arXiv 1106.43762011-06-22nucl-thnucl-ex

核中低能ω（\to π^0 γ）介子光生

Low energy ω(\to π^0 γ) meson photoproduction in the nucleus

Swapan Das

备注：: 14 pages, 6 figures
发表信息：: Phys.Rev.C83:064608,2011
DOI：: 10.1103/PhysRevC.83.064608

摘要：

利用TAPS/ELSA合作测量了$ (γ, π^0γ) $反应中的$π^0 γ$不变质量分布谱，以寻找Nb核中$ω$介子的强子参数.我们研究了该反应的机理，认为Nb核中的基元反应是以$ γN \to ωN; ~ ω\to π^0γ$形式进行的。从测量的$ γp \to ωp $反应的四个动量转移分布中提取了该反应的$ω$介子光生振幅。用程函形式描述了$ω$介子的传播和$π^0$介子末态的畸变波函数。用“$t\varrho$“近似计算了$ω$介子传播子和$π^0$介子畸变波函数中的$ω$和$π^0$介子核光学势.对相关性和颜色透明度的影响也进行了研究。对于动量大于200 MeV的核内产生的$ω$介子，计算结果没有显示出介质修正。这是因为$ω$介子主要在核外衰变。最后还研究了截面与末态相互作用的关系。$ω$介子质量分布谱的展宽是由于实验中使用的探测器具有较大的分辨宽度。

英文摘要：

The $π^0 γ$ invariant mass distribution spectra in the $ (γ, π^0γ) $ reaction were measured by TAPS/ELSA collaboration to look for the hadron parameters of the $ω$ meson in Nb nucleus. We study the mechanism for this reaction, where we consider that the elementary reaction in Nb nucleus proceeds as $ γN \to ωN; ~ ω\to π^0γ$. The $ω$ meson photoproduction amplitude for this reaction is extracted from the measured four momentum transfer distribution in the $ γp \to ωp $ reaction. The propagation of the $ω$ meson and the distorted wave function for the $π^0$ meson in the final state are described by the eikonal form. The $ω$ and $π^0$ mesons nucleus optical potentials, appearing in the $ω$ meson propagator and $π^0$ meson distorted wave function respectively, are estimated using the "$t\varrho$" approximation. The effects of pair correlation and color transparency are also studied. The calculated results do not show medium modification for the $ω$ meson produced in the nucleus for its momentum greater than 200 MeV. It occurs since the $ω$ meson dominantly decays outside the nucleus. The dependence of the cross section on the final state interaction is also investigated. The broadening of the $ω$ meson mass distribution spectra is shown to occur due to the large resolution width associated with the detector used in the experiment.

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