This paper reports on a search for heavy resonances decaying into
WW
,
ZZ
or
WZ
using proton–proton collision data at a centre-of-mass energy of
s
=
13
TeV. The data, corresponding to an integrated ...luminosity of 139
fb
1
, were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one
W
or
Z
boson decays leptonically, and the other
W
boson or
Z
boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300–5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. Production through gluon–gluon fusion, Drell–Yan or vector-boson fusion are considered, depending on the assumed model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for scalar particles decaying via narrow resonances into two photons in the mass range 65-600 GeV is performed using 20.3 fb(-1) of √s 8 TeV pp collision data collected with the ATLAS ...detector at the Large Hadron Collider. The recently discovered Higgs boson is treated as a background. No significant evidence for an additional signal is observed. The results are presented as limits at the 95% confidence level on the production cross section of a scalar boson times branching ratio into two photons, in a fiducial volume where the reconstruction efficiency is approximately independent of the event topology. The upper limits set extend over a considerably wider mass range than previous searches.
A
bstract
A search for dark matter (DM) particles produced in association with a hadronically decaying vector boson is performed using
pp
collision data at a centre-of-mass energy of
s
=
13
TeV ...corresponding to an integrated luminosity of 36.1 fb
−1
, recorded by the ATLAS detector at the Large Hadron Collider. This analysis improves on previous searches for processes with hadronic decays of
W
and
Z
bosons in association with large missing transverse momentum (mono-
W/Z
searches) due to the larger dataset and further optimization of the event selection and signal region definitions. In addition to the mono-
W/Z
search, the as yet unexplored hypothesis of a new vector boson
Z
′ produced in association with dark matter is considered (mono-
Z
′ search). No significant excess over the Standard Model prediction is observed. The results of the mono-
W/Z
search are interpreted in terms of limits on invisible Higgs boson decays into dark matter particles, constraints on the parameter space of the simplified vector-mediator model and generic upper limits on the visible cross sections for
W/Z
+DM production. The results of the mono-
Z
′ search are shown in the framework of several simplified-model scenarios involving DM production in association with the
Z
′ boson.
A
bstract
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
bstract
A search for heavy right-handed Majorana or Dirac neutrinos
N
R
and heavy right-handed gauge bosons
W
R
is performed in events with a pair of energetic electrons or muons, with the same or ...opposite electric charge, and two energetic jets. The events are selected from
pp
collision data with an integrated luminosity of 36.1 fb
−1
collected by the ATLAS detector at
s
=
13
TeV. No significant deviations from the Standard Model are observed. The results are interpreted within the theoretical framework of a left-right symmetric model and lower limits are set on masses in the heavy right-handed
W
boson and neutrino mass plane. The excluded region extends to
m
R
R
=
4.7
TeV for both Majorana and Dirac
N
R
neutrinos.
A search for weakly interacting massive dark-matter particles produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and missing transverse ...momentum are considered. The analysis uses
36.1
fb
-
1
of proton–proton collision data recorded by the ATLAS experiment at
s
=
13
TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are interpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour-neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross-section of 300 times the predicted rate for mediators with masses between 10 and
50
GeV
and assuming a dark-matter mass of
1
GeV
and unitary coupling. Constraints on colour-charged scalar simplified models are also presented. Assuming a dark-matter particle mass of
35
GeV
, mediator particles with mass below
1.1
TeV
are excluded for couplings yielding a dark-matter relic density consistent with measurements.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in ...proton-proton collision data at a centre-of-mass energy of ... corresponding to an integrated luminosity of 38 pb^sup -1^. Jets are reconstructed with the anti-k ^sub t^ algorithm with distance parameters R=0.4 or R=0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta p ^sub T^greater than or equal to20 GeV and pseudorapidities |eta|<4.5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2.5 % in the central calorimeter region (|eta|<0.8) for jets with 60less than or equal top ^sub T^<800 GeV, and is maximally 14 % for p ^sub T^<30 GeV in the most forward region 3.2less than or equal to|eta|<4.5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon p ^sub T^, the sum of the transverse momenta of tracks associated to the jet, or a system of low-p ^sub T^ jets recoiling against a high-p ^sub T^ jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-p ^sub T^ jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum ...are reported, using 139 fb
−
1
of integrated luminosity from proton-proton collisions at
s
= 13 TeV, collected by the ATLAS detector at the Large Hadron Collider during Run 2 (2015–2018). This search considers the pair production of top squarks and is sensitive across a wide range of mass differences between the top squark and the lightest neutralino. Additionally, spin-0 mediator dark-matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at 95% confidence level. The results exclude top squark masses up to about 1 TeV, and masses of the lightest neutralino up to about 500 GeV. Limits on dark-matter production are set for scalar (pseudoscalar) mediator masses up to about 250 (300) GeV.
A
bstract
A search for a chargino-neutralino pair decaying via the 125 GeV Higgs boson into photons is presented. The study is based on the data collected between 2015 and 2018 with the ATLAS ...detector at the LHC, corresponding to an integrated luminosity of 139 fb
−
1
of
pp
collisions at a centre-of-mass energy of 13 TeV. No significant excess over the expected background is observed. Upper limits at 95% confidence level for a massless
χ
˜
1
0
are set on several electroweakino production cross-sections and the visible cross-section for beyond the Standard Model processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 310 GeV in
m
χ
˜
1
±
/
χ
˜
2
0
, where
m
χ
˜
1
0
= 0
.
5 GeV, are set. Limits at 95% confidence level are also set on the
χ
˜
1
±
χ
˜
2
0
cross-section in the mass plane of
m
χ
˜
1
±
/
χ
˜
2
0
and
m
χ
˜
1
0
, and on scenarios with gravitino as the lightest supersymmetric particle. Upper limits at the 95% confidence-level are set on the higgsino production cross-section. Higgsino masses below 380 GeV are excluded for the case of the higgsino fully decaying into a Higgs boson and a gravitino.
A search for a heavy neutral Higgs boson,
A
, decaying into a
Z
boson and another heavy Higgs boson,
H
, is performed using a data sample corresponding to an integrated luminosity of 139 fb
-
1
from ...proton–proton collisions at
s
=
13
TeV
recorded by the ATLAS detector at the LHC. The search considers the
Z
boson decaying into electrons or muons and the
H
boson into a pair of
b
-quarks or
W
bosons. The mass range considered is 230–800
GeV
for the
A
boson and 130–700
GeV
for the
H
boson. The data are in good agreement with the background predicted by the Standard Model, and therefore 95% confidence-level upper limits for
σ
×
B
(
A
→
Z
H
)
×
B
(
H
→
b
b
or
H
→
W
W
)
are set. The upper limits are in the range 0.0062–0.380 pb for the
H
→
b
b
channel and in the range 0.023–8.9 pb for the
H
→
W
W
channel. An interpretation of the results in the context of two-Higgs-doublet models is also given.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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