Kevin Pedro (Ph.D. '14, physics) on the Brave New World of Particle Physics

In anticipation of #RestartLHC, we spoke with alumnus Kevin Pedro, Ph.D. '14, physics, about his work with the Large Hadron Collider (LHC), supersymmetry and other particle physics questions he's investigating.

Of all the science fields you could have decided to study, why did you choose particle physics?

I was always interested in science. In middle school, I stumbled across The Particle Adventure, a website developed by the Particle Data Group (with funding from the DOE and NSF) that provides a great introduction to particle physics. From then on, I was fascinated by the idea of understanding the smallest pieces of the universe.

Where has your career taken you since you graduated from Maryland?

I'm now a postdoctoral research associate at Fermi National Accelerator Laboratory in Illinois, continuing to work on the CMS experiment. Fermilab hosts the LHC Physics Center, which is the second largest group in the worldwide CMS Collaboration.

How did your time at Maryland prepare you for your current position?

My time at Maryland prepared me very well for my current position! I traveled frequently to Fermilab as a graduate student, so I was already familiar with the lab when I arrived a few months ago. I also spent some time at CERN in 2012, working on the operation of the CMS detector by monitoring the trigger system (which selects interesting events for us to analyze; the rate of data would otherwise be far too high for even the most advanced computers to handle). I helped take data that was used to discover the Higgs boson and I was onsite at CERN for the official announcement on July 4, 2012, which was very exciting. In the group's own lab at Maryland, I worked on research and development of new scintillators and photodetectors for upgrades to the CMS detector. The Maryland group also has a Tier 3 computing cluster, on which I ran many, many simulations, software tests, and data analysis jobs. For my thesis, I worked with a Maryland postdoc (Matthieu Marionneau, now at ETH) and a Fermilab postdoc (Ketino Kaadze, now at Kansas State) to search for leptoquarks and top squarks, which are certain types of hypothetical new particles. My postdoctoral work so far has drawn heavily on my graduate research.

What is your role in the LHC effort?

I work on the planned upgrades of the calorimeter system, which is part of the CMS detector. It measures the energy deposited by particles produced in LHC collisions. We are studying the effects of radiation damage on the calorimeters and how our planned upgrades can mitigate those effects in order to maintain good performance. In the long term, we will replace a large portion of the calorimeter system with more resilient technology, so those options have to be explored and developed. My personal contribution is mostly in the area of software and simulations: writing and testing algorithms to predict the performance in different scenarios.

I'm part of a group with several other Fermilab scientists and postdocs, as well as researchers from other institutes in the US and abroad, who plan to search for evidence of supersymmetry. We're looking for pair production of gluinos, the supersymmetric partner of the gluon (a particle which transmits the strong nuclear force that binds quarks together into protons and neutrons). We expect the gluinos, if they exist, to decay to numerous hadrons (like protons and neutrons), so we are working on optimizing our ability to isolate that signature from similar signatures that might be produced by standard particles. When the LHC restarts with higher energy collisions, the expected rate of production of gluinos increases significantly, so it's possible that we could observe them with only a relatively small amount of data. In the most popular models of supersymmetry, the lightest type of supersymmetric particle is stable and undetectable, so it escapes the detector with a portion of the gluino's energy. This "missing energy" is the signature we'll initially try to find, because it can be very distinct. If we don't see that, I plan to reinterpret the data to look for alternative models of supersymmetry where there are no stable supersymmetric particles. These models are harder to distinguish from the background events generated by standard particles, but I like a challenge! In my thesis research, I explored certain facets of these alternative models, and I'd like to expand on that with the new data.

What are the big questions researchers hope to answer this time around?

Our primary goal is to find evidence of physics beyond the Standard Model. There are several important questions that we don't yet know how to answer. One question is the hierarchy problem, which can be phrased as: why is the Higgs boson mass, 125 GeV, so much smaller than the Planck mass, 10^19 GeV? Another question is the nature of dark matter. The discovery of supersymmetry, as I discussed above, could potentially address both of these questions (and others, such as the unification of the strong nuclear force with the electromagnetic and weak nuclear forces). Of course, we're also considering many other hypotheses; we could very well rule out the existence of supersymmetry, to the extent that we can probe with the LHC. It's a brave new world in particle physics! For the past 40 years, we've been filling in the particles of the Standard Model, and we even had a pretty good idea that the Higgs boson existed in some form. Now, we're much less certain about what might be out there. We'll also keep investigating the Higgs boson and measuring its properties. If new, massive particles exist, the Higgs boson probably interacts with them somehow.