I won’t bother to write up something about the background of today’s MiniBooNE results, since Tommaso Dorigo has already done a better job than I ever could. He also provides a link to where the live feed of the seminar will be, starting at 11am CDT. I’ll be in class at that time, but an hour later will try and attend the local seminar here at Columbia featuring Mike Shaevitz discussing the results.
And the result is….
No mu-neutrino to electron-neutrino oscillations of the sort that would explain the LSND result and require an extension of the Standard Model (beyond giving masses to the 3 known neutrinos). MiniBooNE was designed specifically to look for this, and has successfully ruled it out at 98% confidence level. They do see something anomalous in their data at low energy, but it is not compatible with being due to the kind of neutrino oscillations they were looking for. It’s also true that they just first got a look at this data two weeks ago, still have a lot of work to do to see if there is some sort of background contamination they hadn’t expected at these energies, or something they didn’t know about low energy cross-sections. Maybe it will take them a while to sort this out, but the bottom line is that what they were looking for is definitely not there.
Press release here, paper to come soon.
Update: For an excellent description of the result from Heather Ray, one of the MiniBooNE experimenters, see this guest posting at Cosmic Variance.
Update:
Warning: serious people should stop reading now, the rest is a low form of entertainment.
For something truly hilarious, you really should be following Lubos’s continually evolving misunderstandings of this experimental result, which he has taken as a reason for launching into another bizarre rant about me and Lee Smolin. As near as I can figure out, Lee and I are responsible for the misguided idea of designing an experiment like MiniBooNE to check into the possibility that LSND was seeing evidence of a sterile neutrino. His posting keeps changing (its URL is miniboone-confirms-lsnd, title now “Miniboone Refutes LSND”), with the early versions saying:
Evidence for several types of neutrino oscillations have been known for a decade or more. That includes atmospheric neutrino oscillations, solar neutrino oscillations, and a lab experiment called LSND in Los Alamos.
A simple oscillation in between two neutrino flavors – electron neutrino and muon neutrino – was a natural candidate to explain the observations but it couldn’t explain details of the LSND data which is why the LSND results were questioned. Another natural candidate was a two-flavor oscillation that includes a sterile neutrino, a new kind of neutrino without a charged partner.
Today, Fermilab’s MiniBooNE experiment has confirmed that the LSND results were correct and a more subtle explanation than the simple two-flavor oscillation is necessary. The result rules out the possibility that the observed oscillation is a two-flavor oscillation involving a new sterile neutrino. Their results indicate that there is something surprising that doesn’t fit the most obvious model.
He does seem to have more recently gotten a clue about this and noticed that it doesn’t confirm the LSND results, editing his posting and adding the standard obsessive rant. I see that in his previous posting (about a Harvard faculty meeting), according to him the proposed new Harvard core curriculum states that “All of science education must lead to increasing food production for the working class in the next 5 years [added to please Peter Woit]”.
It seems that I am not only determining the course of neutrino experiments, but also setting the Harvard core curriculum. My powers are truly immense…
Update: Lubos has now changed the file-name from “miniboone-confirms-lsnd.html” to miniboone-refutes-lsnd.html, and deleted the comments from people explaining to him that he was confused. The new version starts off with:
I have erased several comments that only increased the amount of confusion, changed the filename to break links from crackpots’ blogs, and hope that the text below is now more or less OK.
Hi CG,
I was about to write the same as Robert. One should add that this applies for flavour neutrinos with masses smaller than 1/2 times the Z0 mass (somewhere around 45GeV) , you find a very brief summary here. Best,
B.
Thankyou very much Bee and Robert for your comments. I still admit that I find the idea of there only being 3 families very strange, though it is possible that, if there were heavier eigenstates, they might not be stable, ie only the first 3 eigenstates are stable, and hence are observed. Or it is possible that the notion of being able to think of a neutrino as a particle also becomes meaningless after reaching a certain energy because the local structure of space encompassing the object is no longer properly Lorentzian, but I am starting to wander into the realm of the highly speculative here.
Nonetheless, I just want to clarify– since the Z_{0} has a finite energy (~45GeV, you said I think)– surely this limits the analysis of which you speak to the measurement of neutrinos of mass less than or equal to this value? So you could have very heavy neutrinos that you are missing? Or is that a silly question? I understand that the first few neutrino flavours are [[extremely]] light, and a significant mass difference between families 3 and 4 (presuming there is a 4) seems very unlikely.
