This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139
fb
-
1
of
pp
collision data at
s
=
13
TeV collected between 2015 and 2018 during ...Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of
Z
→
μ
μ
and
J
/
ψ
→
μ
μ
decays, and the minimisation of systematic uncertainties, allows the efficiencies of criteria for muon identification, primary vertex association, and isolation to be measured with an accuracy at the per-mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several hundred GeV, and across the full muon detector acceptance of
|
η
|
<
2.7
.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb
-
1
of proton–proton collision data with a centre-of-mass energy of
s
=
13
TeV
...collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti-
k
t
jet algorithm with radius parameter
R
=
0.4
is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets (
|
η
|
<
1.2
) vary from 1% for a wide range of high-
p
T
jets (
250
<
p
T
<
2000
GeV
), to 5% at very low
p
T
(
20
GeV
) and 3.5% at very high
p
T
(
>
2.5
TeV
). The relative jet energy resolution is measured and ranges from (
24
±
1.5
)% at 20
GeV
to (
6
±
0.5
)% at 300
GeV
.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Electron and photon triggers covering transverse energies from 5
GeV
to several
TeV
are essential for the ATLAS experiment to record signals for a wide variety of physics: from Standard Model ...processes to searches for new phenomena in both proton–proton and heavy-ion collisions. To cope with a fourfold increase of peak LHC luminosity from 2015 to 2018 (Run 2), to
2.1
×
10
34
cm
-
2
s
-
1
, and a similar increase in the number of interactions per beam-crossing to about 60, trigger algorithms and selections were optimised to control the rates while retaining a high efficiency for physics analyses. For proton–proton collisions, the single-electron trigger efficiency relative to a single-electron offline selection is at least 75% for an offline electron of 31
GeV
, and rises to 96% at 60
GeV
; the trigger efficiency of a 25
GeV
leg of the primary diphoton trigger relative to a tight offline photon selection is more than 96% for an offline photon of 30
GeV
. For heavy-ion collisions, the primary electron and photon trigger efficiencies relative to the corresponding standard offline selections are at least 84% and 95%, respectively, at 5
GeV
above the corresponding trigger threshold.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in
pp
collisions at
s
= 13 TeV at the ...Large Hadron Collider are considered using an integrated luminosity of 139 fb
−
1
, corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of
c
- or
b
-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass.
A
bstract
A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb
−
1
of proton-proton collisions at
s
= 13 TeV, recorded ...with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark,
pp
→
tbH
+
→
tbtb
, is explored in the
H
+
mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and
b
-tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass; they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and
M
h
125
scenarios.
The results of a search for electroweakino pair production
p
p
→
χ
~
1
±
χ
~
2
0
in which the chargino (
χ
~
1
±
) decays into a
W
boson and the lightest neutralino (
χ
~
1
0
), while the heavier ...neutralino (
χ
~
2
0
) decays into the Standard Model 125 GeV Higgs boson and a second
χ
~
1
0
are presented. The signal selection requires a pair of
b
-tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the
W
boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139
fb
-
1
of
s
=
13
TeV
pp
collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of
χ
~
1
±
/
χ
~
2
0
up to 740 GeV are excluded at 95% confidence level for a massless
χ
~
1
0
.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb
of
= 13 TeV
collision data recorded by the ATLAS experiment at the LHC ...in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark,
, which decays promptly into two quarks through
-parity-violating couplings. Top squarks with masses in the range
are excluded at 95% confidence level. If the decay is into a
-quark and a light quark, a dedicated selection requiring two
-tags is used to exclude masses in the ranges
and
. Additional limits are set on the pair-production of massive colour-octet resonances.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
A search for exotic decays of the Higgs boson into a pair of spin-zero particles,
H
→
aa
, where the
a
-boson decay sin to
b
-quarks promptly or with a mean proper lifetime
cτ
a
up to 6 mm ...and has a mass in the range of 20–60 GeV, is presented. The search is performed in events where the Higgs boson is produced in association with a
W
or
Z
boson, giving rise to a signature of one or two charged leptons (electrons or muons) and multiple jets from
b
-quark decays. The analysis is based on the dataset of proton-proton collisions at
s
=
13
TeV recorded in 2015 and 2016 by the ATLAS detector at the CERN Large Hadron Collider, corresponding to an integrated luminosity of 36.1 fb
−1
. No significant excess of events above the Standard Model background prediction is observed, and 95% confidence-level upper limits are derived for the production cross-sections for
pp
→
WH
,
ZH
and their combination, times the branching ratio of the decay chain
H
→
aa
→ 4
b
. For
a
-bosons which decay promptly, the upper limit on the combination of cross-sections for
WH
and
ZH
times the branching ratio of
H
→
aa
→ 4
b
ranges from 3.0 pb for
m
a
= 20 GeV to 1.3 pb for
m
a
= 60 GeV, assuming that the ratio of
WH
to
ZH
cross-sections follows the Standard Model prediction. For
a
-bosons with longer proper lifetimes, the most stringent limits are 1.8 pb and 0.68 pb, respectively, at
cτ
a
∼ 0.4 mm.
A
bstract
A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a
τ
-lepton is presented. The search is based on a dataset of
pp
collisions at
s
= 13 TeV ...recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb
−
1
. Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying
τ
-lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing
b
-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying
τ
-lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into
tτ
and
bν
. Scalar leptoquarks decaying exclusively into
tτ
are excluded up to masses of 1
.
43 TeV while, for a branching fraction of 50% into
tτ
, the lower mass limit is 1
.
22 TeV.
A
bstract
Limits are set on the pair production of scalar leptoquarks, where all possible decays of the leptoquark into a quark (
t
,
b
) and a lepton (
τ
,
ν
) of the third generation are ...considered. The limits are presented as a function of the leptoquark mass and the branching ratio into charged leptons for up-type (LQ
3
u
→
tν
/
bτ
) and down-type (LQ
3
d
→
bν
/
tτ
) leptoquarks. Many results are reinterpretations of previously published ATLAS searches. In all cases, LHC proton-proton collision data at a centre-of-mass energy of
s
= 13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb
−1
. Masses below 800 GeV are excluded for both LQ
3
u
and LQ
3
d
independently of the branching ratio, with masses below about 1 TeV being excluded for the limiting cases of branching ratios equal to zero or unity.
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