This document reviews the existing results of inclusive top quark pair production cross section measurements in proton-proton collisions at a center of mass energies of 7 and 8 TeV performed with the ...ATLAS detector at the Large Hadron Collider. These measurements cover the different analysis channels, single lepton, dilepton and all hadronic channel, as well as dedicated analysis for channels including tau leptons decaying hadronically. All measurements shown in this document are in good agreement with the Standard Model expectation.
This article documents the performance of the ATLAS muon identification and reconstruction using the LHC dataset recorded at
s
=
13
TeV in 2015. Using a large sample of
J
/
ψ
→
μ
μ
and
Z
→
μ
μ
...decays from 3.2 fb
-
1
of
pp
collision data, measurements of the reconstruction efficiency, as well as of the momentum scale and resolution, are presented and compared to Monte Carlo simulations. The reconstruction efficiency is measured to be close to
99
%
over most of the covered phase space (
|
η
|
<
2.5
and
5
<
p
T
<
100
GeV). The isolation efficiency varies between 93 and
100
%
depending on the selection applied and on the momentum of the muon. Both efficiencies are well reproduced in simulation. In the central region of the detector, the momentum resolution is measured to be
1.7
%
(
2.3
%
) for muons from
J
/
ψ
→
μ
μ
(
Z
→
μ
μ
) decays, and the momentum scale is known with an uncertainty of
0.05
%
. In the region
|
η
|
>
2.2
, the
p
T
resolution for muons from
Z
→
μ
μ
decays is
2.9
%
while the precision of the momentum scale for low-
p
T
muons from
J
/
ψ
→
μ
μ
decays is about
0.2
%
.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Dijet events are studied in the proton-proton collision data set recorded at s=13 TeV with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to integrated luminosities ...of 3.5 fb−1 and 33.5 fb−1 respectively. Invariant mass and angular distributions are compared to background predictions and no significant deviation is observed. For resonance searches, a new method for fitting the background component of the invariant mass distribution is employed. The data set is then used to set upper limits at a 95% confidence level on a range of new physics scenarios. Excited quarks with masses below 6.0 TeV are excluded, and limits are set on quantum black holes, heavy W′ bosons, W* bosons, and a range of masses and couplings in a Z′ dark matter mediator model. Model-independent limits on signals with a Gaussian shape are also set, using a new approach allowing factorization of physics and detector effects. From the angular distributions, a scale of new physics in contact interaction models is excluded for scenarios with either constructive or destructive interference. These results represent a substantial improvement over those obtained previously with lower integrated luminosity.
The large rate of multiple simultaneous proton–proton interactions, or pile-up, generated by the Large Hadron Collider in Run 1 required the development of many new techniques to mitigate the adverse ...effects of these conditions. This paper describes the methods employed in the ATLAS experiment to correct for the impact of pile-up on jet energy and jet shapes, and for the presence of spurious additional jets, with a primary focus on the large 20.3
fb
-
1
data sample collected at a centre-of-mass energy of
s
=
8
TeV
. The energy correction techniques that incorporate sophisticated estimates of the average pile-up energy density and tracking information are presented. Jet-to-vertex association techniques are discussed and projections of performance for the future are considered. Lastly, the extension of these techniques to mitigate the effect of pile-up on jet shapes using subtraction and grooming procedures is presented.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one ...high-mass displaced vertex with five or more tracks, and uses 32.8 fb−1 of s=13 TeV pp collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95% C.L. exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of O(10−2)−O(10) ns in a simplified model inspired by split supersymmetry.
A
bstract
This paper describes a measurement of the
Z
/
γ
*
boson transverse momentum spectrum using ATLAS proton-proton collision data at a centre-of-mass energy of
s
=
7
TeV at the LHC. The ...measurement is performed in the
Z
/
γ
*
→
e
+
e
−
and
Z
/
γ
*
→
μ
+
μ
−
channels, using data corresponding to an integrated luminosity of 4.7 fb
−1
. Normalized differential cross sections as a function of the
Z
/
γ
*
boson transverse momentum are measured for transverse momenta up to 800 GeV. The measurement is performed inclusively for
Z
/
γ
*
rapidities up to 2.4, as well as in three rapidity bins. The channel results are combined, compared to perturbative and resummed QCD calculations and used to constrain the parton shower parameters of Monte Carlo generators.
Due to its potential risk to human health and ecology, the presence of heavy metals in water demands of techniques to determine them in a simple and economical way. Currently, new developments of ...light emitters and detectors open a window of opportunities to use optical properties to analyze contaminated water. In this paper, a silicon sensor developed to extend its sensitivity up to the UV range is used to determine heavy metals in water. Cadmium, Zinc, Lead, Copper and Manganese mixed in pure water at different concentrations were used as test samples. The photocurrent obtained by the light that passes through the samples was used to determine the optical transmittance of pure and contaminated water. Preliminary results show a good separability between samples, which can be used for qualitative and quantitative detection of such heavy metals in water.
Distributions of transverse momentum
p
T
ℓ
ℓ
and the related angular variable
ϕ
η
∗
of Drell–Yan lepton pairs are measured in 20.3 fb
-
1
of protonΓÇôproton collisions at
s
=
8
 TeV with the ...ATLAS detector at the LHC. Measurements in electron-pair and muon-pair final states are corrected for detector effects and combined. Compared to previous measurements in proton–proton collisions at
s
=
7
 TeV, these new measurements benefit from a larger data sample and improved control of systematic uncertainties. Measurements are performed in bins of lepton-pair mass above, around and below the
Z
-boson mass peak. The data are compared to predictions from perturbative and resummed QCD calculations. For values of
ϕ
η
∗
<
1
the predictions from the Monte Carlo generator
ResBos
are generally consistent with the data within the theoretical uncertainties. However, at larger values of
ϕ
η
∗
this is not the case. Monte Carlo generators based on the parton-shower approach are unable to describe the data over the full range of
p
T
ℓ
ℓ
while the fixed-order prediction of
Dynnlo
falls below the data at high values of
p
T
ℓ
ℓ
.
ResBos
and the parton-shower Monte Carlo generators provide a much better description of the evolution of the
ϕ
η
∗
and
p
T
ℓ
ℓ
distributions as a function of lepton-pair mass and rapidity than the basic shape of the data.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper presents measurements of W ± Z production in p p collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and ...muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb - 1 . The measured inclusive cross section in the detector fiducial region is σ W ± Z → ℓ ' ν ℓ ℓ = 35.1 ± 0.9 ( stat ) ± 0.8 ( sys ) ± 0.8 ( lumi ) fb , for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 ± 2.1 fb . Cross sections for W + Z and W - Z production and their ratio are presented as well as differential cross sections for several kinematic observables. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the W ± Z system. From the analysis of events with a W and a Z boson associated with two or more forward jets an upper limit at 95% confidence level on the W ± Z scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 ± 0.01 fb . Limits on anomalous quartic gauge boson couplings are also extracted.
The production of two prompt
J
/
ψ
mesons, each with transverse momenta
p
T
>
8.5
GeV and rapidity
|
y
|
<
2.1
, is studied using a sample of proton-proton collisions at
s
=
8
TeV, corresponding to ...an integrated luminosity of 11.4 fb
-
1
collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised
J
/
ψ
production, is measured as a function of the transverse momentum of the lower-
p
T
J
/
ψ
meson, di-
J
/
ψ
p
T
and mass, the difference in rapidity between the two
J
/
ψ
mesons, and the azimuthal angle between the two
J
/
ψ
mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two
J
/
ψ
mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be
σ
eff
=
6.3
±
1.6
(
stat
)
±
1.0
(
syst
)
mb.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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