This paper presents the observation of four-top-quark (
t
t
¯
t
t
¯
) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140
fb
-
1
at a ...centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured
t
t
¯
t
t
¯
signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The
t
t
¯
t
t
¯
production cross section is measured to be
22
.
5
-
5.5
+
6.6
fb, consistent with the SM prediction of
12.0
±
2.4
fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect
t
t
¯
t
t
¯
production.
A
bstract
Measurements of the production cross-sections of the Standard Model (SM) Higgs boson (
H
) decaying into a pair of
τ
-leptons are presented. The measurements use data collected with the ...ATLAS detector from
pp
collisions produced at the Large Hadron Collider at a centre-of-mass energy of
s
= 13 TeV, corresponding to an integrated luminosity of 139 fb
−
1
. Leptonic (
τ
→
ℓν
ℓ
ν
τ
) and hadronic (
τ
→ hadrons
ν
τ
) decays of the
τ
-lepton are considered. All measurements account for the branching ratio of
H → ττ
and are performed with a requirement
|y
H
| <
2
.
5, where
y
H
is the true Higgs boson rapidity. The cross-section of the
pp → H → ττ
process is measured to be 2
.
94
±
0.21
stat
−
0.32
+
0.37
(syst) pb, in agreement with the SM prediction of 3
.
17
±
0
.
09 pb. Inclusive cross-sections are determined separately for the four dominant production modes: 2
.
65
±
0.41
stat
−
0.67
+
0.91
(syst) pb for gluon-gluon fusion, 0
.
197
±
0.028
stat
−
0.026
+
0.032
(syst) pb for vector-boson fusion, 0
.
115
±
0.058
stat
−
0.040
+
0.042
(syst) pb for vector-boson associated production, and 0
.
033
±
0.031
stat
−
0.017
+
0.022
(syst) pb for top-quark pair associated production. Measurements in exclusive regions of the phase space, using the simplified template cross-section framework, are also performed. All results are in agreement with the SM predictions.
A
bstract
The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a
b
-quark ...pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb
−
1
, were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of
s
= 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is
0.35
−
0.34
+
0.36
. This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
This paper presents the muon momentum calibration and performance studies for the ATLAS detector based on the
pp
collisions data sample produced at
s
= 13 TeV at the LHC during Run 2 and ...corresponding to an integrated luminosity of 139
fb
-
1
. An innovative approach is used to correct for potential charge-dependent momentum biases related to the knowledge of the detector geometry, using the
Z
→
μ
+
μ
-
resonance. The muon momentum scale and resolution are measured using samples of
J
/
ψ
→
μ
+
μ
-
and
Z
→
μ
+
μ
-
events. A calibration procedure is defined and applied to simulated data to match the performance measured in real data. The calibration is validated using an independent sample of
Υ
→
μ
+
μ
-
events. At the
Z
(
J
/
ψ
)
peak, the momentum scale is measured with an uncertainty at the 0.05% (0.1%) level, and the resolution is measured with an uncertainty at the 1.5% (2%) level. The charge-dependent bias is removed with a dedicated in situ correction for momenta up to 450 GeV with a precision better than 0.03
TeV
-
1
.
A
bstract
Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample ...corresponding to 139 fb
−
1
of proton-proton collisions at a centre-of-mass energy of
s
= 13 TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers
Q
. The strong coupling constant
α
s
is extracted as a function of
Q
, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of
α
s
m
Z
=
0.1175
±
0.0006
exp
.
−
0.0017
+
0.0034
theo
.
, while the global fit to the asymmetry distributions yields
α
s
m
Z
=
0.1185
±
0.0009
exp
.
−
0.0012
+
0.0025
theo
.
.
Constraining the spatial and thermal structure of the gaseous component of circumstellar disks is crucial for understanding star and planet formation. Models predict that the NeII line at 12.81 mu m ...detected in young stellar objects (YSOs) with Spitzer traces disk gas and its response to high-energy radiation, but such NeII emission may also originate in shocks within powerful outflows. To distinguish between these potential origins for mid-infrared NeII emission and to constrain disk models, we observed 32 YSOs using the high-resolution (R ~ 30,000) mid-infrared spectrograph VISIR at the Very Large Telescope. We detected the 12.81 mu m NeII line in 12 objects, tripling the number of detections of this line in YSOs with high spatial and spectral resolution spectrographs. We obtain the following main results. (1) In Class I objects the NeII emission observed from Spitzer is mainly due to gas at a distance of more than 20-40 AU from the star, where neon is, most likely, ionized by shocks due to protostellar outflows. (2) In transition and pre-transition disks, most of the emission is confined to the inner disk, within 20-40 AU from the central star. (3) Detailed analysis of line profiles indicates that, in transition and pre-transition disks, the line is slightly blueshifted (2-12 km s super(-1)) with respect to the stellar velocity, and the line width is directly correlated with the disk inclination, as expected if the emission is due to a disk wind. (4) Models of EUV/X-ray-irradiated disks reproduce well the observed relation between the line width and the disk inclination, but underestimate the blueshift of the line.
