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    15370 research outputs found

    W, Z, and QCD

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    The analyses of W and Z vector bosons, photon, and jets production have been carried out by the ATLAS and CMS collaborations using datasets collected during LHC Run 2, comprising from 36.3 fb−1 to 140 fb−1. Unfolded differential production cross sections as well as event shape observables have been measured, allowing to achieve tests of perturbative quantum chromodynamics, extractions of fundamental parameters of the Standard Model, and constraints on parton density functions

    Inclusive and differential σtt¯ measurements using the ATLAS detector

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    Measurements of the total and differential top-quark pair-production cross-sections in proton proton collisions at 13 TeV with the ATLAS detector at the Large Hadron Collider (LHC) are presented. The measurements use data collected by ATLAS during the entire LHC Run 2 (2015 - 2018) corresponding to an integrated luminosity of 140 fb−1. The measurements are performed in the di-lepton channel, requiring an opposite-charge high-pT electron-muon pair and b-tagged jets. The experimental uncertainties due to the identification of b-quark jets are constrained in-situ by data. The total cross-section is compared to predictions by theoretical QCD calculations at next-to-next-to-leading (NNLO) order. Absolute and normalised single- and double-differential cross-sections are calculated as a function of single-lepton and dilepton kinematic variables, featuring finer granularity and extended kinematic range compared to previous ATLAS measurements. The results are compared with multiple predictions from next-to-leading-order QCD matrixelement generators matched with parton-shower generators

    Neutrino anomalies and future prospects in neutrino physics

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    I give an overview of some of the several anomalies appearing in neutrino oscillation experiments, setting particular focus to the reactor antineutrino anomaly and the Gallium anomaly. I will discuss these two anomalies in some detail and, in particular, compare their explanation due to neutrino oscillations in presence of a light sterile neutrino among each other and also with the bounds from the analyses of reactor spectral ratio data, β-decay data, and solar neutrino data

    Hunting for the second Higgs resonance at LHC

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    According to perturbative calculations, the effective potential of the Standard Model should have a new minimum, well beyond the Planck scale, which is much deeper than the electroweak vacuum. Since it is not obvious that gravitational effects can become so strong to stabilize the potential, most authors have accepted the metastability scenario in a cosmological perspective. This perspective is needed to explain why the theory remains trapped into our electroweak vacuum but requires to control the properties of matter in the extreme conditions of the early Universe. As an alternative, we review the completely different idea of an effective potential which, as at the beginning of the Standard Model, is restricted to the pure Φ4 sector but is consistent with the now existing analytical and numerical studies. In this approach, where the electroweak vacuum is the lowest energy state, beside the resonance of mass mh = 125 GeV defined by the quadratic shape of the potential at its minimum, the Higgs field should exhibit a second resonance with a mass (MH) theor = 690 ± 10 (stat) ± 20 (sys) GeV associated with the zero-point energy which determines the potential depth. In spite of its large mass, this would couple to longitudinal W’s with the same typical strength as the low-mass state at 125 GeV and represent a relatively narrow resonance of width ΓH = 30 ÷ 36 GeV, mainly produced at LHC by gluon-gluon fusion. Thus it is interesting that, in the LHC data, there are various indications for a new resonance in the expected mass range with a statistical significance which is far from being negligible and could become an important new discovery by just adding two missing samples of RUN2 data

    YSF talk: Search for new physics in top quark production with additional leptons using the framework of effective field theory

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    This analysis presents a search for new physics impacting associated top quark production within the context of effective field theory (EFT). Making use of 138 fb−1 of proton-proton collisions at √s = 13 TeV collected by the CMS experiment at the CERN LHC during 2016-2018, the analysis selects events with multiple jets, b-tagged jets, and two same-sign leptons or three or more leptons. The data are further binned according to kinematical distributions associated with the transverse momentum of the objects in the event. The effects of 26 dimensionsix EFT operators are incorporated into the simulation, allowing for the predicted yields in each observable bin to be parameterized in terms of the strengths of the 26 EFT operators. A simultaneous fit of the 26 EFT parameters to the observed data is performed, and confidence intervals are extracted. The results are consistent with the standard model prediction

    The measurement of muon g−2 at Fermilab

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    The Muon g −2 Experiment at Fermilab (E989) was built to repeat and improve the previous E821 Experiment at Brookhaven National Laboratory (BNL), aiming to reduce the experimental error by a factor of 4 to the final accuracy of 140 parts per billion (ppb). On April 7th, 2021, the E989 collaboration published the first result based on the first year of data taking (Run-1), measuring aμ = 0.001 165 920 40(54) with a precision of 460 ppb. The measured value is consistent with the BNL measurement and strengthens the long-standing tension with the data-driven SM prediction to a combined discrepancy of 4.2σ. On the theory side, however, new efforts involving lattice-QCD techniques are starting to question the current consensus on the theoretical prediction, demanding new improvements on both the experimental and theoretical sides. The Muon g−2 Experiment at Fermilab has now concluded its sixth and final year of data taking, and a new result based on the Run-2 and Run-3 data was published in August 2023. This paper briefly describes the Muon g − 2 Experiment at Fermilab and its current status

    Evidence of the off-shell Higgs and Higgs decay width constraints at ATLAS

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    This paper reports a search for off-shell Higgs boson production and the measurement of the Higgs decay width using the full Run-2 pp collision dataset, corresponding to an integrated luminosity of 139 fb−1, collected by the ATLAS detector at the Large Hadron Collider. In this analysis, the Higgs boson production modes include gluon-gluon fusion, vector-boson fusion, and VH, while the Higgs boson decay channels ZZ → 4l and Z'Z → 22ν (l = e or μ) are considered. The background-only hypothesis is rejected at the confidence level of 3.3 σ (2.2 σ) for the observed (expected) result, providing evidence of the off-shell Higgs boson. The combination of the off-shell and on-shell Higgs boson measurements can constrain the Higgs decay width to be 4.5+3.3−2.5 MeV, with an upper limit of 10.5 MeV at the 95% confidence level

    The muon g−2 within the Standard Model

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    We summarize recent developments in the Standard-Model evaluation of the anomalous magnetic moment of the muon aμ, both in the hadronic-lightby-light and hadronic-vacuum-polarization contributions. The current situation for the latter is puzzling as we are confronted with multiple discrepancies that are not yet understood. We present updated fits of a dispersive representation of the pion vector form factor to the new CMD-3 data set and quantify the tensions with the other high-statistics e+e− → π+π− experiments in the contribution to aμ in the energy range up to 1 GeV, as well as in the corresponding contribution to the intermediate Euclidean window

    Rare and semileptonic decays and LFNU at LHCb

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    The couplings of electroweak gauge bosons and the different lepton families are universal in the Standard Model. However, recent measurements have shown deviations from this behavior, which could potentially be due to contribution from new physics. The lepton flavour universality tests done at the LHCb experiment using tree-level and rare B decays, lepton flavour violating decays and decay rate measurements of some rare decays are presented

    Rare and very rare decays of hyperons and heavy baryons at LHCb

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    This contribution presents the most recent results related to rare and very rare decays involving hyperons and heavy baryons at the LHCb experiment. The new results encompass the decays Λ0 b → D−s p and Ξ++cc → Ξ+c π+, using data obtained from proton-proton collisions at a center-of-mass energy of 13 TeV during the LHC Run 2 data-taking, corresponding to a total integrated luminosity of ∼ 6 fb−1. Additionally, this contribution includes the investigation of the Σ+ → pμ+μ− decay, which was already explored during Run 1, and outlines prospects for the ongoing Run 2 analysis

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