arXiv 1201.60412012-01-29hep-exphysics.data-an

关于ATLAS双光子和四轻子衰变道中过剩的意义

On the significance of the excesses in the ATLAS diphoton and four lepton decay channels

Gioacchino Ranucci

备注：: 10 pages, 6 figures

摘要：

本说明描述了最近发布的ATLAS数据的统计意义的评估希格斯粒子搜索的衰变通道，特别是适合于低质量区，特别是双光子和四轻子衰变通道。除了提供所考虑的通道，单独或组合，在110至146 GeV的低质量范围内的显着性评价，一些细节的配置文件的可能性程序所采用的计算也进行了描述。特别强调的是寻找其他地方的效果，它会出现在一个新的信号进行搜索时，在一个广泛的质量范围内，因此分别指定本地和全球的意义。当组合在一起时，发现在两个通道中检测到的局部过量的全局p值等于0.033或0.013，分别对应于1.8 σ和2.2 σ的显著性，这取决于每个通道中预期信号的幅度的相互独立性或依赖性的假设。在其他获得的结果中，单独采取的两个通道的局部和全局意义的计算与合作报告的结果一致，而只有一个微小的差异被发现为他们的组合局部意义。最后，说明了一些考虑有关的低统计四轻子衰变通道，显示不同的搜索策略的轮廓似然方法，例如扫描统计，可以导致一个显着不同的意义，增强到3.3西格玛的全球影响。

英文摘要：

This note describes an assessment of the statistical significance of the recently released ATLAS data regarding the Higgs search in the decay channels especially suited for the low mass region, in particular the diphoton and four lepton decay channels. Besides providing the significance evaluation of the considered channels, alone or combined, in the low mass range from 110 to 146 GeV, some details of the profile likelihood procedure employed for the calculations are described, too. Special emphasis is given to the look elsewhere effect, which arises when the search of a new signal is carried out over a broad mass range, therefore specifying separately local and global significances. When combined together, the global p-value of the localized excesses detected in the two channels is found equal to either 0.033 or 0.013, corresponding, respectively, to a significance of 1.8 sigma and 2.2 sigma depending upon the assumption of mutual independence or dependence of the amplitudes of the expected signal in each channel. Among the other obtained results, the local and global significances of the two channels individually taken are computed in good agreement with those reported by the Collaboration, while only a minor discrepancy is found for their combined local significance. Finally, some considerations are illustrated related to the low statistics four lepton decay channel, showing that a search strategy different from the profile likelihood method, e.g. scan statistics, can result in a substantially different significance, enhanced to a 3.3 sigma global effect.

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