Logo: to the web site of Uppsala University

An amplitude analysis of the Cabibbo-favored decay D+ -> K-pi+pi+pi 0 is performed, using 7.93 fb-1 of e+e- collision data collected with the BESIII detector at the center-of-mass energy of 3.773 GeV. The branching fractions of the intermediate processes are measured, with the dominant contribution D+-> K<overline>& lowast;8920 rho 770+\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ {D}<^>{+}\to {\overline{K}}<^>{\ast }{(892)}<^>0\rho {(770)}<^>{+} $$\end{document} observed to have a branching fraction of (4.35 +/- 0.07stat.+/- 0.17syst.)%. With the detection efficiency derived from the amplitude analysis, the absolute branching fraction of D+-> K-pi+pi+pi 0 is measured to be (6.35 +/- 0.04stat.+/- 0.07syst.)%.

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 J^P = 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.

The Ξ^0⁢(−)_𝑏 → Ξ_𝑐⁢(3055)⁺⁽⁰⁾⁢(→𝐷⁺⁽⁰⁾⁢Λ)⁢𝜋⁻ decay chains are observed, and the spin-parity of Ξ_𝑐⁢(3055)⁺⁽⁰⁾ baryons is determined for the first time. The measurement is performed using proton-proton collision data at a center-of-mass energy of √𝑠 =13  TeV, corresponding to an integrated luminosity of 5.4  fb⁻¹, recorded by the LHCb experiment between 2016 and 2018. The spin-parity of the Ξ_𝑐⁢(3055)⁺⁽⁰⁾ baryons is determined to be 3/2⁺ with a significance of more than 6.5⁢𝜎 (3.5⁢𝜎) compared to all other tested hypotheses. The up-down asymmetries of the Ξ^0⁢(−)_𝑏 → Ξ_𝑐⁢(3055)⁺⁽⁰⁾⁢𝜋⁻ transitions are measured to be −0.92±0.10±0.05 (−0.92±0.16±0.22), consistent with maximal parity violation, where the first uncertainty is statistical and the second is systematic. These results support the hypothesis that the Ξ_𝑐⁢(3055)⁺⁽⁰⁾ baryons correspond to the first 𝐷-wave 𝜆-mode excitation of the Ξ_𝑐 flavor triplet.

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 Lambda and K-S(0) 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.

A measurement of the CP -violating parameters in B⁰_s → D∓s K± decays is reported, based on the analysis of proton-proton collision data collected by the LHCb experiment corresponding to an integrated luminosity of 6 fb⁻¹ at a centre-of-mass energy of13 TeV . The measured parameters are obtained with a decay-time dependent analysis yielding C_f = 0.791 ± 0.061 ± 0.022, ^A∆Γ_f = −0.051 ± 0.134 ± 0.058, A^∆Γ¯_f = −0.303 ± 0.125 ± 0.055,S_f = −0.571 ± 0.084 ± 0.023 and S_f = −0.503 ± 0.084 ± 0.025, where the first uncertainty is statistical and the second systematic. This corresponds to CP violation in the interference between mixing and decay of about 8.6 σ. Together with the value of the B_s⁰ mixing phase−2β_s, these parameters are used to obtain a measurement of the CKM angle γ equal to (74 ± 12)^◦ modulo 180^◦, where the uncertainty contains both statistical and systematic contributions. This result is combined with the previous LHCb measurement in this channelusing 3 fb⁻¹ resulting in a determination of γ = (81⁺¹²₋₁1)^◦.

A time-dependent, flavour-tagged measurement of CP violation is performed with B-0 -> D+D- and B-s(0)-> D+ (s) D- (s)decays, using data collected by the LHCb detector in proton-proton collisions at a centre-of-mass energy of 13TeV corresponding to an integrated luminosity of 6 fb(-1). In B-0 -> D+D- decays the CP-violation parameters are measured to be S-D(+) (-)(D) = -0.552 +/- 0.100 (stat) +/- 0.010 (syst), C-D(+) (-)(D) = 0.128 +/- 0.103 (stat) +/- 0.010 (syst). In B-s(0)-> D+ (s) D- (s) decays the CP-violating parameter formulation in terms of phi(s) and |lambda| results in phi s = -0.086 +/- 0.106 (stat) +/- 0.028 (syst) rad, |lambda (+)(D) (-)(s D) (s) | = 1.145 +/- 0.126 (stat) +/- 0.031 (syst). 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 B-0 -> D+D- decays with a significance exceeding six standard deviations.

