What is luminosity and how does it affect particle collisions?

[nesp]

In a particle accelerator where, say, protons are accelerated in opposite directions and made to collide, how are the particles brought close enough to actually collide? Protons are extremely small, and their mutual positive charges repel. How does the collider manage to target protons so precisely that they collide?

 

[reilly]

They don't. Rather they rely on the fact that there is a finite probability that a collision will take place -- think of beam density as an unnormalized probability distribution. I'm far from expert in this topic, but I suspect making the probability of collisions as high as is practically possible is a major design concern.
Regards,
Reilly Atkinson

 

[Severian]

Simply put, they have lot and lots of photons in each bunch. Most of them miss (which is actually good because if they all hit it would take a while to clean up the mess).

 

[ZapperZ]

There is something in beam physics called the "luminosity". It is roughly defined as the number of particles per unit area per unit time times the opacity of the target or colliding particle, usually expressed in either the cgs units cm-2 s-1 or b-1 s-1. The integrated luminosity is the integral of the luminosity with respect to time. What this number tells you is roughly the probability of collision between the particle.

This was the main problem of Run II of the Tevatron a while ago - they didn't have the expected luminosity that was needed if they were to have any chance of detecting a Higgs boson. That problem right now appears to have been solved with the help of a better electron cooling technique on the proton beams.

Zz.