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"Froidevaux, D"
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Life on Muskrat Creek : a homestead family in Wyoming
Composed of writings by Ethel Waxham Love, a Wellesley College graduate who married Scottish rancher John Love and went to live on his ranch in 1910, and her son, J. David Love, who later became an eminent geologist, Life on Muskrat Creek tells the fascinating story of a family's day-to-day life on an isolated ranch in early twentieth-century Wyoming. Readers will learn about the family's persistence despite a variety of challenges, including a near-fatal bout with Spanish influenza, life-threatening encounters with livestock and wildlife, as well as disastrous episodes of fires, floods, blizzards, and drought. The book's depiction of more ordinary events is equally engaging: Ethel describes her adjustment to married life and raising children with little support from neighbors, women friends, or a wider family network; David recounts growing up in a wild and remote place where there was no local school, but where he learned from the land, his parents, and the hardy people who stopped by the ranch. The two perspectives create a lively and provocative record of western history--back cover.
Book
Luminosity determination in pp collisions at s=13 TeV using the ATLAS detector at the LHC
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
.
Journal Article
Measurement of the c-jet mistagging efficiency in tt¯ events using pp collision data at s=13 TeV collected with the ATLAS detector
A technique is presented to measure the efficiency with which c-jets are mistagged as b-jets (mistagging efficiency) using tt¯ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known W→cs branching ratio, which allows a measurement to be made in an inclusive c-jet sample. The data sample used was collected by the ATLAS detector at s=13 TeV and corresponds to an integrated luminosity of 139 fb-1. Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and tt¯ decay products that yields the highest likelihood value. The distribution of the b-tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b-jet tagging requirement.
Journal Article
Measurements of WH and ZH production in the H→bb¯ decay channel in pp collisions at 13Te with the ATLAS detector
Measurements of the Standard Model Higgs boson decaying into a bb¯ pair and produced in association with a W or Z boson decaying into leptons, using proton–proton collision data collected between 2015 and 2018 by the ATLAS detector, are presented. The measurements use collisions produced by the Large Hadron Collider at a centre-of-mass energy of s=13Te, corresponding to an integrated luminosity of 139fb-1. The production of a Higgs boson in association with a W or Z boson is established with observed (expected) significances of 4.0 (4.1) and 5.3 (5.1) standard deviations, respectively. Cross-sections of associated production of a Higgs boson decaying into bottom quark pairs with an electroweak gauge boson, W or Z, decaying into leptons are measured as a function of the gauge boson transverse momentum in kinematic fiducial volumes. The cross-section measurements are all consistent with the Standard Model expectations, and the total uncertainties vary from 30% in the high gauge boson transverse momentum regions to 85% in the low regions. Limits are subsequently set on the parameters of an effective Lagrangian sensitive to modifications of the WH and ZH processes as well as the Higgs boson decay into bb¯.
Journal Article
Search for a scalar partner of the top quark in the all-hadronic tt¯ plus missing transverse momentum final state at s=13 TeV with the ATLAS detector
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.
Journal Article
Evidence for tt¯tt¯ production in the multilepton final state in proton–proton collisions at s=13 TeV with the ATLAS detector
A search is presented for four-top-quark production using an integrated luminosity of 139 fb
-
1
of proton–proton collision data at a centre-of-mass energy of
13
TeV
collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be
24
-
6
+
7
fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.
Journal Article
Measurements of top-quark pair differential and double-differential cross-sections in the ℓ+jets channel with pp collisions at s=13 TeV using the ATLAS detector
Single- and double-differential cross-section measurements are presented for the production of top-quark pairs, in the lepton + jets channel at particle and parton level. Two topologies, resolved and boosted, are considered and the results are presented as a function of several kinematic variables characterising the top and tt¯ system and jet multiplicities. The study was performed using data from pp collisions at centre-of-mass energy of 13 TeV collected in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider (LHC), corresponding to an integrated luminosity of 36fb-1. Due to the large tt¯ cross-section at the LHC, such measurements allow a detailed study of the properties of top-quark production and decay, enabling precision tests of several Monte Carlo generators and fixed-order Standard Model predictions. Overall, there is good agreement between the theoretical predictions and the data.
Journal Article
Inclusive and differential cross-sections for dilepton tt¯ production measured in s = 13 TeV pp collisions with the ATLAS detector
A
bstract
Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (
t
t
¯
) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a
pp
collision energy of
s
= 13 TeV and correspond to an integrated luminosity of 140 fb
−
1
. The measurements use events containing an oppositely charged
eμ
pair and
b
-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton
p
T
distributions is obtained by reweighting the
t
t
¯
sample so as to reproduce the top-quark
p
T
distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be
σ
t
t
¯
=
829
±
1
stat
±
13
syst
±
8
lumi
±
2
beam
pb
,
where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
Journal Article
Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in s = 13 TeV pp collisions with the ATLAS detector
A
bstract
A search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of
R
-parity-conserving supersymmetry are considered: direct pair-production of sleptons
ℓ
~
ℓ
~
, with each decaying into a charged lepton and a
χ
~
1
0
neutralino, and direct pair-production of the lightest charginos
χ
~
1
±
χ
~
1
∓
, with each decaying into a
W
-boson and a
χ
~
1
0
. The lightest neutralino
χ
~
1
0
is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where
m
ℓ
~
−
m
χ
~
1
0
and
m
χ
~
1
±
−
m
χ
~
1
0
are close to the
W
-boson mass (‘moderately compressed’ regions). The search uses 139 fb
−
1
of
s
= 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the
ℓ
~
χ
~
1
0
and
χ
~
1
±
χ
~
1
0
mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.
Journal Article
Measurement of the tt¯ production cross-section and lepton differential distributions in eμ dilepton events from pp collisions at s=13TeV with the ATLAS detector
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.
Journal Article