A pinboard by
Timothy Raben

Postdoc, University of Kansas


Grazing collisions of extremely high energy particles to understand nature and find new particles

Colliding particles at very small angles involves fundamental physics but until recently good experimental and theoretical descriptions have at times been lacking.

In a particle collider, the probability for particles to scatter increases with energy over a very large range of energies. However, this result, known since the 60s, has never quite completely describable using known physics techniques (quantum field theory). Theoretically the issue process is described by a regime where one must carefully re-sum infinite series’ of vanishingly small contributions while skirting the boundary of perturbative physics. Experimentally, when particles collide, measurements are needed of particle jets produced almost directly along the axis of collision; it is difficult to build detectors where a beam of particles must also travel! Progress in the past 20 years has at times offered more questions than answers!

Here at KU we are able to work hand in hand with experimentalists making new measurements of these forward jets, while at the same time improving the theoretical description. In these so-called “forward collisions” can be described by a process where the protons head toward a collision and exchange a particle: the Pomeron. Our work tackles this complicated physics on three fronts. First, how we can re-sum more and more of the important contributions that describe Pomeron exchange? Unlike most particle collisions, where physicists can describe them using a finite number of contributing effects, Pomeron exchange involves an infinite number of effects. We are showing how to include more and more of these infinite contributions in the description of the Pomeron. Secondly, when particles like the proton are sped up to higher and higher energies they actually become denser: there are more and more partons (the quarks and gluons that make up the proton) floating around inside. We are describing how to connect these denser protons, which are very complicated, to the exchange of the Pomeron. And finally, the need to resum these infinite contributions and look at very forward interactions put us on the boundary of what is traditionally called Perturbative Physics. As a counterpoint, we are also using techniques that come from string theory to describe the string-Pomeron and model these events from a NON-perturbative perspective!