So, what’s wrong with the CDF measurement of Lambda_b lifetime? June 19, 2007Posted by apetrov in Particle Physics, Physics, Science.
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…