Observation of a New Ξb− Resonance

Abstract

From samples of pp collision data collected by the LHCb experiment at ffiffi ffi s p ¼ 7, 8 and 13 TeV, corresponding to integrated luminosities of 1.0, 2.0 and 1.5 fb −1 , respectively, a peak in both the Λ In the constituent quark model [1,2], baryonic states form multiplets according to the symmetry of their flavor, spin, and spatial wave functions. The masses, widths, and decay modes of these states give insight into their internal structure [3]. The Ξ − mass or width determination, as they have larger systematic uncertainties due to modeling of the mass resolution.The LHCb detector [25,26] is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks [25,26]. Events are selected online by a trigger, which consists of a hardware stage, based on information from the calorimeter and muon systems, followed by a software stage, which applies a full event reconstruction [27,28].

Triply charmed and bottom baryons in a constituent quark model

“…This model has been extended to deal with the radiative decays of the B c meson states [53], Ω baryon states [54], singly baryon states [55][56][57]. 4 In this model, the quark-photon electromagnetic (EM) coupling at the tree level is adopted as…”

“…In 2017, five extremely narrow Ω c (X) states, Ω c (3000), Ω c (3050), Ω c (3066), Ω c (3090) and Ω c (3119), were observed in the Ξ + c K − channel by the LHCb Collaboration [3]. Very recently four bottom baryon resonances Ξ b (6227) − [4], Σ b (6097) ± [5], Λ b (6146/6152) 0 [6] were observed at LHCb as well. Except for the singly and doubly heavy baryons, the LHC facility may provide good opportunities for discovering the missing triply heavy baryons [7,8].…”

LHCb gets closer to discovering the second doubly charmed baryon

“…No significant signal is seen in the mass range from 3.4 to 3.8 GeV. To put this result in context, the Ξ ++ cc baryon was seen by LHCb in decay modes Λ c K − π + π + [2] (2017) and Ξ + c π + [3] (2018). The weighted average of the Ξ ++ cc mass is 3621.24 ± 0.65 (stat.)…”

“…As a result of the internal cd → su process in the decay of Ξ + cc , its lifetime is several times shorter than that of Ξ ++ cc : For example, Ref.[9] finds τ (Ξ + cc ) = 53 fs, and τ (Ξ ++ cc ) = 185 fs. (The latter was measured by LHCb to be 256 +24 −22 ± 14 fs [10].) The validity of the prediction of M(Ξ ++ cc ) [9] and the signal of its isospin partner not far from its predicted mass [5] lend credence to an estimate of the mass of the ccūd tetraquark using †…”

“…± 0.31 (syst.) MeV [3].The Ξ ++ cc and Ξ + cc have the quark content ccu and ccd, respectively. Under the isospin symmetry of the strong interactions they form an isodoublet, like the proton and the neutron.…”