A measurement of the time-dependent ratio of the D-0 -> K+ to (D) over bar (0) pi(-) decay rates is reported. The analysis uses a sample of proton-proton collisions corresponding to an integrated luminosity of 6 fb- 1 recorded by the LHCb experiment from 2015 through 2018 at a center-of-mass energy of 13 TeV. The D-0 meson is required to originate from a D*(2010)(+) -> D-0 pi(+) decay, such that its flavor at production is inferred from the charge of the accompanying pion. The measurement is performed simultaneously for the K+ pi(-) and K- pi(+) final states, allowing both mixing and CP-violation parameters to be determined. The value of the ratio of the decay rates at production is determined to be R-K pi = (343.1 +/- 2.0) x 10(-5). The mixing parameters are measured to be c(K pi) = (51.4 +/- 3.5) x 10(-4) and c(K pi)(0) = (13 +/- 4) x 10(-6), where root R(K pi)c(K pi) is the linear coefficient of the expansion of the ratio as a function of decay time in units of the D-0 lifetime, and c(K pi)(0) is the quadratic coefficient, both averaged between the K+ pi(-) and K- pi(+) final states. The precision is improved relative to the previous best measurement by approximately 60%. No evidence for CP violation is found.

Measurements are presented of the cross-section for the central exclusive production of J/ψ→μ+μ− and ψ(2S)→μ+μ− processes in proton-proton collisions at √s=13 TeV with 2016–2018 data. They are performed by requiring both muons to be in the LHCb acceptance (with pseudorapidity 2<ημ±<4.5) and mesons in the rapidity range 2.0<y<4.5. The integrated cross-section results are

σJ/ψ→μ+μ−(2.0<yJψ<4.5,2.0<ημ±<4.5)=400±2±5±12pb,

σψ(2S)→μ+μ−(2.0<yψ(2S)<4.5,2.0<ημ±<4.5)=9.40±0.15±0.13±0.27 pb,

where the uncertainties are statistical, systematic and due to the luminosity determination. In addition, a measurement of the ratio of ψ(2S) and J/ψ cross-sections, at an average photon-proton centre-of-mass energy of 1 TeV, is performed, giving

σψ(2S)σJ/ψ=0.1763±0.0029±0.0008±0.0039,

where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the involved branching fractions. For the first time, the dependence of the J/ψ and ψ(2S) cross-sections on the total transverse momentum transfer is determined in pp collisions and is found consistent with the behaviour observed in electron-proton collisions.

We measure the Born cross section for the reaction 𝑒+⁢𝑒−→𝜂⁢ℎ𝑐 from √𝑠 =4.129 to 4.600 GeV using datasets collected by the BESIII detector running at the BEPCII collider. A resonant structure in the cross-section line shape near 4.200 GeV is observed with a statistical significance of 7⁢𝜎. The parameters of this resonance are measured to be 𝑀=4188.8±4.7±8.0  MeV/𝑐2 and Γ=49±16±19  MeV, where the first uncertainties are statistical and the second systematic.

The branching fraction ratios of and 𝐵¯⁰→𝐷*^+⁢𝜏−⁢¯𝜈_𝜏 decays are measured with respect to their muonic counterparts, using a data sample corresponding to an integrated luminosity of 2.0  fb⁻¹ collected by the LHCb experiment in proton-proton collisions at √𝑠 =13  TeV. The reconstructed final states are formed by combining 𝐷+ mesons with 𝜏⁻ → 𝜇⁻⁢¯𝜈_𝜇⁢𝜈_𝜏 candidates, where the 𝐷⁺ is reconstructed via the 𝐷⁺ → 𝐾⁻⁢𝜋⁺⁢𝜋⁺ decay. The results are 𝑅⁡(𝐷⁺) = 0.249±0.043±0.047, 𝑅⁡(𝐷*⁺) = 0.402±0.081±0.085, where the first uncertainties are statistical and the second systematic. The two measurements have a correlation coefficient of −0.39 and are compatible with the standard model.