Thursday, March 14, 2013

CMS Diphoton Higgs Data Finally In

More Higgs Boson Mass Data

The combined CMS Higgs boson mass estimate now including both ZZ and diphoton channels is 125.8 +/- 0.4 +/- 0.4 GeV.  This measurement is indistinguishable from the 125.99 value of (W+W+Z)/2, but is increasingly a bit of a stretch for (top plus W)/2.

The crude average of the two ATLAS measurements averaged with the combined CMS measurement gives a central Higgs mass value of about 125.7 GeV.

As an aside, the vacuum expectation value of the Higgs field is the 1/sqrt(sqrt(2)*GF) 246 GeV, where GF = 1.16639(2)*10^-5 is the Fermi coupling constant. More precisely, it is 246.2279579 GeV.   This value was determined from a measurement of the lifetime of the muon.  It has a theoretical value equal to the square of the weak force coupling constant divided by the square of the W boson mass, times the square root of two divided by eight.  The Higgs boson mass less one half of the Higgs field vev is to a the same precision of the Higgs boson mass is about 2.5 GeV.

New CMS Cross-Section Data Shows No Diphoton Excess

In the diphoton channel at that mass there are tagged and untagged consistencies with the Standard Model.  The untagged is consistent with the Standard Model expectation at about one sigma, and the tagged is consistent at a bit more than 2 sigma, with the overall deviation from the Standard Model in the diphoton channel declining.

As Strassler explains (my main source is a couple of Moriond talk slides): "To repeat: with more data, CMS does not confirm the excess that they saw in July, and does not confirm the excess seen currently by ATLAS. "

The overall fit with the Standard Model in all decay channels is 0.88 +/- 0.21 where 1 is a perfect match with the Standard Model expection, thus the Higgs cross-sections, overall fit the SM Higgs cross-sections at a considerably less than one sigma level.  Overall measured ZZ production strength is an almost perfect fit to the Standard Model expectation and overall measured diphoton production strength is within one sigma of the Standard Model expectation with a full dataset.  The relative WW v. ZZ production rates were a near perfect match for the Standard Model expectation.

All of the other LHC Higgs data to date was summarized here.

The combined CERN experiment has announced that this is really a Higgs boson and not merely a Higgish boson.

All But One BSM Higgs Boson Model Tested Is Ruled Out By CMS Data

The data fit the SM Higgs boson and disfavors all alternative models tested thus far at the 2 sigma confidence level or more except 0h+ (i.e. the light, neutral, even parity SUSY Higgs boson).  There was no detailed discussion of how a SUSY 0H+ was ruled out.  This suggests that the other four SUSY Higgs bosons, if SUSY is correct and similar to the MSSM, must all have similar masses and those masses may be far in excess of the LHC detection limits. 

So, even if SUSY is out there at extremely high energy scales, at LHC energies, the Standard Model may turn out to be completely consistent with all experimental evidence.

Failure to find any BSM experimental data at all at the LHC, which is where we are headed so far, would tremendeously constrain any alternatives to it.  Even though it doesn't strictly speaking, rule out all string theories and supersymmetry theories, it effectively makes all leading BSM theories far less interesting and shifts the focus from Beyond The Standard Model to Within The Standard Model (WSM) to find deep theories that imply the gum and duct tape version we have to explain it all.

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