CERN Accelerating science

NA61/SHINE efforts in support of the US Neutrino Physics Program

Since neutrinos are charge-less, they cannot be accelerated and steered with magnets as typically done at a particle accelerator. To create a neutrino beam, researchers accelerate charged protons and impinge them onto a fixed target of a few interaction lengths that are typically made of beryllium or carbon. The resulting particle interactions, both primary and tertiary, produce charged pions and kaons exiting the target. Physicists then focus these particles into beams, at which point they decay into daughters, including neutrinos, which roughly follow the direction of the parent. As neutrino research advances and more statistics are accumulated systematic errors become important and therefore it is essential to have a precise knowledge of parent properties to reduce the overall errors when extracting the fundamental properties of neutrinos from final data.

The NA61/SHINE experiment (offspring of NA49) was approved in October 2008. Prior to approval it took neutrino inspired data in a pilot run during September 2007, with 600,000 triggers on a thin carbon target and 200,000 triggers on the replica (long) T2K target in support of the neutrino program at JPARC (Japan). This was followed with extensive data-taking for the T2K neutrino physics program with thin (6 million triggers in 2009) and long targets (10 million triggers in 2010). The incorporation of these data into the T2K neutrino flux prediction significantly reduced the beam uncertainties and greatly enhanced the physics output of T2K. The SHINE detector was primarily designed to study strongly interacting matter, quark-gluon plasma and the production of composite particles. It can therefore reconstruct particles produced from interactions in a high track density environment with great precision (see Figure 1).

Figure 1: Typical Event 60 GeV pion on Be 

Due to the success of the T2K experience a new partnership between scientists from US institutions and CERN was initiated to improve flux predictions for the US neutrino program at Fermilab. Researchers from Fermilab, Los Alamos National Lab, University of Colorado, and University of Pittsburgh wishing to improve the understanding of the interactions between the protons and the target recently joined the NA61/SHINE collaboration.  The collection of these precise hadro-production measurements will support Fermilab experiments such as MINOS(+), MINERnA, NOnA, and DUNE.

A pilot run took place in 2012 with the first extensive data collection phase scheduled for Fall 2015. Unfortunately the vertex magnet suffered problems with its cryogenic system. Moreover it was recommended replacing the magnet safety system before any further operation of the magnets. Therefore the 2015 run was cut short and data was collected with the vertex magnets off precluding any differential cross-section measurements. However these data sets are presently being used for determining important total cross-sections. CERN made a major effort to repair the cryo-system and build a new safety system over the winter and the magnets were successfully powered on again in May 2016. The group took their first data with a completely operational detector starting with one week in late July, and a six-week period in September-October 2016. The beam-target configurations used were: 60 GeV/c pions on carbon and beryllium, 60 GeV/c protons on carbon, beryllium, and aluminum, and 120 GeV/c protons on carbon (see Figure 2) and beryllium. For each setting 2.2 - 4 million events were recorded, close to the groups goal of ~3 million in each mode.

Figure 2: Data collection time-line for proton on Carbon at 120 GeV mode. ~4 million triggers recorded over a 6 day period.

The team hopes for at least two more years of data-taking at CERN. The plan is to take additional statistics in some of the configurations we collected in 2016 as well as other beam/target/energy combinations, including possible long targets, to allow us to fill out the matrix of primary and secondary interaction hadro-production cross-sections applicable to Fermilab neutrino beams. The design of the DUNE target should be ready by the end of the long shutdown and we hope to take data with a replica target at that time.