Enhanced production of Λb0\Lambda_{b}^{0} baryons in high-multiplicity pppp collisions at s=13\sqrt{s} = 13 TeV

The production rate of $\Lambda_{b}^{0}$ baryons relative to $B^{0}$ mesons in $pp$ collisions at a center-of-mass energy $\sqrt{s} = 13$ TeV is measured by the LHCb experiment. The ratio of $\Lambda_{b}^{0}$ to $B^{0}$ production cross-sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the value measured in $e^{+}e^{-}$ collisions, and increases by a factor of $\sim2$ with increasing multiplicity. At relatively low transverse momentum, the ratio of $\Lambda_{b}^{0}$ to $B^{0}$ cross-sections is higher than what is measured in $e^{+}e^{-}$ collisions, but converges with the $e^{+}e^{-}$ ratio as the momentum increases. These results imply that the evolution of heavy $b$ quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with a statistical hadronization model and implications for the mechanisms enforcing quark confinement are discussed.Comment: All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-027.html (LHCb public pages

Search for the Bs0 → μ+μ−γ decay

A search for the fully reconstructed B0 s → µ +µ −γ decay is performed at the LHCb experiment using proton-proton collisions at √ s = 13 TeV corresponding to an integrated luminosity of 5.4 fb−1 . No signifcant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are set B(B 0 s → µ +µ −γ) < 4.2 × 10−8 , m(µ +µ −) ∈ [2mµ, 1.70] GeV/c2 , B(B 0 s → µ +µ −γ) < 7.7 × 10−8 , m(µ +µ −) ∈ [1.70, 2.88] GeV/c2 , B(B 0 s → µ +µ −γ) < 4.2 × 10−8 , m(µ +µ −) ∈ [3.92, mB0 s ] GeV/c2 , at 95% confdence level. Additionally, upper limits are set on the branching fraction in the [2mµ, 1.70] GeV/c2 dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals

First observation of the Λb0 → D+D−Λ decay

The Λ 0 b → D+D−Λ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.3 fb−1 . Using the B0 → D+D−K0 S decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to be R = σΛ0 b σB0 × B(Λ0 b → D+D−Λ) B(B0 → D+D−K0 S ) = 0.179 ± 0.022 ± 0.014 , where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, B(B0 → D+D−K0 S ), and the cross-section ratio, σΛ0 b /σB0 , previously measured by LHCb are used to derive the branching fraction of the Λ 0 b → D+D−Λ decay B(Λ0 b → D+D−Λ) = (1.24 ± 0.15 ± 0.10 ± 0.28 ± 0.11) × 10−4 , where the third and fourth contributions are due to uncertainties of B(B0 → D+D−K0 S ) and σΛ0 b /σB0 , respectively. Inspection of the D+Λ and D+D− invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λ 0 b → D∗+D−Λ decay is also observed for the first time as a partially reconstructed component in the D+D−Λ invariant mass spectrum

Amplitude analysis of the radiative decay Bs0 → K+K−γ

A search for radiative decay of B0 s mesons to orbitally excited K+K− states is performed using proton proton collisions recorded by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1 . The dikaon spectrum in the mass range mKK < 2400 MeV/c 2 is dominated by the ϕ(1020) resonance that accounts for almost 70% of the decay rate. Considering the possible contributions of f2(1270), f ′ 2 (1525) and f2(2010) meson states, the overall tensor contribution to the amplitude is measured to be F{f2} = 16.8 ± 0.5 (stat.) ± 0.7 (syst.)%, mostly dominated by the f ′ 2 (1525) state. Several statistically equivalent solutions are obtained for the detailed resonant structure depending on whether the smaller amplitudes interfere destructively or constructively with the dominant amplitude. The preferred solution that corresponds to the lowest values of the ft fractions along with constructive interference leads to the relative branching ratio measurement B(B0 s → f ′ 2γ) B(B0 s → ϕγ) = 19.4 +0.9 −0.8 (stat.) +1.4 −0.5 (syst.) ± 0.5 (B)%, where the last uncertainty is due to the ratio of measured branching fractions to the K+K− final state. This result represents the first observation of the radiative B0 s → f ′ 2 (1525)γ decay, which is the second radiative transition observed in the B0 s sector

