LHCb

Abstract:

A search for the charmless baryonic decay $B^{+}\to \overline{\mathrm{\Lambda }}p\overline{p}p$ is performed using proton-proton collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ . The branching fraction for this decay is measured for the first time relative to that of the topologically similar decay $B^{+}\to J/\psi K^{+}$ , with $J/\psi \to \overline{\mathrm{\Lambda }}p{K}^{-}$ . The branching fraction is measured to be $\mathcal{B}(B^{+}\to \overline{\mathrm{\Lambda }}p\overline{p}p)=(2.15\pm 0.35\pm 0.12\pm 0.28)\times {10}^{-7}$ , where the first uncertainty is statistical, the second is systematic, and the third arises from the uncertainty in the normalization channel branching fraction. The $CP$ asymmetry is measured to be ${\mathcal{A}}_{CP}=(5.4\pm 15.6\pm 2.4)\%$ , where the uncertainties are statistical and systematic. The background-subtracted invariant-mass distributions of $\overline{\mathrm{\Lambda }}p$ and $\overline{p}p$ pairs exhibit pronounced enhancements at both kinematic thresholds, in contrast to a uniform phase-space distribution.

Abstract:

Volume 1 of the FCC Feasibility Report presents an overview of the physics case, experimental programme, and detector concepts for the Future Circular Collider (FCC). This volume outlines how FCC would address some of the most profound open questions in particle physics, from precision studies of the Higgs and EW bosons and of the top quark, to the exploration of physics beyond the Standard Model. The report reviews the experimental opportunities offered by the staged implementation of FCC, beginning with an electron-positron collider (FCC-ee), operating at several centre-of-mass energies, followed by a hadron collider (FCC-hh). Benchmark examples are given of the expected physics performance, in terms of precision and sensitivity to new phenomena, of each collider stage. Detector requirements and conceptual designs for FCC-ee experiments are discussed, as are the specific demands that the physics programme imposes on the accelerator in the domains of the calibration of the collision energy, and the interface region between the accelerator and the detector. The report also highlights advances in detector, software and computing technologies, as well as the theoretical tools/reconstruction techniques that will enable the precision measurements and discovery potential of the FCC experimental programme. The content and structure of this report are guided by the scope and priorities defined in the mandate of the FCC Feasibility Study. It is therefore not intended to serve as an exhaustive review of the full physics potential of FCC. Several topics, already covered in earlier reports such as the FCC CDR, are not reiterated here or are addressed only briefly, in alignment with the study’s focus. This volume reflects the outcome of a global collaborative effort involving hundreds of scientists and institutions, aided by a dedicated community-building coordination, and provides a targeted assessment of the scientific opportunities and experimental foundations of the FCC programme.

Abstract:

The ratio between the branching fractions of the B0 → ρ(770)0γ and B0 → K*(892)0γ decays is measured with proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. The measured value isBB0→ρ7700γBB0→K∗8920γ=0.0189±0.0007±0.0005, where the first uncertainty is statistical and the second systematic. The branching fraction for B0→ ρ(770)0γ decays is hence obtained asBB0→ρ7700γ=7.9±0.3±0.2±0.2×10−7, where the last uncertainty is due to the branching fraction of the normalisation mode. This result assumes that both the ρ(770)0 and K*(892)0 decays saturate the dihadron mass spectra considered in the analysis. It is consistent with the current world-average value and by far the most precise measurement to date.

Abstract:

A study of charm mixing and CP violation in D0 → K±π∓π±π∓ decays is performed using data collected by the LHCb experiment in proton-proton collisions from 2015 to 2018, corresponding to an integrated luminosity of 6 fb−1. The ratio of promptly produced D0 → K+π−π+π− to D0 → K−π+π−π+ decay rates is measured as a function of D0 decay time, both inclusive over phase space and in bins of phase space. Taking external inputs for the D0−D¯0$$ {D}^0-{\overline{D}}^0 $$ mixing parameters x and y allows constraints to be obtained on the hadronic parameters of the charm decay. When combined with previous measurements from charm-threshold experiments and at LHCb, improved knowledge is obtained for these parameters, which is valuable for studies of the angle γ of the Unitarity Triangle. An alternative analysis is also performed, in which external inputs are taken for the hadronic parameters, and the mixing parameters are determined, including ∆x and ∆y, which are nonzero in the presence of CP violation. It is found that x=0.85−0.24+0.15%$$ x=\left(0.{85}_{-0.24}^{+0.15}\right)\% $$, y=0.21−0.27+0.29%$$ y=\left(0.{21}_{-0.27}^{+0.29}\right)\% $$, ∆x = (−0.02 ± 0.04) % and Δy=0.02−0.03+0.04%$$ \Delta y=\left(0.0{2}_{-0.03}^{+0.04}\right)\% $$. These results are consistent with previous measurements and the hypothesis of CP conservation.

Abstract:

We present a Monte Carlo-based simulation stack that provides time-of-flight (ToF)-resolved blood flow index (BFi) and has been validated against continuous-wave (CW) and time-resolved BFi measurements in both tissue-mimicking phantoms and in-vivo. Using this simulation, we evaluated the influence of key parameters including source-detector separation, ToF selection, and minimum resolvable lag on brain sensitivity by comparing simulated pulsatile blood flow signals from scalp and brain layers. We used these results to optimise the design of CoMind Research One (R1), a 16-channel interferometric time-of-flight-resolved optical neuromonitoring system that operates in real time and enables high-fidelity measurements of field autocorrelation at times-of-flight exceeding 1 ns. We validated this system and demonstrated its depth sensitivity using homogeneous and bi-layer dynamic tissue-mimicking phantoms. The advancements in optical throughput, depth selectivity, and robustness demonstrated by CoMind R1 pave the way for clinical translation and broader adoption of non-invasive optical measurements of cerebral blood flow.