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Z轴的直线长度（4430）

Line Shapes of the Z(4430)

Eric Braaten, Meng Lu

备注：
4 pages, 1 figure
发表信息：
Phys.Rev.D79:051503,2009
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摘要：

贝尔合作组最近发现了第一个明显的奇异介子：Z^+（4430），它衰变为psi' pi^+，因此具有夸克含量c c-bar u-d-bar。由于Z^+的质量接近D_1的D棒^* 阈值，因此人们将Z^+解释为一种粲介子分子，其成分是D_1^+ D棒^{*0} $ and D^{*+} D-bar_1^0$的S波叠加。如果这种解释是正确的，那么Z^+的结合能与其组分D_1的宽度γ_1的比值很小，可以用来预测其线形的性质。它在通道psi' pi^+中的半峰全宽应该约为sqrt{3} γ_1 = 35 MeV，这与Z^+的测量宽度一致。Z^+也应该通过其组分D_1的衰变而衰变为D^* D棒^* π。D^* D-bar^* pi的线形峰的能量应该比psi' pi^+线形峰的能量高出约γ_1/sqrt{12} = 6 MeV。D^* D-bar^* pi中的线形也应该更宽且不对称，在高能侧有一个肩部，这可以归因于D_1 D-bar^* 产生过程中的阈值增强。

英文摘要：

The Belle Collaboration recently discovered the first manifestly exotic meson: Z^+(4430), which decays into psi' pi^+ and therefore has quark content c c-bar u d-bar. The proximity of its mass to the D_1 D-bar^* threshold has motivated the interpretation of the Z^+ as a charm meson molecule whose constituents are an S-wave superposition of D_1^+ D-bar^{*0}$ and D^{*+} D-bar_1^0$. If this interpretation is correct, the small ratio of the binding energy of the Z^+ to the width Gamma_1 of its constituent D_1 can be exploited to predict properties of its line shapes. Its full width at half maximum in the channel psi' pi^+ should be approximately sqrt{3} Gamma_1 = 35 MeV, which is consistent with the measured width of the Z^+. The Z^+ should also decay into D^* D-bar^* pi through decay of its constituent D_1. The peak in the line shape for D^* D-bar^* pi should be at a higher energy than the peak in the line shape for psi' pi^+ by about Gamma_1/sqrt{12} = 6 MeV. The line shape in D^* D-bar^* pi should also be broader and asymmetric, with a shoulder on the high energy side that can be attributed to a threshold enhancement in the production of D_1 D-bar^*.

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