Study of b-hadron decays to Λc^+h-h' final states

Decays of Ξ − b and Ω − b baryons to Λ + c h −h ′− final states, with h −h ′− being π −π −, K−π\ud − and K−K− meson pairs, are searched for using data collected with the LHCb detector. The data sample studied corresponds to an integrated luminosity of 8.7 fb−1 of pp collisions collected at centre-of-mass energies √ s = 7, 8 and 13 TeV. The products of the relative branching fractions and fragmentation fractions for each signal mode, relative to the B− → Λ + c pπ− mode, are measured, with Ξ − b → Λ + c K−π −, Ξ − b → Λ + c K−K− and Ω − b → Λ + c K−K− decays being observed at over 5 σ significance. The Ξ − b → Λ + c K−π − mode is also used to measure the Ξ − b production asymmetry, which is found to be consistent with zero. In addition, the B− → Λ + c pK− decay is observed for the first time, and its branching fraction is measured relative to that of the B− → Λ + c pπ− mode

Amplitude analysis of the B0→K*0μ+μ− decay

An amplitude analysis of the B 0 → K * 0 μ + μ − decay is presented using a dataset corresponding to an integrated luminosity of 4.7     fb − 1 of p p collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the standard model, are extracted directly from the data through a q 2 -unbinned amplitude analysis, where q 2 is the μ + μ − invariant mass squared. Long-distance contributions, which originate from nonfactorizable QCD processes, are systematically investigated, and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of b - to s -quark transitions, with the largest discrepancy from the standard model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations

Measurements of the branching fraction ratio B(ϕ → μ+μ−) / B(ϕ → e+e−) with charm meson decays

Measurements of the branching fraction ratio B(ϕ → μ+μ−) / B(ϕ → e+e−) with Ds+→π+ϕ and D+→ π+ϕ decays, denoted Rϕπs and Rϕπd, are presented. The analysis is performed using a dataset corresponding to an integrated luminosity of 5.4 fb−1 of pp collision data collected with the LHCb experiment. The branching fractions are normalised with respect to the B+ → K+J/ψ(→ e+e−) and B+ → K+J/ψ(→ μ+μ−) decay modes. The combination of the results yieldsRϕπ=1.022±0.012stat±0.048syst. The result is compatible with previous measurements of the ϕ → ℓ+ℓ− branching fractions and predictions based on the Standard Model

Terrestrial gamma radiation dose rate in Cienfuegos, Cuba

This study assesses the level of background radiation for Cienfuegos Province, Cuba. Measurements of outdoor gamma radiation (of terrestrial and cosmic origin) in air were performed at 198 locations using a GPS navigator and a dose meter (SRP-68-01, 30 × 25 mm NaI detector). The average absorbed dose was found to be 73.9 nGy h-1 (17.2–293.9 nGy h-1), corresponding to an annual effective dose of 74.7 μSv (21–324 μSv). When compared with the data available for other places, the absorbed gamma doses obtained in this study indicate a background radiation level that falls within natural limits for the Damuji, Salado and Caonao watersheds; however, the Arimao and Gavilanes watersheds present levels of the absorbed dose and annual effective dose comparable with high background radiation areas. An isodose map of the terrestrial gamma dose rate in Cienfuegos was drawn using the GIS application “Arc View”. This study provides important baseline data of radiation exposure in the area

Terrestrial gamma radiation dose rate in Cienfuegos, Cuba

This study assesses the level of background radiation for Cienfuegos Province, Cuba. Measurements of outdoor gamma radiation (of terrestrial and cosmic origin) in air were performed at 198 locations using a GPS navigator and a dose meter (SRP-68-01, 30 × 25 mm NaI detector). The average absorbed dose was found to be 73.9 nGy h-1 (17.2–293.9 nGy h-1), corresponding to an annual effective dose of 74.7 μSv (21–324 μSv). When compared with the data available for other places, the absorbed gamma doses obtained in this study indicate a background radiation level that falls within natural limits for the Damuji, Salado and Caonao watersheds; however, the Arimao and Gavilanes watersheds present levels of the absorbed dose and annual effective dose comparable with high background radiation areas. An isodose map of the terrestrial gamma dose rate in Cienfuegos was drawn using the GIS application “Arc View”. This study provides important baseline data of radiation exposure in the area