April 1, 2006

MINOS

We’ve got several people, working on MINOS, here at UT. So I should be more clued-in than I am. But I learn from Andrew Jaffe that they have released their first data.

They have measured oscillation between the 2nd and 3rd families of neutrinos and inferred a value of $\Delta m_{2 3}^2= (3.1\pm 0.6 (\text{statistical}) \pm 0.1 (\text{systematic})) \times 10^{-3} \text{eV}^2$. The mixing is also close to maximal.

MINOS results for $\Delta m_{2 3}^2$ v.s. $\sin^2(2\theta_{2 3})$, compared to those of Super-Kamiokande and K2K. (MINOS Press Release)

These are really impressive first results from an experiment which should produce even better results down the road.

PVLAS

For reasons that escape me, both Sean and Luboš have recent posts about the PVLAS experiment which made a splash last summer, purporting to detect vacuum birefringence in a strong (5 Tesla) magnetic field (see also a more recent conference proceedings). This, obviously, suggests an axion-like field, $a$, with a coupling $\mathcal{L}=\dots -\frac{g}{4} a F_{\mu\nu}\tilde{F}^{\mu\nu}$ to photons. But it’s pretty much impossible to reconcile the apparent strength of the coupling, $1.7\times 10^{-6} \text{GeV}^{-1} \lesssim g \lesssim 1.0\times 10^{-5} \text{GeV}^{-1}$, suggested by PVLAS with astrophysical bounds from energy transport in stars and from the CAST experiment (see, e.g., the review by George Raffelt).

That’s not to say that people haven’t tried. Proposing a model in which the aforementioned “axion” is composite, with compositeness scale of a few KeV, built out of preons with electric charges $\sim 10^{-9}e$, and possibly also requiring the photon to have a small mixing with another unbroken $U(1)$ gauge boson, and hoping that the whole Rube Goldbergesque contraption is not already ruled out by a host of existing experiments, is, even the authors admit, a bit of a stretch.

Andreas Ringwald has a review of the status of these proposals. The smart money’s on the experimental result going away.

Posted by distler at April 1, 2006 3:24 PM

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Re: MINOS

Dear Jacques,

to be honest, I have not studied the paper how to evade the astrophysical bounds, and according to your description, I would clearly hate it, too.

Still, if the result of their experiment is real, we will have to explain it, won’t we?

All the best
Lubos

Posted by: Lubos Motl on April 1, 2006 8:12 AM | Permalink | Reply to this

Re: MINOS

to be honest, I have not studied the paper how to evade the astrophysical bounds…

The perils of the blogosphere, eh?

Still, if the result of their experiment is real, we will have to explain it, won’t we?

Ah, youth

Posted by: Jacques Distler on April 1, 2006 9:19 AM | Permalink | PGP Sig | Reply to this

Re: MINOS

And the non-physicists are left to wonder whether or not this is an April Fool’s joke… Watch, one of those equations serves no purpose other than to reveal, when solved, the secret message: “All your quarks are belong to us!”

And look at the comments–is Lubos playing along? “…we will have to explain it, won’t we?” to which Jacques responds, “Ah, youth…” Curiouser and curiouser!

Posted by: Anonymous Coward on April 1, 2006 1:32 PM | Permalink | Reply to this

Re: MINOS

Yeah anonymous, for instance, will we have to explain that the yukawa coupling of top is unity within one sigma?? (as of last month, =0.991 \+- 0.013). It seems we will, but not now nor the next month nor the next year. We will probably sit to be sure if it keeps within one sigma at increased precision after all the tevatron runs and fits, and still we will wait for the LHC to settle a decision about which model should we to use to start with; and then we will try.

Nor to speak of explaining now one experiment with only one measure by an unusual laboratory or team. We will…

Posted by: Alejandro Rivero on April 3, 2006 11:17 AM | Permalink | Reply to this

Re: MINOS

Dear Jacques,

it should be clear that much like you, I would also bet that the “axion” result will go away. But on the other hand, it is certainly not the purpose of physics to make all new results go away. Call this approach immature or blogospheric, for me it will be important anyway.

In this particular case, I feel that all the people who wrote about it - including Sean, me, Chad Orzel, and Natelson plus the commenters - would agree that such a potentially surprising experiment deserves our attention.

There is an interesting possibility that this particular experiment - one of the few things we were told that disagree with the SM - will survive. It is a less likely possibility but this fact is compensated by the property that it is more interesting for new physics.

I am certainly not the only one in theory who has not quantitatively mastered and verified the astrophysical bounds on the axions. Moreover, I still find lab experiments like this one to be a more clean way to learn new physics than astrophysical bounds.

Best
Lubos

Posted by: Lubos Motl on April 1, 2006 7:58 PM | Permalink | Reply to this

Re: MINOS

It could be interesting to compare the reception of “new physics” experiments today against the reception of Lamb Shift in the forties. In that case it can be said that the Shelter Island meetings contributed to get theoretist attracted into the result, but on the other hand one can read the letters from Pauli, far in Zurich, equally excited about it.

Posted by: Alejandro Rivero on April 3, 2006 4:40 AM | Permalink | Reply to this

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