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Browsing Física de partículas y campos by Author "Abicht N. J."
ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
(SPRINGER, 2023/07/31) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Adam Bourdarios C.; Adamczyk L.; Adamek L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adorni S.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Ait Tamlihat M.; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.
The flavour-tagging algorithms developed by the AvTLAS Collaboration and used to analyse its dataset of root s = 13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model t (t) over bar events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.
Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS
(ELSEVIER, 2023/11/10) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
Parton energy loss in the quark-gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb-1 of Pb+Pb data and 260 pb-1 of pp data, both at root sNN = 5.02 TeV, with the ATLAS detector. The process pp -> gamma +jet+X and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum (pT) above 50 GeV and reported as a function of jet pT. This selection results in a sample of jets with a steeply falling pT distribution that are mostly initiated by the showering of quarks. The pp and Pb+Pb measurements are used to report the nuclear modification factor, RAA, and the fractional energy loss, Sloss, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The RAA and Sloss values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss. (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 SCOAP3.
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ ? 4l events with the ATLAS detector at ?s=13 TeV
(SPRINGER, 2023/12/15) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Afolder A. A.; Afk Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
Inclusive and differential cross-sections for dilepton t(t)over-bar production measured in ?s=13 TeV pp collisions with the ATLAS detector
(SPRINGER, 2023/07/17) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Adam Bourdarios C.; Adamczyk L.; Adamek L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adorni S.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Ait Tamlihat M.; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.
Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (t (t) over bar) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of root s = 13TeV and correspond to an integrated luminosity of 140 fb(-1). The measurements use events containing an oppositely charged e mu pair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p(T) distributions is obtained by reweighting the t (t) over bar sample so as to reproduce the top-quark p(T) distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be sigma(t (t) over bar) = 829 +/- 1 (stat) +/- 13 (syst) +/- 8 (lumi) +/- 2 (beam) pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the H ? WW* ? e??? decay channel at 13 TeV with the ATLAS detector
(AMER PHYSICAL SOC, 2023/10/11) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
The vector-boson production cross section for the Higgs boson decay in the H -> WW* -> e nu mu nu channel is measured as a function of kinematic observables sensitive to the Higgs boson production and decay properties as well as integrated in a fiducial phase space. The analysis is performed using the proton-proton collision data collected by the ATLAS detector in Run 2 of the LHC at root s = 13 TeV center-of-mass energy, corresponding to an integrated luminosity of 139 fb(-1). The different flavor final state is studied by selecting an electron and a muon originating from a pair of W bosons and compatible with the Higgs boson decay. The data are corrected for the effects of detector inefficiency and resolution, and the measurements are compared with different state-of-the-art theoretical predictions. The differential cross sections are used to constrain anomalous interactions described by dimension-six operators in an effective field theory.
Measurement of the B0s ? ?? effective lifetime with the ATLAS detector
(SPRINGER, 2023/09/28) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
This paper reports the first ATLAS measurement of the B-s(0) -> mu mu effective lifetime. The measurement is based on the data collected in 2015-2016, amounting to 26.3 fb(-1) of 13TeV LHC proton-proton collisions. The proper decay-time distribution of 58 +/- 13 background-subtracted signal candidates is fit with simulated signal templates parameterised as a function of the B-s(0) effective lifetime, with statistical uncertainties extracted through a Neyman construction. The resulting effective measurement of the B-s(0) -> mu mu lifetime is 0.99(-0.07)(+0.42) (stat.) +/- 0.17 (syst.) ps and it is found to be consistent with the Standard Model.
Measurement of the cross-sections of the electroweak and total production of a Z? pair in association with two jets in pp collisions at ?s=13 TeV with the ATLAS detector
(ELSEVIER, 2023/11/10) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Adam Bourdarios C.; Adamczyk L.; Adamek L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.
This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Z gamma pair in association with two jets. The analysis uses 140 fb(-1)of LHC proton-proton collision data taken at root s=13 TeV recorded by the ATLAS detector during the years 2015-2018. Events with a Zboson candidate decaying into either an e(+) e(-) or mu(+) mu(-) pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and by using the information about the centrality of the system and is measured with an observed and expected significance well above five standard deviations. The fiducial pp -> Z gamma jj cross-section for the electroweak production is measured to be 3.6 +/- 0.5fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be 16.8(-1.8)(+2.0) fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions. (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/).
