Y（9.46 GeV）和胶子发现（对PLUTO结果的批判性回顾）
Y(9.46 GeV) and the gluon discovery (a critical recollection of PLUTO results)
摘要：
在DORIS e+e-储存环（DESY）上利用PLUTO实验首次研究了Y（9.46GeV）的强子衰变。为了确定PLUTO对胶子发现的贡献，作为合作的成员，我们重新考虑了它在1978年和1979年上半年产生的所有材料。结果清楚地表明，Y共振的主要衰变是由3个胶子强子化为3个喷注所介导的。相对<P_T>于推力轴，这是由PLUTO自己在附近的连续厘米秒观测到的。2-夸克喷流事件的能量。相反，平均球度<S>，更多的拓扑变量和动量分布显示出净差异与相同的数据，结果兼容jettiness只有在超过2个射流的情况下。作为三体衰变（因此有3个喷流）的结果，平面度由低值表示<P_out>，这完全是一个与模型无关的结果。带电的多重性被观察到比在连续介质中更大，并且在MC 3胶子喷注像夸克一样碎裂的情况下，正如胶子喷注所预期的那样。1979年6月，PLUTO测量了3-胶子衰变的矩阵元，定量地符合QCD（即使在强子化之后，这并没有掩盖微扰预言），并通过排除自旋0和自旋1/2证明了胶子的自旋1性质。像夸克喷流一样的胶子强子化，如3-胶子喷流MC，与拓扑数据和多重性是相容的;这是第一个（确定的）胶子喷流的实验研究。PLUTO的结果被DORIS的其他实验和后来更复杂的探测器所证实。在更高的能量下，在PETRA，自旋为1的胶子的存在被PLUTO和另外3个通过测量胶子辐射的实验证实，软胶子通过喷流加宽，硬胶子通过夸克发射胶子喷流（现在清晰可见）。
英文摘要：
The hadronic decays of Y(9.46GeV) were first studied by PLUTO experiment at DORIS e+e- storage ring (DESY). To determine the contribution of PLUTO to the discovery of the gluon, as members of the collaboration, we have reconsidered all the material produced by it in 1978 and the first half of 1979. It results clearly that the experiment demonstrated the main decay of the Y resonance to be mediated by 3 gluons hadronizing into 3 jets. Jettiness resulted evident by the <P_T> with respect to the thrust axis, which was as observed by PLUTO itself at nearby continuum c.m.s. energies for 2-quark jet events. Instead, the average sphericity <S>, more topological variables and the momentum distribution showed a net difference with the same data, results compatible with jettiness only in case of more than 2 jets. Flatness as consequence of a 3-body decay (therefore 3 jets) was indicated by the low <P_out>, altogether a result independent of models. The charged multiplicity was observed to be larger than in the continuum and in case of MC 3 gluon jets fragmenting like quarks, as expected for gluon jets. In June 1979 PLUTO measured the matrix element of the 3-gluon decay to be quantitatively according QCD (even after hadronization, which does not obscure the perturbative predictions) and demonstrated the spin 1 nature of the gluon by excluding spin 0 and spin 1/2. The gluon hadronization like a quark jet, as in 3-gluon jet MC, was compatible with topological data and multiplicity; this was the first experimental study of (identified) gluon jets. The PLUTO results were confirmed both by other experiments at DORIS and later by more sophisticated detectors. At higher energies at PETRA the existence of gluons of spin 1 was confirmed by PLUTO and by 3 more experiments by measuring the gluon radiation, soft gluons by jet broadening, hard gluons by the emission of (now clearly visible) gluon jets by quarks.
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