[Paper Review] Measurement of the muon-neutrino charged-current quasi-elastic cross-section in the SciBooNE experiment

J. L. Alcaraz-Aunion, J. Walding|arXiv (Cornell University)|Sep 30, 2009

Muon and positron interactions and applications13 citations

TL;DR

This paper presents the first absolute measurement of the muon-neutrino charged-current quasi-elastic (CCQE) cross section in the 0.6–1.6 GeV energy range using the SciBooNE experiment at Fermilab. By combining SciBar and MRD detectors and employing a likelihood-based fit to constrain background contributions, the measured cross section agrees with NEUT generator predictions using an axial mass of 1.21 GeV, with systematic uncertainties dominated by neutrino flux modeling.

ABSTRACT

SciBooNE is a neutrino and anti-neutrino cross-section experiment at Fermilab, USA. The SciBooNE experiment is summarised and two independent CCQE analyses are described. For one of the analyses, an absolute muon-neutrino CCQE cross-section in the neutrino energy region (0.6-1.6) GeV is shown and the technique developed for such a purpose is also explained. The total cross-section measured over this energy range agrees well with expectations, based on the NEUT event generator and using a value of 1.21 GeV for the CCQE axial mass.

Motivation & Objective

• To measure the absolute $ν_\mu$-CCQE cross section on a nuclear target in the 0.6–1.6 GeV energy range, a region critical for future oscillation experiments.
• To reduce background contamination in CCQE event selection using multi-track topology and muon confidence level (MuCL) cuts.
• To extract the absolute cross section using a likelihood-based fit that reweights NEUT-simulated events by energy-dependent parameters and accounts for non-QE backgrounds.
• To assess systematic uncertainties, particularly from neutrino flux modeling, using HARP data and the Sanford-Wang parameterization.
• To validate theoretical predictions from the NEUT event generator with an axial mass of 1.21 GeV against data.

Proposed method

• The analysis uses two independent CCQE selection methods, with the primary result based on the SciBar-MRD analysis, which identifies muons via their decay electron signature and range-out in the MRD.
• Events are selected using fiducial volume cuts, beam window timing, and vertex activity cuts to enhance CCQE purity in 1-track and 2-track ($\mu$ + p) samples.
• A muon confidence level (MuCL) variable is used to suppress non-muon tracks, and a CCQE cut is applied using the reconstructed neutrino energy and energy deposits to reject non-QE events.
• A likelihood function is minimized to fit observed data to simulated events, with parameters $a_k$ reweighting the NEUT-simulated cross section in 10 neutrino energy bins, and $F_N$ and $a_{bck}$ adjusting normalization and non-QE background levels.
• The absolute cross section is computed as $\sigma_{\nu_\mu}(E_\nu^k) = F_N \times a_k \times \sigma^{NEUT}_{\nu_\mu}(E_\nu^k)$, where $\sigma^{NEUT}$ is the NEUT-predicted cross section.
• Systematic uncertainties are evaluated using HARP measurements of pion production and flux modeling, with the dominant contribution from $\pi^+$ production in the Be target.

Experimental results

Research questions

• RQ1 What is the absolute $ν_\mu$-CCQE cross section in the 0.6–1.6 GeV energy range, as measured in a high-statistics neutrino experiment?
• RQ2 How well do NEUT generator predictions with an axial mass of 1.21 GeV agree with the measured cross section?
• RQ3 What is the impact of neutrino flux uncertainties on the cross section measurement, and which components dominate the systematic error?
• RQ4 How effective are the MuCL and CCQE cut techniques in suppressing non-QE background in the 2-track ($\mu$ + p) and ($\mu$ + $\pi$) samples?
• RQ5 Can a likelihood fit with energy-dependent reweighting parameters ($a_k$) accurately extract the absolute cross section from data?

Key findings

• The measured $ν_\mu$-CCQE cross section in the 0.6–1.6 GeV range is consistent with the NEUT generator prediction using an axial mass of 1.21 GeV.
• The 1-track sample has a CCQE purity of 65.2% and a 52.9% efficiency, while the 2-track ($\mu$ + p) sample achieves 68.5% purity and 11.1% efficiency.
• The 2-track ($\mu$ + $\pi$) sample, used to constrain non-QE backgrounds, has a purity of 32.3% and a data-to-MC ratio of 1.14.
• The dominant systematic uncertainty arises from the neutrino flux modeling, particularly the uncertainty in $\pi^+$ production rates in the Be target, as measured by HARP.
• The cross section measurement is consistent with the NEUT prediction across the entire energy range, with the data/MC ratio within 3% of unity for all samples.
• The reconstructed muon lifetime of $2.003 \pm 0.047$ $\mu$s is consistent with the known value, validating the muon identification and decay electron tagging.