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arXiv 0902.2049hep-ph
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QCD求和规则中的自旋3/2五夸克态

Spin-3/2 Pentaquark in QCD Sum Rules

P. Gubler, D. Jido, T. Kojo, T. Nishikawa, M. Oka

摘要:

对同位旋I=0,自旋宇称J^P = 3/2^ \pm的奇异+1五夸克重子,给出了QCD求和规则方法.自旋3/2态被认为比自旋1/2态窄,因此可以为实验观察到的窄宽度θ^+提供自然的解释。为了在QCD求和规则计算中得到可靠的结果,我们强调了建立宽Borel窗的重要性,在宽Borel窗中,算子乘积展开的收敛性和谱函数足够的低质量强度是有保证的。为此,我们采用了两个独立的双折射的差异,使高能量的连续贡献被抑制。在Borel窗口内确认了物理量相对于Borel质量的稳定性。发现求和定则给出了质量约为1.4 \pm 0.2 GeV的(I,J^P)=(0,3/2^+)态的肯定证据,而我们不能提取到(0,3/2^-)态的任何证据.

英文摘要:

The QCD sum rule method is formulated for the strangeness +1 pentaquark baryon with isospin I=0 and spin-parity J^P = 3/2^\pm. The spin-3/2 states are considered to be narrower than the spin-1/2 ones, and thus may provide a natural explanation for the experimentally observed narrow width of Θ^+. In order to obtain reliable results in QCD sum rule calculations, we stress the importance of establishing a wide Borel window, where convergence of the operator product expansion and sufficient low-mass strength of the spectral function are guaranteed. To this end, we employ the difference of two independent correlators so that the high-energy continuum contribution is suppressed. The stability of the physical quantities against the Borel mass is confirmed within the Borel window. It is found that the sum rule gives positive evidence for the (I, J^P) = (0, 3/2^+) state with a mass of about 1.4 \pm 0.2 GeV, while we cannot extract any evidence for the (0, 3/2^-) state.

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