CERN have a new press release out today while latest results are being presented at the QCD part of the Moriond conference. There are further updates since last week including the long awaited CMS results for the diphoton decay channel. The diphoton rate relative to standard model is now 0.8 +- 0.3, much lower than before and a huge disappointment for hopes of beyond-standard-model physics.
In the press release the CMS and ATLAS spokespeople are quoted as follows
“The preliminary results with the full 2012 data set are magnificent and to me it is clear that we are dealing with a Higgs boson though we still have a long way to go to know what kind of Higgs boson it is.” said CMS spokesperson Joe Incandela.
“The beautiful new results represent a huge effort by many dedicated people. They point to the new particle having the spin-parity of a Higgs boson as in the Standard Model. We are now well started on the measurement programme in the Higgs sector,” said ATLAS spokesperson Dave Charlton.
So does this mean that they have officially conceded that it really is the Higgs boson and not some HHiggs-like imposter? The official line is now that “they find that the new particle is looking more and more like a Higgs boson, the particle linked to the mechanism that gives mass to elementary particles. It remains an open question, however, whether this is the Higgs boson of the Standard Model of particle physics, or possibly the lightest of several bosons predicted in some theories that go beyond the Standard Model.”
It’s a bit meally mouthed but nevertheless, most c0mmentators are interpreting this to mean that they have agreed that it is a Higgs boson of some sort.
The crux was the spin measurements which both teams agree disfavours spin 2 with positive parity at a 2 to 3 sigma level. The real Higgs boson has spin zero with positive parity and all other spin possibilities are directly ruled out by the fact that it decays to two spin-one photons. Negative spin zero is not quite so strongly ruled out but this is not being billed as such an important observation.
|particle propertty||Can it be determined with LHC run 1 data?||Does CERN think it is deterministic for a Higgs boson?||current status|
|Decay modes||YES||YES||WW,γγ,ZZ,ττ observed, bb,Zγ,μμ etc ongoing|
|Other Production modes||NO||NO||gluon fusion OK, VBF, VH and ttH ongoing|
|no exotic decay modes||NO||NO||preliminary results from ATLAS|
|Spin = 0||YES||YES||spin zero verified to about 2 or 3 sigma in each experiment|
|Parity = positive||NO||NO||negative parity is disfavoured but not ruled out|
|W fusion||NO||NO||nothing yet reported|
|Higgs self-coupling||NO||NO||nothing yet reported|
In summary, the things that CERN has decided are crucial for determining that this is a Higgs boson are thankfully exactly the things that can be determined from run 1 but there are plenty of other observations to keep them busy for run 2 and beyond.