LHC stops … to regenerate more powerful!
2012 was quite a year for the CERN Large Hadron Collider [LHC]! A year of fundamental achievements both in physics and technology, successfully marking the end of the first 3 years period of data taking of LHC. A two years technical stop is now foreseen to allow improvements that will not only permit the machine to reach its full design energy (7 TeV per beam) and increased luminosity, but also allow the experiments to reach their utmost performance.
So far the LHC has been making continuous progress, exceeding the more optimistic luminosity goals and beam reliability. In the last week of operation the LHC team also succeeded to halve the space between particles bunches, a further step forward to higher luminosity. “This new achievement augurs well for the next LHC run starting in 2015″, said CERN’s Director for Accelerators and Technology, Stephen Myers. “High intensity beams are vital for the success of the LHC program. More intense beams mean more collisions and a better chance of observing rare phenomena.”
On the 4 July 2012 the announcement from ATLAS and CMS experiments of the discovery of a new particle compatible with the theoretically predicted “Higgs boson” filled a hole in the experimental confirmation of the Standard Model. If further studies confirm the properties of this new particle, “that would be a momentous achievement, and testimony to the generation-spanning talent, dedication and patience of thousands of scientists and engineers from around the world”, said CERN’s Director-General Rolf Heuer. “The other possibility is that the new particle is not a Standard Model Higgs, but that it completes the Standard Model and takes us further. This would be incredibly exciting, opening up new avenues for exploration of the universe beyond the Standard Model.”
There are other important results to crown the LHC physicists’ efforts. The TOTEM experiment confirmed what was discovered at CERN ISR in the seventies, that the proton continues to become larger with energy. The LHCf experiment measured the neutral pion production at very low angles thus providing inputs for models of ultra-high-energy cosmic-ray showers. The results by ATLAS and CMS on Super-Symmetry and new physics are pushing limits toward higher scale stimulating a critical revision of theoretical ideas. The LHCb experiment has shown evidence for CP violation in the charm sector and has measured the long awaited decay B0s → μμ, a further piece of agreement with the Standard Model.
Heavy ions collisions were measured by ALICE, ATLAS and CMS. In such collisions an extreme state of matter is created, with higher temperatures and energy densities than ever achieved before in any laboratory. In such a state, deconfinement occurs: the quarks and gluons that in ordinary matter are trapped inside hadrons such as protons and neutrons, are liberated, recreating conditions similar to those present in the early Universe during the first few microseconds after the Big Bang. This matter shows very strong quenching, i.e. strong particle absorption, even with respect to hard probes like heavy flavours, high momentum particles and jets. Few hours of proton-lead collisions delivered by LHC in September 2012 confirmed that the quenching observed in lead-lead collisions is not an initial state effect, namely that the origin of such a strong suppression cannot be related to the structure of the colliding nuclei but to the hot matter produced.
In 2013 LHC is scheduled with a challenging final 4 weeks operation in proton-lead mode, thus completing its goals for the first running period. After the long technical stop, collisions will be resumed in 2015 and the higher energy and the higher luminosity will certainly bring new and exciting results.
