NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) is a multi-purpose experimental facility to study hadron production in hadron-proton, hadron-nucleus and nucleus-nucleus collisions at the CERN Super Proton Synchrotron. It recorded the first physics data with hadron beams in 2009 and with ion beams (secondary 7Be beams) in 2011. NA61/SHINE has greatly profited from the long development of the CERN proton and ion sources and the accelerator chain as well as the H2 beamline of the CERN North Area. The latter has recently been modified to also serve as a fragment separator as needed to produce the Be beams for NA61/SHINE. Numerous components of the NA61/SHINE set-up were inherited from its predecessors, in particular, the last one, the NA49 experiment. Important new detectors and upgrades of the legacy equipment were introduced by the NA61/SHINE Collaboration. This paper describes the state of the NA61/SHINE facility — the beams and the detector system — before the CERN Long Shutdown I, which started in March 2013.

An extension of the NA61/SHINE physics program utilizing hadron production measurements for Fermilab neutrino beams is proposed. The initiative originated from the US groups (the US-NA61 Collaboration) and is supported by the NA61/SHINE Collaboration. The US groups intend to join the NA61/SHINE Collaboration to perform these measurements. We wish to collect dedicated and optimized high-precision hadron production data needed for improved neutrino beams modeling necessary for ongoing and future experiments at Fermilab. Presented is a schedule, analysis and a detector upgrade plan to expose thin targets and replicas of targets used at Fermilab to the NA61/SHINE hadron beam to accumulate a suitably large sample of events to provide a data set which would be essential for future neutrino beams including running experiments using the NuMI and LBNF facilities.

The NA61/SHINE collaboration performed measurements of pC interactions at 31 GeV/c beam momentum with a full size replica of the T2K target (1.9 interaction length) during a pilot run in 2007. Larger statistics runs were also conducted in 2009 and 2010. The NA61/SHINE setup consists in a large acceptance spectrometer located on the H2 beamline of the SPS at CERN. For the first time, the kinematical phase space of interest for an accelerator based neutrino experiment (i.e. kinematical phase space of pions/kaons exiting the target and producing neutrinos in the direction of the near and far detectors) is fully covered by a single hadron production experiment. In a first stage, yields of positively charged pions were measured at the surface of the target. The analysis of the 2007 data set presented here demonstrates that a) high quality long target data were successfully taken with the NA61/SHINE apparatus, and b) for the first time, the T2K neutrino flux predictions can effectively be re-weighted with the NA61/SHINE long target data.

As neutrino long baseline experiments enter a new domain of precision, important systematic errors due to poor knowledge of production cross-sections for pions and kaons require more dedicated measurements for precise neutrino flux predictions. The cosmic ray experiments require dedicated hadron production measurements to tune simulation models used to describe air shower profiles. Among other goals, the NA61-SHINE (SPS Heavy Ion and Neutrino Experiment) experiment at the CERN SPS aims at precision measurements (5% and below) for both neutrino and cosmic ray experiments: those will improve the prediction of the neutrino flux for the T2K experiment at J-PARC and the prediction of muon production in the propagation of air showers for the Auger and KASCADE experiments. Motivations for new hadron production measurements are briefly discussed. NA61-SHINE took data during a pilot run in 2007 and in 2009 with different Carbon targets. The NA61-SHINE setup and preliminary spectra for positive and negative pions obtained with the 2007 thin (4% interaction length) Carbon target data are presented. The use of the NA61 data for the T2K neutrino flux predictions is finally discussed in further details.