Characteristic Time and Decay Processes Strong Decay Baryon

Characteristic Time and Decay Processes

Strong Decay Baryon and Meson Heavy baryons produced in high energy collisions have lots of spare energy already and this is how they break up so quickly to form a more stable baryon ( eventually if not immediately a proton) and a meson. e. g.

Strong decay Exotic hadrons produced in collisions generally decay very quickly hadron It takes light about 10 -24 -10 -23 seconds to cross an unstable hadron. In this time the hadron will decay. This is called the characteristic time for the strong force to cause a decay. All strongly decaying hadrons will produce a proton eventually

Examples of particles decaying by the effect of the strong force: Mean lifetime 5. 58 × 10− 24 s Often a proton and a meson are the direct products Here a neutron is made – but that will eventually decay to form a proton

Electromagnetic decay • You have already seen electromagnetic decay in the case of an electron/positron pair. We get annihilation - + Remember that MESONS are quark/antiquark pairs (e. g. a neutral pion π0 is and it is possible for these antiparticles to annihilate each other in the same way This process has a characteristic time always greater than 10 -21 s or 100 times slower than processes due to the strong force.

Weak Interaction Processes The weak interaction is always characterised by: a change in quark flavour and the involvement of leptons e. g. ordinary negative beta decay e u W- Weak processes typically take 10 -8 or 10 -10 s d νe

It is possible for mesons to undergo weak decay as well (because they contain quarks) The positive pion is the pair W+ This is how most mesons decay u

Characteristics of Decay Processes Decay Recognised process by: Exchange particle Typical Time strong Only hadrons involved gluons 10 -24 - 10 -23 s weak Quarks flip leptons involved W- 10 -8 s Electro- photons magnetic exchanged or produced W+ <10 -21 s photon