CERN – Going Up Alleys

July 5, 2013July 5, 2013

One year after Higgsdependence Day

Just over a year ago, the ATLAS and CMS experiments reported strong evidence for the existence of a new particle who was was about 126 times that of the proton. It was a boson; this meant that it carries an internal unit of angular momentum (“spin”) whose value is an integer multiple of Planck’s Constant ( $\hbar = 1.054 571 726(47)\times 10^{−34}\, \mathrm{J \cdot s}$ ). Those were about the most honest and scientifically accurate statements we could make. We did not know for sure it’s actual spin; we were not positive if it was one particle or two, since different decay modes yielded slightly different masses that might indicate the presence of two closely spaced new particles.

One of the figures from the ATLAS paper entitled "Evidence for the spin-0 nature of the Higgs boson using ATLAS data." This plot summarizes some of the work that SMU student Tingting Cao contributed to the measurement of the spin and parity quantum numbers of the 126-GeV boson, now considered to be the Higgs Boson. — One of the figures from the ATLAS paper entitled “Evidence for the spin-0 nature of the Higgs boson using ATLAS data.” This plot summarizes some of the work that SMU student Tingting Cao contributed to the measurement of the spin and parity quantum numbers of the 126-GeV boson, now considered to be the Higgs Boson.

But since that time, a year has passed, and both experiments have been extremely busy. Yesterday, ATLAS submitted to the journal Physics Letters B a pair of papers that summarizes our belief, based on the scientific evidence, of the nature of this particle. Already, by earlier this year, ATLAS and CMS were saying that this was no longer a “Higgs-like” boson – it was probably the Higgs Boson predicted to exist in the 1960s. Now, by collecting the analysis efforts together and refining the techniques for assessing the properties of the newly discovered particle, we are ready to say (in print, and for peer review, for the whole community to review) that this is a spin-0 particle whose couplings to the known Standard Model particles are very “Standard-Model-like” – meaning that, for all intents and purposes, the data supports the hypothesis that this is the Higgs Boson of the Standard Model.

And with that assessment in hand, I think it’s time for high-energy physics to accept that the last great untested prediction of the Standard Model has been tested, and it’s time to elevate this grand description of nature to “The Standard Theory of Particle Physics.” For when a set of ideas so beautiful and powerful withstands the brutal an unending onslaught of experimental science that this one has, it is time to elevate it from “model” to “theory.”

The papers submitted on July 4, 2013, to Physics Letters B, are here:

“Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC.” Submitted to Physics Letters B. Available for download at arXiv:1307.1427

“Evidence for the spin-0 nature of the Higgs boson using ATLAS data”. Submitted to Physics Letters B. Available for download at arXiv:1307.1432

April 1, 2012April 1, 2012

Scenes from CERN: March 27-April 1

In an effort to stay awake on the first day of jet lag (my first day at CERN), I spent time thinking about how to adapt our existing electrically charged Higgs boson search – geared toward the decay of top quarks – to a new, heavy Higgs search where the Higgs is produced alongside a top quark.

After dinner on the first night, we go to the top of the building that houses the CERN Main Auditorium and take photos of CERN at dusk.

CERN at night, as photographed from my CERN Hostel Room. I will never forget what my father said to me once when he took me to Boston College, his graduate alma mater. He told me that when the lights were on in the lab at night, you knew there were people in there staying up later than you, working on harder problems than you.

The new courtyard outside the CERN Restaurant No. 1 looks like some alien sawblade.

Mont Blanc stands huge and gorgeous on a particularly clear day.

The Jura are the mountains to the west of CERN (Mt. Blanc and the Alps are far to the east). The strange tower in the foreground is a water tower. It was also my signature goal during my runs at CERN, each of which was about 2.5 miles and involved running a few laps around a ring-road (part of an accelerator complex at CERN) just below the water tower.

A beautiful tree is blossoming. On this day, the blossoms were beginning to blow off in the wind, leaving behind the buds of leaves.

Sharing the same courtyard as the tree above was a fenced off area. Danger! Radiation!

A tour visitor center housed in the same space as the LHC magnet testing facility. This is a display part of an LHC superconducting dipole magnet.

The superconducting magnet test facility. It looks like a busy train station, complete with information signs on the platforms. One of these magnets is currently operating at 26 Kelvin. The magnets can be slid into place and hooked up to services, mimicking the conditions they experience 150m below us in the LHC tunnel.

The cryogens cooling the magnet superconductors to 26 Kelvin, if released into the air, are capable of liquifying the nitrogen in the air. Even if they warm up enough to avoid the liquid nitrogen state, they are still capable of causing the water in the air to rapidly precipitate out. Safety videos of this process shown during CERN training show a cryogen release, followed by cloud formation and precipitation.

A cutaway section of a superconducting dipole magnet shows the complex multi-layered inner workings.

Spare LHC magnets are housed here, in case they are needed.

A panoramic shot of the LHC control room. Just about a day later, LHC delivered the first 8 TeV proton-proton collisions.

Yes, please, continue to speak loudly outside my office. PLEASE.

March 26, 2012March 26, 2012

CERN in the Spring

It’s time to go to CERN. The LHC has been delivering beam for a few weeks now, with a record 8 TeV center-of-mass energy having been achieved. The ATLAS detector stands ready for for first proton-proton collisions at this energy. This week is the ATLAS Physics and Performance week, and I am taking some time away from teaching to travel to CERN and focus on research.

Our SMU ATLAS group has been exploring some new directions in the search for and measurement of the Standard Model Higgs Boson. Our students and post-docs have been leading this effort so far, and my hope is to leap into the fray for a week and get my feet wet on the analysis. We’ve been partnering with physicists from outside of SMU, so this has been a very rewarding study for a new direction. I am also hoping to catch up on my own interests in the electrically charged Higgs Boson; our publication on last year’s data is imminent, and it’s time to think about new directions in that search as well. This week is an opportunity to step away from teaching and research – thanks to my co-professor in my course – and focus on research.

For now, though, this trip is just a lot of sitting in airports and waiting to get to CERN. This is the part I hate; the flights are just long enough to make me impatient and just short enough to prevent me from getting a really good night’s sleep on the plane. When I wake up tomorrow, I’ll be in Switzerland, ready to clear passport control and get my rental car. I don’t mind so much the arriving . . . but the waiting to arrive gets on my nerves.

Well, I guess I cannot complain too much. I have a Ph.D. thesis draft to read and markup in preparation for the thesis defense of one of our SMU graduate students. I also have at least two paper drafts to read and edit. It’s nice to be focused on physics papers for a change. Besides, if they are detailed enough and I am tired enough, I might just get more sleep than I originally planned for.