UPDATE: before you read the text below, one useful bit of information. The author of the analysis described below is not a member of ALEPH since 2004. He got access to the data as any of you could, since the ALEPH data is open access by now. There would be a lot to discuss about whether it is a good thing (I think so) or not that any regular joe or jane can take collider data and spin it his or her own way and claim new physics effects, but let's leave it for some other post. What is important is that ALEPH is not behind this publication, and members of it have tried to explain to the author that the claim was bogus. Indeed, on the matter of the source of the signal: it is clearly spurious, as the muons are collinear with the b-jets emitted in the Z decay. A plot in the paper indeed shows that the pt_rel of the muons is what you should expect from semileptonic b decays... but this is rather technical so let's leave it at that.

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Funny as it is always the usual suspects. ALEPH had a reputation for anomaly chasing in the past, and apparently members of the collaboration, although nowadays dispersed in other experiments, continue to show the clear signs of bump-happiness that distinguished them in the LEP era.
What am I talking about ? ALEPH is one of the four experiments that instrumented the Large Electron-Positron collider, LEP, a machine constructed at CERN in the late eighties to study the properties of the Z boson. 
The four detectors collected 16 million Z boson decays (a number now collectable in just a few days by the LHC, but back then unprecedented) and studied electroweak parameters with great precision in the nineties; then LEP got upgraded to LEP II, a more powerful machine which could reach the center-of-mass energy of 208 GeV. The hope was that by increasing above the Z mass the collision energy, associated ZH production events would show up. 

Unfortunately, 208 GeV were less than the required 91+125=216 necessary to produce in significant amount the Higgs, and the machine was dismantled to leave space for the Large Hadron Collider in the same tunnel, in 2002. But not without vocal opposition from who else but ALEPH collaborators, who swore to have seen the first hints of the Higgs at a mass of 114 GeV, with over 3-sigma significance... That claim was later revised to a mere 1.7 standard deviations effect, when the LHC construction had in the meantime happily started. But I am divagating. 

So, ALEPH. Aleph saw a 4-sigma excess of 4-jet events when LEP II was still ramping up its energy, in 1996. The claim of seeing a new particle signal was never made too explicitly - if I remember correctly, the collaboration only spoke of evidence in its publication; other experiments did not confirm, and the matter ended there. But Aleph also saw other signs of new physics in its otherwise illustrious career. One example was a signal of sbottom quarks in the summer of 2000, in confirmation of an anomalous excess of dijet events with multiple leptons seen by CDF. That story is told in chapter 12 of my recent book "Anomaly", so I will again leave the topic here.

And now, 14 years after the shutdown of LEP II, somebody by the name of Arno Heister, an Aleph collaborator, resurrects the Aleph data to claim that it contains a dimuon resonance. The single-man analysis is described in a preprint published today in the Arxiv. Basically the search looks for Z->bb decays in LEP data, and reconstructs the invariant mass of opposite-sign muon pairs. A wiggle in the mass distribution at 30 GeV is interpreted as a signal, and a lot of pages of the paper are spent describing how the wiggle has a discovery-level significance, or almost like it.

One thing I found strange is that the paper only discusses 91-GeV data -i.e., data collected by LEP, not LEP II. One would think that the higher center-of-mass energy would help in the search of heavy particles, but maybe this need not be the case here. Anyway, the analysis is rather thorough, and seems to address many of the questions one would normally ask in these cases. The signal seen in dimuon data is paralleled by a smaller signal in electron-positron events.  The money plot - or maybe, just one of them - is shown below. On the left is the mass spectrum of dimuon pairs, on the right the spectrum of dielectrons.




A number of checks are described, as well as a lengthy discussion of the significance. When all is said and done, taking into account the look-elsewhere effect on mass search range and allowed signal shape (i.e. the natural width of the resonance, which is kept floating in the fits), the author estimates an effect of about  3-sigma significance. Not an observation-level claim, no, but an interesting one. I am sure many of my colleagues will amuse themselves reading the paper this weekend or in the next few days.