LHC - Findings

Findings

CERN scientists estimated that, if the Standard Model is correct, a single Higgs boson may be produced every few hours, and that over a few years enough data to confirm or disprove the Higgs boson unambiguously and to obtain sufficient results concerning supersymmetric particles would be gathered to draw meaningful conclusions. On the other hand, some extensions of the Standard Model predict additional particles, such as the heavy W' and Z' gauge bosons, whose existence might already be probed after a few months of data collection.

The first physics results from the LHC, involving 284 collisions which took place in the ALICE detector, were reported on 15 December 2009. The results of the first proton–proton collisions at energies higher than Fermilab's Tevatron proton–antiproton collisions were published by the CMS collaboration in early February 2010, yielding greater-than-predicted charged-hadron production.

After the first year of data collection, the LHC experimental collaborations started to release their preliminary results concerning searches for new physics beyond the Standard Model in proton-proton collisions. No evidence of new particles was detected in the 2010 data. As a result, bounds were set on the allowed parameter space of various extensions of the Standard Model, such as models with large extra dimensions, constrained versions of the Minimal Supersymmetric Standard Model, and others.

On 24 May 2011, it was reported that quark–gluon plasma (the densest matter besides black holes) has been created in the LHC.

Between July and August 2011, results of searches for the Higgs boson and for exotic particles, based on the data collected during the first half of the 2011 run, were presented in conferences in Grenoble and Mumbai. In the latter conference it was reported that, despite hints of a Higgs signal in earlier data, ATLAS and CMS exclude with 95% confidence level (using the CLs method) the existence of a Higgs boson with the properties predicted by the Standard Model over most of the mass region between 145 and 466 GeV. The searches for new particles did not yield signals either, allowing to further constrain the parameter space of various extensions of the Standard Model, including its supersymmetric extensions.

On 13 December 2011, CERN reported that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 115-130 GeV. Both the CMS and ATLAS detectors have also shown intensity peaks in the 124–125 GeV range, consistent with either background noise or the observation of the Higgs boson.

On 22 December 2011, it was reported that a new particle had been observed, the χ_b (3P) bottomonium state.

On 4 July 2012, both the CMS and ATLAS teams announced the discovery of a boson in the mass region around 125-126 GeV, with a statistical significance at the level of 5 sigma. This meets the formal level required to announce a new particle which is "consistent with" the Higgs boson, but scientists are cautious as to whether it is formally identified as actually being the Higgs boson, pending further analysis.

On 8 November 2012 the LHCb team reported on an experiment seen as a "golden" test of supersymmetry theories in physics, by measuring the very rare decay of the B_s meson into two muons (B_s0 → μ+-). The results, which match those predicted by the non-supersymmetrical Standard Model rather than the predictions of many branches of supersymmetry, show the decays are less common than some forms of supersymmetry predict, though could still match the predictions of other versions of supersymmetry theory. The results as initially drafted are stated to be short of proof but at a relatively high 3.5 sigma level of significance.