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CHARM-2007: day 2 *August 8, 2007*

*Posted by apetrov in Particle Physics, Physics, Science.*

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Here is the day two of the CHARM-2007 conference. The day started with Brendan Casey talking about rare D-decays. This is quite interesting, since these decays are sensitive to indirect effects of new physics. Among other things, he talked about D_s decays to fully leptonic final states. These decays are rare not because they are generated by quantum effects (so-called penguins), but simply because of the structure of weak interactions inducing the so-called helicity suppression of the decay — the decay probability is proportional to square of the lepton mass in the final state. This means that the largest decay probability would be for tau+tau-neutrino final state. The interesting this about that transition is that it is also sensitive to effects of the charged Higgs, required in supersymmetric extensions of the Standard Model. He reported on the ratio of Ds -> tau nu/Ds -> mu nu decay probabilities corrected for the kinematical effects and took a ratio of that ratio (he-he) to the theoretical calculation. I cannot verify this at the moment (I cannot look again at his transparencies), but he says it is 0.78 +- 0.12, which is away from expected unity. This might mean that there is a charged Higgs contribution there (I’m speculating). There were also talks by H. Muramatsu and Fred Harris (for R. Ping, who didn’t get his visa) on charmonium decays. In particular, it was reported on the status of the so-called “rho-pi” (or 12%) puzzle. Then Zaza Metreveli gave a great talk about spectroscopy and ways of using it for things like measuring strong coupling in charmonium decays.

The second installment was more theoretical. It started with Estia Eichten’s talk on charmonium states above threshold — he talked about the weird X(3872) state and various ways of explaining it. He didn’t like our cool paper on the subject. Bob McErlath talked about new physics in heavy quarkonium decays. I was surprised to learn that there are essentially no model-independent constraints on the neutralino mass, one of the primary candidates for the Dark Matter particles in SUSY (it has to be heavier than 2 eV to insure that dark matter is dominated by its cold component). In fact, he claims that it can be so light that heavy quarkonium can decay into it. Who knew… Nora Brambilla talked about theory of extraction of mass and strong coupling in heavy quarkonium decay in non-relativistic QCD. It’s been kown for years that the definition of quark mass in QCD is not trivial, as quarks never appear as free states due to confinement. So one needs a convenient definition — and there are several. Jo Dudek gave a nice talk on radiative charmonium decays in lattice QCD.

After lunch there were many talks on hadronic decays of charmed mesons. Jon Rosner talked about extraction of strong phases with U-spin triangles (U-spin is a subgroup of flavor SU(3)). Alex Bondar gave a telephone talk about his elegant method of extraction of phase gamma (or phi_3 in Japan) in B decays to charmed meson with D-meson Dalitz plot analysis. We also had talks on various ways of doing Dalitz plot analysis. The problem there is more of the “memory” than physics — Dalitz plot analyses were popular in the sixties, so not so many people are fully versed in those analyses nowdays. In particular, the simplest analysis that is done by many people nowdays (using the so-called isobar method) violates unitarity.

Stay tuned for day 3 and final day of the conference.

I’m not sure it’s entirely fair to say we’ve forgotten how to do Dalitz plot analyses since the sixties. My understanding is the work of that era had very different goals (looking for C-violation in eta decays, for instance); today we’re much more focused on intermediate resonances, and the technology to simultaneously have such interpretations and preserve unitarity is, I believe, still hotly debated.

Great conference coverage – I’m slowly reconstructing what happened…