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Register a new userFirst Observation of Coherent $pi^0$ Production in Neutrino Nucleus Interactions with $E_{ u}<$ 2 GeV
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The MiniBooNE experiment at Fermilab has amassed the largest sample to date of $pi^0$s produced in neutral current (NC) neutrino-nucleus interactions at low energy. This paper reports a measurement of the momentum distribution of $pi^0$s produced in mineral oil (CH$_2$) and the first observation of coherent $pi^0$ production below 2 GeV. In the forward direction, the yield of events observed above the expectation for resonant production is attributed primarily to coherent production off carbon, but may also include a small contribution from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino flux, the sum of the NC coherent and diffractive modes is found to be (19.5 $pm$1.1 (stat) $pm$2.5 (sys))% of all exclusive NC $pi^0$ production at MiniBooNE. These measurements are of immediate utility because they quantify an important background to MiniBooNEs search for $ u_{mu} to u_e$ oscillations.
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Neutrino-induced coherent charged pion production on nuclei, $stackrel{(-)}{ u}_mu Atomu^pmpi^mp A$ is a rare, inelastic interaction in which a small squared four-momentum $| t|$ is transferred to the recoil nucleus leaving it intact in the reaction. In the scintillator tracker of MINERvA, we remove events with evidence of particles from nuclear breakup and reconstruct $| t|$ from the final state pion and muon. We select low $| t|$ events to isolate a sample rich in coherent candidates. By selecting low $| t|$ events we produce a model-independent measurement of the differential cross section for coherent scattering of neutrinos and anti-neutrinos on carbon. We find poor agreement with the predicted kinematics in neutrino generators used by current oscillation experiments.
Neutrino-induced charged-current coherent kaon production, $ u_{mu}Arightarrowmu^{-}K^{+}A$, is a rare, inelastic electroweak process that brings a $K^+$ on shell and leaves the target nucleus intact in its ground state. This process is significantly lower in rate than neutrino-induced charged-current coherent pion production, because of Cabibbo suppression and a kinematic suppression due to the larger kaon mass. We search for such events in the scintillator tracker of MINERvA by observing the final state $K^+$, $mu^-$ and no other detector activity, and by using the kinematics of the final state particles to reconstruct the small momentum transfer to the nucleus, which is a model-independent characteristic of coherent scattering. We find the first experimental evidence for the process at $3sigma$ significance.
Charged pion production via charged current $ u_{mu}$ interactions on plastic (CH) is studied using the MINERvA detector exposed to the NuMI wideband neutrino beam at Fermilab. Events with hadronic invariant mass W $<$ 1.4 GeV are selected to isolate single pion production, which is expected to occur primarily through the $Delta(1232)$ resonance. Cross sections as functions of pion production angle and kinetic energy are reported and compared to predictions from different theoretical calculations and generator-based models, for neutrinos ranging in energy from 1.5 GeV to 10 GeV. The data are best described by calculations which include significant contributions from pion intranuclear rescattering. These measurements constrain the primary interaction rate and the role of final state interactions in pion production, both of which need to be well understood by neutrino oscillation experiments.
Forward single $pi^0$ production by coherent neutral-current interactions, $ u mathcal{A} to u mathcal{A} pi^0$, is investigated using a 2.8$times 10^{20}$ protons-on-target exposure of the MINOS Near Detector. For single-shower topologies, the event distribution in production angle exhibits a clear excess above the estimated background at very forward angles for visible energy in the range~1-8 GeV. Cross sections are obtained for the detector medium comprised of 80% iron and 20% carbon nuclei with $langle mathcal{A} rangle = 48$, the highest-$langle mathcal{A} rangle$ target used to date in the study of this coherent reaction. The total cross section for coherent neutral-current single-$pi^0$ production initiated by the $ u_mu$ flux of the NuMI low-energy beam with mean (mode) $E_{ u}$ of 4.9 GeV (3.0 GeV), is $77.6pm5.0,(text{stat}) ^{+15.0}_{-16.8},(text{syst})times10^{-40},text{cm}^2~text{per nucleus}$. The results are in good agreement with predictions of the Berger-Sehgal model.
First data on coherent threshold pi^0 electroproduction from the deuteron taken by the A1 Collaboration at the Mainz Microtron MAMI are presented. At a four-momentum transfer of q^2=-0.1 GeV^2/c^2 the full solid angle was covered up to a center-of-mass energy of 4 MeV above threshold. By means of a Rosenbluth separation the longitudinal threshold s wave multipole and an upper limit for the transverse threshold s wave multipole could be extracted and compared to predictions of Heavy Baryon Chiral Perturbation Theory.
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