Sunday, July 17, 2011

Lattice 2011, Day Five

Sorry for the delayed update; I was too tired to blog last night.

The first plenary of the fifth day started with a talk by David Kaplan with the intriguing title "Listening to Noise". The topic of the talk was in fact noise, which of course affects baryonic correlators particularly badly. Studying unitary fermions as a toy model, David Kaplan showed that the distribution of the measured correlator values approaches a log-normal distribution, i.e. their logarithms approach a normal distribution. Exploiting this, one can attempt to use the cumulants of the measured distribution to extract an effective mass with reduced noise, and this does indeed work in the case of unitary fermions. For QCD, additional tricks may be needed.

The next talk was given by Kostas Orginos, who gave a review of hadron interactions on the lattice. This is still a very difficult problem, and new and better methods will be needed to make progress.

The last talk before the break was on a non-scientific topic, namely the situation in Japan after the great earthquake, presented by Shojo Hashimoto. Besides the terrible loss of life and the large number of people made homeless by the tsunami, the subsequent nuclear meltdown at Fukushima has further worsened the impact of the disaster. Not only have numerous towns been contaminated by Cs-137 (it takes a real physicist to show a curve of the measured radiation and remark upon the perfect exponential curve described by the decay of I-131), but also the power supply has been adversely affected by the shutdown of the nuclear power plants; a shortfall of 10-15% is expected in the summer, and hence power-intensive scientific facilities such as PACS-CS can only run at night. The US and the UK have stepped into the gap and have donated computer time on their machines to Japanes colleagues.

The second plenary was devoted to flavour physics. Enrico Lunghi spoke about the tensions observed in the unitarity triangle fits between sin(2β) and the branching ratio B --> τν, in (g-2)μ, φBs, and the branching ratio Bs --> μ+μ-. The LHCb experiment should be able to clarify the situation soon.

This was followed by a review of heavy-flavour physics on the lattice by Christine Davies, who summarised the different approaches (NRQCD, HQET, Fermilab, relativistic heavy quarks on fine lattices with highly improved actions) and results for the charm and bottom masses and the decay constants and form factors of charm and bottom mesons, as well as for the B meson mixing parameters.

The plenary session closed with the invitation to LATTICE 2012 to be held in Cairns, Australia, from 24th to 29th June 2012.

In the afternoon there were parallel sessions one last time (this included my own talk in the last possible slot).