I gave my seminar at Syracuse yesterday. I had a very busy day – not a dull moment in the entire visit! I spent a lot of time meeting with faculty on the LHCb experiment, a B-physics experiment based at the LHC. While not one of the experiments that gets a lot of press, LHCb is no less critical. There is still much work to be done in the flavor sector, and as the data sets of BaBar and Belle age LHCb will step up to help answer some of the big questions about the universe.
One of these is the question of the unitarity of the quark mixing matrix in the Standard Model. The Standard Model tells us that when you break the electroweak symmetry and introduce mass into the theory (ala the Higgs Mechanism), you find the relationship between the up-type and down-type quarks to be describes by a single 9-element matrix, whose complex product with itself is unitary – that is, equal to the matrix equivalent of the number “1”. This unitarity property gives us tremendous predictive power over nature, but the property itself is something to be tested.
LHCb will become the key experiment aimed at measuring a parameter of the unitarity matrix: the unitarity angle called “gamma”. When you express the unitarity property of the quark mixing matrix, you obtain an equation that relate the bottom quark to other quarks. This formula can be visualized as expressing the closure of a triangle – that is a three-sided objects whose sides connect together into a closed shape. The internal angles of the triangle must add to 180-degrees. If you measure the angles, by measuring distinct natural phenomena each sensitive to one of the three internal angles, their experimental sum should be 180-degrees. If they don’t add up, then either the unitarity property is not respected in nature, or there are other particles competing with the quarks to cause the phenomena that are being measured.
LHCb will go for gamma, the third and (it seems) the hardest of the three angles. BaBar and Belle have made tremendous measurements of beta and alpha, and while attempts are being made to measure gamma it is proving very hard to do it with our data samples. LHCb is gunning for gamma.
My talk appeared to go very well. I got a lot of questions about the eta_b measurement, keeping me on my toes about my ability to describe the analysis cleanly and clearly. The after-seminar dinner started with lots more questions, and the topics of conversation proceeded in a delightful random walk from there.
I had a great time. I thought I’d be pretty worn out by now, but I feel pumped.
Today, I traveled to Montreal for my seminar at McGill University tomorrow. I got here early enough that I was able to spend some time walking the campus and talking to my host. The drive was pretty simple, and I rather enjoyed the grilling about my research from the Canadian border guard. It was specifically suggested that I must have some very interesting theories about the beginning of the universe. “None that are correct,” I responded.
