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Xi_b mass comparison June 16, 2007

Posted by dorigo in news, physics, science.

The recent discovery of the new Xi_b baryon has been announced first by D0 at Fermilab on June 12th, and then in a back-to-back seminar of D0 and CDF findings, which was given yesterday at the usual place – the “wine and cheese seminar” at 1-west in Fermilab’s Wilson Hall.

The mass of the baryon is in good agreement with theoretical estimates, which – for heavy hadrons – are relatively easy to make and less error-prone, because the large mass of the heaviest quark in the bag (the bottom quark in this case, but the same goes for charm-quark hadrons to some extent) makes the system easier to model.

So let us compare the findings of D0 and CDF with theory. A picture is worth a thousand words… Here it is:

As you can see, the two measurements are in agreement with the theory bands. CDF has by far the more precise determination, thanks to its better measurement of track momenta (in particular, muons in this case).

I will have more to say soon about the details of the analysis procedure, but now I am off to a weekend in the dolomites… 

Ok ok before I go: here are two plots from CDF. The first is the mass of J/psi Xi combinations – the signal which provided the mass measurement in CDF. The second is the mass of Xi_c pion combinations, one that has not yielded a mass combination yet. CDF will improve its analysis with these latter decays!


1. Kea - June 17, 2007

What’s with the black bits on the D0 (er, rather large) error bars? OK, maybe I should look at their paper….

2. Gordon Watts - June 17, 2007

Sys vs stat error. So, I have to ask, and sorry if this is a bit snarky (it isn’t meant to be) — but why didn’t CDF submit a paper for this? What part of the analysis is missing?

3. Louise - June 17, 2007

A new baryon is very exciting!

4. dorigo - June 17, 2007

Hi Kea, yes, as Gordon explains, the black parts are the additional error due to the quadrature of stat + systematics, the inner bar is only statistical.

Gordon, I think the authors wanted to put together the all-hadronic decay mode (which, as you’ve seen, does not quote a mass yet, mainly because of different systematics from the two-track SVT trigger) with the other result before publishing. As always, CDF acts as if we are the only ones doing this business 🙂

Yep Louise, filling the gaps in the quark model gives a sense of understanding the structure of matter few other things do.


5. Fred - June 18, 2007

Just curious, but why don’t we have the media hoopla that accompanied some recent events that were considered rumorish? I googled news and found several related articles but many copies of the same.

6. dorigo - June 18, 2007

I have no idea Fred, but finding Xi baryons is not nearly as much a news as finding the Higgs… I guess it did not cross the line of media interest.

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