David Bacher

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.

Abstract:

The observation of a wide peaking structure in the $B_c^{+}\gamma$ mass spectrum is reported using proton-proton collision data collected by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of $9{\mathrm{fb}}^{-1}$ . The statistical significance over the background-only hypothesis exceeds seven standard deviations. The width of the observed structure is larger than the expectation from a single-peak hypothesis, and is well described by an effective minimal model consisting of two narrow peaks located at $6704.8\pm 5.5\pm 2.8\pm 0.3\mathrm{MeV}/c^2$ and $6752.4\pm 9.5\pm 3.1\pm 0.3\mathrm{MeV}/c^2$ . The uncertainty terms are statistical, systematic, and associated to the knowledge of the $B_c^{+}$ mass, respectively. The measured peak locations are in line with theoretical predictions for lowest excited $P$ -wave $B_c^{+}$ states, marking the first observation of orbitally excited beauty-charm mesons and providing important insights into the internal dynamics of hadrons containing two heavy quarks.

Abstract:

A search for the decay B0→ ϕϕ is made using pp collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb−1. No significant signal is observed, and an upper limit on the branching fraction of 1.3 (1.4) × 10−8 at 90 (95)% confidence level is set. This result supersedes the previous LHCb study and improves the upper limit by a factor of two.

Abstract:

A bstract A search for the decay B 0 → ϕϕ is made using pp collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of 9 fb − 1 . No significant signal is observed, and an upper limit on the branching fraction of 1 . 3 (1 . 4) × 10 − 8 at 90 (95)% confidence level is set. This result supersedes the previous LHCb study and improves the upper limit by a factor of two.

Abstract:

A study of the difference in the CP asymmetries between Λ b 0 → J / ψ p π - and Λ b 0 → J / ψ pK - decays, Δ A CP , is performed using proton-proton collision data collected by the LHCb experiment in the years 2015–2018, corresponding to an integrated luminosity of 6 fb - 1 . This quantity is measured to be Δ A CP = ( 4.03 ± 1.18 ± 0.23 ) % , where the first uncertainty is statistical and the second is systematic. When combined with the previous LHCb result, a value of Δ A CP = ( 4.31 ± 1.06 ± 0.28 ) % is obtained, corresponding to a significance of 3.9 σ against the CP symmetry hypothesis. Studies of triple-product asymmetries, which provide an additional probe of CP violation, show no significant deviation from CP symmetry.