Search for non-resonant Higgs boson pair production in the final state in pp collisions at = 13 TeV with the ATLAS detector
Physics Letters B
Published On 2020/2/10
A search for non-resonant Higgs boson pair production, as predicted by the Standard Model, is presented, where one of the Higgs bosons decays via the H→ b b channel and the other via one of the H→ W W⁎/Z Z⁎/τ τ channels. The analysis selection requires events to have at least two b-tagged jets and exactly two leptons (electrons or muons) with opposite electric charge in the final state. Candidate events consistent with Higgs boson pair production are selected using a multi-class neural network discriminant. The analysis uses 139 fb− 1 of pp collision data recorded at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. An observed (expected) upper limit of 1.2 (0.9− 0.3+ 0.4) pb is set on the non-resonant Higgs boson pair production cross-section at 95% confidence level, which is equivalent to 40 (29− 9+ 14) times the value predicted in the Standard Model.
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Physics Letters B
Published On
2020/2/10
Volume
801
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135145
Authors
Silvia Behar Harpaz
Technion - Israel Institute of Technology
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High Energy Physics
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Xiaofeng Wang
Tsinghua University
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Physics Department
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283
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185
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supernova
time-domain astronomy
AGN
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Stephane Willocq
University of Massachusetts Amherst
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272
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167
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Eric Torrence
University of Oregon
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Particle Physics
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Jonathan Butterworth
University College London
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Professor of Physics
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Glen Cowan
Royal Holloway, University of London
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Masahiro Kuze
Tokyo Institute of Technology
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Professor Department of Physics
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Andreas Warburton
McGill University
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Joey Huston
Michigan State University
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Physics Letters B
Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at s= 13 TeV, corresponding to 139 fb− 1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the a particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the a decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in …
2024/2/21
Article DetailsMartin Grunewald
University College Dublin
Physics Letters B
Measurements of azimuthal anisotropy of nonprompt D0 mesons in PbPb collisions at sNN= 5.02 TeV
Measurements of the elliptic (v 2) and triangular (v 3) azimuthal anisotropy coefficients are presented for Image 1 mesons produced in Image 2 hadron decays (nonprompt Image 1 mesons) in lead-lead collisions at s NN= 5.02 TeV. The results are compared with previously published charm meson anisotropies measured using prompt Image 1 mesons. The data were collected with the CMS detector in 2018 with an integrated luminosity of 0.58 nb− 1. Azimuthal anisotropy is sensitive to the interactions of quarks with the hot and dense medium created in heavy ion collisions. Comparing results for prompt and nonprompt Image 1 mesons can assist in understanding the mass dependence of these interactions. The nonprompt results show lower magnitudes of v 2 and v 3 and weaker dependences on the meson transverse momentum and collision centrality than those found for prompt Image 1 mesons. The results are …
2024/2/12
Article DetailsFabrizio Illuminati
Università degli Studi di Salerno
Physics Letters B
Gravitationally modulated quantum correlations: Discriminating classical and quantum models of ultra-compact objects with Bell nonlocality
We investigate the relation between quantum nonlocality and gravity at the astrophysical scale, both in the classical and quantum regimes. Considering a gedanken experiment involving particle pairs orbiting in the strong gravitational field of ultra-compact objects, we find that the violation of Bell inequality acquires an angular modulation factor that strongly depends on the nature of the gravitational source. We show how such gravitationally-induced modulation of quantum nonlocality readily discriminates between black holes (both classical and inclusive of quantum corrections) and string fuzzballs, i.e., the true quantum description of ultra-compact objects according to string theory. These findings promote Bell nonlocality as a potentially key tool in putting quantum gravity to the test.
