Results are presented from the measurement by ATLAS of long-range (
|
Δ
η
|
>
2
) dihadron angular correlations in
s
=
8
and 13 TeV
pp
collisions containing a
Z
boson. The analysis is performed using ...19.4
fb
-
1
of
s
=
8
TeV data recorded during Run 1 of the LHC and 36.1
fb
-
1
of
s
=
13
TeV data recorded during Run 2. Two-particle correlation functions are measured as a function of relative azimuthal angle over the relative pseudorapidity range
2
<
|
Δ
η
|
<
5
for different intervals of charged-particle multiplicity and transverse momentum. The measurements are corrected for the presence of background charged particles generated by collisions that occur during one passage of two colliding proton bunches in the LHC. Contributions to the two-particle correlation functions from hard processes are removed using a template-fitting procedure. Sinusoidal modulation in the correlation functions is observed and quantified by the second Fourier coefficient of the correlation function,
v
2
,
2
, which in turn is used to obtain the single-particle anisotropy coefficient
v
2
. The
v
2
values in the
Z
-tagged events, integrated over
0.5
<
p
T
<
5
GeV, are found to be independent of multiplicity and
s
, and consistent within uncertainties with previous measurements in inclusive
pp
collisions. As a function of charged-particle
p
T
, the
Z
-tagged and inclusive
v
2
values are consistent within uncertainties for
p
T
<
3
GeV.
A
bstract
A measurement of the production of a prompt
J/ψ
meson in association with a
W
±
boson with
W
±
→
μν
and
J/ψ
→
μ
+
μ
−
is presented for
J/ψ
transverse momenta in the range 8
.
5–150 GeV and ...rapidity |
y
J/ψ
|
<
2
.
1 using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of
s
= 8 TeV and correspond to an integrated luminosity of 20
.
3 fb
−
1
. The ratio of the prompt
J/ψ
plus
W
±
cross-section to the inclusive
W
±
cross-section is presented as a differential measurement as a function of
J/ψ
transverse momenta and compared with theoretical predictions using different double-parton-scattering cross-sections.
A
bstract
A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy
s
= 8 TeV is used to study inclusive single diffractive dissociation,
pp → X p
. The intact ...final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system
X
are measured in the central detector components. The fiducial range of the measurement is
−
4
.
0
<
log
10
ξ < −
1
.
6 and 0
.
016
< |t| <
0
.
43 GeV
2
, where
ξ
is the proton fractional energy loss and
t
is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1
.
59
±
0
.
13 mb. Cross sections are also measured differentially as functions of
ξ
,
t
, and ∆
η
, a variable that characterises the rapidity gap separating the proton and the system
X
. The data are consistent with an exponential
t
dependence, d
σ/
d
t ∝
e
Bt
with slope parameter
B
= 7
.
65
±
0
.
34 GeV
−
2
. Interpreted in the framework of triple Regge phenomenology, the
ξ
dependence leads to a pomeron intercept of
α
(0) = 1
.
07
±
0
.
09.
The ATLAS Muon Trigger "Slice" Sidoti, A.; Bellomo, M.; Biglietti, M. ...
IEEE transactions on nuclear science,
02/2008, Volume:
55, Issue:
1
Journal Article
Peer reviewed
The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of selecting interesting candidate events in proton-proton collisions at 14 TeV center of mass energy, while rejecting ...the enormous number of background events. The trigger system architecture is organized in three levels. From a bunch crossing rate of 40 MHz, the First Level trigger, hardware implemented, will reduce this rate to around ~75 kHz. Then the software based High Level Trigger (HLT), composed by the Second Level Trigger and the Event Filter reduces the rate to 200 Hz. In this paper, we will present the implementation of the muon trigger ldquoslice,rdquo signal efficiencies, background rejection rates, and system performances (execution time, memory consumption, etc.) for online muon selection based on Monte Carlo simulations and results obtained on real events collected during cosmic data taking runs.
Finding unequivocal evidence of dark matter interactions in a particle detector is a major goal of research in physics. Liquid argon time projection chambers offer a path to probe Weakly Interacting ...Massive Particles scattering cross sections on nuclei down to the so-called neutrino floor, in a mass range from a few GeV to hundreds of TeV. Based on the successful operation of the DarkSide-50 detector at LNGS, a new and more sensitive experiment, DarkSide-20k, has been designed and is now under construction. A thorough understanding of the DarkSide-50 detector response and, therefore, of all types of events observed in the detector, is essential for the optimal design of the new experiment. In this article, we report on a specific set of events, namely, standard two-pulse scintillation–ionization signals with a third small amplitude pulse, occurring within the 440μs data acquisition window of standard events. Some of these events are due to the photoionization of the TPC cathode. We compare our results with those published by collaborations using liquid xenon time projection chambers, which observed a similar phenomenon, and, in particular, with a recent paper by the LUX Collaboration (D.S. Akerib et al. Phys.Rev.D 102, 092004 (2020)) From the measured rate of these events, we estimate for the first time the quantum efficiency of the tetraphenyl butadiene deposited on the DarkSide-50 cathode at wavelengths of around 128 nm, in liquid argon. Also, both experiments observe events likely related to the photoionization of impurities in the liquid. The probability of photoelectron emission per unit length turns out to be an order of magnitude lower in DarkSide-50 than in LUX.
