Accelerator Neutrinos

Abstract:

Entanglement is a key property of quantum systems. In this Letter the first measurements of quantum entanglement between spins in pairs of $Z$ bosons are reported, using proton-proton collision data from the Large Hadron Collider (LHC) at center-of-mass energies of 13 and 13.6 TeV, recorded with the ATLAS detector. Measurements of angular observables sensitive to $Z{Z}^{*}$ spin-density-matrix elements in the $H\to Z{Z}^{*}\to {\ell }^{+}{\ell }^{-}{\ell }^{+}{\ell }^{-}$ process yield coefficients $C_{2,1,2,-1}=-0.71\pm 0.45$ and $C_{2,2,2,-2}=0.08\pm 0.44$ , consistent with their Standard Model predictions. A complementary hypothesis test using the full angular distribution, and relying on several Standard Model assumptions in the decays, provides substantially higher sensitivity to quantum correlations and disfavors the separable-state hypothesis at a significance of 4.7 standard deviations (expected $4.9\sigma$ ) relative to the entangled Standard Model hypothesis. These results provide strong evidence of quantum entanglement between massive bosons (spin qutrits) at the electroweak scale.

Abstract:

The MicroBooNE detector is a liquid argon time projection chamber (LArTPC) that produces three-dimensional images of particle interactions using ionization charge collected by anode wire plane arrays and scintillation light collected by a light detection system. In addition to testing long-standing experimental neutrino anomalies and performing measurements of neutrino interactions with argon nuclei using the Fermilab Booster Neutrino Beam, MicroBooNE aims to develop methodologies for rare beyond the Standard Model and off-beam physics searches. Looking ahead to future LArTPC experiments such as the upcoming Deep Underground Neutrino Experiment (DUNE), achieving high sensitivity and livetime for non-beam physics while satisfying data processing and storage constraints will require data-driven, intelligent, and online or real-time data selection techniques. MicroBooNE serves as a useful testbed for the development of such techniques, which are essential for reducing data rates and preserving rare signals with high accuracy. In this paper, we describe a fast data selection algorithm suitable for online execution to identify decay electrons from stopping cosmic ray muons in the MicroBooNE detector utilizing ionization charge information, and present its performance using MicroBooNE data. This work demonstrates the feasibility of online, charge-based, and topology-driven data selection in a LArTPC and provides an important proof-of-principle for applying such techniques to other LArTPC experiments.

Abstract:

This work presents single-differential electron-neutrino charged-current cross sections on argon measured using the MicroBooNE detector at the Fermi National Accelerator Laboratory. The analysis uses data recorded when the Neutrinos at the Main Injector beam was operating in both neutrino and antineutrino modes, with exposures of $2\times {10}^{20}$ and $5\times {10}^{20}$ protons on target, respectively. A selection algorithm targeting electron-neutrino charged-current interactions with at least one proton, one electron, and no pions in the final topology is used to measure differential cross sections as a function of outgoing electron energy, total visible energy, and the cosine of the opening angle between the electron and the most energetic proton. The interaction rate as a function of proton multiplicity is also reported. The total cross section is measured as $[4.1\pm 0.3(\mathrm{stat})\pm 1.1(\mathrm{syst})]\times {10}^{-39}{\mathrm{cm}}^2/\text{nucleon}$ . The unfolded cross-section measurements are compared to predictions from neutrino event generators commonly employed in the field. Good agreement is seen across all variables within uncertainties.

Abstract:

Precise neutrino-nucleon amplitudes are essential ingredients for predicting neutrino event rates in current and upcoming long-baseline neutrino oscillation experiments. A common neutrino interaction with a low reaction threshold and with most of the energy carried by two final state particles is quasielastic scattering, for which the nucleon axial form factor, $F_A(Q^2)$ , is a dominant source of uncertainty. Improvements to the nucleon axial form factor rely on neutrino scattering data with elementary targets to reduce or eliminate the need for nuclear modeling systematics. This work examines constraints on the nucleon axial form factor that can be achieved from datasets of neutrino scattering on deuterium targets, Lattice QCD predictions, and from the recent hydrogen target data from the MINERvA Collaboration. Significant tension is found between hydrogen and deuterium target data, suggesting that extractions from deuterium underestimate both the central value and uncertainty of the form factor. Parametrizations for and uncertainties of the nucleon axial form factor using the $z$ expansion are provided.

Abstract:

A search is performed for the electroweak pair production of charginos and associated production of a chargino and neutralino, each of which decays through an $R$ -parity-violating coupling into a lepton and a $W$ , $Z$ , or Higgs boson. This search targets the Higgs boson decay channel of the charginos and neutralinos, using events with three or more $b$ -tagged jets and one or two electrons or muons. The analyzed data corresponds to an integrated luminosity of $140{\mathrm{fb}}^{-1}$ and $56{\mathrm{fb}}^{-1}$ of proton-proton collision data produced by the Large Hadron Collider at center-of-mass energies of $\sqrt{s}=13\mathrm{TeV}$ and $\sqrt{s}=13.6\mathrm{TeV}$ , respectively, collected by the ATLAS experiment between 2015 and 2023. The data are found to be consistent with predictions from the Standard Model. The results are interpreted as limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model. Limits are also set on the production of charginos and neutralinos for a minimal supersymmetric Standard Model with an additional $B-L$ gauge symmetry that is spontaneously broken. Charginos and neutralinos with masses between 150 GeV and 1100 GeV are excluded at 95% confidence level for a scenario in which they decay via Higgs bosons, assuming equal decay branching fractions to each lepton flavor. Additional limits on chargino and neutralino production are derived for flavor-specific decay scenarios where the charginos decay into a single lepton flavor.