At the Large Hadron Collider (LHC) at Geneva, collisions of lead nuclei are used to create a thermodynamic system described by fluid dynamics under extreme conditions. The temperature of the short-lived system is sufficiently large in order to release the building blocks of matter at a subnucleonic scale, quarks and gluons. This state of matter is commonly called Quark Gluon Plasma (QGP). The space-time evolution of heavy-ion collisions at the LHC is described by close-to-ideal hydrodynamics after a short lapse of time. However, key features of the early stages of these collisions are largely unknown. These characteristics are crucial to understand the applicability limits of hydrodynamics and to understand thermalisation of a strongly interacting system.
In recent publications, it was pointed out that the dilepton production in the intermediate mass scale between 1.5 and 5 GeV/c² is highly sensitive to the ´thermalisation´ time scale towards the equilibrium QGP.
In addition, the LHC provides highly energetic proton and heavy-ion beams. They allow us to access the hadronic structure of the projectiles at very small fractional longitudinal momenta and at the same time still relatively large four momentum transfers. This configuration enables hence for perturbative calculations allowing the extraction of hadron structure information at very small fractional longitudinal momenta.
The theoretically best understood process in hadronic collisions is the production of dilepton pairs, the so-called Drell-Yan process. However, so far, no measurement down to 3 GeV/c² at a hadron collider has been published despite its theoretical motivation to test the lowest fractional momenta. In fact, at masses below around 30 GeV/c², semileptonic decays from heavy-flavour hadron decays start to dominate the dilepton production. This process has obscured any attempt to extract dilepton production in this kinematic domain.
The first goal of the thesis is the first measurement of Drell-Yan dimuons at low invariant masses at the LHC in proton-proton collisions that will be taken in 2024. This measurement will be based on novel background rejection techniques exploiting the forward geometry of LHCb. In a second part, the feasibility of the measurement in heavy-ion collisions will be investigated in the present and the future LHCb set-up. Depending on the outcome of the studies, a measurement in heavy-ion collisions will be conducted.