Very narrow excited Ωc baryons

Abstract

Recently LHCb reported the discovery of five extremely narrow excited Ω c baryons decaying into Ξ + c K − . We interpret these baryons as bound states of a c-quark and a P -wave ss-diquark. For such a system there are exactly five possible combinations of spin and orbital angular momentum. The narrowness of the states could be a signal that it is hard to pull apart the two s-quarks in a diquark. We predict two of spin 1/2, two of spin 3/2, and one of spin 5/2, all with negative parity. Of the five states two can decay in S-wave and three can decay in D-wave. Some of the D-wave states might be narrower than the S-wave states. We discuss relations among the five masses expected in the quark model and the likely spin assignments and compare with the data. A similar pattern is expected for negative-parity excited Ω b states. An alternative interpretation is noted in which the heaviest two states are 2S excitations with J P = 1/2 + and 3/2 + , while the lightest three are those with J P = 3/2 − , 3/2 − , 5/2 − expected to decay via D-waves. In this case we expect J P = 1/2 − Ω c states around 2904 and 2978 MeV.PACS codes: 12.39. Jh, 13.20.Jf, 13.25.Jx, 14.40 The proposed values of spin-parity J P are ours. An alternative set of assignments is shown in parentheses.State Mass (MeV) a Width (MeV) Proposed J P Ω c (3000) 0 3000.4 ± 0.2 ± 0.1 4.5 ± 0.6 ± 0.3 1/2 − (3/2 − ) Ω c (3050) 0 3050.2 ± 0.1 ± 0.1 0.8 ± 0.2 ± 0.1 1/2 − (3/2 − ) < 1.2 MeV, 95% CL Ω c (3066) 0 3065.6 ± 0.1 ± 0.3 3.5 ± 0.4 ± 0.2 3/2 − (5/2 − ) Ω c (3090) 0 3090.2 ± 0.3 ± 0.5 8.7 ± 1.0 ± 0.8 3/2 − (1/2 + ) Ω c (3119) 0 3119.1 ± 0.3 ± 0.91.1 ± 0.8 ± 0.4 5/2 − (3/2 + ) < 2.6 MeV, 95% CL a Additional common error of +0.3,-0.5 MeV from M (Ξ + c ) uncertainty. I IntroductionVery recently LHCb reported the discovery of five extremely narrow excited Ω c baryons decaying into Ξ + c K − [1], with masses and widths shown in Table I. We quote also our favored spin-parity assignment for these states, which we shall choose among the 5! = 120 possible permutations if all five states are P -wave excitations of the ss diquark with respect to the charmed quark. Some more recent calculations [2-6] that appeared after the first version of this paper reach the same conclusion. In parentheses we note an alternative assignment if the two heaviest states are 2S excitations.This discovery raises some immediate questions, which we address in detail: In Sec. II we comment on P -wave css baryons. We then analyze spin-dependent forces for the css system in Sec. III, building upon similar results [7] obtained previously for the negative-parity Σ c states. We evaluate the energy cost for a P -wave css excitation in Sec. IV, carry our results over to the Ω b system in Sec. V, discuss alternative interpretations of the spectrum in Sec. VI, and conclude in Sec. VII. Details of calculating the spin-dependent mass shifts are presented in Appendix A, with a linearized approximation in Appendix B.II P -wave c(ss) system Consider the (ss) in c(ss) to be an S-wave color3 c diquark....

Strong decays of exotic and nonexotic heavy baryons in the chiral quark-soliton model

“…A simpler interpretation that they are p-wave or radial and p-wave excitations of the ss-diquark c-quark system has been put forward in Refs. [18][19][20][21][22][23]. Both radial and p-wave excitations have been also studied in the framework of the QCD sum rules [24][25][26][27][28], in a phenomenological approach [29] and on the lattice [30].…”

Observed Ωc0 resonances as pentaquark states

“…While one may also expect that the next-to-lowest state in our model may correspond for the observed Ω c (3000) 0 , since once the values of coupling strength constants for Goldstone boson exchange are taken to be 0.9 times of the ones given in [19,21,22], the resulting energy for the next-to-lowest state is 2980 MeV, while the three higher states almost keep as what they are. The Ω 0 c resonances have also been investigated by using various of quark models [7,8,10,12,16] since the observation by LHCb collaboration. In [7,8,16], the Ω 0 c states are interpreted as system with one diquark and one charm quark, and the parities for all the five observed states are assigned to be negative, but with different spin quantum numbers.…”

“…The Ω 0 c resonances have also been investigated by using various of quark models [7,8,10,12,16] since the observation by LHCb collaboration. In [7,8,16], the Ω 0 c states are interpreted as system with one diquark and one charm quark, and the parities for all the five observed states are assigned to be negative, but with different spin quantum numbers.…”

“…Consequently, observation of the five states is of significant importance for us to understand structure of the Ω states with narrow width lying at ∼ 3000 MeV, and what kind of structure of these states should be. In fact, just after the LHCb announcement, various of theoretical investigations on the structure and quantum numbers of Ω 0 c resonances have been done, using the QCD sum rule method [3][4][5][6], quark-diquark picture [7][8][9], chiral quark model [10,11], constituent quark model [12], lattice QCD [13], chiral quark-soliton model [14], and in several very recent works, the decay behaviours of the observed Ω 0 c are also investigated [15][16][17]. On the other hand, one may notice that two hidden charm pentaquark states have been announced by LHCb collaboration in 2015 [18], one of these two states also has narrow decay width.…”

Dynamical study of Ωc0 in the chiral quark model

“…In Ref. [4], Karliner and Rosner suggested that the parity was negative for all of the five states: two J P ¼ 1/2 − states [Ω c ð3000Þ 0 and Ω c ð3050Þ 0 ], two J P ¼ 3/2 − states [Ω c ð3066Þ 0 and Ω c ð3090Þ 0 ], and one J P ¼ 5/2 − state [Ω c ð3119Þ 0 ]. These exciting announcements and the theoretical work along with the pentaquarks P þ c discovered also by the LHCb Collaboration in 2015 [5] have brought us more understanding of the world of microcosmic particles.…”