TheLarge Hadron Collider (LHC)has donecolliding protons with lead ions for the first time. Until now, the LHC had only collided with equal particles (proton-proton), so the collision of protons against nuclei presents important technical challenges, according to the National Center for Particle, Astroparticle and Nuclear Physics (CPAN).
According to the head of CERN’s lead ion team, John Jowett, this projectit allows “asymmetric collisions in energy” which, as he has indicated “is a challenge for experiments”. In addition, he pointed out that, at the accelerator level, “there is no difference in the size of the particles, but the difference in the size of the beam, and the fact that the size changes at different speeds, can affect how the particles behave. in collisions “.
The LHC typically accelerates two proton beams in opposite directions – from 0.45 to 4 teraelectronvolts (TeV) – before colliding them at a total energy of 8 TeV. Radio Frequency (RF) cavities, components of the accelerator that contain electromagnetic fields that drive the particles, provide the energy, but also keep the two beams in strict sync by pulling them back when necessary. The problem arises because the independent rings through which the two beams circulate are contained within a single magnet, a system that links the momentum of one beam with that of the other, but the particles have different speeds: a lead core, which contains 82 protons, is accelerated from 36.9 to 328 TeV, while a proton accelerates from 0.18 to 1.58 TeV.
To compensate for these speed differences between protons and lead ions, it is necessary to tune the radio frequency cavities to different frequencies for each beam. “First of all, the collisions are asymmetric in energy, which is challenging for experiments. At the accelerator level we don’t really see the difference in particle size, but the difference in the size of the beam, and the fact that the size changes at different speeds, it can affect how the particles behave in collisions. “
There are other challenges. The LHC typically accelerates two proton beams in opposite directions (from 0.45 teraelectronvolts or TeV to 4 TeV) before colliding them to a total energy of 8 TeV. Radio Frequency (RF) cavities, components of the accelerator that contain electromagnetic fields that drive the particles, provide the energy, but also keep the two beams in strict sync by pulling them back when necessary. The problem arises because the independent rings through which the two beams circulate are contained within a single magnet, a system that links the momentum of one beam with that of the other, but the particles have different speeds: a lead core, which contains 82 protons, is accelerated from 36.9 to 328 TeV, while a proton accelerates from 0.18 to 1.58 TeV. To compensate for these speed differences between protons and lead ions, it is necessary to tune the radio frequency cavities to different frequencies for each beam. “The RF systems of the two rings can be synchronized only at maximum energy before collisions, when the small difference in velocity between both types of particles can be absorbed by small changes in the orbits,” explains Jowett.
The most complicated for the LHC
According to Carlos Salgado, theoretical physicist at the University of Santiago de Compostela at CERN, this game of synchronization of the speeds and curvatures of the beams “is the most complicated system to achieve in the LHC”. In the RHIC collider, from the Brookhaven National Laboratory (USA), collisions also occur between heavy ions (in this case gold nuclei) but according to Salgado they are easier to produce since the magnets are independent, so beam speeds and curvatures can be better synchronized.
“It is the first time that collisions between protons and heavy nuclei have occurred”, explains Salgado. Protons have previously collided with fixed nuclei, not moving ones. Following a successful test today, the main operating cycle with these types of collisions will run from January to February 2013, in which they will be the last LHC collisions before the throttle blackout for maintenance.
According to Salgado, this type of collision has two fundamental uses: first, it serves to calibrate the measurements made in the collisions between heavy ions already experienced by the LHC in periods of 2010 and 2011. This type of collision tries to reproduce the called? quark-gluon plasma ?,the primordial “soup” of matter that must have existed moments after the Big Bangand for which extreme temperatures are produced, 100,000 times higher than the interior of the Sun.
On the other hand, “this type of collision is used to study the behavior of matter at very high energies“, like those that only the CERN accelerator is capable of producing. This particular state of matter has characteristics predicted by theory, but never observed before.
