Search Talks

Achieving picosecond-level timing in large-scale detector systems requires front-end electronics that combine excellent time resolution with low power consumption and full integration. In this seminar we present FastIC+, an 8-channel front-end ASIC in 65 nm CMOS for the readout of photosensors with intrinsic gain (SiPMs, PMTs, MCPs), which provides on-chip digitization of both arrival time and energy at 12.5 mW per channel.

We will describe the architecture of the chip, including the current-mode input stage capable of handling both signal polarities, the parallel time, energy and trigger branches, and the Time-to-Digital Converter based on a PLL generating 16 phases at 1.28 GHz, yielding a 24.4 ps time bin. We will then review the experimental characterization: a single-photon time resolution of (98 ± 1) ps FWHM with 3×3 mm² SiPMs, and coincidence time resolutions of (85 ± 1) ps FWHM with 2×2×3 mm³ LGSO crystals and (130 ± 1) ps FWHM with 2.8×2.8×20 mm³ LYSO:Ce,Ca — to our knowledge the first sub-100 ps CTR reported with on-chip digitization. Comparisons between analog and digital readout modes demonstrate that the internal TDC contributes negligibly to the overall timing budget, which remains dominated by sensor jitter.

Finally, we will discuss how this development, which began within the framework of CERN medical applications, has had an impact into other domains. In particular, it led to the design of the FastRICH chip, developed for the sensor readout of the LHCb RICH detector, which will become the first RICH detector with timing capability, while the FastIC family continues to find broad dissemination in other fields, most notably in time-of-flight PET instrumentation and mass spectrometry.

Measurements of the CKM matrix element Vcb are presented using proton–proton collision data collected with the CMS detector during the LHC Run 2 and Run 3 periods. The measurements exploit top-quark pair events in which one top quark decays via a W boson to a final state with an electron or a muon and neutrinos, and the other top quark decays via a W boson to a charm quark and a bottom quark. The analyses rely on dedicated CMS jet-flavor tagging algorithms to efficiently and precisely identify jets originating from charm and bottom quarks. Binned maximum-likelihood fits are performed to extract the branching fraction of the decay of a W boson to a charm quark and a bottom quark. This measurement is then used to infer the magnitude of the CKM matrix element Vcb, providing a direct determination of this fundamental parameter from top-quark events.

Three-body forces in nuclear physics account for effects that cannot be captured by pairwise interactions alone in many-body systems. These forces have traditionally been constrained through two-body scattering experiments and measurements of bound-state properties. Direct experimental information on three-body dynamics in well-controlled systems of three free, unbound particles has so far been inaccessible due to the lack of a suitable experimental technique, leaving a significant part of the three-body continuum unexplored.

In this seminar, I will present the first femtoscopic measurement of the genuine three-proton correlation function in pp collisions at 13.6 TeV with ALICE at the LHC. This observable encodes information about the final-state interactions among three protons emitted at femtometer-scale separations in the collision. Direct comparison with state-of-the-art three-body calculations reveals sensitivity to the partial-wave structure of the nuclear interaction, establishing three-baryon femtoscopy as an effective scattering experiment with unbound nucleons in a 3→3 process that is not feasible with any other experimental method. The measurement also reveals the first experimental signature of an effective long-range attraction emerging from three-body continuum dynamics.

The newly established method will make it possible to exploit the abundant production of hadrons at the LHC to investigate three-body interactions that are poorly constrained or entirely unknown. I will conclude with a discussion of future measurements of three-body interactions involving hyperons, which could have important implications for hypernuclear physics and for the equation of state of dense matter, including that found in neutron stars.