Surveying exotic pentaquarks with the typical QQqqq¯ configuration

Abstract

As a hot issue, exploring exotic pentaquarks is full of challenges and opportunities for both theorist and experimentalist. In this work, we focus on a type of pentaquark with the QQqqq (Q = b, c; q = u, d, s) configuration, where their mass spectrum is estimated systematically. Especially, our result indicates that there may exist some stable or narrow exotic pentaquark states. Obviously, our study may provides valuable information for further experimental search for the QQqqq pentaquarks. With the running of LHCb and forthcoming Belle II, we have a reason to believe that these predictions present here can be tested.

Exotic pentaquark states with the qqQQQ¯ configuration

“…In the SU(3) f flavor space, the qqQQQ states belong to the flavor symmetric 6 f and antisymmetric3 f representations ( Fig. 1), which is similar to the situation for part of the QQqqq states [88]. For the nnQQQ (n = u, d) case, the isovector states (I = 1) and the isoscalar states (I = 0) do not mix since we do not consider isospin breaking effects.…”

“…Here, M i represents the effective quark mass for the ith quark or antiquark and it takes account of effects from kinetic energy, color confinement, and other terms in realistic potential models. The effective constant C ij ∼ δ 3 ( r ij ) /(m i m j ) reflects the coupling strength between the i-th quark and the j-th quark, which depends on the quark masses and the spatial wave functions of the ground states [88]. The Pauli matrix σ i and Gell-Mann matrix λ i (−λ * i ) act on the spin and color wave functions of the i-th quark (antiquark), respectively.…”

“…Mesons Baryons Baryons Using the mass formula M = i M i + H CMI and the obtained parameters, one sees that the estimated masses of conventional hadrons are in general higher than the measured values, which is illustrated in Table V. The reason is that the adopted model and parameters could not account for the necessary attractions for all the hadrons. Overestimated masses with this approach were also obtained in various tetraquark and pentaquark states [83][84][85][86][87][88][89][90]. To make a more reasonable estimation, we use the improved mass formula by replacing i M i in Eq.…”

“…In the present study for pentaquark states, we choose the baryon-meson thresholds as the mass scales, where the reference baryon-meson system should have the same constituent quarks with a considered system. The attraction not incorporated in the original approach is somehow phenomenologically compensated in this procedure [88].…”

“…When the spacial contributions are encoded into effective quark masses and coupling parameters, the Hamiltonian can be written as the form containing just the quark mass term and the color-spin interaction term and one gets the CMI model. There are many studies about the mass spectrum for multiquark systems within this model [83][84][85][86][87][88][89][90][91]. The qualitative properties of the obtained spectra are helpful for us to search for relevant exotic states.…”