LHCb

Abstract:

Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D⁰D⁰π⁺ mass spectrum just below the D^*+D⁰ mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar [Formula: see text] tetraquark with a quark content of [Formula: see text] and spin-parity quantum numbers J^P = 1⁺. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D^*+ mesons is consistent with the observed D⁰π⁺ mass distribution. To analyse the mass of the resonance and its coupling to the D^*D system, a dedicated model is developed under the assumption of an isoscalar axial-vector [Formula: see text] state decaying to the D^*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the [Formula: see text] state. In addition, an unexpected dependence of the production rate on track multiplicity is observed.

Abstract:

We review the most precise tests of the CKM model of flavour physics performed by the LHCb collaboration during 2021. These include world best measurements of both time-dependent and time-independent CP violation in charm decays, the first observation of a nonzero mass difference of the neutral charm-meson eigenstates, and the most precise determination to date of the mass difference between the B0s eigenstates. A new simultaneous combination of measurements of the CKM angle γ and of charm decays allows to improve the precision on the decay-width difference of the neutral charm-meson eigenstates by a factor of 2 with respect to the combination of charm results only.

Abstract:

The TORCH detector provides low-momentum particle identification, combining Time of Flight (TOF) and Cherenkov techniques to achieve charged particle pi/K/p separation between 2–20 GeV/c over a flight distance of 10 m. The measurement requires a timing resolution of 70 ps for single Cherenkov photons. For precision photon detection, customised Micro-Channel Plate Photomultiplier Tubes (MCP-PMTs) with high precision TOF measurement electronics have been developed. The electronics measures time-over-threshold from the MCP-PMT and features a 10-Gigabit Ethernet readout. This paper reports the design and performance of a 5120-channel system which currently instruments a pair of MCP-PMTs, but has the capacity to read out ten customised MCP-PMT devices in the future.