Extending the physics reach of the fixed-target programme at the LHCb experiment

Exploiting the forward geometry of its spectrometer, along with its excellent tracking and particle identification performance, the LHCb experiment at CERN has been conducting a pioneering fixed-target physics programme since 2015, studying collisions between the LHC beams and injected gaseous targets. This thesis presents my contributions to the extension of the LHCb fixed-target program. I developed an innovative technique based on time-of-flight measurement for the identification of low-momentum nuclei and antinuclei, an unforeseen capability in the LHCb detector. Using a sample of proton-helium collisions collected in 2016, it has been possible to identify the first deuteron candidates in the LHCb data. Exploiting this technique will enable the measurement of antideuteron production in the unique high-energy fixed-target regime, shedding light on the mechanisms behind the production of antinuclei in collisions between primary cosmic rays and the interstellar medium. The flux of light antinuclei, as measured by experiments such as the AMS-02 spectrometer, is expected to be a sensitive probe to exotic contributions, given that their secondary production is suppressed, so that in some models its production could be dominated by a hypothetical Dark Matter particle annihilation or decay process. An upgrade of the fixed-target system has been carried out in view of future data taking, consisting mainly of the installation of an advanced gas feed system and a 20 cm-long storage cell to confine the gas in a region upstream of the nominal LHCb interaction point. During my Ph.D. program, I was responsible for gas flow studies within the upgraded system to understand and quantify the impact of non-noble gases on the LHC machine, aiming for approval for their injection. I developed a time-dependent simulation algorithm to assess the deterioration of the surfaces exposed to the non-noble gases, demonstrating that the level of deterioration expected is within the acceptance levels for LHC operation. I also contributed to the integration of the new fixed-target system into the LHCb control system by implementing its SCADA system to gather and elaborate on the data coming from the vacuum system and allow the monitoring of its status. With the significant increase in luminosity and the wider choice of gas species offered by the target upgrade, this work lays the way for the implementation of a unique laboratory for QCD studies at the LHC.