Measurement of the Higgs boson mass with H ? ?? decays in 140 fb-1 of ?s=13 TeV pp collisions with the ATLAS detector
(ELSEVIER, 2023/12/10) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
The mass of the Higgs boson is measured in the H -> gamma gamma decay channel, exploiting the high resolution of the invariant mass of photon pairs reconstructed from the decays of Higgs bosons produced in proton-proton collisions at a centre-of-mass energy root s = 13 TeV. The dataset was collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider, and corresponds to an integrated luminosity of 140 fb(-1). The measured value of the Higgs boson mass is 125.17 +/- 0.11 (stat.) +/- 0.09 (syst.) GeV and is based on an improved energy scale calibration for photons, whose impact on the measurement is about four times smaller than in the previous publication. A combination with the corresponding measurement using 7 and 8 TeV pp collision ATLAS data results in a Higgs boson mass measurement of 125.22 +/- 0.11 (stat.) +/- 0.09 (syst.) GeV. With an uncertainty of 1.1 per mille, this is currently the most precise measurement of the mass of the Higgs boson from a single decay channel.
Measurement of the ttcross section and its ratio to the Z production cross ?section using pp collisions at ?s=13.6 TeV with the ATLAS detector
(ELSEVIER, 2024/01/01) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
The inclusive top-quark-pair production cross section rrtt and its ratio to the Z-boson production cross section have been measured in proton-proton collisions at root s = 13.6 TeV, using 29 fb-1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be rrtt = 850 +/- 3(stat.) +/- 18(syst.) +/- 20(lumi.) pb. The ratio of the ttand the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e- and mu+mu- events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ttcross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, Rtt/Z = 1.145 +/- 0.003(stat.) +/- 0.021(syst.) +/- 0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
Measurements of multijet event isotropies using optimal transport with the ATLAS detector
(SPRINGER, 2023/10/10) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
A measurement of novel event shapes quantifying the isotropy of collider events is performed in 140 fb(-1) of proton-proton collisions with root s = 13TeV centre-of-mass energy recorded with the ATLAS detector at CERN's Large Hadron Collider. These event shapes are defined as the Wasserstein distance between collider events and isotropic reference geometries. This distance is evaluated by solving optimal transport problems, using the 'Energy-Mover's Distance'. Isotropic references with cylindrical and circular symmetries are studied, to probe the symmetries of interest at hadron colliders. The novel event-shape observables defined in this way are infrared- and collinear-safe, have improved dynamic range and have greater sensitivity to isotropic radiation patterns than other event shapes. The measured event-shape variables are corrected for detector effects, and presented in inclusive bins of jet multiplicity and the scalar sum of the two leading jets' transverse momenta. The measured distributions are provided as inputs to future Monte Carlo tuning campaigns and other studies probing fundamental properties of QCD and the production of hadronic final states up to the TeV-scale.
Observation of W?? triboson production in proton-proton collisions at ?s=13 TeV with the ATLAS detector
(ELSEVIER, 2024/01/01) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Adamek L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.
This letter reports the observation of () production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of root= 13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb-1. Events with a leptonically-decaying boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of () and () events is measured to be fid = 13.8 +/- 1.1(stat)+2.1-2.0(syst) +/- 0.1(lumi) fb, in agreement with the Standard Model prediction.
Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS
(SPRINGER, 2023/11/27) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Adamek L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.
Searches for long-lived particles (LLPs) are among the most promising avenues for discovering physics beyond the Standard Model at the Large Hadron Collider (LHC). However, displaced signatures are notoriously difficult to identify due to their ability to evade standard object reconstruction strategies. In particular, the ATLAS track reconstruction applies strict pointing requirements which limit sensitivity to charged particles originating far from the primary interaction point. To recover efficiency for LLPs decaying within the tracking detector volume, the ATLAS Collaboration employs a dedicated large-radius tracking (LRT) passwith loosened pointing requirements. During Run 2 of the LHC, the LRT implementation produced many incorrectly reconstructed tracks and was therefore only deployed in small subsets of events. In preparation for LHC Run 3, ATLAS has significantly improved both standard and large-radius track reconstruction performance, allowing for LRT to run in all events. This development greatly expands the potential phase-space of LLP searches and streamlines LLP analysis workflows. This paper will highlight the above achievement and report on the readiness of the ATLAS detector for track-based LLP searches in Run 3.
