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Thursday 14 March 2013

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...as it turns on two light bulbs less often than expected...

OK, I was inspired by this title of an article about Pope Francis. But you should have no doubts about it: the Higgs boson is even more humble and obedient than the Indian-born Argentinian chemist and the son of a railway worker who was just chosen as the new Bishop of Rome by puppets of Hugo Chavez who controlled the job contest from Hell.



What I want to say is that the anomalously high chance that the \(126\GeV\) Higgs boson splits into two photons, \(h\to\gamma\gamma\), is no longer anomalously high. ATLAS and CMS used to suggest that the rate could be up to \(1.8\) times the Standard Model prediction. However, ATLAS updated the figure to something like \(1.5\pm 0.3\) (which is pretty much one) a week ago and today, CMS updated its results and the new value is even lower than expected, \(0.8\pm 0.3\). Calculate the ATLAS+CMS average and you will find out that the decay rate is what it should be within less than one sigma.

Lots of experimental LHC papers were recently published that demonstrate that all measurable properties of the Higgs boson agree with the Standard Model within the error margin that is getting smaller. Of course that the agreement won't be quite perfect but the deviation may turn out to be much lower than what the LHC may resolve today.




Many phenomenology papers were written in the recent year that were inspired by the possibility that the diphoton rate is higher than it is in the Standard Model. The announcement today shows how shaky such a motivation usually is. You may be attracted by 2-sigma bumps if you don't see any excesses that are more significant. But chances are very high that even this only excess above the simplest theory that you observe is just a fluke. It was almost certainly the case of the Higgs diphoton branching ratio, too.

Experimental anomalies are usually flimsy foundations for new theories, especially if their statistical significance is unimpressive. Only robust top-down arguments represent a reliably solid foundation to construct theories of physics, both at high energies and the effective ones. In other words, all good fundamental physics should start and end with string theory. Crackpots will never understand this point but it's not my fault.




There's no longer any anomaly suggested by the experiments in the behavior of the Higgs boson that would deserve attention and I personally guess that new physics will be first observed via a new particle, not an anomalous property of the Higgs boson (I can't promise you any deadline, however).

Today, the media are full of the stories that now the LHC physicists really think that what they found is the Higgs boson. Even the Drudge Report has the God particle as the "story of the day". Spin-two, pseudoscalar, and other bizarre alternatives and impostors have been pretty much ruled out. But it's extremely excessive to suggest that something qualitative has changed this week. Those theories have been de facto dead for half a year.

There are lots of papers presented at the Moriond 2013 conference that I could talk about – papers with results compatible with the Standard Model. I find these things boring given their null contents. But let me mention one paper that at least has some history. In June 2011, Tommaso Dorigo hyped a very bad measurement by CDF at the Tevatron that claimed that the top-antitop mass difference (which must be zero due to the CPT-theorem i.e. essentially due to the Lorentz symmetry, of course) was \[

(3.3\pm 1.4_{\rm stat}\pm 1.0_{\rm syst})\GeV.

\] Their U.S. colleagues in the D0 collaboration debunked that preposterous result. But it's interesting to see what CMS may determine with the 2012 data. Their value of the top-antitop mass difference is \[

(0.27\pm 0.20_{\rm stat}\pm 0.12_{\rm syst})\GeV.

\] That's compatible with zero, of course. Note that both the mean value as well the error margins shrank by roughly one order of magnitude! This is the progress in the experimental reach and precision that we witnessed in less than two years.

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