A new Bs mixing results from D0

A first direct measurement of the oscillation frequency of Bs mesons (for the rest of you out there: Bs mesons are neutral particles made by a b and an s quark, which mutate into their antiparticle and back at astonishing fast speed, through second order weak interactions; their oscillation frequency was not known until a few days ago) was presented a few days ago by the D0 collaboration in La Thuile, where the Moriond conference is taking place in the middle of a nice ski resort.

It has to be said that the measurement is nothing really new: already in 1999 an analysis of old data had concluded that Delta(M) for Bs mesons was (14.8+-2.7+-1.8)/ps (you can find it in D.Abbaneo et al., J.High Energy Phys. JHEP08 (1999) 004 ), and two years ago Cheng-Ju S. Lin had showed -curiously, again in Moriond- that all past measurements could be averaged to a combined world result of 17.3/ps (with a significance of about 2 sigma).  The new D0 result, consistent with both these estimates, and with a significance of about three sigma, is a great confirmation, but not a real ground breaker.

That said, chapeau to D0, who beat CDF in a time rush for the first direct measurement of Bs oscillations.

Now for CDF. We have a better suited detector for B physics measurements – the Silicon Vertex Tracker, a hardware trigger that measures track momentum and impact parameter in 10 microseconds, with a precision close to that achievable offline – and more experience in the field (D0 only installed a silicon vertex detector and central spectrometer for Run II). We have more data on tape, more people working at analyses, more everything – some claim ours is bigger, too. But we lost.

I am not in B physics, luckily, so I can criticize happily my fellow collaborators. But I am not doing it purposelessly: I feel there is something to be said about CDF inertia – and not just the CDF B physics group.

Ever since D0 joined it in the business of Tevatron data collection and analysis (before 1992 only CDF was there), CDF has always had a snobistic attitude toward their cousins: we have a preconception that we do things better, that our results are more precise and more thoroughly checked, that our detector is better built, and that therefore we will win whatever race with them – no need to get ourselves overworked.

It worked for the top quark (we observed the first events in 1994, although we published an “evidence” paper and waited until D0 was just able to join us one year later to publish two back-to-back “discovery” papers), why should it not work for the rest of the big races ?

The publication process of CDF data analyses is baroque, bordering the grotesque. Once a group finalizes their result and presents it at internal meetings, the result has to be blessed. This involves three rounds of scrutiny, the full documentation of the analysis in internal notes, and often the fight with skeptics who like to sit at meetings and play “shoot the sitting duck” with the unfortunate colleague presenting the result. Usually, when an important result is on, the physicists who produced it are asked to perform additional checks of various kinds, and defend it with internal referees. When all of that is through, and not a day earlier, the result can be shown at Physics conferences.

After that happens, one would like to get the result on a Physics journal as soon as possible – to be cited!!! But just then, another much longer nightmare starts, when a process called “godparenting” begins and three knowledgeable colleagues (the godparents) are designated to scrutinize every detail of the work. Then a draft paper is produced, and in the following two weeks all the collaborators can play “shoot the duck” in written form, by sending criticism and demanding yet more checks. Then a second draft follows, and the process repeats…. In the end, usually six months pass between the blessing of a result at the physics meeting and the forwarding of a paper to a journal.

Ironically, CDF was working at their own Bs mixing analysis with a “blind” technique, waiting to collect enough data to be sure of getting a 5-sigma measurement. We do have a better result than D0 in store, but we only know about it – it will take time before we let the world know about it. But one thing I can leak: D0’s measurement is not a fluctuation.