The MINERvA experiment observes an excess of events containing electromagnetic showers relative to the expectation from Monte Carlo simulations in neutral-current neutrino interactions with mean beam energy of 4.5 GeV on a hydrocarbon target. The excess is characterized and found to be consistent with neutral-current π0 production with a broad energy distribution peaking at 7 GeV and a total cross section of 0.26±0.02(stat.)±0.08(sys.)×10-39 cm2. The angular distribution, electromagnetic shower energy, and spatial distribution of the energy depositions of the excess are consistent with expectations from neutrino neutral-current diffractive π0 production from hydrogen in the hydrocarbon target. These data comprise the first direct experimental observation and constraint for a reaction that poses an important background process in neutrino-oscillation experiments searching for νμ to νe oscillations.
Bibliographical noteFunding Information:
This work was supported by the Fermi National Accelerator Laboratory under U.S. Department of Energy (DOE) Award No. DE-AC02-07CH11359, which included the MINERvA construction project. Construction support was also granted by the United States National Science Foundation (NSF) under Grant No. PHY-0619727 and by the University of Rochester. Support for participating scientists was provided by the NSF and DOE (USA), CAPES and CNPq (Brazil), CoNaCyT (Mexico), CONICYT (Chile), CONCYTEC, DGI-PUCP, and IDI/IGI-UNI (Peru), and Latin American Center for Physics (CLAF). We thank the MINOS Collaboration for use of its near detector data. We acknowledge the dedicated work of the Fermilab staff responsible for the operation and maintenance of the NuMI beam line, MINERvA, and MINOS detectors and the physical and software environments that support scientific computing at Fermilab.
© 2016 American Physical Society.