Studies for current and future high-intensity operation of CERN's secondary M2 beamline

Abstract

The AMBER experiment is aiming at studying the fundamental QCD processes generating the hadronic degrees of freedom by measuring the excitation spectra of strange mesons, as well as the valence and sea quark, and gluon contributions in the kaon and pion. For these physics measurements high-intensity pion and kaon beams are important. The M2 secondary beamline at CERN’s SPS can operate in high-intensity, high-energy hadron and muon mode, and it can also deliver low-intensity, low-energy electron beams. As the mixed hadron secondary beam is produced from protons on target, kaons are a minority. Therefore, it is important to increase their relative abundance or to make maximal use of the low fraction. <br /> To achieve the former, the RF separation technique is investigated, which makes use of the velocity difference that distinct particle species have for the same momentum. Studies and proposed developments of the beam optics are discussed resulting in an optimised beam transmission and species separation. The performance of such a system is simulated and evaluated in terms of kaon rate and purity in the beam. <br /> The optimal use of the kaon fraction is studied in terms of a conventional beam approach. A limiting factor of the current beam performance is multiple scattering that complicates particle identification. Improvements concerning vacuum upgrades and beam optics are estimated with simulations. With those beam performance improvements, simulations of the AMBER strange-meson spectroscopy campaign have been performed to estimate the needed time for the measurement. <br /> The NA64 experiment is another user of the M2 line. It explores the muon beam for dark matter searches, for which the knowledge of any background is crucial. One of the major sources is the in-flight decays of hadrons that are wrongly identified as muons. Therefore, a precise determination of the number of hadrons in the muon beam is essential. To estimate their contribution, variance reduction techniques in Monte Carlo simulations are employed. With those the hadron contamination is evaluated. <br /> A potential future user of the muon beam is the MUonE experiment studying the hadronic contribution to the electromagnetic coupling constant in elastic muon-electron scattering. During a test campaign a calorimeter has been calibrated with the available electron beam. The simulation of the beamline model, which has been used to estimate the electron spectrum, is validated and benchmarked with the collected data.