arXiv 2105.014352021-05hep-ph

衍射对轻子-质子深度非弹性散射的贡献：QCD动量求和规则和部分子分布的意义

The Diffractive Contribution to Deep Inelastic Lepton-Proton Scattering: Implications for QCD Momentum Sum Rules and Parton Distributions

Stanley J. Brodsky, Valery E. Lyubovitskij, Ivan Schmidt

备注：: 8 pages, 4 figures
发表信息：: Phys. Lett. B 824, 136801 (2022)
DOI：: 10.1016/j.physletb.2021.136801

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摘要：

深度非弹性轻子-质子散射（DIS）$\ell p \to \ell' X$的截面包括衍射深度非弹性（DDIS）贡献$\ell p \to \ell' p' X$，其中质子保持完整，具有大于0.9的大纵向动量分数$x_F$和小横向动量。可以用$t$通道中的Pomeron交换鉴定的DDIS事件占所有DIS事件的大约$10\%$。因此，当测量DIS时，无论是否检测到终态质子$p'$，都会自动将领先扭曲比约克缩放DDIS事件作为DIS截面的贡献。在这样的事件中，DDIS事件中末态质子$p'$携带的丢失的动量部分$x_{p'} \sim 0.9$可能与质子福克结构中海夸克或胶子携带的光锋动量部分错误地识别。正如我们将在这篇文章中指出的，产生DDIS事件的QCD Pomeron交换振幅既不服从算子乘积展开，也不满足动量和规则。因此，我们的结论是，在DIS实验中测量的夸克和胶子分布将被错误识别，除非测量明确排除DDIS事件和正确确定的部分子分布函数（PDF）来自DIS数据需要明确减去DDIS的贡献从整个DIS截面。

英文摘要：

The cross section for deep inelastic lepton-proton scattering (DIS) $\ell p \to \ell' X$ includes a diffractive deep inelastic (DDIS) contribution $\ell p \to \ell' p' X$, in which the proton remains intact with a large longitudinal momentum fraction $x_F$ greater than 0.9 and small transverse momentum. The DDIS events, which can be identified with Pomeron exchange in the $t$-channel, account for approximately $10\%$ of all of the DIS events. Thus, when one measures DIS, one automatically includes the leading-twist Bjorken-scaling DDIS events as a contribution to the DIS cross section, whether or not the final-state proton $p'$ is detected. In such events, the missing momentum fraction $x_{p'} \sim 0.9$ carried by the final-state proton $p'$ in the DDIS events could be misidentified with the light-front momentum fraction carried by sea quarks or gluons in the protons' Fock structure. As we shall show in this article, the underlying QCD Pomeron-exchange amplitude which produces the DDIS events does not obey the operator product expansion nor satisfy momentum sum rules. Thus we conclude that the quark and gluon distributions measured in DIS experiments will be misidentified, unless the measurements explicitly exclude the DDIS events and that a correct determination of the parton distribution functions (PDFs) derived from the DIS data requires the explicit subtraction of the DDIS contribution from the full DIS cross section.

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