1. 2012

    Why, oh Y(4140) are you so tantalizing?

    Note: I’m posting this from the road, so it will be somewhat lacking in pictures and details. Stay tuned for an update that fills all that in!

    I’ve spent a lot of time poring over the results coming out of the Hadron Collider Physics conference this week, and I’ve noticed a trend. Higgs candidate cross sections are consistent with the standard model. B meson branching ratios are consistent with the standard model. Multijet event counts are consistent with the standard model. Maybe you can see where this is going. Vector boson production rates are consistent with the standard model. CMS rediscovered an unknown particle. Meson masses are consistent with—

    Wait, what?

    Yeah, that happened. CMS announced the second observation ever [PDF] of a mysterious new particle which defies classification.

    This mystery object, called the Y(4140) or sometimes X(4140), was first seen in 2009 by CDF, one of the experiments at the Tevatron. It wasn’t just a slight fluctuation, either; the CDF data excluded the background-only hypothesis at more than a \(5\sigma\) level, which is the threshold physics uses to define a proper discovery. Certainly much ado has been made about less strong statistical …

  2. 2012

    Extra! Extra! Higgs results from HCP 2012

    The Hadron Collider Physics conference is nearing its end now, and that means one thing: Higgs results! The LHC collaborations have just presented their updated measurements of the Higgs boson candidate whose discovery was announced in July, based on the \(\SI{7}{fb^{-1}}\) of new data that was collected in late summer.

    I’ll jump straight to the punch line: what they see is mostly consistent with the new particle actually being a plain old standard model Higgs boson (although it’s not absolutely confirmed yet). Which is kind of disappointing, because it indicates a lack of exciting new stuff to discover. Back in July when the discovery of the particle was originally announced, there were some slight discrepancies between the results obtained by the experiments and the predictions, and a lot of physicists were hoping that was a hint at something new and unexpected, but it’s looking more and more as though that is not the case.

    Anyway. On to the results. As in the original announcement, ATLAS and CMS are searching for the Higgs in five different channels: they’re trying to detect five different sets of particles that the standard model Higgs boson can decay …

  3. 2012

    B meson decay and the calculation of cross sections

    Now that I’ve finished my quest to identify the misbehaving sinc function, I can bring you the latest news from the Hadron Collider Physics conference in Kyoto, Japan. This is a major conference at which several new results from the LHC experiments are being announced — an exciting time for the physics world indeed!

    B meson-muon decay

    The most interesting result to come out of the conference so far is an observation by the LHCb experiment of a \(\mathrm{B}^0_s\) meson, made of bottom and antistrange quarks, decaying to a muon-antimuon pair. This is a reaction that physicists have been searching for since 1987. This year, the LHCb collaboration has actually seen it happen — or at least, they’ve collected enough statistical evidence to be fairly confident (\(3.5\sigma\)) that it does happen — for the first time.

    It’s not quite as dramatic a discovery as that makes it sound, though; the reason \(\mathrm{B}^0_s\to\mu^+\mu^-\) has never been seen before is that it’s incredibly rare. B mesons are not exactly easy to produce, and then once you’ve got one, the standard model predicts that only one out of every 300 million will …