A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb
of
... TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of mass-degenerate sleptons.
A
bstract
This paper presents a search for direct electroweak gaugino or gluino pair production with a chargino nearly mass-degenerate with a stable neutralino. It is based on an integrated ...luminosity of 36.1 fb
−1
of
pp
collisions at
s
=
13
TeV collected by the ATLAS experiment at the LHC. The final state of interest is a disappearing track accompanied by at least one jet with high transverse momentum from initial-state radiation or by four jets from the gluino decay chain. The use of short track segments reconstructed from the innermost tracking layers significantly improves the sensitivity to short chargino lifetimes. The results are found to be consistent with Standard Model predictions. Exclusion limits are set at 95% confidence level on the mass of charginos and gluinos for different chargino lifetimes. For a pure wino with a lifetime of about 0.2 ns, chargino masses up to 460 GeV are excluded. For the strong production channel, gluino masses up to 1.65 TeV are excluded assuming a chargino mass of 460 GeV and lifetime of 0.2 ns.
A
bstract
A search for new phenomena in events with two same-charge leptons or three leptons and jets identified as originating from
b
-quarks in a data sample of 36.1 fb
−1
of
pp
collisions at
s
=
...13
TeV recorded by the ATLAS detector at the Large Hadron Collider is reported. No significant excess is found and limits are set on vector-like quark, four-top-quark, and same-sign top-quark pair production. The observed (expected) 95% CL mass limits for a vector-like
T
- and
B
-quark singlet are
m
T
> 0.98 (0.99) TeV and
m
B
> 1.00 (1.01) TeV respectively. Limits on the production of the vector-like
T
5/3
-quark are also derived considering both pair and single production; in the former case the lower limit on the mass of the
T
5/3
-quark is (expected to be) 1.19 (1.21) TeV. The Standard Model four-top-quark production cross-section upper limit is (expected to be) 69 (29) fb. Constraints are also set on exotic four-top-quark production models. Finally, limits are set on same-sign top-quark pair production. The upper limit on
uu
→
tt
production is (expected to be) 89 (59) fb for a mediator mass of 1 TeV, and a dark-matter interpretation is also derived, excluding a mediator of 3 TeV with a dark-sector coupling of 1.0 and a coupling to ordinary matter above 0.31.
A
bstract
A search for charged Higgs bosons heavier than the top quark and decaying via
H
±
→
tb
is presented. The data analysed corresponds to 36.1 fb
−1
of
pp
collisions at
s
=
13
TeV and was ...recorded with the ATLAS detector at the LHC in 2015 and 2016. The production of a charged Higgs boson in association with a top quark and a bottom quark,
pp
→
tbH
±
, is explored in the mass range from
m
H
± = 200 to 2000 GeV using multi-jet final states with one or two electrons or muons. Events are categorised according to the multiplicity of jets and how likely these are to have originated from hadronisation of a bottom quark. Multivariate 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, which range from 2.9 pb at
m
H
± = 200 GeV to 0.070 pb at
m
H
± = 2000 GeV. The results are interpreted in two benchmark scenarios of the Minimal Supersymmetric Standard Model.
A
bstract
A search for pair production of a scalar partner of the top quark in events with four or more jets plus missing transverse momentum is presented. An analysis of 36.1 fb
−1
of
s
=
13
TeV ...proton-proton collisions collected using the ATLAS detector at the LHC yields no significant excess over the expected Standard Model background. To interpret the results a simplified supersymmetric model is used where the top squark is assumed to decay via
t
˜
1
→
t
∗
χ
˜
1
0
and
t
˜
1
→
b
χ
˜
1
±
→
b
W
∗
χ
˜
1
0
, where χ
1
0
(χ
1
±
) denotes the lightest neutralino (chargino). Exclusion limits are placed in terms of the top-squark and neutralino masses. Assuming a branching ratio of 100% to
t
χ
˜
1
0
, top-squark masses in the range 450–1000 GeV are excluded for
χ
˜
1
0
masses below 160 GeV. In the case where
m
t
˜
1
∼
m
t
+
m
χ
˜
1
0
, top-squark masses in the range 235–590 GeV are excluded.
