# How use the Higgs branching ratio plot to extract information about the Higgs mass compared to experiment?

What does the plot of higgs branching ratio (see figure below) say about the higgs mass anyway? How can one use it as a guide to find the higgs mass experimentally?

If we e.g. go to $M_H=126$ GeV (in figure below) and then read off the different branching ratio: then if experiment agrees with this, it would mean that the higgs mass is $126$ GeV?

• The best sensitivity is the peak in the invariant mass distribution of two photons from a Highs decay. – innisfree Apr 13 '14 at 14:44
• So what does the above figure tell you? Why is it so interesting? What's its use and purpose? – Your Majesty Apr 13 '14 at 16:09

Before we knew the mass of the Higgs boson, a plot like this one was useful for identifying the best channels to look at to detect the Higgs in various mass ranges. For example, it tells us that if the Higgs is more massive than about $160-180\text{ GeV}$, it usually decays to $WW$ or $ZZ$ boson pairs, so the experiments had better be prepared to detect $WW$ and $ZZ$ events. Or if the Higgs is less than $130\text{ GeV}$, it usually decays to $b\bar{b}$, so the detectors had better be prepared to detect that.
What this plot doesn't tell you is the backgrounds to each channel - that is, other processes that are expected to produce the same final set of particles but don't involve a Higgs boson. For example, a quark and antiquark from a proton could interact and produce a virtual $Z$ boson which decays into a $b\bar{b}$ pair. This would be considered a background to the Higgs $b\bar{b}$ channel. As you can imagine, a channel that has large backgrounds (that is, many other processes that will produce the same final particles) will not be particularly good for searching for the Higgs boson. Some of the channels that have large Higgs branching ratios also have very large backgrounds - the $gg$ channel, for instance - so it's not particularly important for the detectors to look for them. Conversely, some channels that have small branching ratios (i.e. a Higgs rarely decays that way) are still useful for the Higgs search because they have small backgrounds (i.e. very little else produces that kind of event). The $\gamma\gamma$ channel is one of these.