Stephen Sekula – Page 59 – Going Up Alleys

February 15, 2009February 15, 2009

Let’s go Higgs hunting

When we proposed the taking of the world’s largest sample of Upsilon(3S) mesons (which then led also to the taking of the world’s largest sample of Upsilon(2S) mesons), a key component of the proposal was coverage of low-mass Higgs boson scenarios. Such scenarios can arise in extensions of the minimal supersymmetric Standard Model, and could have eluded detection even at the most famous electron-positron “Higgs factory” – LEP at CERN.

Our friends at the CLEO experiment released their results in a search for a low-mass Higgs boson, decaying into muons or tau leptons, just months after we concluded our data-taking on the Upsilon(3S) and Upsilon(2S) [1]. It was a bit frustrating to see CLEO reach this milestone before we had analyzed the data. But, they had at their disposal just 21.5M Upsilon(1S) decays. In contrast, BaBar collected 122 million Upsilon(3S) and 99 million Upsilon(2S); contained in the two of those samples is a rich subsample of 24 million Upsilon(1S) produced by the charged two-pion transition from the parent Upsilon(3S) or Upsilon(2S) mesons. Taken together, BaBar possesses the world’s most powerful sample of mesons to throw at the question of whether or not there is a low-mass Higgs boson.

This past week, at the Aspen Conference on Particle Physics, BaBar unleashed its first results in the search for the low-mass Higgs decaying into leptons. Presented by Kevin Flood from the University of Wisconsin-Madison, BaBar has performed an extensive search for the process of an Upsilon(3S) decaying into a low-mass Higgs by emitting a photon [2]. This means of searching for the Higgs was first suggested over thirty years ago by Frank Wilczek [3].

In contrast to the CLEO result, which only looked for a Higgs up to a mass of about 3.6 GeV, BaBar went all the way up above the Upsilon(1S) mass at 9.46 GeV. This was important for several reasons. First, simply covering the mass range is critical to conclusively ruling in or out the Higgs. In addition, there are several places in the mass spectrum of specific interest, most importantly the mass region of the bottomonium ground state [4]. Why? Since the bottomonium ground state and certain hypothetical low-mass Higgses share the same quantum numbers, nature lets them mix one into the other. It could be that the state we thought was the bottomonium ground state is mixing with a Higgs, and when it does so it can then decay readily into leptons. We were anxious to see if a “bump” in the muon spectum appeared at that region.

CLEO excluded the rate at which this decay to a Higgs occurred down to the level of a few parts per million, the best limits to date on such a process. BaBar, with just its Upsilon(3S) sample, has improved on the CLEO results in most of their mass range by a factor of two, and above their mass range has set the most stringent limits to date (down to a few parts per million) on a low-mass Higgs boson produced in this way. We see no evidence that the bottomonium ground state decays to leptons, and from this data we conclude that the rate at which the ground state decays to muons is less than 0.8%. The limit curves in the full mass region, and in several zoomed regions, are shown below.

Mining this rich, unique sample of mesons will continue, as we press deeper into space of exotic physics that can be achieved with a precision experiment at the luminosity frontier.

[1] http://arxiv.org/abs/0807.1427v1

[2] http://indico.cern.ch/getFile.py/access?contribId=63&sessionId=15&resId=1&materialId=slides&confId=38534 and available on the arXiv at http://arxiv.org/abs/0902.2176v1

[3] Phys.Rev.Lett.39:1304,1977. http://www.slac.stanford.edu/spires/find/hep/www?irn=241814

[4] http://steve.cooleysekula.net/goingupalleys/2008/07/07/behold-the-elusive-ground-state-of-bottomonium/

January 1, 2009

Book finds

During breaks, I take the opportunity to enrich my bookshelf. One of the best ways to do this is a used book store. There are a few stores that I have completely fallen in love with, for the simple reason that their science sections are out of this world. One of them is in Mountain View, CA, and the other is in Niantic, CT. During this break, I’ve gotten my hands on a few interesting titles that will come in handy in improving scientific communication and expression. In addition, some of them are just a little unnerving. Here I list the titles, authors, and brief synopsis, as well as what I hope to get from them.

