A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton ...final state. The analyzed proton-proton collision data taken at a center-of-mass energy of root s = 13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015-2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV.
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.
The top quark mass is measured using a template method in the
t
t
¯
→
lepton
+
jets
channel (lepton is
e
or
μ
) 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
20.2
fb
-
1
. The
t
t
¯
→
lepton
+
jets
channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (
b
). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative
b
-to-light-jet energy scale factor. The mass of the top quark is measured to be
m
top
=
172.08
±
0.39
(
stat
)
±
0.82
(
syst
)
GeV
. A combination with previous ATLAS
m
top
measurements gives
m
top
=
172.69
±
0.25
(
stat
)
±
0.41
(
syst
)
GeV
.
High-voltage pixel sensors for ATLAS upgrade Perić, I.; Kreidl, C.; Fischer, P. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
11/2014, Letnik:
765
Journal Article
Recenzirano
Odprti dostop
The high-voltage (HV-) CMOS pixel sensors offer several good properties: a fast charge collection by drift, the possibility to implement relatively complex CMOS in-pixel electronics and the ...compatibility with commercial processes. The sensor element is a deep n-well diode in a p-type substrate. The n-well contains CMOS pixel electronics. The main charge collection mechanism is drift in a shallow, high field region, which leads to a fast charge collection and a high radiation tolerance. We are currently evaluating the use of the high-voltage detectors implemented in 180nm HV-CMOS technology for the high-luminosity ATLAS upgrade. Our approach is replacing the existing pixel and strip sensors with the CMOS sensors while keeping the presently used readout ASICs. By intelligence we mean the ability of the sensor to recognize a particle hit and generate the address information. In this way we could benefit from the advantages of the HV sensor technology such as lower cost, lower mass, lower operating voltage, smaller pitch, smaller clusters at high incidence angles. Additionally we expect to achieve a radiation hardness necessary for ATLAS upgrade. In order to test the concept, we have designed two HV-CMOS prototypes that can be readout in two ways: using pixel and strip readout chips. In the case of the pixel readout, the connection between HV-CMOS sensor and the readout ASIC can be established capacitively.
The modification of the production of
J
/
ψ
,
ψ
(
2
S
)
, and
Υ
(
n
S
)
(
n
=
1
,
2
,
3
) in
p
+Pb collisions with respect to their production in
pp
collisions has been studied. The
p
+Pb and
pp
...datasets used in this paper correspond to integrated luminosities of
28
nb
-
1
and
25
pb
-
1
respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of
J
/
ψ
and
ψ
(
2
S
)
are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor,
R
p
Pb
for
J
/
ψ
and
Υ
(
n
S
)
. No significant modification of the
J
/
ψ
production is observed while
Υ
(
n
S
)
production is found to be suppressed at low transverse momentum in
p
+Pb collisions relative to
pp
collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central
p
+Pb collisions.
A measurement of
J
/
ψ
and
ψ
(
2
S
)
production is presented. It is based on a data sample from Pb+Pb collisions at
s
NN
=
5.02
TeV
and
pp
collisions at
s
=
5.02
TeV
recorded by the ATLAS detector at ...the LHC in 2015, corresponding to an integrated luminosity of
0.42
nb
-
1
and
25
pb
-
1
in Pb+Pb and
pp
, respectively. The measurements of per-event yields, nuclear modification factors, and non-prompt fractions are performed in the dimuon decay channel for
9
<
p
T
μ
μ
<
40
GeV in dimuon transverse momentum, and
-
2
<
y
μ
μ
<
2
in rapidity. Strong suppression is found in Pb+Pb collisions for both prompt and non-prompt
J
/
ψ
, increasing with event centrality. The suppression of prompt
ψ
(
2
S
)
is observed to be stronger than that of
J
/
ψ
, while the suppression of non-prompt
ψ
(
2
S
)
is equal to that of the non-prompt
J
/
ψ
within uncertainties, consistent with the expectation that both arise from
b
-quarks propagating through the medium. Despite prompt and non-prompt
J
/
ψ
arising from different mechanisms, the dependence of their nuclear modification factors on centrality is found to be quite similar.
A search for an invisibly decaying Higgs boson or dark matter candidates produced in association with a leptonically decaying Z boson in proton–proton collisions at s=13 TeV is presented. This search ...uses 36.1 fb−1 of data collected by the ATLAS experiment at the Large Hadron Collider. No significant deviation from the expectation of the Standard Model backgrounds is observed. Assuming the Standard Model ZH production cross-section, an observed (expected) upper limit of 67% (39%) at the 95% confidence level is set on the branching ratio of invisible decays of the Higgs boson with mass mH=125 GeV. The corresponding limits on the production cross-section of the ZH process with the invisible Higgs boson decays are also presented. Furthermore, exclusion limits on the dark matter candidate and mediator masses are reported in the framework of simplified dark matter models.
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