Measurement of a Neutrino-Induced Charged Current Single Neutral Pion Cross Section at MicroBooNE
Micro Booster Neutrino Experiment (MicroBooNE) is a Liquid Argon Time Projection Chamber (LArTPC) operating in the Booster Neutrino Beamline at Fermi National Accelerator Laboratory. MicroBooNE's physics goals include studying short basline $\nu$ oscillation and performing a suite of low energy $\nu$ cross section measurements. Of particular interest to MicroBooNE, and the broader LArTPC community, are electromagnetic showers; these showers are at the heart of searches for charged current $\nu_e$ interactions, including MicroBooNE's flagship search for a MiniBooNE-like low energy excess (LEE). Neutral current $\pi^0$'s, which decay into 2 electromagnetic showers ($\gamma$'s), are the dominant source of non-$\nu_e$ backgrounds in searches for $\nu_{\mu}\rightarrow\nu_e$ oscillations in LArTPCs, such as the LEE. While precise measurements of this neutral current channel will provide a tight constraint on our modeling uncertainties, such events are particularly difficult to iden tify in data with our current tools, as there is often little or no activity at the neutrino interaction point. Charged current interactions, on the other hand, have simpler topologies with a long $\mu$ track that anchors to the interaction vertex. With a vertex in hand, we can develop automated reconstruction tools for neutrino-induced shower topologies (like the $\gamma$'s from $\pi^0$ decay). Thus, in studying charged current $\pi^0$ interactions, we are developing tools that can potentially be used to reconstruct an important LEE background, while also studying the physics of neutrino interactions, of which data is sparse for argon. This thesis reports the world's first measurement of the absolute, flux-averaged cross section of $\nu_{\mu}$-charged current single $\pi^0$ production on argon. The analysis chain begins with the selection of inclusive $\nu_\mu$ charged current events, where a candidate $\mu$ and neutrino interaction vertex are identified. These events are t hen passed to a reconstruction framework where electromagnet! ic shower candidates are reconstructed using computer visualization tools. Finally, the cross section is calculated on two reconstructed topologies: those with at least two reconstructed showers and those with at least one. Additionally, this work describes the first fully-automated electromagnetic shower reconstruction process employed by a LArTPC to perform a cross section analysis. We measure the flux averaged cross section on argon at 824 MeV via the two and one shower selections respectively to be \par \noindent $\sigma_{\geq2 Shower}$ = (2.56 $\pm$ $0.50_{stat}$ $\pm$ $0.31_{genie}$ $\pm$ $0.37_{flux}$ $\pm$ $0.31_{det}$) $\times$ $10^{-38}$ $\frac{cm^2}{Ar}$, \par \noindent $\sigma_{\geq 1 Shower}$ = (2.64 $\pm$ $0.33_{stat}$ $\pm$ $0.36_{genie}$ $\pm$ $0.38_{flux}$ $\pm$ $0.35_{det}$) $\times$ $10^{-38}$ $\frac{cm^2}{Ar}$.