Hello from Anaheim, California!
Yes it is that time of year: the April APS (American Physical Society) meeting. It has become tradition that each year in April, the membership of the APS in the Division of Particles and Fields meets together with the membership of somewhat related divisions: Astrophysics, Nuclear Physics, Computational Physics, Physics of Beams, and Plasma Physics. I find these meetings particularly broadening, as I can sometimes hear about topics that I do not necessarily get exposure to all of the time in my day-to-day work in hadron collider physics. In fact, some of the more entertaining session titles I have seen here include “Black Holes: Nature’s Ultimate Spinmeisters“, “Much Ado about Nothing: The Quantum Vacuum“, and “So Many Dynamos: Flow-Generated Magnetic Fields in Nature, in the Computer, and in the Lab“. (I believe the latter also wins for longest session title, barely beating out the more straightforward and understandable– for me at least– “Precision Measurements, Fundamental Symmetries, and Tests of the Standard Model“.)
Other interesting topics at this meeting, such as “Nuclear Weapons at 65“, “The Status of Arms Control“, and “Best Practices in K12 Physics Teacher Education Programs” are a result of the inclusion of the Forum on Society, the Forum on Education, and other such broad-interest topics in this meeting. Yet in my opinion one of the most important roles that these APS (and the Divisional) meetings play is to provide a forum for students to give 10-15 minute parallel session talks on their own analysis. At other conferences it is rare to have single-result talks rather than summaries, and summaries are generally given to more senior people. This is often the first (and sometimes only) chance a graduate student has to prepare a talk for a non-expert (non-working group) audience. With these talks they learn to prepare a summary of their work with an appropriate level of detail, omitting jargon, timing it properly, and most importantly, stating the big picture (the context) of their work, as well as the bottom line. When I was a graduate student I found the APS meetings to be valuable training in public presentations. For this reason I sent my student, David Cox, from Fermilab to Anaheim to present his own recent work on our searches for a massive top-like, perhaps 4th generation, quark (“tprime“) at the Tevatron. He has actually had practice giving talks at other meetings, but this is still good experience for him. He is also attending useful career sessions for graduate students as well.
My own main purpose for attending this meeting has been to present results in an invited plenary talk on Top Quark Physics, which I delivered on Saturday morning during one of several plenary sessions. My talk focused on results from the Tevatron‘s CDF and D0 experiments, not from the LHC. This was in fact a tall order for a 30 minute talk, since the large datasets from Run 2 of the Tevatron, together with the years of experience with these detectors and analysis tools, have meant a plethora of interesting and innovative results from CDF and D0 constantly being released to the public. Measurements of the top quark mass for example, the all-important electroweak parameter, have reached sensitivities to less than a percent relative, much better than the Run 2 goal of 3 GeV. Yet some relatively new measurements, such as the studies of the difference between the mass of the top quark and the mass of the anti-top quark (expected to be zero if CPT is conserved), still have very little statistical sensitivity due to the difficulty of the measurement.
The measurements of the forward-backward asymmetry AFB in top pair production have received attention earlier this year not only because both CDF and D0 continue to see a 2-sigma (or more) discrepancy with the theoretical predictions, but also because there appears to be a dependence on the invariant mass of the top pair system, which could imply the existence of new high-mass particles decaying to top quarks. (The original AFB measurement at the Tevatron was actually performed by my postdoc, Tom Schwarz — CDF Top Group Convener, when he was a thesis student at U. Michigan, and we’ve continued to study this anomaly with our collaborators from Michigan since then.) This measurement has generated quite a bit of theoretical interest so I was happy to take some time for these measurements, along with many other interesting topics, such as whether the top quark really has an exotic -4/3 charge instead of the +2/3 charge of the Standard Model.
While the Tevatron is producing spectacular results in the area of top quark physics (and many other areas), the reality is that even at half of the design energy, the LHC will soon outshine the Tevatron for most measurements. The production cross section (production rate) for top pairs at the 7 TeV LHC is much greater than at the ~2 TeV Tevatron due to the higher energies available. Measurements of things like the top-antitop mass difference, or the top quark charge, will soon have better sensitivity at the LHC. It may take a little longer for the LHC experiments to catch up in the area of the precision top mass measurement, mainly due to the complicated systematic uncertainties that need to be taken into account, but eventually the Tevatron will be bested there as well. The AFB measurement will be difficult to challenge or improve upon at the LHC, however, since the asymmetry is thought to result from quark-antiquark annihilation, which is much more dominant at the Tevatron’s proton anti-proton collider than the proton-proton collider of the LHC. For that we will still have more to say from the Tevatron’s final datasets.
Giving this talk has been a nice way for me to pay tribute to the amazing results from dedicated analysts at the Tevatron over the ~16 years since the top quark was discovered there. Although the Tevatron is scheduled to close down later this year , I cannot help be excited about the new projects I and many others are working on at the LHC. Some are topics that we could barely touch at the Tevatron such as boosted top quarks, which I am currently working on at CMS. (See Flip Tanedo’s recent post on this subject from Atlas.) Some, like our tprime searches, have shown hints of excess events on the tails of the distribution, so we are excited to see whether this excess grows at the LHC. Regardless of the particular topic, we are all approaching the LHC with the knowledge we have gained from the Tevatron, and are excited to continue to explore the particle frontier with the greater rates and energies of the LHC. And we are definitely on the look-out for discoveries!