Alternatively, I suppose, you might have that the transition between Z_{0}’s and eigenvalue 4 neutrinos is forbidden by limitations on how the geometry can degenerate, hence making it possible for mass
(continued from last post)
less than 45 GeV evalue 4 neutrinos to occur, but again this seems very highly speculative.
(for some reason my last post got clipped too, I have no idea why >
My spam filter ate my original response to CG, which I just liberated.
There is some number of generations above which you lose asymptotic freedom, but otherwise, any number of generations is possible. Particles in the second and third generation are already unstable, if there are higher generations they would also be unstable. The only way to get more generations of the same kind as we know now would be if their neutrinos are very massive so that the Z can’t decay into them.
If you start speculating about new generations with neutrinos having completely different properties due to changing the structure of spacetime, you can get all sorts of things, but unfortunately I have to discourage attempts to engage in this kind of speculation here….
CG,
on the issue of the number of generations and number of neutrinos I can only add that the observations of the abundances of Helium and Deuterium (ie the predictions of Big Bang Nucleosynthesis: BBN) actually constrain the total number of active + sterile neutrinos (with some caveat). The SM generations are instead active by definition.
So I would keep the Z decay as the main “argument” for having 3 light SM neutrinos, with BBN being a more general probe.
Incidentally, while it is true that BBN finds roughly 3 neutrinos, some analyses in these days claim that other cosmological probes give evidence for more than 3 neutrinos. The extra ones have therefore to be sterile. But it’s still uncertain ground.
Bee, regarding the cross sections you may be right in having some uneasiness. Maybe one could ask someone in the collaboration for more details.
Best, Marco
Hi Marco,
Maybe one could ask someone in the collaboration for more details.
That’s what I did, but haven’t yet come to any conclusions. Check my blog every now and then, I will try to write something if I can answer that question. Best,
B.
Bee said:
Check my blog every now and then .
Of course! No need to say: I already do so…
Thanks,
Marco
If there turns out to be a fourth generation, it will be discovered at LHC. There are strong constraints on such a fourth generation, but who knows?
so that desperate theorists could move to sterile neutrinos with CPT-violating masses…
That’s what I am afraid going to happen. Everybody whose model is in danger now will jump and add some extra parameters, try to get published before also this window closes …
Here we go, these people really move fast:
http://arxiv.org/abs/0704.2593
CPT and lepton number violation in neutrino sector: Modified mass matrix of neutrino coupled to gravity
Authors: Monika Sinha, Banibrata Mukhopadhyay
Abstract: We study the consequences of CPT and lepton number violation in neutrino sector. […]
The oscillations between different kinds of neutrino
and antineutrino flavor have been observed form solar,
atmospheric and LSND data. The three pieces of observation
indicate three values of mass-squared difference
of three different orders. With three families of neutrino,
one can obtain only two independent mass-squared differences.
Therefore, observations require the introduction
of fourth neutrino which must be sterile in the standard
model. But many difficulties arise with the introduction
of fourth neutrino as discussed in literature (e.g. see [1]).
As an alternate proposal to accommodate the results,
many authors have proposed CPT violation in neutrino
sector [2, 3, 4]. One can either introduce a new particle
(sterile neutrino) or allow CPT violation to take care of
all experimental results with present data. However, very
recently, MiniBooNE results have been declared which
shows that LSND experimental results can not be explained
simply by neutrino oscillation.
Hi
to comment about the Limit from Z0 decays. This limit did not say that you only have 3 neutrinos.
The Z0 width count number of left neutrinos!!
If you have any lighter massive neutrinos then half Z0 mass then you always have 3 effective neutrinos, because the the unitarity constraint.
There is a mistake between flavor eigenstates and mass eigenstates.
If you have very heavy massive neutrinos, above half Z0 mass, then you test steriles neutrinos because the heavier states are suppressed.
The best, Orlando Peres
MINI-BOONE and LSND are correct. In this week appear a paper that says that that can made compatible the negative resulys of MINI-BOOne and positive results of LSND.
They work in 3+2 scenario, with CP violation. why CP violation? because LSND measure anti-neutrinos and MINI-BOONE measures neutrinos.
The paper is http://arxiv.org/abs/0705.0107.
They compute for all parameters the best fit point and found out for a slight non-zero CP phase you can have a stronger suppression of nu_mu -> nu_e probability and non-zero anti nu_mu -> anti nu_e probability.
The values for difference of masses is around 1 eV^2 and 2 eV^2.
the best, Orlando Peres