Enhanced production of Λb0 baryons in high-multiplicity pp collisions at √s = 13 TeV

The production rate of Λ 0 b baryons relative to B 0 mesons in p p collisions at a center-of-mass energy √ s = 13     TeV is measured by the LHCb experiment. The ratio of Λ 0 b 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 ∼ 2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ 0 b 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 several models and implications for the mechanisms enforcing quark confinement are discussed

Measurement of Λb0 , Λc+ , and Λ decay parameters using Λb0→Λc+h− decays

A comprehensive study of the angular distributions in the bottom-baryon decays Λ0 b → Λ c+h−(h = π, K), followed by Λþ c → Λhþ with Λ → pπ− or Λþ c → pK0 S decays, is performed using a data sample of proton-proton collisions corresponding to an integrated luminosity of 9 fb−1 collected by the LHCb experiment at center-of-mass energies of 7, 8, and 13 TeV. The decay parameters and the associated charge-parity (CP) asymmetries are measured, with no significant CP violation observed. For the first time, the Λ0 b → Λþ c h− decay parameters are measured. The most precise measurements of the decay parameters α, β, and γ are obtained for Λþ c decays and an independent measurement of the decay parameters for the strange-baryon Λ decay is provided. The results deepen our understanding of weak decay dynamics in baryon decays

Modification of χc1(3872) and ψ(2S) production in pPb collisions at √sNN = 8.16 TeV

The LHCb Collaboration measures production of the exotic hadron χc1(3872) in proton-nucleus collisions for the first time. Comparison with the charmonium state ψ(2S) suggests that the exotic χc1(3872) experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify χc1(3872) production rates. This is the first measurement of the nuclear modification factor of an exotic hadron

Fraction of χc decays in prompt J/ψ production measured in pPb collisions at √sNN = 8.16 TeV

The fraction of χ c 1 and χ c 2 decays in the prompt J / ψ yield, F χ c → J / ψ = σ χ c → J / ψ / σ J / ψ , is measured by the LHCb detector in p Pb collisions at √ s NN = 8.16     TeV . The study covers the forward ( 1.5 < y ∗ < 4.0 ) and backward ( − 5.0 < y ∗ < − 2.5 ) rapidity regions, where y ∗ is the J / ψ rapidity in the nucleon-nucleon center-of-mass system. Forward and backward rapidity samples correspond to integrated luminosities of 13.6 ± 0.3 and 20.8 ± 0.5     nb − 1 , respectively. The result is presented as a function of the J / ψ transverse momentum p T , J / ψ in the range 1 < p T , J / ψ < 20     GeV / c . The F χ c → J / ψ fraction at forward rapidity is compatible with the LHCb measurement performed in p p collisions at √ s = 7     TeV , whereas the result at backward rapidity is 2.4 σ larger than in the forward region for 1 < p T , J / ψ < 3     GeV / c . The increase of F χ c → J / ψ at low p T , J / ψ at backward rapidity is compatible with the suppression of the ψ ( 2 S ) contribution to the prompt J / ψ yield. The lack of in-medium dissociation of χ c states observed in this study sets an upper limit of 180 MeV on the free energy available in these p Pb collisions to dissociate or inhibit charmonium state formation