Measurement of Exclusive $π^+$--argon Interactions Using ProtoDUNE-SP

TL;DR

This work reports a first-principles measurement of exclusive π^+–argon inelastic cross sections in the $500$–$800\,\mathrm{MeV}$ range, separating absorption, charge-exchange, and other inelastic channels using the ProtoDUNE-SP LArTPC. The analysis employs a data-driven, iterative MC reweighting framework and a thin-slice cross-section extraction method to mitigate model dependence, supported by a detailed simulation of hadron–nucleus interactions (Geant4 Bertini, INCL++, Genie hN/hA) and a robust reconstruction chain in LArSoft. The results show consistency with Geant4 Bertini and INCL++ as well as GENIE hN, while excluding GENIE hA, and provide essential inputs for final state interactions and secondary interactions in DUNE and SBN neutrino analyses. This advances the precision of neutrino energy reconstruction and flavor identification in liquid argon detectors by constraining pion interactions with argon in a key energy regime, with ongoing work to finalize the total inelastic cross section.

Abstract

We present the measurement of $π^{+}$--argon inelastic cross sections using the ProtoDUNE Single-Phase liquid argon time projection chamber in the incident $π^+$ kinetic energy range of 500 -- 800 MeV in multiple exclusive channels (absorption, charge exchange, and the remaining inelastic interactions). The results of this analysis are important inputs to simulations of liquid argon neutrino experiments such as the Deep Underground Neutrino Experiment and the Short Baseline Neutrino program at Fermi National Accelerator Laboratory. They will be employed to improve the modeling of final state interactions within neutrino event generators used by these experiments, as well as the modeling of $π^{+}$--argon secondary interactions within the liquid argon. This is the first measurement of $π^+$--argon absorption at this kinetic energy range as well as the first ever measurement of $π^{+}$--argon charge exchange.

Figures (7)

• Figure 1: Bird's-eye view of the beam-side drift volume of ProtoDUNE-SP (one half of the full detector). The vertical, dotted line indicates the cut in the reconstructed $z$ position used within the event selection. Along the top of the illustration is the Cathode Plane Assembly (CPA) which separates the two drift volumes. Each beam-side Anode Plane Assembly (APA) is shown at the bottom. Note that the non-beam-side drift volume is not shown as it is not used within the analysis.
• Figure 2: Event displays of selected interaction candidates for $\pi^+$--argon absorption \ref{['fig:abs_evdisp']}, charge exchange \ref{['fig:cex_evdisp']}, and other \ref{['fig:other_evdisp']} interactions using the event selection described in Sec. \ref{['sec:Selection']}. The candidate beam pion track begins near wire 60, tick 4800 and travels toward the bottom right of each figure, as highlighted by the solid, red arrow. The dashed ellipse in \ref{['fig:abs_evdisp']} highlights two proton candidate tracks, and in \ref{['fig:cex_evdisp']} it highlights a candidate $\gamma$ resulting from a $\pi^0$ decay. In \ref{['fig:other_evdisp']}, the secondary $\pi^\pm$ is highlighted with a dashed arrow. Candidate cosmic-ray tracks can be seen crossing through the figures as well.
• Figure 3: Selected event distributions from the ProtoDUNE-SP MC with stacked contributions from true event types along with event distributions observed in data.
• Figure 4: Uncertainties relative to the best-fit cross section values for absorption \ref{['fig:abs_errs']}, charge exchange \ref{['fig:cex_errs']}, and other interactions \ref{['fig:other_errs']}. The legend is shown in \ref{['fig:leg_errs']}.
• Figure 5: Event distributions observed by ProtoDUNE-SP (black circles) compared to pre-fit (dashed blue histogram) and post-fit MC (solid red histogram) using 4 fit iterations. The error bars on the bins of the data distribution (often smaller than the data point markers themselves) represent the estimated statistical errors.