document: The spins and parities of Θ+ and Ξ−− are not yet known experimentally. In this new wave of pentaquark research, most theoretical papers take the spin equal to 1/2. The parity is more controversial. In chiral soliton or Skyrme models the parity is positive [4]. In constituent quark models it is usually positive. In the present approach, the parity of the pentaquark is given by P=(−)ℓ+1, where ℓ is the angular momentum associated with the relative coordinates of the q4 subsystem. We analyze the case where the subsystem of four light quarks is in a state of orbital symmetry [31]O and carries an angular momentum ℓ=1. Although the kinetic energy of such a state is higher than that of the totally symmetric [4]O state, the [31]O symmetry is the most favourable both for the flavour–spin interaction [12] and the colour–spin interaction [13]. In the first case the statement is confirmed by the comparison between the realistic calculations for positive parity [12] and negative parity [14], based on the same quark model [15]. In Ref. [12] the antiquark was heavy, c or b, and accordingly the interaction between light quarks and the heavy antiquark was neglected, consistent with the heavy quark limit. In Ref. [16] an attractive spin–spin interaction between s̄ and the light quarks was incorporated and shown that a stable or narrow positive parity uudds̄ pentaquark can be accommodated within such a model. This interaction has a form that corresponds to η meson exchange [17] and its role is to lower the energy of the whole system.
doc_bio_tags: O O O O O O O B O O O O O O O B I I I I O O O O O O O O O O O O O O O B I O B I O O O O O O B I I O O O O O O O O O B I I I O O O O O B O O B I I I I I I I I I I O O O O O O O O O B I O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O B I O O O B O O O O O B I O O O O O O B I O B O O B I O O O O O O O O O O O O B O O O O O O O O O O O O O O O B I O O O O O O O B I I I I I I
extractive_keyphrases: ℓ angular momentum associated with the relative coordinates of the q4 subsystem antiquark chiral soliton colour–spin interaction constituent quark models flavour–spin interaction heavy quark kinetic energy light quarks lower the energy of the whole system new wave of pentaquark research parity of the pentaquark pentaquark quark s̄ skyrme models spin–spin interaction η meson ξ−−
abstractive_keyphrases: comparison between the realistic calculations for positive parity [12] and negative parity [14], based on the same quark model [15] heavy antiquark interaction between light quarks and the heavy antiquark was neglected, consistent with the heavy quark limit o symmetry p=(−)ℓ+1 quark model spins and parities of θ+ and ξ−− subsystem of four light quarks is in a state of orbital symmetry take the spin equal to 1/2 totally symmetric [4]o state uudds̄ pentaquark η meson exchange θ+