Photoproduction of $ \pi^{0}$-pairs off protons and off neutrons
Photoproduction of $ \pi^{0}$-pairs off protons and off neutrons
复制标题
$ pi^{0}$-质子和中子对的光产生
DOI：
10.1140/epja/i2015-15142-8
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
The Atlas Collaboration
中科院分区：
文献类型：
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作者：
M. Dieterle;M. Oberle;J. Ahrens;J. Annand;H. Arends;K. Bantawa;P. Bartolome;R. Beck;V. Bekrenev;H. Berghäuser;A. Braghieri;D. Branford;W. Briscoe;J. Brudvik;S. Cherepnya;S. Costanza;B. Demissie;E. Downie;P. Drexler;L. Fil’kov;A. Fix;S. Garni;D. Glazier;D. Hamilton;E. Heid;D. Hornidge;D. Howdle;G. Huber;O. Jahn;T. Jude;A. Käser;V. Kashevarov;I. Keshelashvili;R. Kondratiev;M. Korolija;B. Krusche;V. Lisin;K. Livingston;I. Macgregor;Y. Maghrbi;J. Mancell;D. Manley;Z. Marinides;J. Mcgeorge;E. McNicoll;D. Mekterović;V. Metag;S. Mićanović;D. Middleton;A. Mushkarenkov;A. Nikolaev;R. Novotný;M. Ostrick;P. Otte;B. Oussena;P. Pedroni;F. Phéron;A. Polonski;S. Prakhov;J. Robinson;T. Rostomyan;S. Schumann;M. Sikora;D. Sober;A. Starostin;T. Strub;I. Supek;M. Thiel;A. Thomas;M. Unverzagt;N. Walford;D. Watts;D. Werthmüller;L. Witthauer;The Atlas Collaboration
摘要：我们已经测量了光生$ \pi^{0}\pi^{0}$对离开自由质子和离开束缚在氘核中的核子的总截面、角分布和不变质量分布。这些实验是在美因茨的MAMI加速器设施中使用格拉斯哥光子标记光谱仪和Crystal Ball/TAPS探测器进行的。加速器提供1508和1557 MeV的电子束，在薄的辐射箔中产生韧致辐射。标记光子束覆盖能量高达1400 MeV。来自自由质子靶的数据与先前的测量结果非常一致，并且仅用于测试分析程序。自由质子和准自由质子的微分截面（角分布和不变质量分布）的结果在形状上几乎相同，但在绝对大小上相差15%。因此，存在适度的终态相互作用效应。准自由中子的数据类似于第二共振区的质子数据（最终状态不变质量高达$ \约1550$ MeV），其中两个反应都由$ N（1520）3/2^{-} \rightarrow \Delta（1232）3/2^{+}\pi$衰变主导。在更高的能量下，角分布和不变质量分布是不同的。对第三共振区中不变质量分布形状的简单分析与质子的$ N^{\星星}\rightarrow N\sigma$衰变的强贡献一致，而中子的反应则由通过$ \Delta\pi$中间态的连续衰变主导。的数据进行比较，从两个Pion-MAID模型和Bonn-Gatchina耦合通道分析的预测。
Abstract.Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $ \pi^{0}\pi^{0}$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final-state invariant masses up to $ \approx 1550$ MeV), where both reactions are dominated by the $ N(1520)3/2^{-} \rightarrow \Delta(1232)3/2^{+}\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $ N^{\star}\rightarrow N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $ \Delta\pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled-channel analysis.