A
bstract
The dynamics of isolated-photon plus two-jet production in
pp
collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to ...an integrated luminosity of 36
.
1 fb
−
1
. Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state,
γ
+ jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from S
herpa
and P
ythia
as well as the next-to-leading-order QCD predictions from S
herpa
are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data.
The CDF-II time-of-flight detector Cabrera, S; Fernández, J; Gómez, G ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2002, Volume:
494, Issue:
1
Journal Article
Peer reviewed
A Time-of-Flight (TOF) detector, based on plastic scintillator and fine-mesh photomultiplier tubes, has been added to the CDF-II experiment. Since August 2001, the TOF system has been fully ...instrumented and integrated into the CDF-II data acquisition system. The TOF system will provide particle identification of low momentum charged pions, kaons and protons in
p
p
̄
collisions. With a design resolution goal of about
100
ps
, separation between charged kaons and pions is expected at the 2 sigma level for momenta below
1.6
GeV/c
, which enhances CDF's b-flavor tagging capabilities. We describe the design of the TOF detector and discuss its on-line and off-line calibration. Some performance benchmarks using proton–antiproton collision data are presented.
A search is presented for direct top squark pair production using events with at least two leptons including a same-flavour opposite-sign pair with invariant mass consistent with the
Z
boson mass, ...jets tagged as originating from
b
-quarks and missing transverse momentum. The analysis is performed with proton–proton collision data at
s
=
8
TeV
collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20.3 fb
-
1
. No excess beyond the Standard Model expectation is observed. Interpretations of the results are provided in models based on the direct pair production of the heavier top squark state (
t
~
2
) followed by the decay to the lighter top squark state (
t
~
1
) via
t
~
2
→
Z
t
~
1
, and for
t
~
1
pair production in natural gauge-mediated supersymmetry breaking scenarios where the neutralino (
χ
~
1
0
) is the next-to-lightest supersymmetric particle and decays producing a
Z
boson and a gravitino (
G
~
) via the
χ
~
1
0
→
Z
G
~
process.
One correction is noted for the paper. The branching fraction ($\mathcal{B}$($W →{ℓv}$) = 0.3246 was not included in the conversion of the observed cross-section limit, σ x $\mathcal{B}$( $t →Wb$) x ...($\mathcal{B}$($W →{ℓv}$) < 2.9to the coupling constants $κ_{ugt}$ and $κ_{cgt}$ and the branching fractions $\mathcal{B}$( $t →ug$) and $\mathcal{B}$( $t →cg$). The inclusion leads to weaker observed exclusion limits on the coupling constants divided by the scale of new physics of $k_{ugt}$/ Λ <10 x 10-3 TeV-1 and $k_{cgt}$/Λ <23 x 10-3 TeV-1 and on the branching fractions $\mathcal{B}$( $t →ug$) < 1.2 x10-4 and $\mathcal{B}$( $t →cg$) < 6.4 x 10-4. The predicted exclusion limits on the coupling constants divided by the scale of new physics are $k_{ugt}$/ Λ < 9.5 x 10-3 TeV-1and $\mathcal{B}$( $t →cg$)/ Λ < 22 x 10-3 TeV-1 and on the branching fractions $\mathcal{B}$( $t →ug$) < 1.1 x 10-4 and $\mathcal{B}$( $t →cg$) < 5.7 x 10-4. Updated distributions of the observed upper limits on the coupling constants for combinations of cgt and ugt channels are shown in Figure 10a and on the branching fractions in Figure 10b.
Aria is a plant hosting a Formula omitted cryogenic isotopic distillation column, the tallest ever built, which is being installed in a mine shaft at Carbosulcis S.p.A., Nuraxi-Figus (SU), Italy. ...Aria is one of the pillars of the argon dark-matter search experimental program, lead by the Global Argon Dark Matter Collaboration. It was designed to reduce the isotopic abundance of Formula omitted in argon extracted from underground sources, called Underground Argon (UAr), which is used for dark-matter searches. Indeed, Formula omitted is a Formula omitted-emitter of cosmogenic origin, whose activity poses background and pile-up concerns in the detectors. In this paper, we discuss the requirements, design, construction, tests, and projected performance of the plant for the isotopic cryogenic distillation of argon. We also present the successful results of the isotopic cryogenic distillation of nitrogen with a prototype plant.
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