Image credit: Fermilab.
The collaboration working to design the Long-Baseline Neutrino Experiment (LBNE) in the US has recently made major decisions about the experimental configuration, while the collaboration itself continues to grow. More than 600 researchers have now signed on to an experimental programme that will reach unprecedented sensitivity and precision for addressing the neutrino-mass hierarchy, CP-violation in neutrino mixing and the mixing angle θ13 – recently measured for the first time by the Daya Bay experiment (Daya Bay experiment measures θ13).
The first in the series of decisions involved the configuration of the neutrino beamline. The accelerator complex at Fermilab would be used to generate neutrinos for LBNE. The chosen configuration would send the beam up a small hill before it heads underground towards the LBNE far detector at the Homestake Mine in South Dakota. This configuration would make construction easier and more cost-effective, as well as protect the aquifer at Fermilab.
The collaboration then reached consensus on the depth of the facilities at the site of the far detector, choosing a depth of 4850 ft (1470 m). This is optimal for not only the LBNE scientific programme but for other experiments such as direct dark-matter and neutrinoless double-beta-decay searches.
The last crucial decision was the selection of the technology for LBNE’s far detector. Liquid-argon and water-Cherenkov technologies had both been studied and were considered viable options, but either choice would require a significant scaling-up of existing technology to meet the needs of LBNE. While its scaling-up challenge is greater, liquid-argon has more potential because of the detailed information provided on each neutrino event. After an extensive process that involved physics studies and analysis of the technical feasibility of various configurations – as well as external reviews organized by the collaboration – the project manager made the final recommendation to base the far detector on liquid-argon.
Many steps remain before LBNE becomes reality, notably a decision by the US Department of Energy to proceed with detailed design and eventual construction of the project.