“Beamtimes and Lifetimes” by Sharon Traweek:once a tour guide at SLAC in the Public Information Office, she went on to study high energy physicists at SLAC, KEK, and FNAL as an anthropologist. This falls under the “unnerving” category – it is quite strange to see one’s culture dissected and analyzed. However, I feel like HEP needs an eye-opener, if it is ever to reinvent itself in the public eye as a pursuit worth doing both inherently and for its benefits. Particle physicists must understand their own culture if they are to evolve. Amazingly, most of what she describes in the opening prologue and chapter of her book still seem to apply to our culture. She makes particular note of racial and gender ratios in each department she describes.
“Scientific Papers and Presentations”, by Martha Davis: a guide to doing better at each. The quotes opening each chapter are priceless and speak to the humor and delicacy inherent the scientific enterprise.
“Women Changing Science – Voices from a Field in Transition”, by Mary Morse: Over a decade old, this book likely still holds a number of important observations and themes about the diversity of gender in science. A large section of the book is devoted to interviews; I am very interested in seeing how her interviewees describe their experience.
“The Art of the Personal Essay”, by Philip Lopate: replace “personal essay” with “blog entry” and you pretty much see what I want out of this.
“The Universe and Doctor Einstein”, by Lincoln Barnett: I mentioned in my personal blog [1] (in 2006) that over one summer break in high school my father gave me a book about Einstein and his theory of relativity that crystallized my curiosity about the true nature of the universe. It was a short thing, and I am pretty sure this book was it. I grabbed it just to be safe. I’ll have to read through it to be sure, but skipping to the end I recognized the layout of the several equations in the book (all having to do with time and distance in relativity). This was a scene-changing book for me, something I hope to one day use to inspire somebody else to think harder about the universe.

With just days left in most people’s vacation, I strongly urge you to head to the local used book store and dig up your own gems. If the above sound interesting, check the library. You might find them as useful as I hope to.

[1] http://steve.cooleysekula.net/blog/2006/08/18/test-232/

December 16, 2008December 16, 2008

Gravity, Emerging

Full disclosure: the author of the paper I am about to offer for consumption is a friend and colleague. Our paths have crossed professionally once, when he and his then colleagues at UC Davis explored the consequences of some new physics ideas on the decays of Upsilon mesons. These theoretical studies became the basis of about half the proposal I helped co-author which set BaBar on the course for collecting the world’s largest samples of Upsilon(3S) and Upsilon(2S) mesons. His ideas were also tested by the Belle collaboration, earlier in 2006, in a smaller sample of Upsilon(3S) mesons.

That said, I thought I’d recommend some reading for the holidays as you get on planes and bundle up late at night, feeling guilty about going to sleep rather than thinking about physics. Well, here you go – the solution to your OCD: emergent electroweak gravity.

In short, the paper I am recommending [1] goes something like this. What if gravity is not a force to which we should fit all of our understanding of the universe, but instead a consequence of things we already understand about the universe? Specifically, what the author (McElrath) observes is that weakly interacting relics from the Big Bang have been around for so long, interacting so little, that their wave functions have expanded beyond size of the space between any two of them. This means that, like electrons in a cold conductor below the critical temperature, they are in a superfluid state.

When you have electrons in a cold conductor, where most of the electrons in the conductor are in filled atomic shells and thus below the Fermi surface for the material, the conduction band electrons can weakly bond through phonon interactions and form “Cooper pairs”. It was Cooper himself who first observed that ANY such particle in that state, with ANY attractive interaction (no matter how weak), can exhibit this phenomenon. This idea became foundational in understanding superconductivity.

In this paper, McElrath argues that relic neutrinos with their expanded wave functions do experience just such a weak, attractive force through the exchange of a Z boson (the specific manifestation in this case of the Kohn-Luttinger effect). In that case, they must form bound states that are bosonic. One of these he identifies as having properties identical to the graviton. It’s an intriguing idea.

Have safe travels during this holiday season, and take the time away from the humdrum of reviews, ROOT ntuples, and endless meeting after endless meeting, to curl up with a good idea. This might be one of them.

[1] http://arxiv.org/abs/0812.2696