Measurement of the $$ {\Lambda}_b^0 $$→ J/ψΛ angular distribution and the $$ {\Lambda}_b^0 $$ polarisation in pp collisions

Abstract

This paper presents an analysis of the Λ 0 b → J/ψΛ angular distribution and the transverse production polarisation of Λ 0 b baryons in proton-proton collisions at centreof-mass energies of 7, 8 and 13 TeV. The measurements are performed using data corresponding to an integrated luminosity of 4.9 fb −1 , collected with the LHCb experiment. The polarisation is determined in a fiducial region of Λ 0 b transverse momentum and pseudorapidity of 1 < p T < 20 GeV/c and 2 < η < 5, respectively. The data are consistent with Λ 0 b baryons being produced unpolarised in this region. The parity-violating asymmetry parameter of the Λ → pπ − decay is also determined from the data and its value is found to be consistent with a recent measurement by the BES III collaboration.

Time-reversal asymmetries and angular distributions in Λb → ΛV

“…The most simple one is the naive factorization [18,19,39,40], in which the mesons are produced from weak vertices directly. In particular, the experimental branching ratio of Λ b → pπ − can be explained by light-cone QCD sum rules [39], and the experimental JHEP11(2021)104 results in Λ b → J/ψΛ are well compatible with those in the covariant confined quark model [18,30]. In refs.…”

“…Particularly, the longitudinally polarized fraction, f L (B 0 → φK * 0 ) ≈ 0.5, measured by BarBar [26] and Belle [27], shows that the nonfactorizable (NF) effects play an important role in the B decays with vector mesons in the final states. On the other hand, the angular analyses in Λ b → J/ψΛ [28][29][30] from LHCb show that the polarization fractions are consistent with zero. Furthermore, the Λ b − Λ b production asymmetry has also been studied [31].…”

Inclusive semileptonic Λb decays in the Standard Model and beyond

“…We have to say that measurements of the Λ b polarization at LHC give results compatible with zero [31][32][33][34], which means that the b quarks hadronizing in Λ b are mainly produced by QCD processes. However, a sizable longitudinal Λ b polarization is expected for b quarks produced in Z and top quark decays, as shown by the measurements at LEP [35][36][37].…”

Sensitivity studies on the CKM angle $γ$ in $Λ_b^0 \to DΛ$ decays

“…The decay parameters contain interference information between Sand P -waves. As Λ 0 b produced in pp collisions at LHC is found to be unpolarized [32], the only relevant decay parameter for Λ 0 b → DΛ is…”

“…Predictions based on factorization approach [25,[39][40][41] indicates that the branching fraction of Λ 0 b → DΛ is about 200 times smaller than that of Λ 0 b → J/ψΛ. Around 300 Λ 0 b → D(K − π + )Λ events are expected to be reconstructed based on the data collected by LHCb in the years 2011-2018 [32], and is used for the sensitivity estimation. The numbers for the other channels are scaled accordingly based on the formalism described previously.…”