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تسجيل مستخدم جديدCoherent Pions From Neutrino Scattering Off Nuclei
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We describe a model for pion production off nucleons and coherent pions from nuclei induced by neutrinos in the 1 GeV energy regime. Besides the dominant Delta pole contribution, it takes into account the effect of background terms required by chiral symmetry. Moreover, the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads to coherent pion production cross sections around a factor two smaller than most of the previous theoretical estimates. Nuclear effects like medium corrections on the Delta propagator and final pion distortion are included.
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All available theoretical estimates of neutrino-induced coherent pion production rely on the local approximation for the Delta propagator. The validity of this approximation is scrutinized. It is found that the local approximation overestimates the n
eutrino-induced coherent pion production on nuclei significantly, by up to 100%.
It is pointed out that so far all theoretical estimates of coherent pion production off nuclei induced by neutrinos rely on the local approximation well known in photonuclear physics. The effects of dropping this approximation are discussed. It is fo
und that in a plane wave approximation for the pion the local approximation overestimates the coherent neutrino-induced pion production on nuclei.
Neutrino-nucleus $ u Ato u A$ and antineutrino-nucleus $bar u Ato bar u A$ interactions, when the nucleus conserves its integrity, are discussed with coherent (elastic) and incoherent (inelastic) scattering regimes taken into account. In the first r
egime the nucleus remains in the same quantum state after the scattering and the cross-section depends on the quadratic number of nucleons. In the second regime the nucleus changes its quantum state and the cross-section has an essentially linear dependence on the number of nucleons. The coherent and incoherent cross-sections are driven by a nuclear nucleon form-factor squared $|F|^2$ term and a $(1-|F|^2)$ term, respectively. One has a smooth transition between the regimes of coherent and incoherent (anti)neutrino-nucleus scattering. Due to the neutral current nature these elastic and inelastic processes are indistinguishable if the nucleus recoil energy is only observed. One way to separate the coherent signal from the incoherent one is to register $gamma$ quanta from deexcitation of the nucleus excited during the incoherent scattering. Another way is to use a very low-energy threshold detector and collect data at very low recoil energies, where the incoherent scattering is vanishingly small. In particular, for ${}^{133}text{Cs}$ and neutrino energies of 30--50 MeV the incoherent cross-section is about 15-20% of the coherent one. Therefore, the COHERENT experiment (with ${}^{133}text{Cs}$) has measured the coherent elastic neutrino nucleus scattering (CE$ u$NS) with the inelastic admixture at a level of 15-20%, if the excitation $gamma$ quantum escapes its detection.
The possibility off measuring for the first time neutrino-nuclei coherent scattering has been recently discussed by several experimental collaborations. It is shown that such a measurement may be very sensitive to non-standard interactions of neutrin
os with quarks and might set better constraints than those coming from future neutrino factory experiments. We also comment on other types of new physics tests, such as extra heavy neutral gauge bosons, where the sensitivity to some models is slightly better than the Tevatron constraint and, therefore, could give complementary bounds.
The cross sections for neutrino scattering off the 12C and 16O nuclei are calculated within the framework of the continuum Random Phase Approximation. A model to consider also the final state interactions is developed. Total charge-conserving and cha
rge-exchange cross sections for both electron neutrinos and antineutrinos have been calculated up to projectile energies of 100 MeV. The sensitivity of the cross sections to the residual interaction and to the final state interactions is investigated. A direct comparison between neutrino and electron scattering cross sections calculated under the same kinematic conditions is presented. We found remarkable differences between electromagnetic and weak nuclear responses. The model is applied to describe cross sections of neutrinos produced by muon decay at rest and in supernovae explosions.
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