During Runs 5 and 6, the LHCb experiment at CERN will operate at a luminosity up to 1.5 x 10$^{34}$ cm$^{-2s^-1}$, requiring substantial upgrades to its Electromagnetic Calorimeter (ECAL) to handle high radiation doses and achieve time resolutions of few tens of picoseconds mitigating pile-up effects. The detector under development is a Spaghetti Calorimeter (SpaCal) composed of scintillating fibres (polystyrene or garnet crystals) in a dense absorber (lead or tungsten). Ongoing investigations are focused on the photodetectors (PMTs) selection and their impact on the overall timing performance. Simulation studies of a lead-polystyrene module show that fast PMTs result in worse time resolutions due to the longitudinal showers' fluctuations, which introduce a bias in the time stamps defined by the Constant Fraction Discriminator (CFD) algorithm. A correction procedure has been developed to remove such bias, improving the time resolution by few tens of picoseconds. Additionally, a correlation between signal rise time and shower depth has been observed. Data from a test beam campaign conducted at the CERN SPS in June 2024 have been analysed to measure the timing resolution of two tungsten-polystyrene SpaCal prototypes, comparing four PMT models and two fibre types. By exploiting a rise-time-based correction procedure, time resolutions below 20 ps at high energies have been reached, with the fastest PMTs undergoing larger corrections, as expected from simulations.

A measurement of the CKM angle $\gamma$ is performed in $B^{\pm} \to D K^*(892)^{\pm}$ decays at the LHCb experiment, where $D$ represents a superposition of $D^0$ and $\overline{D}{}^0$ states. Using the dataset collected during Run 1 and Run 2, this analysis represents a comprehensive study of this channel, with the $D$ meson reconstructed in two-body final states $K^{\pm}\pi^{\mp}$, $K^+K^-$ and $\pi^+\pi^-$; four-body final states $K^{\pm}\pi^{\mp}\pi^{\pm}\pi^{\mp}$ and $\pi^+\pi^-\pi^+\pi^-$; and three-body final states $K^0_{S} \pi^+\pi^-$ and $K^0_{S} K^+ K^-$. This measurement constitutes the first observation of the suppressed $B^{\pm} \to [\pi^+K^-]_D K^{*\pm}$ and $B^{\pm} \to [\pi^+K^-\pi^+\pi^-]_D K^{*\pm}$ decays. The combined result gives $\gamma=(63\pm 13)^\circ$.

The LHCb RICH detector will undergo a significant upgrade during LS3 as part of an approved enhancement program to introduce fast-timing information. The upgrade will address the challenges posed by increased particle multiplicity and high occupancy anticipated for the LHC HL phase. Integrating sub-100 ps timing information is crucial for maintaining excellent particle identification (PID) performance. In the RICH detector, Cherenkov photons from a track arrive nearly simultaneously at the detector plane, allowing precise hit time prediction. Determining the primary vertex time (PV T$_0$) is key to accurately predicting the time of arrival of photons on the photodetector plane. By integrating time information in the RICH reconstruction, a software time gate can be applied around the predicted time per track to enhance signal-to-background ratio and PID performance. This contribution describes the integration of fast-timing information into the RICH detector, focusing on a novel method to estimate PV T$_0$ using only RICH information.

The accurate identification of charged hadrons, distinguishing between pions, kaons, and protons, stands as a pivotal aspect in the physics analyses conducted at LHCb. Playing a crucial role in these measurements, the Ring Imaging Cherenkov (RICH) system offers outstanding Particle Identification (PID) capabilities across a wide momentum spectrum, ranging from 2.6 to 100 GeV/$c$. LHCb is planning an Upgrade II in Run 5 and 6 to exploit the full potential of Hi-Lumi LHC and collect ∼ 300 fb$^{−2}$, by operating at instantaneous luminosity 1.0 – 1.5 x 10 $^{34}$ cm$^{−2}$s$^{−1}$. The RICH system will be fully upgraded to cope with such challenging conditions. The objective of the study is to examine different layouts of the RICH system, together with different types of photon detectors and compare the resulting performance to identify the best combination for the future of the experiment.

