Building your own decay

Learning Objectives

  • How existing containers of particles can be filtered.

  • How new particles are made by combining existing particles.

  • How to express particle selections and combinations in options files, the Stripping, and the trigger.

As you might imagine, combining reconstructed tracks under some physical hypothesis is quite a common operation for a particle physicist to perform.

We’ve already manipulated the result of such an operation, so-called composite particles, and in this short series of lessons we’ll see how you can create such composites yourself. The knowledge you’ll gain will give you the ability to understand the large body of existing particle combination and filtering code, as well as the ability to use the Stripping and HLT2 selection frameworks to write new combinations for your analysis.

Data processing flow

Some charged and neutral particles are created in ‘the reconstruction’, either Brunel or the beginning of HLT1 and HLT2. These include ‘stable’ particles like electrons, protons, and charged kaons and pions, and neutrals like photons and neutral pions.

Why aren’t ‘composite’ particles, like D and B mesons, also created in Brunel? What are the advantages and disadvantages of creating particle combinations in a separate step?