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Register a new userElastic hadron-nucleus scattering in neutrino-nucleus reactions and transverse kinematics measurements
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Rescattering following a neutrino-nucleus reaction changes the number, energy, and direction of detectable hadrons. In turn, this affects the selection and kinematic distributions of subsamples of neutrino events used for interaction or oscillation analysis. This technical note focuses on three forms of two-body rescattering. Elastic hadron+nucleus scattering primarily changes the direction of the hadron with very little energy transfer. Secondly, a hadron+nucleon quasi-elastic process leads to the knockout of a single struck nucleon, possibly with charge exchange between the two hadrons. Also, a pion can be absorbed leading to the ejection of two nucleons. There was an error in the code of the {small GENIE} neutrino event generator that affects these processes. We present examples of the change with the fixed version of the scattering process, but also compare these specifically to turning off elastic scattering completely, which is similar to other neutrino event generator configurations or a potential Equick-fix to already generated samples. Three examples are taken from current topics of interest: transverse kinematics observables in quasielastic neutrino reactions, the pion angle with respect to the incoming and outgoing lepton for $Delta$ reactions with a charged pion in the final state, and the angle between two protons in reactions with no pions present. Elastic hadron+nucleus scattering in its unfixed form makes a large distortion in distributions of transverse kinematic imbalances scattering, but only mild distortion in other observables. The distortion of the other two processes is also mild for all distributions considered. The correct form of hadron+nucleus scattering process could play a role in describing the width and center of the sharp peak in the inferred Fermi-motion of the struck nucleon or be benchmarked using (e,ep) data.
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Neutrino-nucleus elastic scattering provides a unique laboratory to study the quantum mechanical coherency effects in electroweak interactions, towards which several experimental programs are being actively pursued. We report results of our quantitative studies on the transitions towards decoherency. A parameter ($alpha$) is identified to describe the degree of coherency, and its variations with incoming neutrino energy, detector threshold and target nucleus are studied. The ranges of $alpha$ which can be probed with realistic neutrino experiments are derived, indicating complementarity between projects with different sources and targets. Uncertainties in nuclear physics and in $alpha$ would constrain sensitivities in probing physics beyond the standard model. The maximum neutrino energies corresponding to $alpha$>0.95 are derived.
Neutrino-nucleus elastic scattering ($ u {rm A}_{el}$) provides a unique laboratory to study the quantum-mechanical (QM) coherency effects in electroweak interactions. The deviations of the cross-sections from those of completely coherent systems can be quantitatively characterized through a coherency parameter $alpha ( q^2 )$. The relations between $alpha$ and the underlying nuclear physics in terms of nuclear form factors are derived. The dependence of cross-section on $alpha ( q^2 )$ for the various neutrino sources is presented. The $alpha ( q^2 )$-values are evaluated from the measured data of the COHERENT CsI and Ar experiments. Complete coherency and decoherency conditions are excluded by the CsI data with $p {=} 0.004$ at $q^2 {=} 3.1 {times} 10^{3} ~ {rm MeV^2}$ and with $p {=} 0.016$ at $q^2 {=} 2.3 {times} 10^{3} ~ {rm MeV^2}$, respectively, verifying that both QM superpositions and nuclear many-body effects contribute to $ u {rm A}_{el}$ interactions.
The quasi-elastic contribution of the nuclear inclusive electron scattering model developed in A. Gil, J. Nieves, and E. Oset: Nucl. Phys. A 627 (1997) 543; is extended to the study of electroweak Charged Current (CC) induced nuclear reactions at intermediate energies of interest for future neutrino oscillation experiments. The model accounts for long range nuclear (RPA) correlations, Final State Interaction and Coulomb corrections. RPA correlations are shown to play a crucial role in the whole range of neutrino energies, up to 500 MeV, studied in this work. Predictions for inclusive muon capture for different nuclei, and for the reactions $^{12}$C$( u_mu,mu^-)X$ and $^{12}$C$( u_e,e^-)X$ near threshold are also given.
We study the sensitivity of detectors with directional sensitivity to coherent elastic neutrino-nucleus scattering (CE$ u$NS), and how these detectors complement measurements of the nuclear recoil energy. We consider stopped pion and reactor neutrino sources, and use gaseous helium and fluorine as examples of detector material. We generate Standard Model predictions, and compare to scenarios that include new, light vector or scalar mediators. We show that directional detectors can provide valuable additional information in discerning new physics, and we identify prominent spectral features in both the angular and the recoil energy spectrum for light mediators, even for nuclear recoil energy thresholds as high as $sim 50$ keV. Combined with energy and timing information, directional information can play an important role in extracting new physics from CE$ u$NS experiments.
The coherent elastic scattering of neutrinos off nuclei has eluded detection for four decades, even though its predicted cross-section is the largest by far of all low-energy neutrino couplings. This mode of interaction provides new opportunities to
study neutrino properties, and leads to a miniaturization of detector size, with potential technological applications. We observe this process at a 6.7-sigma confidence level, using a low-background, 14.6-kg CsI[Na] scintillator exposed to the neutrino emissions from the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. Characteristic signatures in energy and time, predicted by the Standard Model for this process, are observed in high signal-to-background conditions. Improved constraints on non-standard neutrino interactions with quarks are derived from this initial dataset.
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