arXiv 1108.30102011-08hep-phhep-exnucl-exnucl-th

在$γp\to ηp$中寻找窄核子共振

Search for Narrow Nucleon Resonance in $γp\to ηp$

A. V. Anisovich, E. Klempt, V. Kuznetsov, V. A. Nikonov, M. V. Polyakov, A. V. Sarantsev, U. Thoma

备注：: 6 pages, 5 figures

摘要：

本文给出了MAMI的$γp\to pη$新的高统计量数据的分波分析结果。使用已知的宽共振和仅标准背景振幅的拟合不能描述在1660-1750 MeV的质量区域中的横截面中的相对窄的峰化结构，该峰化结构遵循最小值。一个改进的描述的数据可以达到通过假设存在一个窄的共振在一个质量约1700兆电子伏的小的光电耦合或阈值效应。在后一种情况下，所观察到的结构由$S_{11}$分波中的强（共振或非共振）$γp\toωp$耦合来解释。当由GRAAL协作的一部分公布的光束不对称性数据被包括在拟合中时，具有窄$P_{11}$状态的解决方案稍微优选。在该拟合中，假设共振的质量和宽度分别被确定为$M\sim$ 1694 MeV和$Γ\sim 40$ MeV，并且光耦合被确定为$\sqrt{{\rm Br}_{ηN}} A_{1/2}^p \sim 2.6\cdot 10^{-3}$ GeV $^{-1/2}$。目标不对称性和$F$ -可观测的高精度测量是强制性的，以建立这种窄状态的可能存在，并提供必要的信息，以定义哪个分波负责数据中观察到的结构。

英文摘要：

Results of a partial wave analysis of new high-statistics data on $γp\to pη$ from MAMI are presented. A fit using known broad resonances and only standard background amplitudes can not describe the relatively narrow peaking structure in the cross section in the mass region of 1660-1750 MeV which follows a minimum. An improved description of the data can be reached by either assuming the existence of a narrow resonance at a mass of about 1700 MeV with small photo-coupling or by a threshold effect. In the latter case the observed structure is explained by a strong (resonant or non-resonant) $γp\toωp$ coupling in the $S_{11}$ partial wave. When the beam asymmetry data, published by part of the GRAAL collaboration, are included in the fit, the solution with a narrow $P_{11}$ state is slightly preferred. In that fit, mass and width of the hypothetical resonance are determined to $M\sim$1694 MeV and $Γ\sim 40$ MeV, respectively, and the photo-coupling to $\sqrt{{\rm Br}_{ηN}} A_{1/2}^p \sim 2.6\cdot 10^{-3}$ GeV$^{-1/2}$. High precision measurements of the target asymmetry and $F$-observable are mandatory to establish the possible existence of such a narrow state and to provide the necessary information to define which partial wave is responsible for the structure observed in the data.

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