639 research outputs found
Erratum: Recommendations to distinguish behavioural variant frontotemporal dementia from psychiatric disorders (Brain (2020) 143 DOI: 10.1093/brain/awaa018)
No full textThe authors apologize for misspelling the last name of the author Ratnavalli Ellajosyula. This has now been corrected
Heavy vector-like quarks decaying to exotic scalars: a case study with triplets
No full textWe investigate the pair production of a vector-like quark triplet with hypercharge 5/3 decaying into top quark and a complex scalar triplet with hypercharge 1 at the LHC. This novel scenario, featuring particles with exotic charges - two quarks with charge 8/3 and 5/3 and a scalar with charge 2 - serves as a unique window to models based on the framework of partial compositeness, where these particles naturally emerge as bound states around the TeV scale. Leveraging on the LHC data we establish exclusion limits on the masses of the vector-like quark and the scalar triplet. Subsequently, we design an analysis strategy aimed at improving sensitivity in the region which is still allowed. Our analysis focuses on two specific regions in the parameter space: the first entails a large mass gap between the vector-like quarks and the scalars, so that the vector-like quarks can decay into the scalars; the second involves a small mass gap, such that this decay is forbidden. To simplify the parameter space, both vector-like quarks and scalars are assumed to be degenerate or almost degenerate within the triplets, such that chain decays between fermions and scalars are suppressed. As a result, we found that final states characterized by a same-sign lepton pair, multiple jets, and high net transverse momentum (i.e. effective mass) will play a pivotal role to unveil this model and, more in general, models characterised by multiple vector-like quarks around the same mass scale during the high luminosity LHC phase.22 pages, 10 figures, 8 tables. Simulation banners are attached as ancillary files, v2: references updated, matches JHEP versio
Measurement of electroweak Z(v (v)over-bar)gamma jj production and limits on anomalous quartic gauge couplings in pp collisions at root s=13 TeV with the ATLAS detector
No full textThe electroweak production of Z(v (v) over bar)gamma in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton-proton collisions at a centre-of-mass energy of 13TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb(-1) collected by the ATLAS detector during the 2015-2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial Z( v (v) over bar)gamma jj cross section for electroweak production is measured to be 0.77(-0.30)(+0.34) fb and is consistent with the Standard Model prediction. Evidence of electroweak Z( v (v) over bar)gamma jj production is found with an observed significance of 3.2 sigma for the background-only hypothesis, compared with an expected significance of 3.7 sigma. The combination of this result with the previously published ATLAS observation of electroweak Z(v (v) over bar)gamma jj production yields an observed (expected) signal significance of 6.3 sigma (6.6 sigma). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.For complete list of authors see http://dx.doi.org/10.1007/JHEP06(2023)082</p
Measurements of azimuthal anisotropies of jet production in Pb collisions at root(NN)-N-s=5.02 TeV with the ATLAS detector
No full textThe azimuthal variation of jet yields in heavy-ion collisions provides information about the path-length dependence of the energy loss experienced by partons passing through the hot, dense nuclear matter known as the quark-gluon plasma. This paper presents the azimuthal anisotropy coefficients v(2), v(3), and v(4) measured for jets in Pb + Pb collisions at root(NN)-N-s =5.02 TeV using the ATLAS detector at the LHC. The measurement uses data collected in 2015 and 2018, corresponding to an integrated luminosity of 2.2 nb(-1). The v(n) values are measured as a function of the transverse momentum of the jets between 71 and 398 GeV and the event centrality. A nonzero value of v(2) is observed in all but the most central collisions. The value of v(2) is largest for jets with lower transverse momentum, with values up to 0.05 in mid-central collisions. A smaller, nonzero value of v(3) of approximately 0.01 is measured with no significant dependence on jet p(T) or centrality, suggesting that fluctuations in the initial state play a small but distinct role in jet energy loss. No significant deviation of v(4) from zero is observed in the measured kinematic region.For complete list of authors see http://dx.doi.org/10.1103/PhysRevC.105.064903</p
Vector-like quarks [Elektronisk resurs] : Status and new directions at the LHC
