Editorial
Dear Readers,
The year 2011 comes to an end with fireworks from CERN.
On 13 December a special seminar was held in CERN’s main auditorium, where the spokespersons of the two major experimental collaborations at the Large Hadron Collider [LHC], Fabiola Gianotti (ATLAS) and Guido Tonelli (CMS), presented their results from the search for a new particle, a fundamental and desperately wanted ingredient of the Standard Model: the Brout-Englert-Higgs-Guralnik-Hagen-Kibble boson, currently called ‘the Higgs’.
The combined data from the two experiments correspond to the whole of the collected statistics of proton-proton interactions, at a center-of-mass energy of 7 TeV, since the startup of the LHC in 2010. Different possible decay channels have been studied via an accurate invariant mass analysis, seeking for an electrically neutral, spin zero state over a wide mass range. Both experiments find very interesting candidate Higgs events in up to five different decay modes, in particular in the 2 photons, 2 charged leptons + 2 neutrinos and 4 charged leptons channels, in a very narrow mass region: 116-130 GeV/c2 (ATLAS) and 115-127 GeV/c2 (CMS).
The corresponding local significance for a Higgs signal centered around 125 GeV/c2 goes from 2.6σ (CMS) to 3.6σ (ATLAS), while the global one goes from 1.9σ to 2.3σ. The mass falls within the narrow window still allowed by the exclusion limits previously established by the CERN electron-positron collider [LEP] and more recently at the Fermilab Tevatron, a proton-antiproton collider which was shut down in September this year. Both ATLAS and CMS experiments have also excluded, at the 95 per cent confidence level, a wide region on the higher mass side.
If confirmed next year with further statistics, this result will be a breaking discovery in subnuclear physics. The discovery of the Higgs would nicely complete the Standard Model puzzle, as theoretically predicted for over four decades to explain the origin of the masses of the gauge bosons and of the elementary fermionic constituents, leptons and quarks.
Such Higgs evidence would follow a tremendous harvest of results this year: superluminal neutrinos from CERN to Gran Sasso, as measured by the OPERA experiment with the CNGS beam; and more recently the direct CP symmetry violation in the charm meson sector, as observed at a surprisingly high rate by another experiment (LHCb) at the CERN LHC.
Great excitement and challenging promises are in the air, which is indeed excellent for physics.
With my very best wishes to all of you for a joyful and successful 2012,
Luisa Cifarelli
EPS President
See also: the European Physical Society press release Chasing the Higgs: well done CERN!