2024/4/18
Article DetailsIgor Altsybeev
St. Petersburg State University
Physics Letters B
Measurement of the low-energy antitriton inelastic cross section
In this Letter, the first measurement of the inelastic cross section for antitriton–nucleus interactions is reported, covering the momentum range of 0.8≤ p< 2.4 GeV/c. The measurement is carried out using data recorded with the ALICE detector in pp and Pb–Pb collisions at a centre-of-mass energy per nucleon of 13 TeV and 5.02 TeV, respectively. The detector material serves as an absorber for antitriton nuclei. The raw yield of (anti) triton nuclei measured with the ALICE apparatus is compared to the results from detailed ALICE simulations based on the Image 1 toolkit for the propagation of (anti) particles through matter, allowing one to quantify the inelastic interaction probability in the detector material. This analysis complements the measurement of the inelastic cross section of antinuclei up to A= 3 carried out by the ALICE Collaboration, and demonstrates the feasibility of the study of the isospin dependence of …
2024/1/1
Article DetailsIgor Altsybeev
St. Petersburg State University
Physics Letters B
Measurement of the radius dependence of charged-particle jet suppression in Pb–Pb collisions at sNN= 5.02 TeV
The ALICE Collaboration reports a differential measurement of inclusive jet suppression using pp and Pb–Pb collision data at a center-of-mass energy per nucleon–nucleon collision s NN= 5.02 TeV. Charged-particle jets are reconstructed using the anti-k T algorithm with resolution parameters R= 0.2, 0.3, 0.4, 0.5, and 0.6 in pp collisions and R= 0.2, 0.4, 0.6 in central (0–10%), semi-central (30–50%), and peripheral (60–80%) Pb–Pb collisions. A novel approach based on machine learning is employed to mitigate the influence of jet background. This enables measurements of inclusive jet suppression in new regions of phase space, including down to the lowest jet p T≥ 40 GeV/c at R= 0.6 in central Pb–Pb collisions. This is an important step for discriminating different models of jet quenching in the quark–gluon plasma. The transverse momentum spectra, nuclear modification factors, derived cross section, and …
2024/2/1
Article DetailsIgor Altsybeev
St. Petersburg State University
Physics Letters B
Measurements of inclusive J/ψ production at midrapidity and forward rapidity in Pb–Pb collisions at sNN= 5.02 TeV
The measurements of the inclusive J/ψ yield at midrapidity (| y|< 0. 9) and forward rapidity (2.5< y< 4) in Pb–Pb collisions at s NN= 5.02 TeV with the ALICE detector at the LHC are reported. The inclusive J/ψ production yields and nuclear modification factors, R AA, are measured as a function of the collision centrality, J/ψ transverse momentum (p T), and rapidity. The J/ψ average transverse momentum and squared transverse momentum (< p T> and< p T 2>) are evaluated as a function of the centrality at midrapidity. Compared to the previous ALICE publications, here the entire Pb–Pb collisions dataset collected during the LHC Run 2 is used, which improves the precision of the measurements and extends the p T coverage. The p T-integrated R AA shows a hint of an increasing trend towards unity from semicentral to central collisions at midrapidity, while it is flat at forward rapidity. The p T-differential R AA shows a …
2024/2/1
Article DetailsIgor Altsybeev
St. Petersburg State University
Physics Letters B
Skewness and kurtosis of mean transverse momentum fluctuations at the LHC energies
The first measurements of skewness and kurtosis of mean transverse momentum (< p T>) fluctuations are reported in Pb–Pb collisions at s NN= 5.02 TeV, Xe–Xe collisions at s NN= 5.44 TeV and pp collisions at s= 5.02 TeV using the ALICE detector. The measurements are carried out as a function of system size< d N ch/d η>| η|< 0.5 1/3, using charged particles with transverse momentum (p T) and pseudorapidity (η), in the range 0.2< p T< 3.0 GeV/c and| η|< 0.8, respectively. In Pb–Pb and Xe–Xe collisions, positive skewness is observed in the fluctuations of< p T> for all centralities, which is significantly larger than what would be expected in the scenario of independent particle emission. This positive skewness is considered a crucial consequence of the hydrodynamic evolution of the hot and dense nuclear matter created in heavy-ion collisions. Furthermore, similar observations of positive skewness for minimum …
2024/2/23
Article DetailsIgor Altsybeev
St. Petersburg State University
Physics Letters B
Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb–Pb and Xe–Xe collisions
The pseudorapidity dependence of elliptic (v 2), triangular (v 3), and quadrangular (v 4) flow coefficients of charged particles measured in Pb–Pb collisions at a centre-of-mass energy per nucleon pair of s NN= 5.02 TeV and in Xe–Xe collisions at s NN= 5.44 TeV with ALICE at the LHC are presented. The measurements are performed in the pseudorapidity range− 3.5< η< 5 for various centrality intervals using two-and multi-particle cumulants with the subevent method. The flow probability density function (pdf) is studied with the ratio of flow coefficient v 2 calculated with four-and two-particle cumulant, and suggests that the variance of flow pdf is independent of pseudorapidity. The decorrelation of the flow vector in the longitudinal direction is probed using two-particle correlations. The results measured with respect to different reference regions in pseudorapidity exhibit differences, argued to be a result of saturating …
2024/3/1
Article DetailsLuis Fraile
Universidad Complutense de Madrid
Physics Letters B
Magnetic moments of thallium isotopes in the vicinity of magic N= 126
The magnetic dipole moments (μ) of 209 Tl g (N= 128) and 207 Tl m (N= 126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾ 207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ (Tl g, I π= 1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with I π= 1/2+.
