LHCb

Abstract:

A time-dependent, flavour-tagged measurement of CP violation is performed with B0→ D+D− and Bs0→Ds+Ds− decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 6 fb−1. In B0→ D+D− decays the CP-violation parameters are measured to beSD+D−=−0.552±0.100stat±0.010syst, CD+D−=0.128±0.103stat±0.010syst. In Bs0→Ds+Ds− decays the CP-violating parameter formulation in terms of ϕs and |λ| results inϕs=−0.086±0.106stat±0.028systrad, ∣λDs+Ds−∣=1.145±0.126stat±0.031syst. These results represent the most precise single measurement of the CP-violation parameters in their respective channels. For the first time in a single measurement, CP symmetry is observed to be violated in B0→ D+D− decays with a significance exceeding six standard deviations.

Abstract:

The first full amplitude analysis of B+ → ψ(2S)K+π+π− decays is performed using proton-proton collision data corresponding to an integrated luminosity of 9 fb−1 recorded with the LHCb detector. The rich K+π+π− spectrum is studied and the branching fractions of the resonant substructure associated with the prominent K1(1270)+ contribution are measured. The data cannot be described by conventional strange and charmonium resonances only. An amplitude model with 53 components is developed comprising 11 hidden-charm exotic hadrons. New production mechanisms for charged charmonium-like states are observed. Significant resonant activity with spin-parity JP = 1+ in the ψ(2S)π+ system is confirmed and a multi-pole structure is demonstrated. The spectral decomposition of the ψ(2S)π+π− invariant-mass structure, dominated by X0 → ψ(2S)ρ(770)0 decays, broadly resembles the J/ψϕ spectrum observed in B+ → J/ψϕK+ decays. Exotic ψ(2S)K+π− resonances are observed for the first time.

Abstract:

Charged-particle trajectories are usually reconstructed with the LHCb detector using combined information from the tracking devices placed upstream and downstream of the 4 T m dipole magnet. Trajectories reconstructed using only information from the tracker downstream of the dipole magnet, which are referred to as T tracks, have not been used for physics analysis to date. The challenges of the reconstruction of long-lived particles with T tracks for physics use are discussed and solutions are proposed. The feasibility and the tracking performance are studied using samples of long-lived Λ and KS0 hadrons decaying between 6.0 and 7.6 m downstream of the proton–proton collision point, thereby traversing most of the magnetic field region and providing maximal sensitivity to magnetic and electric dipole moments. The reconstruction can be expanded upstream to about 2.5 m for use in direct searches of exotic long-lived particles. The data used in this analysis have been recorded between 2015 and 2018 and correspond to an integrated luminosity of 6 fb-1. The results obtained demonstrate the possibility to further extend the decay volume and the physics reach of the LHCb experiment.