研究人员报告了在大型强子对撞机的CMS实验中，通过同时产生三个由粲夸克-反夸克对组成的J/ψ介子来研究双和三部分散射。研究人员观察到这一过程——通过将J/ψ介子衰变为一对带相反电荷的介子来重构——具有超过五个标准差的统计显著性。
研究小组测量了包含基准截面为272+141-104(stat)±17(syst)fb，并将其与单、双和三部分散射情况下三重J/ψ介子产生的理论预期进行了比较。假设多重硬散射概率因式分解为单分量散射截面，双分量散射和三分量散射是测量过程的主要贡献。
据了解，质子由三个价夸克、两个上夸克和一个下夸克组成，由胶子和大量的夸克-反夸克对连接在一起。夸克和胶子统称为部分子。在质子-质子碰撞中，每个质子通常只有一个部分经历了硬散射——称为单部分散射——使每个质子的其余部分只受到轻微扰动。
附：英文原文
Title: Observation of triple J/ψ meson production in proton-proton collisions
Author: anonymous
Issue&Volume: 2023-01-19
Abstract: Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of quark-antiquark pairs. Collectively, quarks and gluons are referred to as partons. In a proton-proton collision, typically only one parton of each proton undergoes a hard scattering – referred to as single-parton scattering – leaving the remainder of each proton only slightly disturbed. Here, we report the study of double- and triple-parton scatterings through the simultaneous production of three J/ψ mesons, which consist of a charm quark-antiquark pair, in proton-proton collisions recorded with the CMS experiment at the Large Hadron Collider. We observed this process – reconstructed through the decays of J/ψ mesons into pairs of oppositely charged muons – with a statistical significance above five standard deviations. We measured the inclusive fiducial cross-section to be 272+141104(stat)±17(syst)fb, and compared it to theoretical expectations for triple-J/ψ meson production in single-, double- and triple-parton scattering scenarios. Assuming factorization of multiple hard-scattering probabilities in terms of single-parton scattering cross-sections, double- and triple-parton scattering are the dominant contributions for the measured process.
DOI: 10.1038/s41567-022-01838-y
Source: https://www.nature.com/articles/s41567-022-01838-y