Question: Sorry for the specific question; how do we know that the particles detected as a result of the collisions at CERN actually originated from the particles involved in the collision and were not created or altered from / by the combination of high energy fields and the energy released from the collision?

Michele Faucci Giannelli answered on 11 Mar 2015:

The short answer is because we know very well what we are colliding.
Let me be a bit more specific. The LHC accelerate protons which are then collided in 4 points around the ring where the experiment are located.
We know protons very well having studied in much details in other experiments. For example the experiment at the DESY laboratory collided electrons (which are fundamental, so point-like) to the protons which we know have a structure. You can imagine those experiments as a big microscope which is probing the structure of the proton. The results of those experiments is an unprecedented understanding of the proton structure which is a fundamental information for all measurements at LHC (we call them parton density functions or PDF).
We also have another type of experience which is in using protons as projectiles in other accelerators at lower energy, for example at the SPS and the TEVATRON. So we know how a proton behave when it is accelerated and we can easily extrapolate to the energy of LHC.
Hope this answer your question, if not please add a comment.