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arXiv 0903.3697hep-ex
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双光子碰撞中中性π介子对产生的高统计研究

High-statistics study of neutral-pion pair production in two-photon collisions

S. Uehara

备注：
22 pages, 10 figures
发表信息：
Phys.Rev.D79:052009,2009
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摘要：

在$γγ$质心系统中，测量了$γγ\to π^0 π^0$过程在0.6GeV的运动学范围内的微分截面，能量和π散射角分别为$|\cos θ^*|<0.8$和$< W < 4.1$ GeV.这些结果是基于KEKB $e^+ e^-$对撞机Belle探测器收集的223 fb $^{-1}$数据样本。微分截面拟合在能量区域1.7 GeV $< W <$ 2.5 GeV，以确认在G波双光子生产的两个π介子。在高能区，我们观察到$χ_{c0}$粲偶素态的产生，并得到了它的双光子衰变宽度和$π^0π^0$的分支分数的乘积。我们还比较了所观察到的角依赖性和比率的截面中性介子和带电介子对生产QCD模型。的能量和角度依赖性高于3.1 GeV是兼容的$π^+π^-$通道中测量的，此外，我们发现，截面比，$σ(π^0π^0)/σ(π^+π^-)$，是$0.32 \pm 0.03 \pm 0.05$平均在3.1-4.1 GeV的区域。

英文摘要：

The differential cross sections for the process $γγ\to π^0 π^0$ have been measured in the kinematic range 0.6 GeV $< W < 4.1$ GeV, $|\cos θ^*|<0.8$ in energy and pion scattering angle, respectively, in the $γγ$ center-of-mass system. The results are based on a 223 fb$^{-1}$ data sample collected with the Belle detector at the KEKB $e^+ e^-$ collider. The differential cross sections are fitted in the energy region 1.7 GeV $< W <$ 2.5 GeV to confirm the two-photon production of two pions in the G wave. In the higher energy region, we observe production of the $χ_{c0}$ charmonium state and obtain the product of its two-photon decay width and branching fraction to $π^0π^0$. We also compare the observed angular dependence and ratios of cross sections for neutral-pion and charged-pion pair production to QCD models. The energy and angular dependence above 3.1 GeV are compatible with those measured in the $π^+π^-$ channel, and in addition we find that the cross section ratio, $σ(π^0π^0)/σ(π^+π^-)$, is $0.32 \pm 0.03 \pm 0.05$ on average in the 3.1-4.1 GeV region.

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