Pursuit of paired dijet resonances in the Run 2 dataset with ATLAS
(AMER PHYSICAL SOC, 2023/12/13) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using 140 fb(-1) of proton-proton collisions at ffiffiffisp root s = 13 TeV recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. Resonances are searched for in the invariant mass of the tetrajet system, and in the average invariant mass of the pair of dijet systems. A data-driven background estimate is obtained by fitting the tetrajet and dijet invariant mass distributions with a four-parameter dijet function and a search for local excesses from resonant production of dijet pairs is performed. No significant excess of events beyond the Standard Model expectation is observed, and upper limits are set on the production cross sections of new physics scenarios.
Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of ?-leptons with the ATLAS detector
(SPRINGER, 2023/10/03) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
A search for a new heavy scalar particle X decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle S is presented. The search uses a proton-proton (pp) collision data sample with an integrated luminosity of 140 fb(-1) recorded at a centre-of-mass energy of root s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in X mass ranging from 500 to 1500 GeV, with the corresponding S mass in the range 200-500 GeV. The search selects events with two hadronically decaying tau-lepton candidates from H -> tau(+)tau(-) decays and one or two light leptons (l = e, mu) from S -> VV (V = W, Z) decays while the remaining V boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section sigma(pp -> X -> SH) assuming the same SM-Higgs boson-like decay branching ratios for the S -> VV decay. Upper limits on the visible cross-sections sigma(pp -> X -> SH -> WW tau tau) and sigma(pp -> X -> SH -> ZZ tau tau) are also set in the ranges 3-26 fb and 6-33 fb, respectively.
Search for a new pseudoscalar decaying into a pair of muons in events with a top-quark pair at?s=13 TeV with the ATLAS detector
(AMER PHYSICAL SOC, 2023/11/28) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Adamek L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.
A search for a new pseudoscalar a-boson produced in events with a top-quark pair, where the a-boson decays into a pair of muons, is performed using root s=13 TeV pp collision data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb(-1). The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons e mu mu and mu mu mu. No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: pp -> tta and pp -> tt with t -> H(perpendicular to)b, H-perpendicular to -> W(perpendicular to)a, where a ->mu mu, in the mass ranges 15 GeV<72 GeV and 120 GeV <= m(H +/-)<= 160 GeV.
Search for an axion-like particle with forward proton scattering in association with photon pairs at ATLAS
(SPRINGER, 2023/07/31) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Hoffman A. C. Abusleme; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Adamek L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.; Al Khoury K.
A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of root s = 13TeV were analysed, corresponding to an integrated luminosity of 14.6 fb(-1). A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150-1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04-0.09TeV-1 at 95% confidence level.
Search for direct production of electroweakinos in final states with one lepton, jets and missing transverse momentum in pp collisions at ?s=13 TeV with the ATLAS detector
(SPRINGER, 2023/12/27) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Afolder A. A.; Afk Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Aktas S.; Al Khoury K.
Searches for electroweak production of wino-like chargino pairs, (chi) over tilde (+)(1)(chi) over tilde (-), 1, and of wino-like chargino and next-to-lightest neutralino, (chi) over tilde (+/-)(1)(chi) over tilde (0)(2), are presented. The models explored assume that the charginos decay into a W boson and the lightest neutralino, (chi) over tilde chi(+/-)(1) -> W-+/- (chi) over tilde (0)(1) The next-to-lightest neutralinos are degenerate in mass with the chargino and decay to (chi) over tilde (0)(1) and either a Z or a Higgs boson, (chi) over tilde (0)(2) -> Z (chi) over tildeX(1)(0) or h (chi) over tilde (0)(1). The searches exploit the presence of a single isolated lepton and missing transverse momentum from the W boson decay products and the lightest neutralinos, and the presence of jets from hadronically decaying Z or W bosons or from the Higgs boson decaying into a pair of b-quarks. The searches use 139 fb(-1) of root s = 13TeV proton-proton collisions data collected by the ATLAS detector at the Large Hadron Collider between 2015 and 2018. No deviations from the Standard Model expectations are found, and 95% confidence level exclusion limits are set. Chargino masses ranging from 260 to 520 GeV are excluded for a massless (chi) over tilde (1)(0) in chargino pair production models. Degenerate chargino and next-to-lightest neutralino masses ranging from 260 to 420 GeV are excluded for a massless (chi) over tilde (1)(0) for (chi) over tilde (0)(2) -> Z (chi) over tilde (0)(1). For decays through an on-shell Higgs boson and for mass-splitting between (chi) over tilde (+/-)(1)/(chi) over tilde (0)(2) and (chi) over tilde (0)(1) as small as the Higgs boson mass, mass limits are improved by up to 40 GeV in the range of 200-260 GeV and 280-470 GeV compared to previous ATLAS constraints.
