Symmetry factor

Grigori Perelman, the guy who (a) proved Thurston’s geometrization conjecture (and, along the way, the famous Poincaré conjecture), (b) was awarded the Fields Medal (the “Nobel Prize of mathematics”), but declined to accept it, (c) is eligible for a $1M Millennium Prize from the Clay Mathematics Institute, but did not claim it, is somewhat of a strange celebrity in Russia. When he sent his papers to ArXiv (and the proofs were checked and found correct), the press was all over him, but he just hid from all the attention in his modest St. Petersburg appartment — and even stayed inside there without going outside! Now, that’s unusual…

Now that press turned their attention to bigger and better things (like Paris Hilton’s affair), he apparently got the long-sought rest… not quite, at least in the geek community! Some fellow (user of LiveJournal) spotted him in St. Petersburg’s subway and snapped some pictures of him (see here). Of course, they will never appear on front-page of CNN or other major news outlets — there is no way that the life of a great scientist is more interesting than the life of a teenager charged with DWI…

My question here is this: what makes people tirelessly watch Paris Hilton or
Britney Spears as they go by their lives, drinking and/or partying? Is it some sublimation of a natural human desire of having everything but doing nothing? Maybe someone should release a computer game “Find Perelman”, where one has to analyse clues, locate the mathematician and convince him to accept his Fields Medal… kinda like “Myst“… This should bring some attention to math… but of course I’m just mumbling…

Today a new preprint from D0 collaboration appeared on ArXiv. They report on a new measurement of Lambda_b-baryon lifetime, working with semileptonic channels of Lambda_b decay. There is something about that baryon.

First, for a number of years (I’d say about 10 years) there was a sizable discrepancy between theoretical predictions and experimental measurements of this lifetime (now, realistically people compared ratios of lifetimes of this baryon and neutral B0 meson — the reason being that many theoretical and experimental uncertainties cancel out in that ratio). This problem seemed to be sorted out a couple of years ago after this paper, which included up-to-date perturbative and non-perturbative corrections to the ratios of Lambda_b and B0 lifetimes and included all previous theoretical updates. The final prediction is 0.86 +- 0.05, which overlaps nicely with the world average of experimental results of 0.80 +- 0.05. This corresponds to the current world-averaged lifetime of Lambda_b-baryons of 1.230 +- 0.074 picoseconds  — that’s a really short lifetime on a human scale of things!
Then, as nicely reported by Tomaso here, CDF had a new number for this lifetime, 1.593 + 0.083 - 0.078  +- 0.033 ps, which is clearly quite a bit above the world-average. Moreover, it is also larger than the D0 number in the same decay channel. Now, today, D0 provided a new number, in a different decay channel (semileptonic), 1.290 + 0.119 - 0.110 (stat) + 0.087 - 0.091 (sys), which is more consistent with the old expt world average (and theoretical predictions) than the CDF’s large number… even given the larger error bars (which is a manifestation of a more challenging measurement when your decay channel involves a neutrino). So, can there be something wrong with the CDF result (or it’s just a statistical fluctuation)… or all other results are fluctuations and CDF is right?

Now, of course they are all consistent at some level… yet it’s interesting that CDF comes out on the upper side of things…