Although amateur sports have become increasingly competitive within recent decades, there are as yet few studies on the possible health risks for athletes. This study aims to determine the impact of ...ultra‐endurance exercise‐induced stress on the number and function of circulating hematopoietic progenitor cells (CPCs) and hematological, inflammatory, clinical, metabolic, and stress parameters in moderately trained amateur athletes. Following ultra‐endurance exercise, there were significant increases in leukocytes, platelets, interleukin‐6, fibrinogen, tissue enzymes, blood lactate, serum cortisol, and matrix metalloproteinase‐9. Ultra‐endurance exercise did not influence the number of CPCs but resulted in a highly significant decline of CPC functionality after the competition. Furthermore, Epstein‐Barr virus was seen to be reactivated in one of seven athletes. The link between exercise‐induced stress and decline of CPC functionality is supported by a negative correlation between cortisol and CPC function. We conclude that ultra‐endurance exercise induces metabolic stress and an inflammatory response that affects not only mature hematopoietic cells but also the function of the immature hematopoietic stem and progenitor cell fraction, which make up the immune system and provide for regeneration.
We present contemporaneous XMM–Newton X-ray and ground-based optical/near-IR spectroscopic observations of the nearby (D ≈ 42 pc), low-mass (mid-M) binary system TWA 30A and 30B. The components of ...this wide (separation ∼3400 au) binary are notable for their nearly edge-on disc viewing geometries, high levels of variability, and evidence for collimated stellar outflows. We obtained XMM–Newton X-ray observations of TWA 30A and 30B in 2011 June and July, accompanied (respectively) by Infrared Telescope Facility SpeX (near-IR) and VLT XSHOOTER (visible/near-IR) spectroscopy obtained within ∼20 h of the X-ray observations. TWA 30A was detected in both XMM–Newton observations at relatively faint intrinsic X-ray luminosities (L
X ∼ 8 × 1027 erg s−1) compared to stars of similar mass and age. The intrinsic (0.15–2.0 keV) X-ray luminosities measured in 2011 had decreased by a factor 20–100 relative to a 1990 (ROSAT) X-ray detection. TWA 30B was not detected, and we infer an upper limit on its X-ray Luminosity of L
X ≲ 3.0 × 1027 erg s−1. We measured a decrease in visual extinction towards TWA 30A (from AV
≈ 14.9 to AV
≈ 4.7) between the two 2011 observing epochs, and we find evidence for a corresponding significant decrease in X-ray absorbing column (N
H). The apparent correlated change in A
V and N
H is suggestive of variable obscuration of the stellar photosphere by disc material composed of both gas and dust. However, in both observations, the inferred N
H to A
V ratio is lower than that typical of the interstellar medium, suggesting that the disc is either depleted of gas or is deficient in metals in the gas phase.
A
bstract
A model-independent search for new physics leading to final states containing a Higgs boson, with a mass of 125.09 GeV, decaying to a pair of photons is performed with 139 fb
−
1
of
s
= 13 ...TeV
pp
collision data recorded by the ATLAS detector at the Large Hadron Collider at CERN. This search examines 22 final states categorized by the objects that are produced in association with the Higgs boson. These objects include isolated electrons or muons, hadronically decaying
τ
-leptons, additional photons, missing transverse momentum, and hadronic jets, as well as jets that are tagged as containing a
b
-hadron. No significant excesses above Standard Model expectations are observed and limits on the production cross section at 95% confidence level are set. Detector efficiencies are reported for all 22 signal regions, which can be used to convert detector-level cross-section limits reported in this paper to particle-level cross-section constraints.
Higgs boson production via gluon–gluon fusion is measured in the
W
W
∗
→
e
ν
μ
ν
decay channel. The dataset utilized corresponds to an integrated luminosity of 139 fb
-
1
collected by the ATLAS ...detector from
s
=
13
TeV proton–proton collisions delivered by the Large Hadron Collider between 2015 and 2018. Differential cross sections are measured in a fiducial phase space restricted to the production of at most one additional jet. The results are consistent with Standard Model expectations, derived using different Monte Carlo generators.
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