The mass M_H of the Higgs particle is given by:

(The derivation of this formula is left as an exercise for the reader but substantial parts of it can be found in the sections on relativistic energy equations in 'annihilation' and K⁰ mass calculation in 'lifetime'.)

where E₁ and E₂ are the photon energies and θ is the angle between their paths. To find M_H we need to measure E₁, E₂ and θ.

Below is the LPPP simulation illustrating the search for the Higgs boson by the decay H → γγ at the LHC.

Use the magnetic field control to change the points and angles at which charged particles meet the calorimeters. This alters how easy it is (or not) to find the towers due to photons.

Use the energy cut off threshold to clear low energy particles from the screen. This will make it easier to find the photon energy deposits (towers) but, if the cutoff is set too high, one or both photons from a genuine Higgs decay might also be lost. Experiment with the settings until you obtain a good yield of candidate events.

Click on 'Measure energies' and measure the two photon energy deposits by clicking on their energy towers. Remember: you are after a pair of deposits which have not left tracks in the inner chamber. It is possible that towers from particles with and without tracks can overlap, so look carefully. If you cannot find two photons, click on 'Fire' to generate another event.

Click on 'Measure angle' once the two photon energies are measured, and measure the included angle between the two photon directions by clicking on it.

The computer will now calculate the invariant mass of the photon pair and add it to the histogram.

After you have carried out three measurements by hand the 'Auto events' option will become available. This will enable you to carry out a large number of automatic measurements using the current set of settings. With some settings the peak will be seen better than with others, so feel free to try a few. If you have set the options correctly, a statistically significant peak will develop soon.

Once you have a distinct peak on your histogram click the 'Fit' button. This generates a line which fits the data. Three numbers are displayed. These show: the invariant mass, the uncertainty of the mass value and the statistical significance of the value with respect to the background data. You are aiming for a significance greater than 5.