Observation of Two New Excited Ξb0 States Decaying to Λb0 K-π+

Two narrow resonant states are observed in the Λb0K-π+ mass spectrum using a data sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the LHCb experiment and corresponding to an integrated luminosity of 6 fb-1. The minimal quark content of the Λb0K-π+ system indicates that these are excited Ξb0 baryons. The masses of the Ξb(6327)0 and Ξb(6333)0 states are m[Ξb(6327)0]=6327.28-0.21+0.23±0.12±0.24 and m[Ξb(6333)0]=6332.69-0.18+0.17±0.03±0.22 MeV, respectively, with a mass splitting of Δm=5.41-0.27+0.26±0.12 MeV, where the uncertainties are statistical, systematic, and due to the Λb0 mass measurement. The measured natural widths of these states are consistent with zero, with upper limits of Γ[Ξb(6327)0]<2.20(2.56) and Γ[Ξb(6333)0]<1.60(1.92) MeV at a 90% (95%) credibility level. The significance of the two-peak hypothesis is larger than nine (five) Gaussian standard deviations compared to the no-peak (one-peak) hypothesis. The masses, widths, and resonant structure of the new states are in good agreement with the expectations for a doublet of 1D Ξb0 resonances

Measurement of the electron reconstruction efficiency at LHCb

The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb−1 of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B+→ J/ψ(e+e−)K+ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below 1%

Measurement of the (1) production cross-section in collisions at √=13 TeV

Using a data sample corresponding to an integrated luminosity of 2.0 fb−1, collected by the LHCb experiment, the production of the (1) state in proton–proton collisions at a centre-of-mass energy of √=13 TeV is studied in the rapidity range 2.0<<4.5 and in the transverse momentum range 6.5<T<14.0GeV. The cross-section for prompt production of (1) mesons relative to that of the / meson is measured using the ⎯⎯⎯ decay mode and is found to be (1)//=1.69±0.15±0.10±0.18. The quoted uncertainties are, in order, statistical, systematic and due to uncertainties on the branching fractions of the /→⎯⎯⎯ and →⎯⎯⎯ decays. The prompt (1) production cross-section is determined to be (1)=1.26±0.11±0.08±0.14μb, where the last uncertainty includes that on the / meson cross-section. The ratio of the branching fractions of -hadron decays to the (1) and / states is measured to be →/→/=0.48±0.03±0.03±0.05, where the last uncertainty is due to those on the branching fractions of the /→⎯⎯⎯ and →⎯⎯⎯ decays. The difference between the / and (1) masses is also determined to be 113.0±0.7±0.1MeV, which is the most precise single measurement of this quantity to date

Observation of new resonances in th lambda(0)(b)pi(+)pi(-) system

We report the observation of a new structure in the Λ 0 b π + π − spectrum using the full LHCb data set of p p collisions, corresponding to an integrated luminosity of 9     fb − 1 , collected at √ s = 7 , 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be m Λ b ( 6146 ) 0 = 6146.17 ± 0.33 ± 0.22 ± 0.16     MeV , m Λ b ( 6152 ) 0 = 6152.51 ± 0.26 ± 0.22 ± 0.16     MeV , Γ Λ b ( 6146 ) 0 = 2.9 ± 1.3 ± 0.3     MeV , Γ Λ b ( 6152 ) 0 = 2.1 ± 0.8 ± 0.3     MeV , with a mass splitting of Δ m = 6.34 ± 0.32 ± 0.02     MeV , where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λ 0 b baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λ b ( 1 D ) 0 states

Observation of new resonances in th lambda(0)(b)pi(+)pi(-) system

We report the observation of a new structure in the Λ 0 b π + π − spectrum using the full LHCb data set of p p collisions, corresponding to an integrated luminosity of 9     fb − 1 , collected at √ s = 7 , 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be m Λ b ( 6146 ) 0 = 6146.17 ± 0.33 ± 0.22 ± 0.16     MeV , m Λ b ( 6152 ) 0 = 6152.51 ± 0.26 ± 0.22 ± 0.16     MeV , Γ Λ b ( 6146 ) 0 = 2.9 ± 1.3 ± 0.3     MeV , Γ Λ b ( 6152 ) 0 = 2.1 ± 0.8 ± 0.3     MeV , with a mass splitting of Δ m = 6.34 ± 0.32 ± 0.02     MeV , where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the Λ 0 b baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of Λ b ( 1 D ) 0 states

Measurement of the electron reconstruction efficiency at LHCb

The single electron track-reconstruction efficiency is calibrated using a sample corresponding to 1.3 fb−1 of pp collision data recorded with the LHCb detector in 2017. This measurement exploits B+→ J/ψ(e+e−)K+ decays, where one of the electrons is fully reconstructed and paired with the kaon, while the other electron is reconstructed using only the information of the vertex detector. Despite this partial reconstruction, kinematic and geometric constraints allow the B meson mass to be reconstructed and the signal to be well separated from backgrounds. This in turn allows the electron reconstruction efficiency to be measured by matching the partial track segment found in the vertex detector to tracks found by LHCb's regular reconstruction algorithms. The agreement between data and simulation is evaluated, and corrections are derived for simulated electrons in bins of kinematics. These correction factors allow LHCb to measure branching fractions involving single electrons with a systematic uncertainty below 1%

Measurement of the lifetimes of promptly produced Omega(0)(c) and Xi(9)(c) baryons

A measurement of the lifetimes of the Omega(0)(c) and Xi(0)(c) baryons is reported using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb(-1) collected by the LHCb experiment. The Omega(0)(c) and Xi(0)(c) baryons are produced directly from proton interactions and reconstructed in the pK(-)K(-)pi(+) final state. The Omega(0)(c) lifetime is measured to be 276.5 +/- 13.4 +/- 4.4 +/- 0.7 fs, and the Xi(0)(c) lifetime is measured to be 148.0 +/- 2.3 +/- 2.2 +/- 0.2 fs, where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty on the D-0 lifetime. These results confirm previous LHCb measurements based on semileptonic beauty-hadron decays, which disagree with earlier results of a four times shorter Omega(c)0 lifetime, and provide the single most precise measurement of the Omega(0 )(c)lifetime. (C) 2021 Science China Press. Published by Elsevier B.V. and Science China Press