Dottorato in FISICA DEGLI ACCELERATORI

Titolo della tesi: Study of features of a multiple targets system for the LEMMA project

Particles colliders have arguably been the most important instruments for particle physics over the past 50 years. The LHC, the highest energy collider to date, at which the Higgs boson was discovered, is a prime example. To continue along the road into the Terra Promissa BSM requires colliders with energy to reach even greater than that of the LHC. Since the electrons and positrons are fundamental particles, their full energy is available in collisions in contrast to protons which are composed of quarks and gluons. Nevertheless, electrons and positrons in a storage ring lose energy by synchrotron radiation, therefore the maximum reachable energy by an electron-positron accelerator is very limited with respect to a hadron-hadron one. As are electrons and positrons, muons are elementary particles but, due to their mass, the energy loss by synchrotron radiation is negligible. Therefore, the idea of a muon collider is very appealing since it would aim to study particle collisions up to tens of TeV energy while offering a cleaner experimental environment with respect to hadronic colliders. One key element in the muon collider design is the muon production with small emittance. In the LEMMA concept, a 45 GeV positron beam, stored in an accumulation ring with high energy acceptance and low angular divergence, is extracted and driven to a target system to produce muon pairs near the kinematic threshold of the process. Produced muons are emitted with naturally low emittance. However, this scheme requires an intensity of the impinging positron beam so high that the energy dissipation and the target maintenance are crucial aspects to be investigated. Both temperature rise and thermal shock are related to the beam spot size at the target for a given material: these aspects are setting a lower bound on the beam spot size itself. A multi-target system can, in principle, alleviate the effects of the deposited power on a single target.