[Paper Review] NESSiE: The Experimental Sterile Neutrino Search in Short-Base-Line at CERN

U. Köse|arXiv (Cornell University)|Apr 26, 2013

Neutrino Physics Research15 references3 citations

TL;DR

NESSiE proposes a high-precision search for sterile neutrinos using a new short-baseline neutrino beam at CERN, employing two magnetic spectrometers (Near and Far) paired with ICARUS-like liquid argon time projection chambers to measure charged-current muon neutrino and antineutrino interactions. The experiment aims to cover the LSND and reactor anomaly parameter space with sensitivity extending beyond current limits, particularly for $\Delta m^2 \sim 2$ eV$^2$ and $\sin^2 2\theta \sim 10^{-2}$, using independent measurements of $\nu_\mu$ and $\bar{\nu}_\mu$ disappearance with low systematic errors.

ABSTRACT

Several different experimental results are indicating the existence of anomalies in the neutrino sector. Models beyond the standard model have been developed to explain these results and involve one or more additional neutrinos that do not weakly interact. A new experimental program is therefore needed to study this potential new physics with a possibly new Short-Base-Line neutrino beam at CERN. CERN is actually promoting the start up of a New Neutrino Facility in the North Area site, which may host two complementary detectors, one based on LAr technology and one corresponding to a muon spectrometer. The system is doubled in two different sites. With regards to the latter option, NESSiE, Neutrino Experiment with Spectrometers in Europe, had been proposed for the search of sterile neutrinos studying Charged Current (CC) muon neutrino and antineutrino ineractions. The detectors consists of two magnetic spectrometers to be located in two sites:"Near" and "Far" from the proton target of the CERN-SPS beam. Each spectrometer will be complemented by an ICARUS-like LAr target in order to allow also Neutral Current (NC) and electron neutrino CC interactions reconstruction.

Motivation & Objective

• To investigate the existence of sterile neutrinos that could explain anomalies in short-baseline neutrino oscillation experiments.
• To explore the parameter space consistent with the LSND, MiniBooNE, reactor, and Gallium anomalies, which suggest a fourth, sterile neutrino with $\Delta m^2 \sim 1-2$ eV$^2$.
• To measure $\nu_\mu$ and $\bar{\nu}_\mu$ disappearance independently using charge identification in magnetic spectrometers to reduce background and systematic uncertainties.
• To achieve high-precision measurements of neutrino flux and interaction spectra at both Near and Far detector sites to detect oscillation-induced spectral distortions.

Proposed method

• Utilize a new CERN neutrino beam facility (CENF) producing 100 GeV protons extracted from the SPS, directed at a graphite target to generate secondary pions and kaons that decay into muon neutrinos and antineutrinos.
• Deploy two identical magnetic spectrometers at Near (119 t effective mass) and Far (476 t) locations to reconstruct muon momentum and charge, enabling separation of $\nu_\mu$ and $\bar{\nu}_\mu$ events.
• Integrate ICARUS-like liquid argon time projection chambers (LAr-TPCs) at each site to detect and reconstruct both charged-current and neutral-current interactions with high precision.
• Use the ratio of reconstructed CC to NC events and spectral distortions between Near and Far detectors to probe oscillations, assuming identical initial spectra in the absence of oscillations.
• Apply independent measurements of $\nu_\mu$ and $\bar{\nu}_\mu$ disappearance to test for CP-violating effects in sterile neutrino mixing.
• Leverage high statistics (e.g., ~1.2 million $\nu_\mu$ CC events in NESSiE alone at Far site with $\Delta m^2 \sim 2$ eV$^2$) to achieve sensitivity beyond existing experiments.

Experimental results

Research questions

• RQ1 Can the LSND and MiniBooNE anomalies be explained by the existence of a sterile neutrino with $\Delta m^2 \sim 1-2$ eV$^2$?
• RQ2 What is the sensitivity of the NESSiE experiment to $\nu_\mu$ disappearance in the $\Delta m^2 \sim 0.2-2$ eV$2$ range, particularly in the context of reactor and Gallium anomalies?
• RQ3 To what extent can the NESSiE spectrometers distinguish $\nu_\mu$ from $\bar{\nu}_\mu$ events using muon charge identification, and how does this improve background suppression?
• RQ4 Can the experiment achieve sensitivity to $\nu_e$ appearance and disappearance modes, and what constraints does this place on sterile neutrino couplings?
• RQ5 How do spectral distortions in the muon momentum distribution between Near and Far detectors enable detection of oscillations due to sterile neutrinos?

Key findings

• The NESSiE spectrometer is expected to reconstruct approximately 40% of all CC events produced in and escaping from the LAr-TPCs at both Near and Far sites, enabling full spectral measurement.
• With 3 years of operation (2 years in neutrino mode, 1 year in antineutrino mode), NESSiE achieves sensitivity to $\nu_\mu$ disappearance that extends beyond the limits set by CDHS and SciBooNE+MiniBooNE, covering a large fraction of the LSND anomaly region.
• For $\Delta m^2 \sim 2$ eV$^2$, the NESSiE spectrometer alone is expected to record ~110,000 $\bar{\nu}_\mu$ CC events at the Far site, with ~280,000 events in the combined NESSiE+LAr configuration.
• The experiment achieves high statistical power for $\nu_\mu$ disappearance, with over 1 million CC events expected in NESSiE alone at the Far site under oscillation hypothesis, enabling precise spectral analysis.
• The NESSiE spectrometers can independently measure $\nu_\mu$ and $\bar{\nu}_\mu$ disappearance, allowing for a direct test of CP violation in the sterile neutrino sector.
• The measured event spectra at Near and Far sites are expected to show significant differences under the oscillation hypothesis, with the largest deviations occurring in the $\nu_\mu$ CC spectrum for $\Delta m^2 \sim 2$ eV$^2$, providing a clear signature for sterile neutrino oscillations.