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Lifetimes of heavy baryons November 10, 2006

Posted by apetrov in Particle Physics.
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Sorry, but this post is kinda technical… There is a new measurement of Lambda-b lifetime in semileptonic decays provided by DO collaboration at Fermilab (their preprint is here). This measurement gives a new number for this lifetime, t = 1.28 ± 0.12 (stat) ± 0.09 (sys) picoseconds. This is a very short time on a scale of things (it takes about the same time for light to move the distance of about a thikness of human hair). But it is also short on the scale of other lifetimes of b-flavored hadrons. In fact, according to this measurement, the ratio of Lambda_b lifetime and a neutral B-meson lifetime is 0.86 ± 0.11, if my math is right (why don’t they just provide this number in the paper!). It is consistent with D0’s previous measurement of that ratio in fully-reconstructed decays is 0.870 ± 0.102 (stat) ± 0.041 (sys).

Now, why did I want to write about that? Well, for starters, it agrees well with our predictions for this ratio,  0.86 ± 0.05. But it does not fare well with the recent CDF number, 1.037 ± 0.058 (results are here), obtained in a fully-reconstructed analysis. Over summer, some of my experimental colleagues even suggested to me to try to understand the reason why this ratio must be one. Well, I kinda like my number…

Maybe someone from CDF could explain to me if this is a statistical fluctuation on their side or there is something more to it… 

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