Research Spotlight: Tier 2 CMS Research with Prof. Vicki Greene
Vanderbilt is a Tier 2 center of the CMS experiment at the Large Hadron Collider, a particle accelerator operated by CERN on the border between France and Switzerland. Being a Tier 2 center means that we receive data for analysis, production and storage from Fermilab, a Tier 1 center in Chicago, which in turn gets the data from CMS. And there’s tons of data, which is measured on the scale of petabytes (each petabyte is 1024 terabytes, and each terabyte is 1024 gigabytes). This requires lots of storage, a fast Internet connection, and lots of processing speed – an ideal task for a high-performance computing center like ACCRE.
Prof. Vicki Greene has been researching relativistic heavy ion physics at Vanderbilt for 23 years, and has been involved in discussions with ACCRE since the very beginning. Her research focuses on the quark-gluon plasma, which is formed by colliding nuclei at close to the speed of light; heating it enough to melt not only the nucleus but the protons and neutrons inside, leaving only a soup of quarks and gluons. Vanderbilt researchers contributed significantly to the discovery of the quark-gluon plasma in 2005. Nowadays, further research is being done to understand its properties as well as smaller systems for creating it, for instance, colliding a single proton with the nucleus instead of two nuclei together.
Having the Tier 2 center embedded at ACCRE provides a symbiotic relationship. Aside from the obvious hardware benefits (“I don’t have the computing power on my laptop, or a hard drive with 9 petabytes of storage”, says Greene), Tier 2 also benefits from having ACCRE’s trusted support team ready to help. In return, the research group contributes new hardware to the system and helps to bolster ACCRE’s image.
Another advantage that ACCRE provides is the ability to run data analysis on hardware that would otherwise go unused, a technique called job pre-emption. Much like a screensaver starts when the computer goes idle and stops when the mouse is moved, the cluster processes CMS data when the hardware goes idle and stops when it is needed for other purposes. By taking advantage of unused CPU cycles, the Tier 2 team can get more done without compromising access to other ACCRE users.