Friday, January 07, 2022

CMS: another bump at \(2.9\TeV\)

This is a very short comment consolidating some LHC events with the apparent mass near \(2.9\TeV\). In the early September 2015, I mentioned a record-breaking CMS event with an electron-positron pair and the invariant mass of \(2.9\TeV\). It was very unlikely to have such a high-energy event at that time. It attracted some phenomenological papers e.g. this one.

At the end of the same month, I mentioned an \(2.9\TeV\) ATLAS event. But confusingly enough, it involved two muons and a jet so the particle would have to be colored i.e. QCD-charged.

But interestingly enough, there was another fluke at ATLAS, in April 2017. Locally, they had a 3.3-sigma \(ZH\) evidence in favor of a \(3\TeV\) boson.

Finally, we are returning to the present. In a fresh today's paper,
Search for high-mass resonances decaying to a jet and a Lorentz-boosted resonance in proton-proton collisions at \(\sqrt s = 13\TeV\),
the CMS collaboration (see the first paragraph of Results, page 7) found the most significant excess worth 3.2 sigma locally, and it is at \[ G_{KK}=2.9\TeV, \qquad m(\phi)=0.4\TeV. \] It is consistent with a Kaluza-Klein gluon, so it would also be a colored particle, compatible with the previous mu-mu-jet ATLAS event. So this could be consistent with the mu-mu-jet event from another detector: a potentially independent confirmation of a new colored particle at \(2.9\TeV\). Note that it can't be the same thing as the electron-positron event because the latter is color-neutral.

Strangely, \(2.8\)-\(2.9\TeV\) is also the interval where the KK gluon could be studied by the LHC according to this 2007 (!!) paper. So maybe some excess is piling up because of some subtle reasons that they understood in 2007 but not the experimenters recently. It would be strange if the 2007 paper predicted the KK gluon mass in this bizarre way. It would suggest that the streetlight effect is not a bias. ;-)

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