Pentaquark ${\Theta }^{+}(1540)$ in the string model

We consider the ${\Theta }^{+}(1540)$ pentaquark in the string model that correctly reproduces the linear Regge trajectories for the case of orbtal excitations of light $q\overline{q}$ mesons and $qqq$ baryons. Assuming (and arguing in favor of) the diquark-antiquark-diquark ($[ud]\overline{s}[ud]$) clustering of this orbitally excited object we found its mass about 290 MeV above the experimental value 1540 MeV. In the model considered this discrepancy could be attributed to the change of the constituent mass of $\overline{s}$ antiquark as compared to that of $s$ quark localized at the string end.

Figure 1

The leading $\omega -f$ trajectory fitted by the relativistic string with nonstrange quarks at the string ends.

Figure 2

The leading $K^{*}$ trajectory fitted by the relativistic string with nonstrange $+$ strange quarks at the string ends.

Figure 3

Model predictions for the leading $\varphi$ trajectory by the relativistic string with strange quarks at the string ends.

Figure 4

The leading $\Lambda$ trajectory fitted by the relativistic string with spin-isospin singlet diquark $+$ strange quark at the string ends.

Figure 5

Possible configurations of the string for ${\Theta }^{+}(1540)$ pentaquark.