(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image) A search is presented for a high-mass Higgs boson in the ..., ..., ..., and ... decay modes using the ATLAS detector at the ...CERN Large Hadron Collider. The search uses proton-proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb... The results of the search are interpreted in the scenario of a heavy Higgs boson with a width that is small compared with the experimental mass resolution. The Higgs boson mass range considered extends up to ... for all four decay modes and down to as low as 140 ..., depending on the decay mode. No significant excess of events over the Standard Model prediction is found. A simultaneous fit to the four decay modes yields upper limits on the production cross-section of a heavy Higgs boson times the branching ratio to ... boson pairs. 95 % confidence level upper limits range from 0.53 pb at ... GeV to 0.008 pb at ... GeV for the gluon-fusion production mode and from 0.31 pb at ... GeV to 0.009 pb at ... GeV for the vector-boson-fusion production mode. The results are also interpreted in the context of Type-I and Type-II two-Higgs-doublet models.
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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.
Rare B decays at LEP Kluit, Peter M.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2001, Letnik:
462, Številka:
1
Journal Article
Recenzirano
The results of the LEP experiments for rare B decays will be reviewed, covering hadronic final states, radiative and other rare decays and results for the inclusive charmless branching ratio.
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 search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic
t
t
¯
plus missing transverse momentum final ...state is presented. The analysis of 139
fb
-
1
of
s
=
13
TeV proton–proton collision data collected using the ATLAS detector at the LHC yields no significant excess over the Standard Model background expectation. To interpret the results, a supersymmetric model is used where the top squark decays via
t
~
→
t
(
∗
)
χ
~
1
0
, with
t
(
∗
)
denoting an on-shell (off-shell) top quark and
χ
~
1
0
the lightest neutralino. Three specific event selections are optimised for the following scenarios. In the scenario where
m
t
~
>
m
t
+
m
χ
~
1
0
, top squark masses are excluded in the range 400–1250 GeV for
χ
~
1
0
masses below 200 GeV at 95% confidence level. In the situation where
m
t
~
∼
m
t
+
m
χ
~
1
0
, top squark masses in the range 300–630 GeV are excluded, while in the case where
m
t
~
<
m
W
+
m
b
+
m
χ
~
1
0
(with
m
t
~
-
m
χ
~
1
0
≥
5
GeV), considered for the first time in an ATLAS all-hadronic search, top squark masses in the range 300–660 GeV are excluded. Limits are also set for scalar third-generation up-type leptoquarks, excluding leptoquarks with masses below 1240 GeV when considering only leptoquark decays into a top quark and a neutrino.
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The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with
pp
collisions at a centre-of-mass energy
s
=
13
TeV. The absolute luminosity scale is determined using ...van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2
pp
data sample corresponds to an integrated luminosity of
140.1
±
1.2
fb
-
1
, i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017–2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of
338.1
±
3.1
pb
-
1
.
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The inclusive top quark pair (
t
t
¯
) production cross-section
σ
t
t
¯
has been measured in proton–proton collisions at
s
=
13
TeV
, using 36.1 fb
-
1
of data collected in 2015–2016 by the ATLAS ...experiment at the LHC. Using events with an opposite-charge
e
μ
pair and
b
-tagged jets, the cross-section is measured to be:
σ
t
t
¯
=
826.4
±
3.6
(
stat
)
±
11.5
(
syst
)
±
15.7
(
lumi
)
±
1.9
(
beam
)
pb
,
where the uncertainties reflect the limited size of the data sample, experimental and theoretical systematic effects, the integrated luminosity, and the LHC beam energy, giving a total uncertainty of 2.4%. The result is consistent with theoretical QCD calculations at next-to-next-to-leading order. It is used to determine the top quark pole mass via the dependence of the predicted cross-section on
m
t
pole
, giving
m
t
pole
=
173
.
1
-
2.1
+
2.0
GeV
. It is also combined with measurements at
s
=
7
TeV
and
s
=
8
TeV
to derive ratios and double ratios of
t
t
¯
and
Z
cross-sections at different energies. The same event sample is used to measure absolute and normalised differential cross-sections as functions of single-lepton and dilepton kinematic variables, and the results are compared with predictions from various Monte Carlo event generators.
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Studies of the spin, parity and tensor couplings of the Higgs boson in the
H
→
Z
Z
∗
→
4
ℓ
,
H
→
W
W
∗
→
e
ν
μ
ν
and
H
→
γ
γ
decay processes at the LHC are presented. The investigations are based on
...25
fb
-
1
of
pp
collision data collected by the ATLAS experiment at
s
=
7
TeV and
s
=
8
TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers
J
P
=
0
+
, is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the
H
→
Z
Z
∗
→
4
ℓ
and
H
→
W
W
∗
→
e
ν
μ
ν
decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.
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A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13
TeV
by the ATLAS detector at the ...Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb
-
1
. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain
b
-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical
Z
′
bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs.
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The performance of the missing transverse momentum (
) 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
, fully calibrated electrons, muons, photons, hadronically decaying
, 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
contributions. The individual terms as well as the overall reconstructed
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
scale and resolution is discussed. Results are shown based on the full 2015 data sample corresponding to an integrated luminosity of
.
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