I recently traveled to Lindau, Germany for the 62nd meeting of Nobel Laureates (http://www.lindau-nobel.org/), an annual meeting of Nobel Laureates and young researchers from around the world. This year’s meeting, by sheer coincidence, was dedicated to Physics (ironic right?).
One of the afternoon sessions for Wednesday July 4th was a panel discussion titled simply as “CERN.” Which was, by sheer coincidence, so well timed. After all, CERN had just finished giving their scientific and public press-releases regarding the discovery of a new boson, with mass of 125.3+/-0.6 GeV, earlier that morning. I had the opportunity to sit in the front row of a room filled with approximately 250 other young researchers, listening to top names in astro- & particle-physics discuss the recent CERN discovery. What follows below is a brief review of the Laureates’ discussion.
The session featured Nobel Laureates David Gross, Martinus Veltman, Carlo Rubbia, and George Smoot. It was chaired by Prof. Dr. Felicitas Pauss, of CERN. Additionally, we were also joined by several CERN Scientists (John Ellis counted among their number!). The air in the room was tense with excitement; and rightly so considering roughly 100 of the young researchers in the room, myself included, participated in high energy physics research in one way or other. And all of us glowed with sheer joy.
However, it was the Nobel Laureates who out shined us all, for they had been waiting for a discovery like this for the majority of their lives! David Gross remarked “[This was a] great day for me, for physics, for all humanity!” David Gross went on to proclaim that this discovery was a “Triumph for CERN…a triumph of theory!” Martinus Veltman followed by saying that this “closes the last gap amongst the Standard Model.”
I don’t think there was any doubt in either Gross’ or Veltman’s mind that a particle like the Higgs Boson existed. However, George Smoot originally had his doubts, “I was critical of the theorists not looking for other solutions,” to which David Gross jokingly forgave Smoot on center stage. Smoot followed up by “commending CERN for being cautious.” He was referring to the fact that both ATLAS and CMS Collaborations have simply stated that we have found a Boson, and that this particle has similar properties to the predicted Standard Model Higgs Boson, but we have not claimed to have found the Higgs Boson. Smoot cautioned us all to be careful, not to rush to judgement, and to continue our studies and cross-checks. Very sound advice in my opinion!
Carlo Rubbia chimed in at this point to say that the value of the experimental cross-section (or the rate of how often this Boson was produced) is almost a factor of 2 larger then the theoretical predictions (measurement from the CMS Collaboration shown in the plot below).
Rubbia commented that this was a “very important new element that warrants consideration,” and asked the CERN scientists who had joined us “what about this factor 2?”
The ATLAS Representative responded by saying that for the H-> gamma gamma channel the ratio measured by ATLAS was 1.9 +/- 0.5, within two sigma of the theoretical prediction, however the overall ratio was 1.3 +/- 1.2, consistent with the Standard Model. The CMS Representative responded by saying that this slight excess we observed is compatible with the Standard Model, and that the CMS Collaboration measures this to be 1.5 +/- 0.4 for the H->Gamma Gamma channel, one sigma above the theoretical prediction.
Gross asked John Ellis what he concludes about the possibility for beyond the standard model physics in light of this Boson’s discovery. Ellis replied by stating that this depends very much on the mass of the Higgs Boson, at 127 GeV the vacuum becomes unstable; and that additional physics is needed to prevent the universe from collapsing.
I found this idea very interesting since the current mass measurements of this new Boson by CMS and ATLAS places its mass between 125 and 126 GeV. However, these results are preliminary, with more data we will be able to narrow down the mass measurement (it might even shift!!). If this Boson we discovered truly is the Higgs Boson, and if a precision mass measurement reveals it’s mass to be above 127 GeV, then we definitely need some new physics to keep the universe in its present state, just as Ellis said!
Martinus Veltman was very curious how CMS and ATLAS were able to make this discovery so quickly. After all, data collection started in 2010 and this month we announced to the world that we had discovered a new Boson. CMS & ATLAS responded by saying increasing the center of mass energy of the LHC beams from 7 to 8 TeV was predicted to give a 30% increase in the rate of Higgs Boson production. Additionally, CMS & ATLAS researchers were able to reduce experimental backgrounds by 15% from 2011 to 2012. On top of these two facts the number of collisions per second taking place in the CMS and ATLAS Detectors was increased dramatically at the end of 2011 and at the start of 2012. All of these were factors contributing to the rapid discovery of this new Boson.
At this point Carlo Rubbia brought up the topic of what’s after the LHC. Rubbia’s idea was to build a muon-muon collider, with a center of mass energy slightly higher then this new Boson’s mass. Rubbia referred to this as a “Higgs Factory,” since he believes that such a machine would be able to produce these new Bosons with a much lower background then what occurs at the LHC, allowing for precision measurements of this Boson’s properties. Gross immediately chimed in with “[a] muon Higgs factory would be fantastic, ideal project for the US to get back into the game if anyone from FermiLab is listening!” which caused several moments of laughter in the lecture hall.
However, Rubbia’s comment was a very serious one and good one in my opinion. Physics needs something after the LHC, many questions are and will still be unanswered. George Smoot was of a similar opinion, stating that “completing the Standard Model is a great triumph, but everyone wants to see us go beyond.” On this note John Ellis stated that he would also like to see a Higgs factory on the agenda in the future. However, Ellis was uncomfortable with the idea of making a machine that would be limited to just producing this new Boson.
I think the final comments from the panel discussion summed up the feeling of everyone in that room, and those of all high energy physicists. David Gross closed by saying “Congratulations to all of you at CERN, are you having a big party tonight!?”
Until Next Time,