First Measurement of Neutrino and Antineutrino Coherent Charged Pion Production on Argon

We report on the first cross section measurements for charged current coherent pion production by neutrinos and antineutrinos on argon. These measurements are performed using the ArgoNeuT detector exposed to the NuMI beam at Fermilab. The cross sections are measured to be $2.6_{-1.0}^{+1.2}(\text{stat}{)}_{-0.4}^{+0.3}(\text{syst})\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{Ar}$ for neutrinos at a mean energy of 9.6 GeV and $5.5_{-2.1}^{+2.6}(\text{stat}{)}_{-0.7}^{+0.6}(\text{syst})\times {10}^{-39}{\mathrm{cm}}^2/\mathrm{Ar}$ for antineutrinos at a mean energy of 3.6 GeV.

Figure 1

An example of CC coherent pion production from a neutrino in ArgoNeuT. The neutrino’s incoming direction is along the horizontal coordinate; the muon track corresponds to the most forward going one, making an angle of 1.2° with the incoming neutrino direction. The opening angle between the muon and the pion track is 10.6°. A kink in the pion trajectory is visible.

Figure 2

Best fit of the signal and background templates to the data. A BDT classification value of $-1$ means backgroundlike, and 1 is signal-like. The background and signal shapes are scaled to minimize an effective ${\chi }^2$ function from which the statistical error is also extracted.

Figure 3

ArgoNeuT’s CC coherent pion cross section measurements (open circle and filled circle) compared to the Rein-Sehgal model as implemented in genie [4] and nuwro [5]. The statistical error is dominant (the systematic uncertainty is shown alone for comparison). Data from other experiments in the same energy range are also shown. These consist of measurements made by SKAT (filled square, open square), CHARM II (diamond) and MINERvA (triangle, inverted triangle) [25, 26, 27]. These measurements are scaled to argon assuming the $A^{1/3}$ dependence from the Rein-Sehgal model.