AMBER: a new QCD facility at the CERN SPS M2 beam line

Abstract

AMBER (NA66) is a newly proposed fixed-target experiment at the M2 beam line of the SPS, devoted to various fundamental QCD measurements, with a proposal recently approved by the CERN Research Board for a Phase-1 program and a Letter of Intent made public for a longer term programme. Such an unrivaled installation would make the experimental hall EHN2 the site for a great variety of measurements to address fundamental issues of strong interactions in the medium and long-term future. The elastic muon-proton scattering process, using high-energy muons, is proposed as a novel approach to the long standing puzzle of the proton charge radius. Such a measurement constitutes a highly-welcomed complementary approach in this area of world-wide activity. Operating with protons, the antiproton production cross section, which is currently know with poor precision, can be measured, which constitutes important input for the upcoming activities in searches for Dark Matter. Especially the world-unique SPS M2 beam line, when operated with high-energy pions, can be used to shed light on the emergence of hadron masses and to address the question of how can we explain the emergence of the proton mass and the nearly masslessness of the pion? The origin of hadron masses is deeply connected to the parton dynamics their differences between baryons and mesons. For a longer-term programme an upgrade of the M2 beam line with radio-frequency separation technique will provide kaon and antiproton beams of high purity. This will allow to perform precise spectroscopy studies and open new unique opportunities to shed new light to the light meson structure and properties.