2024/2/1
Article DetailsElham E Khoda
University of Washington
Physics Letters B
Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS
Semi-visible jets, with a significant contribution to the event's missing transverse momentum, can arise in strongly interacting dark sectors. This results in an event topology where one of the jets can be aligned with the direction of the missing transverse momentum. The first search for semi-visible jets produced via a t-channel mediator exchange is presented. The analysis uses proton-proton collisions with an integrated luminosity of 139 fb−1 and a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during the Run 2 of the LHC. No excess over Standard Model predictions is observed. Assuming a coupling strength of unity between the mediator, a Standard Model quark and a dark quark, mediator masses up to 2.7 TeV are excluded at the 95% confidence level. Upper limits on the coupling strength are also derived.
2024/1/1
Article DetailsElham E Khoda
University of Washington
Physics Letters B
Measurement of the tt¯ cross section and its ratio to the Z production cross section using pp collisions at s= 13.6 TeV with the ATLAS detector
The inclusive top-quark-pair production cross section σ t t¯ and its ratio to the Z-boson production cross section have been measured in proton–proton collisions at 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 σ t t¯= 850±3 (stat.)±18 (syst.)±20 (lumi.) pb. The ratio of the t t¯ and the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+ e− and μ+ μ− events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the t t¯ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, R t t¯/Z= 1.145±0.003 (stat.)±0.021 (syst.)±0.002 (lumi.) is consistent …
2024/1/1
Article DetailsElham E Khoda
University of Washington
Physics Letters B
Search for the Zγ decay mode of new high-mass resonances in pp collisions at s= 13 TeV with the ATLAS detector
This letter presents a search for narrow, high-mass resonances in the Zγ final state with the Z boson decaying into a pair of electrons or muons. The s= 13 TeV pp collision data were recorded by the ATLAS detector at the CERN Large Hadron Collider and have an integrated luminosity of 140 fb− 1. The data are found to be in agreement with the Standard Model background expectation. Upper limits are set on the resonance production cross section times the decay branching ratio into Zγ. For spin-0 resonances produced via gluon–gluon fusion, the observed limits at 95% confidence level vary between 65.5 fb and 0.6 fb, while for spin-2 resonances produced via gluon–gluon fusion (or quark–antiquark initial states) limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb, for the mass range from 220 GeV to 3400 GeV.
2024/1/1
Article DetailsElham E Khoda
University of Washington
Physics Letters B
Observation of Wγγ triboson production in proton-proton collisions at s= 13 TeV with the ATLAS detector
This letter reports the observation of W (ℓ ν) γ γ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of s= 13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb− 1. Events with a leptonically-decaying W 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 W (e ν) γ γ and W (μ ν) γ γ events is measured to be σ fid= 13.8±1.1 (stat)+ 2.1− 2.0 (syst)±0.1 (lumi) fb, in agreement with the Standard Model prediction.
2024/1/1
Article Details