Experimenters at the Tevatron have released data showing the existence of a new baryon, built out of a down, strange and bottom quark, and having a mass of 5.774 +/- .019 GeV. It has been given the name “Ξb“. The FNAL press release is referring to this as a “triple-scoop” baryon, since it contains one quark from each of the three generations. Tommaso Dorigo has a new posting about this.
Postings on this blog tend to involve a certain amount of discussion of bad behavior by theorists, so I guess I should point out here that this story comes with some accusations of less than good behavior by experimentalists in the way this was announced. The press release is all about the announcement of this discovery by the D0 experiment, and about their paper, which was submitted to the arXiv Tuesday night. It turns out though that D0’s competition, CDF, also has had the same result for a while, and it had already been “blessed” but not officially announced. So CDF was “scooped” at the last moment for the “triple-scoop”, and I imagine there are dark accusations going around about how D0 might have found out about this and rushed out the paper and press release. Supposedly there is an informal one-week notification period that the two experiments normally observe to keep this kind of thing from happening. Anyway, looks like they’re trying to fix it up a bit: the FNAL web-site contains a “special announcement” of back-to-back seminars about this, D0 at 1pm, which will “immediately be followed” by a CDF seminar. The D0 seminar is called
First observation of a new b-baryon, Ξb
whereas the CDF seminar is entitled
Observation of a new b-baryon, Ξb
It should be down, strange, and bottom quark.
I remember similar behavior concerning the upper bound on
the number of light neutrinos in the late 80’s. The SLC (sort of
the ILC scheme, except the two beams came from the same machine)
at SLAC had a very small number of events (I think less than 30). Some people at Fermilab were also working at the SLC detector (I forgot the official name) and made sure to get their results out first. Shortly
therafter the SLC was dismantled.
I guess I’m trying to figure out exactly what the result or relevance of finding this particular particle was. I think I get what they found, and I get that it’s historically impressive, but I’m not sure what it means for physics.
Is the idea that the fact this particle exists is a surprise, and gives theorists some new work in explaining how it’s possible? Or was this something they were hoping or planning to find, which validates a prediction of some previous bit of theory? Is the idea that now that this weird crossgenerational baryon has been found, they can do some experiments to explore its properties and thus maybe learn something new about the exact nature of the mysterious quark generations? Or is the spirit just “Golly gee gosh, look at this weird-looking thing that we got to come out of the accelerator”? (Note that I’m not saying this last possibility is at all a bad use of research time.)
Also, does the existence of this thing mean they have to modify any of those nonets or decuplets or whatever that they use to classify hadrons?
the place of this “cascade-bottom” in the baryon multiplets has been known since long – see at Physics News Graphics for a graphical representation of the respective multiplet:
I would be surprised if anything had to be modified in this scheme. The point is, of course, that most of these baryons have not been observed yet, although probably no one doubts that they exist.
Interestingly, the Particle Data Group already lists the Cascade-bottom, if only as a “1-star” particle (meaning “Evidence of existence is poor” – see pdg.lbl.gov/2007/listings/s060.pdf). These first hints at its existence were found about ten years ago in the DELPHI and ALEPH experiments at CERN, but there seems to have been no mass determination at that time. It would be interesting to know how the Fermilab results fit to these earlier data.
I don’t know if this is possible in practice, but it may be interesting to compare the now measured mass of the Xi_b with lattice calculations – for the bottom-charm meson B_c, there has been a quite spectacular agreement between lattice results and experimental data (see e.g. Physics News Update 731, May 2005). Moreover, all kinds of quark potential models used to describe the properties of hadrons work best for heavy quarks such as the bottom. So, it may be possible to check some predictions of these models against experimental data.
To paraphrase Tom Lehrer
Although, D0 is at Fermilab too….
Hmm. Triple-scoop. Must have ice-cream.
I hope that you tolerate an off topic post, Professor Woit.
Someone claiming to be Lubos Motl says that he is leaving science. In the comment area on Tommaso Dorigo’s blog
I apologize if it turns out to be a hoax. I think that I have always been surprised by the vitriol from this man. But at the same time I think that the criticism against string theorists should have always sound more like “you thought outside the box on a tough problem but you are a valuable scientist and you should move on to another approach” and less like “we think you are an idiot.”
Lubos has been saying for a while that he was leaving Harvard after this academic year, and I gather that that’s what’s happening. I don’t know what he intends to do, but perhaps he’ll keep doing physics, just not at Harvard.
Yes, Lubos is “retiring”, but he will continue to think about science. And I bet a dime or two he’ll continue blogging about it too!
So does this mean that Lubos was denied tenure at Harvard?
Lubos is leaving a tenure-track job at Harvard, but he hasn’t been there long enough to have reached the point where they would have to decide about tenure.
I thought assistant professor jobs at Harvard were NOT tenure-track? (ie. To get tenure at places like Harvard, one has to actually apply and compete for a separate tenured job opening? At other less prestigious places, it’s largely an administrative change of job title after a committee review. )
I don’t know exactly how things work at Harvard, but I was under the impression that assistant professor position’s like Lubos’s are nominally tenure-track, although mostly they don’t lead to tenure, and people who accept them are well-aware of this. There are several highly prestigious places in the US like Harvard where most senior hiring is done from outside, but typically there is a tenure-track system in place, even if most people in it don’t actually get tenure.