Measurement of Coherent ${\pi }^{+}$ Production in Low Energy Neutrino-Carbon Scattering

We report the first measurement of the flux-averaged cross section for charged current coherent ${\pi }^{+}$ production on carbon for neutrino energies less than 1.5 GeV, and with a restriction on the final state phase space volume in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso et al., the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. We observe a clear event excess above background, disagreeing with the null results reported by K2K and SciBooNE in a similar neutrino energy region. The measured flux-averaged cross sections are below those predicted by both the Rein-Sehgal and Alvarez-Ruso et al. models.

Figure 1

(a) Diagram for coherent charged pion production model based on Adler’s theorem. The $\mathbb{P}$ epresents the transfer of a Pomeron to the nuclear system. (b) Dominant diagram for the microscopic class of coherent charged pion production models.

Figure 2

The reconstructed $|t|$ distribution after the VA cut and the background tuning procedure have been applied. The errors on the data are statistical only, and the uncertainty on the tuned model is not shown. The model’s prediction of the coherent contribution has been removed from the plot. The small external background component contains events that occur outside the FGD1 fiducial volume, such as interactions occurring in the surrounding magnet volume.

Figure 3

The reconstructed $Q^2$ distribution after background subtraction. The inner error bars represent the statistical uncertainty on the data before background subtraction and the outer the total uncertainty that also includes systematic effects. Correlations between bins are not reflected in the uncertainty displayed on the figure. The last bin is an overflow bin, containing all events with reconstructed $Q^2$ greater than $0.3(\mathrm{GeV}/c{)}^2$.