arXiv subjects
Publications and source records attributed to Tom Hadavizadeh.
Rare leptonic and semi-leptonic decays offer an excellent opportunity to test the Standard Model of Particle Physics. These proceedings report on two recent LHCb measurements. The first is an observation of the rare $J/ψ\to μ^{+}μ^{-}μ^{+}μ^{-}$ decay and the second is a comprehensive measurement of local and nonlocal contributions to the $B^0 \to K^{*0}μ^{+}μ^{-}$ decay.
TORCH is a novel time-of-flight detector, designed to provide charged particle identification of pions, kaons and protons in the momentum range 2-20 GeV/c over a 9.5 m flight path. A detector module, comprising a 10mm thick quartz plate, provides a source of Cherenkov photons which propagate via total internal reflection to one end of the plate. Here, the photons are focused onto an array of custom-designed Micro-Channel Plate Photo-Multiplier Tubes (MCP-PMTs) which measure their positions and arrival times. The target time resolution per photon is 70 ps which, for 30 detected photons per charged particle, results in a 10-15 ps time-of-flight resolution. A 1.25 m length TORCH prototype module employing two MCP-PMTs has been developed, and tested at the CERN PS using a charged hadron beam of 8 GeV/c momentum. The construction of the module, the properties of the MCP-PMTs and the readout electronics are described. Measurements of the collected photon yields and single-photon time resolutions have been performed as a function of particle entry points on the plate and compared to expectations. These studies show that the performance of the TORCH prototype approaches the design goals for the full-scale detector.
Beauty and charm quarks are ideal probes of pertubative Quantum Chromodymanics in proton-proton collisions, owing to their large masses. In this paper the role of multi-parton interactions in the production of doubly-heavy hadrons is studied using simulation samples generated with Pythia, a Monte Carlo event generator. Comparisons are made to the stand-alone generators BcVegPy and GenXicc. New methods of speeding up Pythia simulations for events containing heavy quarks are described, enabling the production of large samples with multiple heavy-quark pairs. We show that significantly higher production rates of doubly-heavy hadrons are predicted in models that allow heavy quarks originating from different parton-parton interactions (within the same hadron-hadron collision) to combine to form such hadrons. Quantitative predictions are sensitive to the modelling of colour reconnections. We suggest a set of experimental measurements capable of differentiating these additional contributions.
Recent measurements of mixing and $CP$ violation in charm decays at LHCb are presented. These include searches for direct $CP$ violation in $D^{0}\rightarrow K_{S}^{0}K_{S}^{0}$, $D_{(s)}^{+}\rightarrow h^{+} π^{0} $ and $D_{(s)}^{+}\rightarrow h^{+}η$ decays, and a search for time-dependent $CP$ violation in $D^{0}\rightarrow h^{+}h^{-}$ decays, where $h^{+}$ is either a $π^{+}$ or $K^{+}$ meson.
TORCH is a time-of-flight detector, designed to provide charged pi/K particle identification up to a momentum of 10 GeV/c for a 10 m flight path. To achieve this level of performance, a time resolution of 15 ps per incident particle is required. TORCH uses a plane of quartz of 1 cm thickness as a source of Cherenkov photons, which are then focussed onto square Micro-Channel Plate Photomultipliers (MCP-PMTs) of active area 53 x 53 mm^2, segmented into 8 x 128 pixels equivalent. A small-scale TORCH demonstrator with a customised MCP-PMT and associated readout electronics has been successfully operated in a 5 GeV/c mixed pion/proton beam at the CERN PS facility. Preliminary results indicate that a single-photon resolution better than 100 ps can be achieved. The expected performance of a full-scale TORCH detector for the Upgrade II of the LHCb experiment is also discussed.