Category: Event

I am pleased to announce my very first search for a post-doctoral researcher. The links to the official advertisement are at the bottom of this announcement [1], and the text of the advertisement is reproduced here. As a new faculty member at SMU, and as a new member of the established SMU ATLAS group, this is a very exciting moment for me. The opportunity to do great research and discover deep meaning in the structure of the universe has never been greater. At this new energy frontier, I look forward to working with a post-doc on the great questions surrounding the cosmos, particularly regarding the nature of dark matter, and to contributing to the development and well-being of the ATLAS experiment during operations. I welcome all interested people to contact me about this opportunity.

[1] SPIRES listing, SMU Listing

I’ve been thinking a lot about cosmology. This is primarily because Jodi is teaching an elective course  for undergraduates this semester. I’ve been sitting in on her lectures and doing the homework so that I can learn more about the subject. What’s been great about it is that I can connect cosmology directly to the particle physics that I love so much. For instance, in a recent homework problem we had to compute the equation of state for a cosmos dominated by a gas made of one kind of particle. Not only was this a fun exercise for thinking about the universe, it also taught me how to arrive at the “matter-dominated” or “radiation-dominated” universe.

A concordance of experimental astrophysics and cosmology has created a rather interesting picture of the real equation of state for our real universe. Observations of baryon acoustic oscillations (BAO), ratios of light elements (related to their production in big bang nucleosynthesis, or BBN), supernova observations, and measurements of the cosmic microwave background have revealed a universe that is dominated not by matter, not even by radiation, but instead by dark energy [1]. Whatever dark energy is, it appears to exert a negative pressure, accelerating the expansion of the universe.

The WMAP satellite [2], launched earlier in this decade, gave us the most stunning pictures to date of the cosmic microwave background. Its ability to render in fine detail the acoustic structure of the CMB allowed us to think about what kinds of players were at work in the early universe, just a few hundred thousand years after the big bang. Like a symphony tuning up and then frozen all at once in time, the tone and timbre of the instruments have been revealed. And yet, we do not know the nature of the instruments. We hear them in the CMB, yes, but we know nothing of their size, shape, number, or other properties.

In order to go deeper, a European experiment called Planck was launched early in the summer. Just this week, it reported its first data from scanning the CMB [3]. Five years of WMAP data were just made available in the last year, and here already we have another experiment out to measure the finer detail of the CMB. It’s refreshing to see one experiment entering its later years as a new experiment comes on line. This means that there won’t be a significant gap between the last and current generation of experiment, and the science can proceed. It also points to the strength of the European space and science programs.

So the work begins anew, and I hope that we soon will learn new things about the cosmic symphony frozen in the CMB. Will those discoveries point the way toward the nature of dark energy? Good news: we’ll know sooner than later.

[1] “Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation,” E. Komatsu, et al., 2009, ApJS, 180, 330-376

[2] http://map.gsfc.nasa.gov/

[3] http://news.bbc.co.uk/2/hi/science/nature/8260711.stm

In the spring of 2008, just months after the last electron-positron collisions at PEP-II, the BaBar collaboration announced discovery of the long-sought ground-state of bottomonium. The evidence seemed overwhelming – a “big peak” at 9389 MeV/c^2 in the mass spectrum recoiling against a photon. The strategy was not new; the idea of looking for the ground state, the eta_b, using Y(3S) → photon + eta_b had been around a long time. What was new was the unprecedented data set available to perform the search and the innovation of the analysts leading the search. I get to say the latter; I had the pleasure of coordinating and reviewing their work [1].

Not half-a-year later, BaBar announced confirmation of the discovery using the related process Y(2S) → photon + eta_b. While it seemed that this was the last word, the discovery that sealed the case for discovery of the ground state, the pure scientist in me wanted one more thing. I wanted to see independent confirmation from a different experiment. Back-of-the-envelope calculations suggested that either Belle or CLEO could achieve this with data they had already taken, albeit with lower significance then that achievable at BaBar.

Extraordinary claims require extraordinary evidence. The claim by my own experiment is not exempt from this basic tenet of science. A conversation last fall with a Cleon (a member of the CLEO collaboration) colleage suggested CLEO was hot on the trail; it would only be a matter of time before they had something to say.

Well, they are speaking! Just days ago, Kamal Seth represented the CLEO collaboration at the BEAUTY 2009 conference and unveiled the results of their search for the eta_b (paper forthcoming) [2]. CLEO took their own clever path on this analysis, just as we took a path that varied from previous searches. They measured the mass of the eta_b to be (9391.8 ± 6.6 ± 2.0) MeV/c^2. They used the process Y(3S) → photon + eta_b, and they found the rate at which this occurs to be (7.1 ± 1.8 ± 1.1) × 10^−4. BaBar and CLEO appear to agree very well on how often this happens, and on the mass of the eta_b.

The saga of the eta_b continues to be rewarding. Computations of hadron properties are being improved by the knowledge of the eta_b mass [3]. There are still questions about the nature of the eta_b, since nobody has yet measured any of its decay modes. What will the future hold? The drive to map out the bottomonium system continues. This program is accompanied by a parallel program of searches for physics beyond the Standard Model. Who knows what we’ll discover?

[1] http://www.symmetrymagazine.org/cms/?pid=1000655

[2] http://beauty2009.physi.uni-heidelberg.de/Programme/talks/thursday-session1/seth.pdf

[3] Search for papers citing the original BaBar eta_b discovery