Monte Carlo in high energy physics

[JoePhysicsNut]

Why is it necessary to use Monte Carlo methods in high energy physics?

There is Feynman calculus to evaluate matrix elements for various interactions and the relativistic Fermi's Golden Rule for decays and scattering to obtain a decay width or differential cross section.

What are we missing that forces us to use Monte Carlo methods to obtain numerical results instead of having functional forms for distributions?

 

[mfb]

Many (most) interactions are way too complicated to study them in an analytic way. In particular, hadron collisions can produce something like 10++ new hadrons - it is impossible to calculate that.

To make things worse, the detector responses are even more complicated - you need simulations.

 

[RGevo]

Matrix elements are used to calculate cross sections in hep.

The Monte Carlo part, including the showering of particles and hadronization etc. are added onto calculations to try to model the rest of the interaction. In general, the part we can calculate perturbatively ( Feynman diagrams etc. ) , we do.

The parts we can't calculate have classical models based on previous experiments ( with theoretical motivations)