Accelerator Neutrinos

Abstract:

The production cross-section of high-mass τ-lepton pairs is measured as a function of the dilepton visible invariant mass, using 140 fb−1 of s=13 TeV proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider. The measurement agrees with the predictions of the Standard Model. A fit to the invariant mass distribution is performed as a function of b-jet multiplicity, to constrain the non-resonant production of new particles described by an effective field theory or in models containing leptoquarks or Z′ bosons that couple preferentially to third-generation fermions. The constraints on new particles improve on previous results, and the constraints on effective operators include those affecting the anomalous magnetic moment of the τ-lepton.

Abstract:

A measurement of off-shell Higgs boson production is performed in the H * → W W channel. The measurement uses a proton–proton collision dataset with an integrated luminosity of 140 fb − 1 collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. Final states in which both W bosons decay leptonically are targeted, and events are categorised based on the flavour of the final-state leptons, the jet multiplicity, and the output of neural network-based classifiers. The data are found to be compatible with the Standard Model expectation. An observed (expected) upper bound on the 95% symmetric confidence level interval is set on the rate of off-shell Higgs boson production at a value of 3.4 (4.4) times the Standard Model prediction. These results are combined with the results from the measurement of on-shell Higgs boson production in the same final states to obtain an observed (expected) upper bound at 95 % confidence level on the Higgs boson total width of 13.1 (17.3) MeV.

Abstract:

We report a new measurement of flux-integrated differential cross sections for charged-current (CC) muon neutrino interactions with argon nuclei that produce no final-state pions ( ${\nu }_{\mu }\mathrm{CC}0\pi$ ). These interactions are of particular importance as a topologically defined signal dominated by quasielasticlike interactions. This measurement was performed with the MicroBooNE liquid argon time projection chamber detector located at the Fermilab Booster Neutrino Beam and uses an exposure of $1.3\times {10}^{21}$ protons on target collected between 2015 and 2020. The results are presented in terms of single- and double-differential cross sections as a function of the final-state muon momentum and angle. The data are compared with widely used neutrino event generators. We find good agreement with the single-differential measurements, while only a subset of generators are also able to adequately describe the data in double-differential distributions. This work facilitates comparison with Cherenkov detector measurements, including those located at the Booster Neutrino Beam.

Abstract:

A search for exotic decays of the Higgs boson $H$ into new scalar or pseudoscalar particles that subsequently decay into $b$ -quarks is presented. The search considers $ZH$ production with several decay scenarios for the Higgs boson; first to a pair of identical scalars, $H\to 2a\to 4b$ , second to a pair of scalars with different masses ( $m_{a1}<m_{a2}$ ), either directly, $H\to a_1{a}_2\to 4b$ , or via a longer decay chain, $H\to a_1{a}_2\to 3a_1\to 6b$ . The analysis uses proton-proton collision data at $\sqrt{s}=13\mathrm{TeV}$ collected with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of $140{\mathrm{fb}}^{-1}$ . No significant excess above the Standard Model prediction is observed. The search sets upper limits at 95% confidence level on the ratio of the Higgs boson production cross section to the SM prediction times the branching ratio of Higgs bosons decaying into $4b$ or $6b$ , between 4% and 25% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to 2a\to 4b)$ , between 24% and 38% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to a_1{a}_2\to 4b)$ , and between 10% and 20% for $\sigma (ZH)/{\sigma }_{\mathrm{SM}}(ZH)\times \mathcal{B}(H\to a_1{a}_2\to 3a_1\to 6b)$ , depending on the masses of the scalar particles.

Abstract:

This article presents a study of single ${\pi }^{+}$ production in neutrino neutral-current interactions ( $\mathrm{NC}1{\pi }^{+}$ ) using the FGD1 hydrocarbon target of the ND280 detector of the T2K experiment. We report the largest sample of such events selected by any experiment, providing the first new data for this channel in over four decades and the first using a sub-GeV neutrino flux. The signal selection strategy and its performance are detailed together with validations of a robust cross section extraction methodology. The measured flux-averaged integrated cross-section is $\sigma =(6.07\pm 1.22)\times {10}^{-41}{\mathrm{cm}}^2/\mathrm{nucleon}$ , $1.3\sigma$ above the NEUT v5.4.0 expectation.