Hidden charm pentaquarks with color-octet substructure in QCD Sum Rules
Abstract
We study the hidden-charm pentaquark states udscc with spins 1/2, 3/2, and 5/2 within the QCD sum-rule approach. First, we construct the currents for the particular configuration of pentaquark states that consist of the flavor singlet three-quark cluster uds of spins 1/2 and 3/2 and the two-quark cluster cc of spin 1, where both clusters are in a color-octet state. From the QCD sum rules obtained by the operator product expansion up to dimension-10 condensates, the extracted masses for the pentaquark states uds-cc are about 4.6 GeV (5.6 GeV) for spin 1/2, about 5.1 GeV (6.0 GeV) for spin 3/2, about 6.1 GeV (5.9 GeV) for spin 5/2, where the masses of the positive parity states are given in parentheses. Additionally, based on the flavor singlet pentaquark states, it is also shown that other pentaquark states of clusters like udc-cs and usc- cd lead to masses similar to the uds- cc case within error bars. Furthermore, in order to see whether any of the states, observed by the LHCb Collaboration, could be understood as the pentaquark of two clusters in the color-octet state, we study the pentaquark formed by the two clusters udc- cu, where the three-quark cluster is assumed to have the same flavor structure as the above uds cluster. We come to the conclusion that if the observed pentaquark will be found to have spin 1/2 and negative parity, then it could be described as a state of two color-octet clusters.