First Observation of a BaryonicBs0Decay

Abstract

We report the first observation of a baryonic B_{s}^{0} decay, B_{s}^{0}→pΛ[over ¯]K^{-}, using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3.0 fb^{-1}. The branching fraction is measured to be B(B_{s}^{0}→pΛ[over ¯]K^{-})+B(B_{s}^{0}→p[over ¯]ΛK^{+})=[5.46±0.61±0.57±0.50(B)±0.32(f_{s}/f_{d})]×10^{-6}, where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the B^{0}→pΛ[over ¯]π^{-} decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of b-quark hadronization probabilities f_{s}/f_{d}.

Observation of charmless baryonic decays B(s)0→pp¯h+hAaij1, Adeva2, Adinolfi3 et al. 2017Phys. Rev. DSelf Cite101100View full textAdd to dashboardCite

“…The analysis is based on a sample of protonproton collision data collected at center-of-mass energies of 7 and 8 TeV,corresponding In recent years, studies by the LHCb Collaboration have greatly increased the knowledge of the decays of B mesons to final states containing baryons. The first observation of a baryonic B þ c decay was reported in 2014 [1], and LHCb recently reported the first observation of a baryonic B 0 s decay [2], the last of the four B meson species for which a baryonic decay mode had yet to be observed.…”

Baryon decays to purely baryonic final states

“…Many B-meson decays to baryonic final states present a characteristic enhancement at (production) threshold in the baryon-antibaryon mass spectrum of multi-body decays [4][5][6][7], a fact that is still not fully understood. Such enhancements are not observed in mesonic final states.…”

Charmless $B$ decays at LHCb

“…The LHCb collaboration has greatly increased the knowledge of baryonic B decays in recent years [5,6,7,8,9,10]. The collaboration had reported the first observation of a two-body charmless baryonic B + decay, B + → pΛ (1520) [6], and the first evidence for a similar B 0 decay, B 0 → pp [5].…”

“…The LHCb analysis measures the branching fraction of the signal decay B 0 s → pΛ K − relative to that of the normalisation mode B 0 → pΛ π − [9]. Due to the long lifetime of the Λ baryon,…”

“…The statistical significance of the B 0 s → pΛ K − decay, above 15standard deviations, is estimated from the change in log-likelihood between fits with and without the B 0 s → pΛ K − signal component[14]. This is the first observation of a baryonic B 0 s decay.The B 0 s → pΛ K − branching fraction is determined to be[9] B(B 0 s → pΛ K − ) + B(B 0 s → pΛ K + ) = 5.46 ± 0.61 ± 0.57 ± 0.50(B) ± 0.32( f s / f d ) × 10 −6 ,where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the B 0 → pΛ π − decay used for nor-malisation, and the fourth uncertainty relates to the knowledge of f s / f d . The dominant source of systematic uncertainty comes from the poor knowledge of other baryonic B decays representing backgrounds to the signals, which implies a challenging description of the spectra and nonnegligible uncertainties on the fit model components.…”