As computational Grids move away from the prototyping state, reliability, performance and ease of use and maintenance become focus areas of their adoption. In this paper, we describe ARC (Advanced ...Resource Connector) Grid middleware, where these issues have been given special consideration.
We present an in-depth view of the existing components of ARC, and discuss some of the new components, functionalities and enhancements currently under development. This paper also describes architectural and technical choices that have been made to ensure scalability, stability and high performance. The core components of ARC have already been thoroughly tested in demanding production environments, where it has been in use since 2002. The main goal of this paper is to provide a first comprehensive description of ARC.
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
%
.
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.
A
bstract
The efficiency to identify jets containing
b
-hadrons (
b
-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs (
t
t
¯
) selected from the 36.1 fb
−1
of ...data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy
s
=
13
TeV. Two methods are used to extract the efficiency from
t
t
¯
events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using
b
-tagging information, is used to select events in which two
b
-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.
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.
A search for doubly charged Higgs bosons with pairs of prompt, isolated, highly energetic leptons with the same electric charge is presented. The search uses a proton–proton collision data sample at ...a centre-of-mass energy of 13 TeV corresponding to 36.1
fb
-
1
of integrated luminosity recorded in 2015 and 2016 by the ATLAS detector at the LHC. This analysis focuses on the decays
H
±
±
→
e
±
e
±
,
H
±
±
→
e
±
μ
±
and
H
±
±
→
μ
±
μ
±
, fitting the dilepton mass spectra in several exclusive signal regions. No significant evidence of a signal is observed and corresponding limits on the production cross-section and consequently a lower limit on
m
(
H
±
±
)
are derived at 95% confidence level. With
ℓ
±
ℓ
±
=
e
±
e
±
/
μ
±
μ
±
/
e
±
μ
±
, the observed lower limit on the mass of a doubly charged Higgs boson only coupling to left-handed leptons varies from 770 to 870 GeV (850 GeV expected) for
B
(
H
±
±
→
ℓ
±
ℓ
±
)
=
100
%
and both the expected and observed mass limits are above 450 GeV for
B
(
H
±
±
→
ℓ
±
ℓ
±
)
=
10
%
and any combination of partial branching ratios.
Electroweak measurements performed with data taken at the electron–positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total ...luminosity of about 3 fb−1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV.
Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron–positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose–Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the branching fraction of W decays to hadrons, B(W→had), and the trilinear gauge-boson self-couplings g1Z, κγ and λγ are determined to be: mW=80.376±0.033GeVΓW=2.195±0.083GeVB(W→had)=67.41±0.27%g1Z=0.984−0.020+0.018κγ=0.982±0.042λγ=−0.022±0.019.
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.
A
bstract
A search is conducted for new resonant and non-resonant high-mass phenomena in dielectron and dimuon final states. The search uses 36.1 fb
−1
of proton-proton collision data, collected at
s
...=
13
TeV by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the Standard Model prediction is observed. Upper limits at 95% credibility level are set on the cross-section times branching ratio for resonances decaying into dileptons, which are converted to lower limits on the resonance mass, up to 4.1 TeV for the E
6
-motivated
Z
χ
′
. Lower limits on the
qqℓℓ
contact interaction scale are set between 2.4 TeV and 40 TeV, depending on the model.
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