A
bstract
The coupling properties of the Higgs boson are studied in the four-lepton (
e
,
μ
) decay channel using 36.1 fb
−1
of
pp
collision data from the LHC at a centre-of-mass energy of 13 TeV ...collected by the ATLAS detector. Cross sections are measured for the main production modes in several exclusive regions of the Higgs boson production phase space and are interpreted in terms of coupling modifiers. The inclusive cross section times branching ratio for
H
→
ZZ
∗
decay and for a Higgs boson absolute rapidity below 2.5 is measured to be 1. 73
− 0.23
+ 0.24
(stat.)
− 0.08
+ 0.10
(exp.) ± 0.04(th.) pb compared to the Standard Model prediction of 1
.
34±0
.
09 pb. In addition, the tensor structure of the Higgs boson couplings is studied using an effective Lagrangian approach for the description of interactions beyond the Standard Model. Constraints are placed on the non-Standard-Model CP-even and CP-odd couplings to
Z
bosons and on the CP-odd coupling to gluons.
Abstract
Core-collapse supernovae are among the most magnificent events in the observable universe. They produce many of the chemical elements necessary for life to exist and their remnants—neutron ...stars and black holes—are interesting astrophysical objects in their own right. However, despite millennia of observations and almost a century of astrophysical study, the explosion mechanism of core-collapse supernovae is not yet well understood. Hyper-Kamiokande is a next-generation neutrino detector that will be able to observe the neutrino flux from the next galactic core-collapse supernova in unprecedented detail. We focus on the first 500 ms of the neutrino burst, corresponding to the accretion phase, and use a newly-developed, high-precision supernova event generator to simulate Hyper-Kamiokande's response to five different supernova models. We show that Hyper-Kamiokande will be able to distinguish between these models with high accuracy for a supernova at a distance of up to 100 kpc. Once the next galactic supernova happens, this ability will be a powerful tool for guiding simulations toward a precise reproduction of the explosion mechanism observed in nature.
A
bstract
Inclusive jet and dijet cross-sections are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The measurement uses a dataset with an integrated luminosity of 3.2 fb
...−1
recorded in 2015 with the ATLAS detector at the Large Hadron Collider. Jets are identified using the anti-
k
t
algorithm with a radius parameter value of
R
= 0
.
4. The inclusive jet cross-sections are measured double-differentially as a function of the jet transverse momentum, covering the range from 100 GeV to 3.5 TeV, and the absolute jet rapidity up to |
y
| = 3. The double-differential dijet production cross-sections are presented as a function of the dijet mass, covering the range from 300 GeV to 9 TeV, and the half absolute rapidity separation between the two leading jets within |
y
|
<
3,
y
∗
, up to
y
∗
= 3. Next-to-leading-order, and next-to-next-to-leading-order for the inclusive jet measurement, perturbative QCD calculations corrected for non-perturbative and electroweak effects are compared to the measured cross-sections.
A
bstract
Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb
−1
s
= 13 TeV
pp
collision data collected by the ATLAS detector at the LHC during ...2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also
s
= 8 TeV
pp
collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy).
The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton–proton collision data with a centre-of-mass energy of
s
=
7
TeV ...corresponding to an integrated luminosity of
4.7
fb
-
1
. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-
k
t
algorithm with distance parameters
R
=
0.4
or
R
=
0.6
, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a
Z
boson, for
20
≤
p
T
jet
<
1000
GeV
and pseudorapidities
|
η
|
<
4.5
. The effect of multiple proton–proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1 % is found in the central calorimeter region (
|
η
|
<
1.2
) for jets with
55
≤
p
T
jet
<
500
GeV
. For central jets at lower
p
T
, the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton–proton collisions and test-beam data, which also provide the estimate for
p
T
jet
>
1
TeV. The calibration of forward jets is derived from dijet
p
T
balance measurements. The resulting uncertainty reaches its largest value of 6 % for low-
p
T
jets at
|
η
|
=
4.5
. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5–3 %.
PDF
