratio of the vacuum expectation values of the two Higgs fields, tan β, for
mA=H > 500 GeV
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