This paper presents for the first time a precise measurement of the production properties of the
Z
boson in the full phase space of the decay leptons. This is in contrast to the many previous ...precise unfolded measurements performed in the fiducial phase space of the decay leptons. The measurement is obtained from proton–proton collision data collected by the ATLAS experiment in 2012 at
s
=
8
TeV at the LHC and corresponding to an integrated luminosity of 20.2 fb
-
1
. The results, based on a total of 15.3 million
Z
-boson decays to electron and muon pairs, extend and improve a previous measurement of the full set of angular coefficients describing
Z
-boson decay. The double-differential cross-section distributions in
Z
-boson transverse momentum
p
T
and rapidity
y
are measured in the pole region, defined as
80
<
m
ℓ
ℓ
<
100
GeV, over the range
|
y
|
<
3.6
. The total uncertainty of the normalised cross-section measurements in the peak region of the
p
T
distribution is dominated by statistical uncertainties over the full range and increases as a function of rapidity from 0.5–1.0% for
|
y
|
<
2.0
to
2
-
7
%
at higher rapidities. The results for the rapidity-dependent transverse momentum distributions are compared to state-of-the-art QCD predictions, which combine in the best cases approximate N
4
LL resummation with N
3
LO fixed-order perturbative calculations. The differential rapidity distributions integrated over
p
T
are even more precise, with accuracies from 0.2–0.3% for
|
y
|
<
2.0
to 0.4–0.9% at higher rapidities, and are compared to fixed-order QCD predictions using the most recent parton distribution functions. The agreement between data and predictions is quite good in most cases.
This Letter reports the observation of WZγ production and a measurement of its cross section using 140.1±1.2 fb^{-1} of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by ...the ATLAS detector at the Large Hadron Collider. The WZγ production cross section, with both the W and Z bosons decaying leptonically, pp→WZγ→ℓ^{'}^{±}νℓ^{+}ℓ^{-}γ (ℓ^{(^{'})}=e, μ), is measured in a fiducial phase-space region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01±0.30(stat)±0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50±0.06 fb. The observed significance of the WZγ signal is 6.3σ, compared with an expected significance of 5.0σ.
A
bstract
A search for nonresonant Higgs boson pair production in the
b
b
¯
γγ
final state is performed using 140 fb
−
1
of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by ...the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this final state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (
H
) boson self-coupling modifier
κ
λ
but also of the quartic
HHVV
(
V
=
W
,
Z
) coupling modifier
κ
2
V
. No significant excess above the expected background from Standard Model processes is observed. An observed upper limit
μ
HH
< 4.0 is set at 95% confidence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confidence intervals for the coupling modifiers are
−
1.4 <
κ
λ
< 6.9 and −0.5 <
κ
2
V
< 2.7, assuming all other Higgs boson couplings except the one under study are fixed to the Standard Model predictions. The results are interpreted in the Standard Model effective field theory and Higgs effective field theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions.
The inclusive Higgs boson production cross-section is measured in the di-photon and the
Z
Z
∗
→
4
ℓ
decay channels using 31.4 and 29.0 fb
-
1
of
pp
collision data respectively, collected with the ...ATLAS detector at a centre-of-mass energy of
s
=
13.6
TeV
. To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are
σ
fid
,
γ
γ
=
76
-
13
+
14
fb, and
σ
fid
,
4
ℓ
=
2.80
±
0.74
fb, in agreement with the corresponding Standard Model predictions of
67.6
±
3.7
fb and
3.67
±
0.19
fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of
σ
(
p
p
→
H
)
=
67
-
11
+
12
pb and
46
±
12
pb at 13.6
TeV
from the di-photon and
Z
Z
∗
→
4
ℓ
measurements respectively. The two measurements are combined into a total cross-section measurement of
σ
(
p
p
→
H
)
=
58.2
±
8.7
pb, to be compared with the Standard Model prediction of
σ
(
p
p
→
H
)
SM
=
59.9
±
2.6
pb.
The inclusive top-quark-pair production cross section rrtt and its ratio to the Z-boson production cross section have been measured in proton-proton collisions at root s = 13.6 TeV, using 29 fb-1 of ...data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be rrtt = 850 +/- 3(stat.) +/- 18(syst.) +/- 20(lumi.) pb. The ratio of the ttand the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e- and mu+mu- events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ttcross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, Rtt/Z = 1.145 +/- 0.003(stat.) +/- 0.021(syst.) +/- 0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
This Letter reports the observation of WZγ production and a measurement of its cross section using 140.1±1.2 fb −1 of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by ...the ATLAS detector at the Large Hadron Collider. The WZγ production cross section, with both the W and Z bosons decaying leptonically, pp → WZγ → ℓ ′ ± νℓ + ℓ − γ ( ℓ (′) = e , μ ), is measured in a fiducial phase-space region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01±0.30(stat)±0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50±0.06 fb. The observed significance of the WZγ signal is 6.3 σ , compared with an expected significance of 5.0 σ .
A measurement of the mass of the Higgs boson combining the Formula Presented and Formula Presented decay channels is presented. The result is based on Formula Presented of proton-proton collision ...data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of Formula Presented. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
Measurements of the differential production cross-sections of prompt and non-prompt
J
/
ψ
and
ψ
(
2
S
)
mesons with transverse momenta between 8 and 360 GeV and rapidity in the range
|
y
|
<
2
are ...reported. Furthermore, measurements of the non-prompt fractions of
J
/
ψ
and
ψ
(
2
S
)
, and the prompt and non-prompt
ψ
(
2
S
)
-to-
J
/
ψ
production ratios, are presented. The analysis is performed using 140 fb
-
1
of
s
=
13
TeV
pp
collision data recorded by the ATLAS detector at the LHC during the years 2015–2018.
The inclusive top-quark-pair production cross section σ$t\overline{t}$ and its ratio to the Z-boson production cross section have been measured in proton–proton collisions at $\sqrt{s}$ = 13.6 TeV, ...using 29 fb—1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be σ$t\overline{t}$ = 850± 3(stat.) ± 18(syst.) ± 20(lumi.) pb. The ratio of the $t\overline{t}$ and the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e— and μ+μ— events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the $t\overline{t}$ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, R$t\overline{t}/Z$ = 1.145 ± 0.003(stat.) ± 0.021(syst.)±0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
Semi-visible jets, with a significant contribution to the event's missing transverse momentum, can arise in strongly interacting dark sectors. This results in an event topology where one of the jets ...can be aligned with the direction of the missing transverse momentum. The first search for semi-visible jets produced via a t-channel mediator exchange is presented. The analysis uses proton-proton collisions with an integrated luminosity of 139 fb—1 and a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during the Run 2 of the LHC. No excess over Standard Model predictions is observed. Assuming a coupling strength of unity between the mediator, a Standard Model quark and a dark quark, mediator masses up to 2.7 TeV are excluded at the 95% confidence level. Upper limits on the coupling strength are also derived.
