Tuesday, May 21, 2019

CMS: an excess for a \(700\GeV\) Higgs

This is a really short blog post whose main point is a graph showing an apparent excess in an LHC search.

In recent months, I discussed several experimental hints for a new Higgs – a Higgs of mass \(96 \GeV\) and, previously, a CP-odd Higgs of mass \(400\GeV\).

Sadly, none of the values of the masses overlap because in the new paper
Search for 2HDM neutral Higgs bosons through the \(H \to ZA \to \ell^+\ell^- b \bar b\) process in proton-proton collisions at \(\sqrt s = 13\TeV\)
the apparent excess suggests \(m_H=700\GeV\).

Here is a small picture of the graph, Figure 7 of the paper:

on page 13 (or 15/20 by the PDF counting). You see that the excluded portion of the parameter space has two parts, one near the \(x\)-axis (with a heavy CP-odd Higgs) and one near the \(y\)-axis (with a heavy CP-even Higgs).

Some excess, locally comparable to 3 sigma in average, may be seen in both parts. The "symmetry" of the chart indicates that they cannot really distinguish which of the two new Higgs particles is CP-odd and which of them is CP-even. It seems that the grey exclusion curve gets repelled from a point in which one of the new Higgs fields has the mass around \(700\GeV\) and the other one has a mass around \(150\GeV\). The excess with a heavier CP-odd Higgs \(A\) seems to be a little bit stronger.

This is "very likely" just a fluctuation but the number of similarly strong fluctuations of this kind is small enough so that I find it reasonable for each of them – if I can catch it at all – to have a blog post.

The apparent excess isn't discussed in the paper at all, as far as I can see.

If you spend a minute by searching TRF for a \(700\GeV\) Higgs, you will find a text from August 2016 reporting an excess in a similar CMS search, Figure 3 on page 12.

The 2016 search had a very similar channel \(b\bar b \tau^+\tau^-\) as the current search – except that the double-Higgs intermediate state wasn't described or required and the leptons were restricted to taus. Also, the 2016 dataset was just 12.9/fb, the new one has a more impressive 139/fb.

Also, the LHC has previously seen a hint of a \(700\GeV\) shadron or shadrino and, obviously, the \(750\GeV\) diphoton resonance that has apparently gone away.

Interestingly, a March 2015 TRF post mentions a third CMS paper with a Higgs excess near \(700\GeV\) in the quark pair plus lepton pair channel, this time involving one neutrino. This paper had quantified the excesses as 2.56 and 2.64 sigma. However, if the 2015-2016 excesses were due to a signal, both ATLAS and CMS would have spectacular discoveries by now. Maybe they have them, they just hide them. ;-)

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