No full textExperimental searches for vector-like quarks have until now only considered their decays into Standard Model particles. However, various new physics scenarios predict additional scalars, so that these vector-like quarks can decay to new channels. These new channels reduce the branching ratios into Standard Model final states, significantly affecting current mass bounds. In this article, we quantitatively assess the relevance and observability of single and pair production processes of vector-like quarks, followed by decays into both standard and exotic final states. We highlight the importance of large widths and the relative interaction strengths with Standard Model particles and new scalars. Then, we review the post-Moriond 2024 status of these models in light of available LHC data and discuss potential future strategies to enhance the scope of vector-like quark searches.</p
Measurement of the polarisation of Wbosons produced in top-quark decays using dilepton events at â\u88\u9as=13TeV with the ATLAS experiment
No full textA measurement of the polarisation of Wbosons produced in top-quark decays is presented, using proton-proton collision data at a centre-of-mass energy of v s= 13TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139fb(-1). The measurement is performed selecting t tevents decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos theta* variable, where theta(*) is the angle between the momentum direction of the charged lepton from the Wboson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the Wboson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos theta* angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f(0) = 0.684 +/- 0.005 (stat.)+/- 0.014 (syst.), f(L)= 0.318 +/- 0.003 (stat.)+/- 0.008 (syst.) and f(R)=-0.002 +/- 0.002 (stat.)+/- 0.014 (syst.), in agreement with the Standard Model prediction. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2023.137829</p
Author Correction: Observation of an ultra-high-energy cosmic neutrino with KM3NeT (Nature, (2025), 638, 8050, (376-382), 10.1038/s41586-024-08543-1)
No full textCorrection to: Naturehttps://doi.org/10.1038/s41586-024-08543-1 Published online 12 February 2025 In the version of the article initially published, M. D. Filipović’s surname appeared incorrectly (as Filipovićv) and has now been amended in the HTML and PDF versions of the article
Correlations between flow and transverse momentum in Xe plus Xe and Pb plus Pb collisions at the LHC with the ATLAS detector : A probe of the heavy-ion initial state and nuclear deformation
No full textThe correlations between flow harmonics v(n) for n = 2, 3, and 4 and mean transverse momentum [pT] in Xe-129 + Xe-129 and Pb-208 + Pb-208 collisions at root s = 5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The v(n)-[p(T)] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality -and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v(2)-[p(T)] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb + Pb and Xe + Xe data confirms that the Xe-129 nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the Xe-129 nucleus from high-energy heavy-ion collisions.For complete list of authors see http://dx.doi.org/10.1103/PhysRevC.107.054910</p
Longitudinal flow decorrelations in Xe+Xe collisions at √sNN=5.44 TeV with the ATLAS detector
No full textThe first measurement of longitudinal decorrelations of harmonic flow amplitudes
v
n
for
n
=
2
–
4
in
Xe
+
Xe
collisions at
√
s
N
N
=
5.44
TeV
is obtained using
3
μ
b
−
1
of data with the ATLAS detector at the LHC. The decorrelation signal for
v
3
and
v
4
is found to be nearly independent of collision centrality and transverse momentum (
p
T
) requirements on final-state particles, but for
v
2
a strong centrality and
p
T
dependence is seen. When compared with the results from
Pb
+
Pb
collisions at
√
s
N
N
=
5.02
TeV
, the longitudinal decorrelation signal in midcentral
Xe
+
Xe
collisions is found to be larger for
v
2
, but smaller for
v
3
. Current hydrodynamic models reproduce the ratios of the
v
n
measured in
Xe
+
Xe
collisions to those in
Pb
+
Pb
collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between
Xe
+
Xe
and
Pb
+
Pb
. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions
A search for an unexpected asymmetry in the production of e(+)mu(-) and e(-)mu(+) pairs in proton-proton collisions recorded by the ATLAS detector at root s=13 TeV
No full textThis search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for e(+)mu(-) and e(-)mu(+) pairs to constrain physics processes beyond the Standard Model. It uses 139 fb(-1) of proton-proton collision data recorded at root s = 13 TeV at the LHC. Targeting sources of new physics which prefer final states containing e(+)mu(-) and e(-)mu(+), the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the R-parity-violating coupling lambda(23)(1)' is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when g(1R)(eu) = g(1R)(mu c) = 1, at 95% confidence level. The limit on the coupling reduces to g(1R)(eu) = g(1R)(mu c) = 0.46 for a mass of 1420 GeV. (C) 2022 The Author(s). Published by Elsevier B.V.For complete list of authors see http://dx.doi.org/10.1016/j.physletb.2022.137106</p
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