Particle decay

I mentioned resonances in a previous post. They're really neat, so I wanted to write a little more about them. For one thing, the particles observed solely as resonances almost invariably decay by the strong force, which has a shorter range and faster decay time than the electromagnetic or weak interactions. In other words, we can often observe electromagnetic or weak decays as particle tracks inside a detector, because the particle has time to travel a measurable distance before it decays.
I mentioned in my previous post that based on certain properties of the scattering peak, we can determine the particle's lifetime. In particular, the peak is at a range of energies, which means there's a certain amount of uncertainty in the energy of the particle, which is called the decay width. Then by using the energy-time uncertainty relation, we can calculate the lifetime of the particle (the little uncertainty in time in which it is permitted to exist).
When a particle can decay in a variety of ways, a number called the total decay width describes the probability that the particle will decay in any unit of time. In particle physics, the probability that a particle decays along a certain path is called the branching ratio. These phrases are bandied about quite a bit, and it took me until just recently to finally figure out what they really meant. It's neat how much the knowledge of just a couple of phrases can deepen the understanding of a vast field like particle decays.