Wednesday, October 31, 2018

CMS excess: a dimuon resonance of mass \(28\GeV\)

Well... the dimuon resonance depends on an extra bottom quark that has to be produced
Aleph at LEP seems to agree with the excess!

The Proton Smash (Halloween)

The Guardian just has published an article by Ian Sample that was useful for me,
Has new ghost particle manifested at Large Hadron Collider?
because I have missed the August 2018 preprint
Search for resonances in the mass spectrum of muon pairs produced in association with \(b\) quark jets in proton-proton collisions at \(\sqrt s= 8\) and \(13\TeV\)
You may see the excess on Figure 1, Page 5 (7/35) of the preprint above. For the invariant mass of \(\mu^+\mu^-\) slightly below \(30\GeV\), you simply see a clear excess. All the events are required to produce a \(b\) quark jet along with the muon pair. They divide the excess to two signal regions, SR1 and SR2, according to \(|\eta|\). When it's below or above \(2.4\), the local significance is 4.2 and 2.9 sigma, respectively.

If you round those to 4 and 3 sigma and if you know the most famous example of the Pythagorean theorem, you may see that the combined local significance of this bump is almost exactly 5 sigma. Strangely enough, however, the large excesses I just mentioned only occurred in the \(8\TeV\) collisions. In the \(13\TeV\) collisions, there were +2.0 sigma excess and –1.4 sigma deficit in the two signal regions.

But it gets better than that. In the 1990s, the Aleph detector at LEP – the electron-positron collider that used to live in the same tunnel as the LHC today – saw an excess in ("almost") the same channel and the same mass:
Observation of an excess at \(30\GeV\) in the opposite sign di-muon spectra of \(Z\to b\bar b+X\) events recorded by the ALEPH experiment at LEP
I have no idea how we could have overlooked – or how I could have forgotten – about that 2016 preprint because Aleph has claimed the local significance to be 5 sigma (wow). The mass of the dimuon resonance is said to be \(30.4\GeV\) at LEP, vaguely compatible with the CMS observation.

It is not clear to me why the excesses from Aleph and \(8\TeV\) CMS, if real, should weaken, disappear, or get inverted at \(13\TeV\). But there could be a subtle story. CERN's Alexandre Nikitenko says that "the backgrounds are perhaps stronger at higher energy" which makes the signal look weaker there. The uncertain tone of that sentence puzzles me: Didn't they have to calculate what the backgrounds actually were before they wrote the paper? ;-)

Climate Mash, this cute video with the original voice, was released (as Flash, mostly dead now) in 2005, just months after some very big hurricanes (that failed to repeat so far) and exactly 13 years ago. Thankfully, the climate alarmists haven't done much to harm the civilization in these 13 years and their climate-powered attacks on Donald Trump aren't significantly different from those against George W. Bush (and Dick Cheney). When it comes to policies, the alarmism has mostly kept the status of an inconsequential religious ritual.

For a musically weaker fresh HEP remake, listen to The Proton Smash which is embedded at the top.

Most such anomalies go away, I think that this one is also more likely than not to go away (partly because its behavior at the highest energy is strange), but if we were discarding these things automatically, the experiments would be useless. So I, for one, will surely observe the fate of this anomaly. Will ATLAS confirm it? Note that the CMS has used 20/fb at \(8\TeV\) plus 36/fb at \(13\TeV\). For the latter dataset, CMS already has a quadrupled amount of data, so it could double the significance if the effect were real. So even the 2.0 sigma excess at \(13\TeV\) could grow to 4.0 sigma (plus minus something).

The Aleph-CMS combination, if we make it informally, is already enough for a claim of a discovery!

The Guardian makes the claim that theorists are generally excited while experimenters are grumpy and skeptical when such anomalies appear. It is so true. I am often closer to the experimenters but I think it's really a natural duty for a scientist to follow some promising anomalies even if he thinks that the probability that they will be real is well below 50%. So I will follow it.

The dimuon anomaly at \(28\GeV\) is analogous in significance to the diphoton anomaly at \(750\GeV\) a few years ago. I think it would be very healthy if we saw an avalanche of the papers trying to explain the possible \(28\GeV\) dimuon anomaly (a Russian paper already links the anomaly to the anomaly of the muon magnetic moment). Sadly, people have been discouraged from doing this kind of serious work. On top of that, CERN and others have been partly occupied by cultural Marxists who "suspend" the skillful people (I mean Alessandro Strumia) who are actually most capable of making research of that kind.

While the anomaly is as cool and exciting as the diphoton anomaly was, we may be forced by some evil forces to be grumpy this time. What a shame. Does it really make for the community to run a collider if analyses of the most interesting anomalies are discouraged and labeled politically incorrect?

At any rate, Alexandre Nikitenko and Yoram Soreq give a CERN talk on Thursday 1 pm dedicated to these anomalies.

Electron's charge, bonus

See Harvard Gazette for a story about the most precise measurement of electron's charge so far, by Harvard's John Doyle et al. (ACME). Via Willie Soon

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