1201.6041 (Gioacchino Ranucci)

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

Gioacchino Ranucci

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.

View original: http://arxiv.org/abs/1201.6041