The Higgs to two photon decay channel

 The identification of a Higgs particle in the mass region from 80 GeV to 130 GeV will be a challenge for the LHC. The dominant decay will be H $\rightarrow$ b$\bar{b}$ but with the large background of QCD-jets this channel will only be possible to observe through associative production as HW and H t$\bar{t}$.

As described in section 2.6.1 a better decay mode will be the rare decay H $\rightarrow$ $\gamma$$\gamma$ with a branching ratio around 10^{- 3}. The theory describing the decay can be found in section 2.3.3 and the dominant production mechanism through gluon fusion in section 2.2.1.

The H $\rightarrow$ $\gamma$$\gamma$ decay has to be observed above a large background of irreducible photon-photon background. The invariant mass distribution of the photon-photon background will vary smoothly across the mass range from 80-130 GeV. A Higgs particle has thus to be discovered as a slight bump on top of a well calibrated background.

In this chapter the main focus will be on the mass resolution of the H $\rightarrow$ $\gamma$$\gamma$ signal and $\gamma$/$\pi^{0}_{}$ separation. The mass resolution is determined solely by the quality of the detector as the natural Higgs width below the threshold of the H $\rightarrow$ W ⁺W ^- decay is of the order 1 MeV, which is much narrower than any obtainable mass resolution. Good mass resolution is important to concentrate as much as possible of the signal into a narrow peak, which will be easier to observe above the continuum background.