Was reported here. Of course if this is real it is very exciting. It leads me to the question: given that it took so long to find this resonance at a meager 38 MeV, is it possible that all SUSY particles are hiding down in the MeV or KeV range (or lower)?
It is not possible that SUSY particles are hiding in keV or MeV range. In particular, there can't be any new charged particles (and similarly new color-charged particles) that would be this light because they would be easily pair-produced and easily detected.
The first (February 2012) claims by different authors (the original ones, Rupp and van Beveren, who made the conjecture) were refused by the COMPASS collaboration (which was used as one of the main pieces of "evidence") here:
COMPASS says that the patterns that attracted the attention or Rupp and van Beveren are due to $\pi^0$, $\eta$, and secondary interactions in the COMPASS spectrometer. Rupp and van Beveren responded that the COMPASS critique is internally inconsistent. It seems more likely to me that COMPASS is right.
The newest Russian experimental paper looks strange to me. For example, it never quotes any confidence levels, as far as I can see, and instead says that there are "almost no errors" in their measurement, a claim that it easily refuted by looking at their chaotic wiggly charts.
An extended discussion may be found on my blog.
I would have loved to put this reply directly under Eef's reply above, but I didn't figure out how this page works quickly enough.
Eef, when you're describing what COMPASS has done, I think that you are misrepresenting our work. We didn't do a MC simulation of the E(38) or of this effect, as you seem to claim. Instead, we ran our usual MC simulation, not including any backgrounds, and then saw a bump appear in exactly the right place. We understand this MC bump as being due to the material in the detector -- basically, $\pi^0$s produced in secondary hadronic interactions downstream of the target will appear as low-mass bumps in this spectrum. Depending on the distance from the target these bumps will have different masses. Therefore we can associate the "mass" of the bump with a specific distance, and lo and behold we find some material in the right place for 38 MeV. The exact height of the bump is of course dependent on the backgrounds present in real data, which are not taken into account in this simulation. For this reason we made the statement that "the COMPASS data do not confirm the existence of this state." (quoting 1204.2349).
In this regard I'm in perfect accord with my co-authors.
You say that you are siding with COMPASS.
However, that is an ambivalent statement.
COMPASS first released the opinion that the signal at around 40 MeV is an artifact of their methods of analysis and their equipment. Since I have no access to their methods and equipment properties, I had to accept such statement. Although I was not convinced.
Later, COMPASS released a Monte-Carlo simulation of the artifact. I showed that that simulation only explains a very small contribution (of about 10 percent) of the measured signal. The main author of the simulation agreed, in private while at a COMPASS meeting in Lisboa, with my observation.
So, with which COMPASS do you side?
Furthermore, the Dubna group consists of several excellent researchers which, moreover, work on new and unique equipment for photo-photon physics.
User1247 pointed out my mistaken reading of the scale in a previous answer, now deleted.
Fortunately I found a pi0 mass plot in LHCB which shows that there is gamma gamma mass resolution to clear this point about a 38 MeV diphoton resonance.
By now they could provide us with a definitive plot.
The paper has been retracted.
Due to non ordinariness of the obtained results (standing out of The Standard Model) and at the request of co-authors the first version of the article is withdrawn for further verification and more detailed description of the experiment and data analysis. The second version is being prepared.