The Standard Model of particle physics (SM) has been challenged in recent years by measurements from the LHCb collaboration of rare B meson decays. These processes involve a $b\to s\ell^+\ell^-$ quark level transition and are highly suppressed in the SM, happening less than once in a million decays. This suppression provides an important testing ground for the flavour sector of the SM, as these processes are sensitive to small contributions from new particles. Ratios of branching fractions containing two different lepton flavours are particularly powerful tests, being theoretically clean. Such measurements test the flavour universality of the lepton couplings. In the SM, the electroweak couplings are universal due to an accidental symmetry of the model. This property has been extensively tested, and is found so far to be consistent with SM predictions. Nonetheless, new measurements can put important constraints on extensions of the SM. This poster will present results from a recent new measurement using $B_s^0 \to\phi\mu^+\mu^-$ and $B_s^0 \to\phi e^+e^-$ decays. The poster will also present progress towards an angular analysis of the $B_s^0 \to\phi e^+e^-$ decay that, together with the measured decay rate, will provide powerful tests of the SM. The analyses are performed using proton-proton collision data collected with the LHCb experiment, which amounts to $9\,\mathrm{fb}^{-1}$ of integrated luminosity.

The Scintillating Fibre tracker (SciFi) at LHCb, operational since 2022, is the primary tracker positioned downstream of the dipole magnet. It is designed to efficiently track particles with high momentum on the order of hundreds of GeV. It consists of three stations, each composed of 5-meter-high modules containing scintillating fibre mats. Each tracker module includes a readout box equipped with silicon photomultiplier sensors (SiPMs) that collect photons generated by particle interactions with the scintillating fibers. For each SiPM channel, the analogue signal is processed by comparing it to a set of three "comparator" thresholds to discriminate signal from dark noise. These thresholds are critical to achieve a high hit efficiency and maintain a low fake track rate and sustainable bandwidth. This poster summarizes the utilization of the Light Injection System (LIS) for calibrating the comparator thresholds for the full system of 512k SiPM channels and 1.5M comparators. An accurate time alignment needed to optimize LIS performance will be discussed, along with the full calibration procedure of fitting SiPM spectra. Challenges faced with the LIS calibration and the strategies used to address them will be presented. This poster demonstrates the role of the light injection system for threshold calibration in ensuring the high hit efficiency for accurate track reconstruction in LHCb.

The increasing computing power and bandwidth of FPGAs opens new possibilities in the field of real-time processing of HEP data. LHCb has introduced a novel a cluster-finder architecture based on FPGAs, aimed at embedding "on-the-fly" hit reconstruction directly in the readout firmware of the VELO pixel detector. Besides shrinking the high-level trigger workload by providing it with pre-reconstructed data, this system enables further opportunities. Thanks to the triggerless readout architecture of LHCb, these reconstructed hit positions are available for every collision, amounting to a flow of 10$^{11}$ hits per second, that can be exploited for unbiased precision monitoring and diagnostics of LHCb interaction region. In this poster, we describe the design, integration and performance of a set of real-time cluster density counters. These counters provide several independent averaged and per-bunch-crossing measurements of instantaneous luminosity, and average beam spot position; they can also be exploited to study the movements of the VELO detector itself. The counters function without any slowdown of data acquisition and achieve statistical precision comparable with offline measurements.

The first measurement of $\phi(1020)$ meson production in fixed-target $p$Ne collisions at $\sqrt{s_{NN}}=68.5$ GeV is presented. The $\phi(1020)$ mesons are reconstructed in their $K^{+}K^{-}$ decay in a data sample consisting of proton collisions on neon nuclei at rest, corresponding to an integrated luminosity of $21.7 \pm 1.4$ nb$^{-1}$, collected by the LHCb detector at CERN. The $\phi(1020)$ production cross-section in the centre-of-mass rapidity range of $-1.8 < y^*<0$ and transverse momentum range of $800 < p_T <6500$ MeV/c is found to be $\sigma=182.7\pm2.7~\text{(stat.)}\pm14.1~\text{(syst)}$ $\mu b$/nucleon. A double-differential measurement of the cross-section is also provided in four regions of rapidity and six regions of transverse momentum of the $\phi(1020)$ meson and compared with the predictions from Pythia and EPOS4, which are found to underestimate the experimental values.

As part of the event: "Exploring farther: machines for new knowledge" , general presentation

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