LHC proton collisions end with record

For the time being, the LHC concluded its last round of proton-proton collisions with an intensity record. Last weekend, 2748 particle bunches circled the 27-kilometre long particle accelerator in opposite directions, twice as many as before. At the beginning of 2013, the LHC will collide protons with lead ions for two months before going into a conversion phase of about two years to develop its full capacity.

“The accelerator and the detectors worked extremely well,” said DESY particle physics director Joachim Mnich. “The LHC already wrote history with the discovery of the new Higgs-like particle.” In July, both large research collaborations at the CMS and ATLAS experiments announced the observation of a new particle which is very similar to the Higgs particle. The Higgs particle which physicists hunted for since 48 years explains how elementary particles get their mass. “With the collisions in ATLAS and CMS measured up to now, we should be able to identify more precisely the particle we have seen in data obtained until July,” said Mnich. About 150 DESY scientists participate in both large LHC experiments; in the past three years each of them recorded several billions of proton-proton collisions, thereby opening up experimental physics at the terascale.

In March, the LHC will cease accelerator operation for about 20 months. In order to prepare it for the run at full capacity, ten thousands of high current connections between the superconducting magnets will be tested and partly replaced. Moreover, all welded connections will be equipped with so-called clamps, a method of mechanical stabilization that was also used at the superconducting HERA proton accelerator. Running will resume beginning of 2015 with a collision energy of up to 14 Tera electron volts, thus producing particle collisions of even higher energy.

Even during the LHC upgrade phase things certainly remain exciting for particle physicists. They will evaluate in detail the complete amount of recorded collision data and possibly discover new phenomena. For the analysis, DESY provides substantial storage and computing capacity which will be used by German and international workgroups.

Moreover, the scientists prepare their detectors and analysis software for the run at full LHC energy. The fast software, for example, which selects whether collision data are to be recorded or discarded, must be accurately adapted to the accelerator’s collision energy. It is a decisive factor for efficient detector operation, and so far it performed extremely well:  from the 6 quadrillions of collisions produced at the LHC, it filtered out the most interesting ones in each experiment. “The new particle physics era opened up with the LHC is very exciting,” said Mnich. “The coming conversion to full energy will further increase its discovery potential. Nevertheless, already now we must begin to plan the next upgrade which from 2020 on will significantly increase the collision rate.”