Malcolm John

Abstract:

A model-independent determination of the CKM angle γ is presented, using the B± → [K+K−π+π−]Dh± and B± → [π+π−π+π−]Dh± decays, with h = K, π. This measurement is the first phase-space binned study of these decay modes, and uses a sample of proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The phase-space bins are optimised for sensitivity to γ, and in each bin external inputs from the BESIII experiment are used to constrain the charm strong-phase parameters. The result of this binned analysis is γ=53.9−8.9+9.5°$$ \gamma ={\left(53.{9}_{-8.9}^{+9.5}\right)}^{{}^{\circ}} $$, where the uncertainty includes both statistical and systematic contributions. Furthermore, when combining with existing phase-space integrated measurements of the same decay modes, a value of γ=52.6−6.4+8.5°$$ \gamma ={\left(52.{6}_{-6.4}^{+8.5}\right)}^{{}^{\circ}} $$ is obtained, which is one of the most precise determinations of γ to date.

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:

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:

The spatial and temporal performance of a telescope system comprising planar silicon sensors bump-bonded to Timepix4-v2 ASICs are assessed at the CERN SPS using a 180 GeV/c mixed hadron beam. The pointing resolution at the centre of the telescope is 2.3 ± 0.1 μm and 2.4 ± 0.1 μm in x and y directions, respectively. The temporal resolution for the combined timestamps on a track using only the information from the Timepix4 planes is found to be 92 ± 5 ps. The telescope is extensively described including its data acquisition system and dedicated software as well as the corrections applied to the raw measurements.