Experimental research on penta-quark baryons with the STB ring

在这个研究项目中，我们观察到了一个窄重子共振N^*(1670)。根据最新的分析，共振的质量和宽度分别为1665-1675 MeV/c^2和10-40 MeV/c^2。共振凹凸出现在η介子光产生实验中获得的总截面数据中，该实验使用的是固体氘靶。在相同的实验条件下，固体氢靶的情况下没有出现凸起。因此，新的共振通过辐射跃迁与中子耦合，而不是与质子耦合。我们考察了具有两个偶数的自旋1/2和3/2态，将这些态逐个与数据进行拟合。对总截面数据和角分布的cos-θ系数进行了拟合。事实证明，诸如S11或D13这样的负奇偶状态比正奇偶状态更好地再现数据，尽管用目前的数据很难确定共振的自旋和奇偶。然而，有几个宽共振，S11(1650)，D15(1675)，F15(1680)，D13(1700)，P11(1700)和P13(1720)，其宽度约为100-200 MeV/c^2。这些宽共振中的任何一个都位于1670 MeV/c^2附近的质量区域。与这些宽态之一具有相同量子数的窄共振不能被构造为三个夸克态的成员。因此，考虑到共振与核子的耦合情况，很自然地将窄共振视为五夸克重子反衰变的一部分。这里，U自旋守恒允许过程γn→N^*(1670)，但禁止跃迁γp→N^&lt；*^+&gt；(1670)。因为γ、n和p的U-自旋分别为0、1和1/2，而N^*(1670)的U-自旋分别为1和3/2。

We have observed a narrow baryon resonance N^*(1670) in this research project. The mass and the width of the resonance are 1665-1675 MeV/c^2 and 10-40 MeV/c^2,respectively, according to the latest analysis up to now. The resonance bump appeared in the total cross section data obtained in an η meson photoproduction experiment using a solid deuterium target. The bump did not show up in the case with a solid hydrogen target under the same experimental condition. Thus, the new resonance couples to the neutron, but not to the proton through radiative transitions. We examined the spin 1/2 and 3/2 states with both parities, fitting these states to the data one by one. The fitting was made for the data of the total cross section and the cosθ coefficients of the angular distributions. A negative parity state such as S11 or D13 has turned out to reproduce the data better than positive parity states, although it is difficult to determine the spin and parity of the resonance definitely with the present data. However, there are several broad resonances, S11(1650),D15(1675),F15(1680),D13(1700),P11(1700), and P13(1720), the width of which is roughly 100-200 MeV/c^2. And any of these broad resonances is placed over the mass region around 1670 MeV/c^2. The narrow resonance with the same quantum numbers as one of these broad states cannot be constructed as a member of three quark states. Taking the coupling situation of the resonance to the nucleons into account, it is natural, therefore, to regard the narrow resonance as a member of the antidecuplet of pentaquark baryons. Here U-spin conservation allows the process γn→ N^*(1670), but prohibits the transition γp→N^<*^+>(1670). Because the U-spin of γ,n, and p is 0,1,and 1/2,respectively, while that of N^*(1670) is 1 and 3/2 for N^<*^+>(1670) in the antidecuplet.