A measurement of the mass of the
W
boson is presented based on proton–proton collision data recorded in 2011 at a centre-of-mass energy of 7 TeV with the ATLAS detector at the LHC, and corresponding ...to
4.6
fb
-
1
of integrated luminosity. The selected data sample consists of
7.8
×
10
6
candidates in the
W
→
μ
ν
channel and
5.9
×
10
6
candidates in the
W
→
e
ν
channel. The
W
-boson mass is obtained from template fits to the reconstructed distributions of the charged lepton transverse momentum and of the
W
boson transverse mass in the electron and muon decay channels, yielding
m
W
=
80370
±
7
(
stat.
)
±
11
(
exp. syst.
)
±
14
(
mod. syst.
)
MeV
=
80370
±
19
MeV
,
where the first uncertainty is statistical, the second corresponds to the experimental systematic uncertainty, and the third to the physics-modelling systematic uncertainty. A measurement of the mass difference between the
W
+
and
W
-
bosons yields
m
W
+
-
m
W
-
=
-
29
±
28
MeV.
The performance of the missing transverse momentum (
E
T
miss
) reconstruction with the ATLAS detector is evaluated using data collected in proton–proton collisions at the LHC at a centre-of-mass ...energy of 13 TeV in 2015. To reconstruct
E
T
miss
, fully calibrated electrons, muons, photons, hadronically decaying
τ
-leptons
, and jets reconstructed from calorimeter energy deposits and charged-particle tracks are used. These are combined with the soft hadronic activity measured by reconstructed charged-particle tracks not associated with the hard objects. Possible double counting of contributions from reconstructed charged-particle tracks from the inner detector, energy deposits in the calorimeter, and reconstructed muons from the muon spectrometer is avoided by applying a signal ambiguity resolution procedure which rejects already used signals when combining the various
E
T
miss
contributions. The individual terms as well as the overall reconstructed
E
T
miss
are evaluated with various performance metrics for scale (linearity), resolution, and sensitivity to the data-taking conditions. The method developed to determine the systematic uncertainties of the
E
T
miss
scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of
3.2
fb
-
1
.
The luminosity determination for the ATLAS detector at the LHC during
pp
collisions at
s
=
8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, ...and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of
δ
L
/
L
=
±
1.9
%
is obtained for the
22.7
fb
-
1
of
pp
collision data delivered to ATLAS at
s
=
8 TeV in 2012.
A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data ...used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.
Combined analyses of the Higgs boson production and decay rates as well as its coupling strengths to vector bosons and fermions are presented. The combinations include the results of the analyses of ...the
H
→
γ
γ
,
Z
Z
∗
,
W
W
∗
,
Z
γ
,
b
b
¯
,
τ
τ
and
μ
μ
decay modes, and the constraints on the associated production with a pair of top quarks and on the off-shell coupling strengths of the Higgs boson. The results are based on the LHC proton-proton collision datasets, with integrated luminosities of up to 4.7
fb
-
1
at
s
=
7
TeV and 20.3
fb
-
1
at
s
=
8
TeV, recorded by the ATLAS detector in 2011 and 2012. Combining all production modes and decay channels, the measured signal yield, normalised to the Standard Model expectation, is
1
.
18
-
0.14
+
0.15
. The observed Higgs boson production and decay rates are interpreted in a leading-order coupling framework, exploring a wide range of benchmark coupling models both with and without assumptions on the Higgs boson width and on the Standard Model particle content in loop processes. The data are found to be compatible with the Standard Model expectations for a Higgs boson at a mass of 125.36 GeV for all models considered.
A
bstract
A search for Higgs boson pair production in the
b
b
¯
b
b
¯
final state is carried out with up to 36.1 fb
−1
of LHC proton-proton collision data collected at
s
=
13
TeV with the ATLAS ...detector in 2015 and 2016. Three benchmark signals are studied: a spin-2 graviton decaying into a Higgs boson pair, a scalar resonance decaying into a Higgs boson pair, and Standard Model non-resonant Higgs boson pair production. Two analyses are carried out, each implementing a particular technique for the event reconstruction that targets Higgs bosons reconstructed as pairs of jets or single boosted jets. The resonance mass range covered is 260–3000 GeV. The analyses are statistically combined and upper limits on the production cross section of Higgs boson pairs times branching ratio to
b
b
¯
b
b
¯
are set in each model. No significant excess is observed; the largest deviation of data over prediction is found at a mass of 280 GeV, corresponding to 2.3 standard deviations globally. The observed 95% confidence level upper limit on the non-resonant production is 13 times the Standard Model prediction.
Higgs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb−1 of proton–proton collision data recorded at s√=13 TeV by the ATLAS experiment at the Large ...Hadron Collider. The inclusive cross-section times branching ratio for H→ZZ∗ decay is measured to be 1.34±0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of 1.33±0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.
A
bstract
A search for the decay of the Standard Model Higgs boson into a
b
b
¯
pair when produced in association with a
W
or
Z
boson is performed with the ATLAS detector. The analysed data, ...corresponding to an integrated luminosity of 36.1 fb
−1
, were collected in proton-proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing zero, one and two charged leptons (electrons or muons) are considered, targeting the decays
Z
→
νν
,
W
→
ℓν
and
Z
→
ℓℓ
. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay into b-quarks and for its production in association with a vector boson. The combination of this result with that of the Run 1 analysis yields a ratio of the measured signal events to the Standard Model expectation equal to 0.90 ± 0.18(stat.)
− 0.19
+ 0.21
(syst.). Assuming the Standard Model production cross-section, the results are consistent with the value of the Yukawa coupling to
b
-quarks in the Standard Model.
A search for charged leptons with large impact parameters using 139 fb−1 of √s = 13 TeV pp collision data from the ATLAS detector at the LHC is presented, addressing a long-standing gap in coverage ...of possible new physics signatures. Results are consistent with the background prediction. This search provides unique sensitivity to long-lived scalar supersymmetric lepton partners (sleptons). For lifetimes of 0.1 ns, selectron, smuon, and stau masses up to 720, 680, and 340 GeV, respectively, are excluded at 95% confidence level, drastically improving on the previous best limits from LEP.
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