Search for excited ?-leptons and leptoquarks in the final state with ?-leptons and jets in pp collisions at ?s=13 TeV with the ATLAS detector
(SPRINGER, 2023/06/29) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hoffman A. C.; Acharya B. S.; Adam Bourdarios C.; Adamczyk L.; Adamek L.; Addepalli S. V.; Addison M. J.; Adelman J.; Adiguzel A.; Adorni S.; Adye T.; Affolder A. A.; Afik Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Ait Tamlihat M.; Aitbenchikh B.; Aizenberg I.; Akbiyik M.; Akesson T. P. A.; Akimov A. V.; Akiyama D.; Akolkar N. N.
A search is reported for excited tau-leptons and leptoquarks in events with two hadronically decaying tau-leptons and two or more jets. The search uses proton-proton (pp) collision data at root s = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015-2018. The total integrated luminosity is 139 fb(-1). The excited tau-lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary tau-lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a tau-lepton. No excess over the background prediction is observed. Excited tau-leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Lambda set to 10 TeV. At the extreme limit of model validity where Lambda is set equal to the excited tau-lepton mass, excited tau-leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a tau-lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.
Search for flavour-changing neutral tqH interactions with H ? ?? in pp collisions at ?s=13 TeV using the ATLAS detector
(SPRINGER, 2023/12/28) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Afolder A. A.; Afk Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Aikot A.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.; Alberghi G. L.
A search for flavour-changing neutral interactions involving the top quark, the Higgs boson and an up-type quark q ( q = c, u) is presented. The proton-proton collision data set used, with an integrated luminosity of 139 fb(-1), was collected at root s = 13TeV by the ATLAS experiment at the Large Hadron Collider. Both the decay process t -> qH in tt production and the production process pp. tH, with the Higgs boson decaying into two photons, are investigated. No significant excess is observed and upper limits are set on the t. cH and the t. uH branching ratios of 4.3x10(-4) and 3.8x10(-4), respectively, at the 95% confidence level, while the expected limits in the absence of signal are 4.7x10(-4) and 3.9x10(-4). Combining this search with ATLAS searches in the H. t+ t- and H. b b final states yields observed (expected) upper limits on the t -> cH branching ratio of 5.8 x 10(-4) (3.0 x 10(-4)) at the 95% confidence level. The corresponding observed (expected) upper limit on the t -> uH branching ratio is 4.0 x 10(-4) (2.4 x 10(-4)).
Search for heavy Higgs bosons with flavour-violating couplings in multi-lepton plus b-jets final states in pp collisions at 13 TeV with the ATLAS detector
(SPRINGER, 2023/12/12) Aad G.; Abbott B.; Abeling K.; Abicht N. J.; Abidi S. H.; Aboulhorma A.; Abramowicz H.; Abreu H.; Abulaiti Y.; Abusleme Hofman A. C.; Acharya B. S.; Bourdarios C. Adam; Adamczyk L.; Adamek L.; Addepalli S. V; Addison M. J.; Adelman J.; Adiguzel A.; Adye T.; Afolder A. A.; Afk Y.; Agaras M. N.; Agarwala J.; Aggarwal A.; Agheorghiesei C.; Ahmad A.; Ahmadov F.; Ahmed W. S.; Ahuja S.; Ai X.; Aielli G.; Tamlihat M. Ait; Aitbenchikh B.; Aizenberg I; Akbiyik M.; Akesson T. P. A.; Akimov A. V; Akiyama D.; Akolkar N. N.; Al Khoury K.
A search for new heavy scalars with flavour-violating decays in final states with multiple leptons and b-tagged jets is presented. The results are interpreted in terms of a general two-Higgs-doublet model involving an additional scalar with couplings to the top-quark and the three up-type quarks (rho(tt),rho(tc), and rho(tu)). The targeted signals lead to final states with either a same-sign top-quark pair, three top-quarks, or four top-quarks. The search is based on a data sample of proton-proton collisions at root s = 13TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). Events are categorised depending on the multiplicity of light charged leptons (electrons or muons), total lepton charge, and a deep-neural-network output to enhance the purity of each of the signals. Masses of an additional scalar boson mH between 200- 630 GeV with couplings rho(tt) = 0.4, rho(tc) = 0.2, and rho(tu) = 0.2 are excluded at 95% confidence level. Additional interpretations are provided in models of R-parity violating supersymmetry, motivated by the recent flavour and ( g - 2) (mu) anomalies.