The branching ratio in particle physics is the fraction of times a particle decays through a particular channel or mode out of all its possible decay paths. It tells us how likely it is for a particle to transform into specific products when it decays.
Key Features:
- Every unstable particle can decay in multiple ways (called decay modes).
- The branching ratio is the probability of one particular mode, expressed as a percentage or a decimal fraction.
- The sum of all branching ratios for a particle equals 100% (or 1 in decimal form), representing all possible decays.
Why it matters:
- Helps physicists identify particles based on how often they decay into certain final states.
- Branching ratios are predicted by theoretical models like the Standard Model. Comparing predictions to experimental values helps test the validity of those models.
- Rare decays with small branching ratios can be signs of new or unknown physics.
Example:
A Higgs boson might decay into different particles like bottom quarks, W bosons, or photons. If the decay into two photons occurs 0.2% of the time, its branching ratio for that mode is 0.002.
In essence, the branching ratio is like a decay fingerprint—it tells us how a particle prefers to decay and provides crucial clues about its nature and the underlying physics.