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arXiv 0801.0251hep-ph
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微扰碎裂

Perturbative fragmentation

B. Z. Kopeliovich, H. -J. Pirner, I. K. Potashnikova, Ivan Schmidt, A. V. Tarasov

摘要:

通过提供一个绝对归一化和保持所有项在(1-z)展开式中,改进了夸克微扰碎裂成π介子的Berger模型,使得计算在所有分数π介子动量z值下都是有效的.我们还取代了非相对论性的波函数的松散结合的π投影到光锥π波函数,这又是从众所周知的模型更现实的程序。完整的计算并不能证实中对$z>0.5$预测的碎裂函数(FF)的(1-z)^2行为,而且只适用于z>0.95的非常大的情况,在这种情况下,它与唯象的FF有合理的一致性。否则,我们观察到完全不同的z依赖性,这大大低估了较小z时的数据。在加入了来自光矢量介子衰变的π介子后,这种分歧有所减少,但仍然很大。过程相关的高扭转项也精确计算,并发现在大z和/或pT是重要的。

英文摘要:

The Berger model of perturbative fragmentation of quarks to pions is improved by providing an absolute normalization and keeping all terms in a (1-z) expansion, which makes the calculation valid at all values of fractional pion momentum z. We also replace the nonrelativistic wave function of a loosely bound pion by the more realistic procedure of projecting to the light-cone pion wave function, which in turn is taken from well known models. The full calculation does not confirm the (1-z)^2 behavior of the fragmentation function (FF) predicted in for $z>0.5$, and only works at very large z>0.95, where it is in reasonable agreement with phenomenological FFs. Otherwise, we observe quite a different z-dependence which grossly underestimates data at smaller z. The disagreement is reduced after the addition of pions from decays of light vector mesons, but still remains considerable. The process dependent higher twist terms are also calculated exactly and found to be important at large z and/or pT.

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