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A Dis-CERNing Discovery
Penn physics students share their stories of being on-hand for the discovery of the Higgs boson.
The summer of 2012 saw a monumental discovery in science: the mysterious Higgs boson particle was finally revealed. In December 2011, Frontiers sat down with physicist Brig Williams, who discussed the progress on finding this elusive particle that could help scientists better understand the basic building blocks of the universe. At the time, Williams was optimistic, but cautious. Months later, the European Organization for Nuclear Research, or CERN, announced a seminar that would address tentative findings for 2012. When word got out that Peter Higgs—who proposed the boson particle—would be attending the conference, excitement detonated through the physics community. On July 4, 2012, CERN physicists announced the discovery of a previously unknown boson. As the science community rejoiced, several Penn students in the Department of Physics and Astronomy reflected on their thoughts about the announcement and the research that led them to this point.
People sometimes wonder how any student can feel ownership of an experiment with more than 3,000 co-authors. To this, I say: my fingerprints cover ATLAS; my photons were the Higgs. And there has been nothing so exhilarating as to strive and teem with so passionate a community, towards something so great. – Jamie Saxon
This summer marked the end of my 6th year working on ATLAS. One of the two large detectors at the LHC, ATLAS measures the particles produced in collisions by the LHC and infers the existence of rare particles (like the Higgs boson) which are produced but decay away in a tiny fraction of a second. One of my main contributions to the experiment was in an area called data acquisition. The chance of producing a Higgs boson in any given LHC collision is very small, so a great many collisions are necessary to see it. (The vast majority of the collisions end up being uninteresting.) The data volume produced by just the part of the detector that Penn works on is gargantuan, comparable to the entire Trans-Atlantic internet bandwidth! Reducing this data to a manageable rate and transporting it while keeping the most interesting collisions is a big challenge. It requires a complicated and precise system of electronics, and helping make this work was my job for multiple years.
Using this carefully collected data, our discovery of a new
particle is a tremendous milestone and validates theoretical predictions made
over 40 years ago. More work remains to find out whether we found exactly what
we expected, or whether nature has some interesting twists in store for us. One
of the great aspects of the discovery was how a breakthrough in our
"esoteric" field made front page news around the world. I think this
was a triumph as well, and hopefully it inspires young students to ask
questions about the world around them and perhaps eventually consider careers
in fundamental science.
I started working on ATLAS as a sophomore in high school. Early on, my tasks were technical but thrilling, because everyone in our group took care to help me understand how each project I worked on fit into the larger picture. In the eight years since, the complexity of my work has evolved in step with the experiment. I first visited CERN in 2004; in 2006 and 2007, I spent my first summers in Geneva to help prepare Penn’s sub-detector (the TRT!) for installation in the experimental cavern. So I have dangled upside down off subterranean scaffolding, to wrench our last cables in place. I have stood at the point where protons collide. I have touched history.
Over my first two years as a graduate student at Penn, I have worked on photons. Photons are tiny pieces of light, but the ones we're looking for in Geneva are more than a billion times more energetic than the ones you see with your eyes. When an interaction between two protons occurs and the information from the sensors in the detector is saved to disk, we retain only the positions of the energy deposited in the detector. From this record, we reconstruct the decay products of the interaction. My work was to choose candidate photons out of this data, for our search for the Higgs decaying to two photons. To accomplish this, I built a neural network to optimally discriminate between photons and other particles. In a very real way, I chose each photon that we used for the discovery of the Higgs!
People sometimes wonder how any student can feel ownership
of an experiment with more than 3,000 co-authors. To this, I say: my
fingerprints cover ATLAS; my photons were the Higgs. And there has been nothing
so exhilarating as to strive and teem with so passionate a community, towards
something so great.
I am one of the more senior graduate students in the ATLAS group (one of seven particle detector experiments) at Penn. Atlas is one of the two experiments at the Large Hadron Collider (LHC) that recently discovered the Higgs boson. The focus of my research has been looking for a particular signature of the Higgs boson that was part of this discovery. I’ve been incredibly fortunate to be able to have played a role in this great achievement. The discovery of the Higgs boson was, literally, decades in the making. As a student at Penn, I’ve been lucky enough to have worked alongside expert physicists, some who have been searching their whole careers for the Higgs boson, in the period when this historic discovery was actually happening. I’ve learned an awful lot, and it’s been a ton of fun!
While doing my research at Penn, I lived at CERN, just along the French-Swiss
border, for almost four years. The thing that I always find the most striking
is just how much of an international collaboration CERN and the LHC are. Not
only is the lab based overseas, but everyday physicists from the US work
side-by-side with colleagues from Europe, Russia, China, Israel, Turkey, and
Japan (just to name a few). Seeing all these great people from all over the
brought world together by science has been truly inspiring.
Having recently started my third year of graduate school, I am one of the junior members of Penn's ATLAS group. ATLAS is one of the two major experiments at the LHC, and Penn has made too many contributions for me to count. Our group is lovingly referred to as "the Penn Army" because we have so many researchers doing so many things.
Many of our students (and postdocs and faculty) work on
searches for the Higgs boson. This particle was predicted by theoretical
physicists in the 1960s, and CERN recently announced the discovery of a new
particle that looks very much like the Higgs. This announcement was made on
July 4 and is sometimes referred to as "Higgsdependence Day" in the
ATLAS community. It is a great achievement in the field because it is the
culmination of nearly half a century worth of work since the Higgs was first
predicted. In fact, I was so inspired by the hard work and dedication of my
colleagues that I changed my area of research to Higgs searches.
I am beginning my third year as a grad student at the University of Pennsylvania, and I have been working on the ATLAS experiment since I was an undergraduate in 2008. Since then I've taken part in a diverse array of activities—including detector commissioning and calibration, data acquisition, and particle identification. What struck me most while working at CERN is the immense amount of collaboration and coordination required to run such a complex experiment. Before one even begins to approach the problem of identifying Higgs events, one must build detectors capable of measuring its decay products, develop ways to identify those decay products, find ways to sift through extraordinary amounts of data on-the-fly to save the most promising events... and on and on. This requires a high level of coordination among thousands of experimentalists over the course of decades.
The weeks leading up to the Higgs discovery announcement
were filled with uncertainty and anticipation. The Penn group is involved in
several Higgs discovery channels; as data continued to pour in from the
experiment the collaboration was beginning to get a clearer picture of what we
had. The information came in fits and starts as each Higgs group updated its
analysis with new data. One of the last analyses to update their results was
the WW decay channel, who kept their results blinded until a week before the
Higgs announcement. I had the fortune to see to see Elliot Lipeles, one of the
Penn professors involved in the analysis return from that unblinding meeting; I
had never seen him smile so broadly. It was clear from the expression on his
face that there was no more uncertainty; we had discovered a new particle.
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