The first omega-

One of the most famous bubble chamber pictures of all – this shows the discovery of the in the Brookhaven National Laboratory 80 inch hydrogen bubble chamber in 1964.

Although the tracks are rather faint, this is a picture with enough characteristic signatures (click here for tutorial step 7) for a clear identification of the without any need for measurement.

The knock-on electron in the bottom left of the picture shows that negative particles turn to the right. The event of interest, which is near this electron, has two outgoing charged tracks, one of which has a significant kink. The next question to ask is, 'Is there a vee pointing to this kink?’ There is a clear candidate but it does not point to the kink or the primary interaction. (You can check this easily by printing off the event and then continuing the curves of the vee until they meet; then, with a ruler, follow back the line joining the point where the vee tracks cross to the vee decay point – it misses both the kink and the primary vertex.)

So where does the vee come from? The picture provides a clue: near the middle on the right hand side a photon has 'materialised’ into an pair in the field of a nucleus. This photon , like the vee, does not point to the kink or the primary vertex but crosses the event downstream of these. Finally, near the top left of the picture, a second photon 'materialises’. These signatures are what one would expect if the had decayed into , with subsequent decay of the to . For the signatures click here.

(The materialisation of both gammas from a in hydrogen is exceedingly rare. The unique identification of this event by inspection, without measurements, was good enough for the physicist concerned to enjoy the pleasure of waking up the director of his laboratory in the middle of the night!)

For the original paper, click here. For some EXCEL calculations of masses, Click here.