Abstract
Measurements of the pi ^pm , K^pm , and proton double differential yields emitted from the surface of the 90-hbox {cm}-long carbon target (T2K replica) were performed for the incoming 31,hbox {GeV}!/!c protons with the NA61/SHINE spectrometer at the CERN SPS using data collected during 2010 run. The double differential pi ^pm yields were measured with increased precision compared to the previously published NA61/SHINE results, while the K^pm and proton yields were obtained for the first time. A strategy for dealing with the dependence of the results on the incoming proton beam profile is proposed. The purpose of these measurements is to reduce significantly the (anti)neutrino flux uncertainty in the T2K long-baseline neutrino experiment by constraining the production of (anti)neutrino ancestors coming from the T2K target.
Highlights
Measurements of the π ±, K ±, and proton double differential yields emitted from the surface of the 90-cm-long carbon target (T2K replica) were performed for the incoming 31 GeV/c protons with the NA61/SHINE spectrometer at the CERN SPS using data collected during 2010 run
The tracking system consists of two Vertex Time Projection Chambers (TPCs) located in the magnetic field with an additional small TPC called the Gap TPC (GTPC) located between them, and two Main TPCs (MTPC-L and MTPC-R), located downstream symmetrically with respect to the beamline
The dominant contribution in the third longitudinal bin (z3) for π ± yields comes from the reconstruction efficiency uncertainty, while the dominant contribution for K ± comes from the Particle identification (PID) uncertainty
Summary
The NA61/SHINE experiment took data for T2K in 2007, 2009 and 2010. In 2007 and 2009, measurements were performed with a 30.92 GeV/c proton beam and a 2-cm-thick carbon target (4% of a nuclear interaction length, λi ) to measure hadron multiplicities (π ±, K ±, p, Ks0, Λ) and the production cross section [5–8]. Production events represent the fraction of inelastic events in which at least one new hadron in the final state is produced By using these measurements, the uncertainty on the neutrino flux in T2K was reduced to about 10% [4]. Measurements with the T2K replica target can directly constrain up to 90% of the neutrino flux because hadron yields at the surface of the target are measured not just for primary interactions, and for re-interactions inside the target [9]. K ± and p yields are measured for the first time This is expected to further reduce the uncertainties on the (anti)neutrino fluxes in T2K from about 10% down to the level of 3–4%. Since (anti)neutrino fluxes in T2K in the energy region above ∼ 2 GeV are produced mainly by kaon decays, the corresponding uncertainties will be greatly reduced
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