Towards femtoscopy with the upgraded LHCb detector: Measurement of proton-proton correlations

The first measurement of the femtoscopic correlation function of p-p pairs with LHCb Run 3 NoBias data and simulation samples is presented. Correlations are clearly observed in data down to low relative momenta, demonstrating the feasibility of femtoscopy in this kinematic regime of the proton pair with the upgraded LHCb detector. The data follows the expected trend of enhancement at low k* and approaches unity at larger values, while simulation exhibits significant deviations already at Monte Carlo truth level. For simulation, we find deviations from the expected behavior that are still under investigation. With the current 2024 and 2025 data sets, the precise extraction of the pp source size is deemed possible, enabling the study of rarer baryon–baryon systems.