A
bstract
A search is conducted for a beyond-the-Standard-Model boson using events where a Higgs boson with mass 125 GeV decays to four leptons (ℓ =
e
or
μ
). This decay is presumed to occur via an ...intermediate state which contains one or two on-shell, promptly decaying bosons:
H
→
ZX/XX
→ 4ℓ, where
X
is a new vector boson
Z
d
or pseudoscalar
a
with mass between 1 and 60 GeV. The search uses
pp
collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 36.1 fb
−1
at a centre-of-mass energy
s
=
13
TeV. No significant excess of events above Standard Model background predictions is observed; therefore, upper limits at 95% confidence level are set on modelindependent fiducial cross-sections, and on the Higgs boson decay branching ratios to vector and pseudoscalar bosons in two benchmark models.
A search for excited states of the Bc(±) meson is performed using 4.9 fb(-1) of 7 TeV and 19.2 fb(-1) of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is ...observed through its hadronic transition to the ground state, with the latter detected in the decay Bc(±)→J/ψπ(±). The state appears in the m(Bc(±)π(+)π(-))-m(Bc(±))-2m(π(±)) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842±4±5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the Bc(±) meson, Bc(±)(2S).
A
bstract
The results of a search for new phenomena in final states with
b
-jets and missing transverse momentum using 139 fb
−
1
of proton-proton data collected at a centre-of-mass energy
s
= 13 TeV ...by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously.
The paper presents a measurement of the Standard Model Higgs Boson decaying to
b
-quark pairs in the vector boson fusion (VBF) production mode. A sample corresponding to 126
fb
-
1
of
s
=
13
TeV
...proton–proton collision data, collected with the ATLAS experiment at the Large Hadron Collider, is analyzed utilizing an adversarial neural network for event classification. The signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model for VBF Higgs production, is measured to be
0
.
95
-
0.36
+
0.38
, corresponding to an observed (expected) significance of 2.6 (2.8) standard deviations from the background only hypothesis. The results are additionally combined with an analysis of Higgs bosons decaying to
b
-quarks, produced via VBF in association with a photon.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The reconstruction and calibration algorithms used to calculate missing transverse momentum (
E
T
miss
) with the ATLAS detector exploit energy deposits in the calorimeter and tracks reconstructed in ...the inner detector as well as the muon spectrometer. Various strategies are used to suppress effects arising from additional proton–proton interactions, called pileup, concurrent with the hard-scatter processes. Tracking information is used to distinguish contributions from the pileup interactions using their vertex separation along the beam axis. The performance of the
E
T
miss
reconstruction algorithms, especially with respect to the amount of pileup, is evaluated using data collected in proton–proton collisions at a centre-of-mass energy of 8
TeV
during 2012, and results are shown for a data sample corresponding to an integrated luminosity of
20.3
fb
-
1
. The simulation and modelling of
E
T
miss
in events containing a
Z
boson decaying to two charged leptons (electrons or muons) or a
W
boson decaying to a charged lepton and a neutrino are compared to data. The acceptance for different event topologies, with and without high transverse momentum neutrinos, is shown for a range of threshold criteria for
E
T
miss
, and estimates of the systematic uncertainties in the
E
T
miss
measurements are presented.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Particle identification using the DELPHI RICH detectors Battaglia, Marco; M. Kluit, Peter
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/1999, Letnik:
433, Številka:
1
Journal Article
Recenzirano
A Cherenkov ring reconstruction algorithm has been developed to determine the mean Cherenkov angle. It is used to study the response of the DELPHI RICH detectors and to identify particles. Results ...from the analysis of real and simulated data samples are presented. Finally, two different techniques for particle identification and their applications to physics analyses are described.
A
bstract
The results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for ...pair production of vector-like top quarks in the
Z
(→νν)
t
+
X
decay channel. LHC
pp
collision data at a centre-of-mass energy of
s
=
13
TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb
−1
. No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like
T
quark pair as a function of the
T
quark mass are derived. The observed (expected) 95% CL lower limits on the
T
mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure
Zt
decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.
This paper reviews and extends searches for the direct pair production of the scalar supersymmetric partners of the top and bottom quarks in proton–proton collisions collected by the ATLAS ...collaboration during the LHC Run 1. Most of the analyses use 20
fb
-
1
of collisions at a centre-of-mass energy of
s
=
8
TeV, although in some case an additional
4.7
fb
-
1
of collision data at
s
=
7
TeV are used. New analyses are introduced to improve the sensitivity to specific regions of the model parameter space. Since no evidence of third-generation squarks is found, exclusion limits are derived by combining several analyses and are presented in both a simplified model framework, assuming simple decay chains, as well as within the context of more elaborate phenomenological supersymmetric models.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
A
bstract
This paper reports searches for heavy resonances decaying into
ZZ
or
ZW
using data from proton-proton collisions at a centre-of-mass energy of
s
=
13
TeV. The data, corresponding to an ...integrated luminosity of 36.1 fb
−1
, were recorded with the ATLAS detector in 2015 and 2016 at the Large Hadron Collider. The searches are performed in final states in which one
Z
boson decays into either a pair of light charged leptons (electrons and muons) or a pair of neutrinos, and the associated
W
boson or the other
Z
boson decays hadronically. No evidence of the production of heavy resonances is observed. Upper bounds on the production cross sections of heavy resonances times their decay branching ratios to
ZZ
or
ZW
are derived in the mass range 300-5000GeV within the context of Standard Model extensions with additional Higgs bosons, a heavy vector triplet or warped extra dimensions. Production through gluon-gluon fusion, Drell-Yan or vector-boson fusion are considered, depending on the assumed model.
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