Contribution of Spin-1 Diquark to the Nucleon Structure Functions

In our previous works [F. Zamani, Phys. Rev. C 68 (2003) 055202-1, F. Zamani and D. Saranchak, Phys. Rev. C 63 (2001) 065202-1, F. Zamani, Phys. Rev. C 58 (1998) 3641] we used both symmetrical (no diquark) core quark distribution and asymmetrical (diquark-quark) core quark distribution to calculate polarized [F. Zamani, Phys. Rev. C 68 (2003) 055202-1, F. Zamani and D. Saranchak, Phys. Rev. C 63 (2001) 065202-1] and unpolarized [F. Zamani, Phys. Rev. C 58 (1998) 3641] nucleon structure functions. For the asymmetrical distribution we considered the superposition of spin-0, isospin-0 and spin-0, isospin-1 states. It turned out that for unpolarized structure functions only the quark-diquark model was able to reproduce experimental results reasonably well [F. Zamani, Phys. Rev. C 58 (1998) 3641]. However, for the polarized case the results were rather mixed. For some cases the symmetrical model was more agreeable with observation [F. Zamani and D. Saranchak, Phys. Rev. C 63 (2001) 065202-1, F. Zamani, Phys. Rev. C 58 (1998) 3641]. Our objective here is to have a core quark distribution that can reproduce observation equally well, whether it is for the polarized structure function or the unpolarized structure function. To achieve this goal we have added the other two possible states to the diquark state [F. Zamani. Submitted to Phys. Rev. C, (2004)]. Namely, spin-1, isospin-0 and spin-1, isospin-1. The calculation is performed in the light-cone frame. The dressed nucleon is assumed to be a superposition of the bare nucleon plus virtual light-cone Fock states of baryon-meson pairs. For bare nucleon we consider both the case of diquark-quark model which is now the superposition of all four diquark states and the case which there is no quark clustering inside the nucleon. The initial distributions are evolved using DGLAP equations. The final results are compared with experimental results and other theoretical predictions.