TextSearch

Experiments A range of experiments at CERN investigate physics from cosmic rays to supersymmetry Diverse experiments at CERN CERN is home to a wide range of experiments. Scientists from institutes all over the world form experimental collaborations to carry out a diverse research programme, ensuring that CERN covers a wealth of topics in physics, from the Standard Model to supersymmetry and from exotic isotopes to cosmic rays. Several collaborations run experiments using the Large Hadron Collider (LHC), the most powerful accelerator in the world. In addition, fixed-target experiments, antimatter experiments and experimental facilities make use of the LHC injector chain. How does a detector work?+ Accelerators use electromagnetic fields to accelerate and steer particles. Radiofrequency cavities boost the particle beams, while magnets focus the beams and bend their trajectory. In a circular accelerator, the particles repeat the same circuit for as long as necessary, getting an energy boost at each turn. In theory, the energy could be increased over and over again. However, the more energy the particles have, the more powerful the magnetic fields have to be to keep them in their circular orbit. A linear accelerator, on the contrary, is exclusively formed of accelerating structures since the particles do not need to be deflected, but they only benefit from a single acceleration pass. In this case, increasing the energy means increasing the length of the accelerator. As physicists have explored higher and higher energies, accelerators have become larger and larger: the size of an accelerator is a compromise between energy, the radius of curvature (if it’s circular), the feasibility and the cost. Colliders are accelerators that generate head-on collisions between particles. Thanks to this technique, the collision energy is higher because the energy of the two particles is added together. The Large Hadron Collider is the largest and most powerful collider in the world. It boosts the particles in a loop 27 kilometres in circumference at an energy of 6.5 TeV (teraelectronvolts), generating collisions at an energy of 13 TeV. What are the characteristics of an accelerator?+ The type of particles, the energy of the collisions and the luminosity are among the important characteristics of an accelerator. An accelerator can circulate a lot of different particles, provided that they have an electric charge so that they can be accelerated with an electromagnetic field. The CERN accelerator complex accelerates protons, but also nuclei of ionized atoms (ions), such as the nuclei of lead, argon or xenon atoms. Some LHC runs are thus dedicated to lead-ion collisions. The ISOLDE facility accelerates beams of exotic nuclei for nuclear physics studies. The energy of a particle is measured in electronvolts. One electronvolt is the energy gained by an electron that accelerates through a one-volt electrical field. As they race around the LHC, the protons acquire an energy of 6.5 million million electronvolts, known as 6.5 tera-electronvolts or TeV. It is the highest energy reached by an accelerator, but in everyday terms, this is a ridiculously tiny energy; roughly the energy of a safety pin dropped from a height of just two centimetres. But an accelerator concentrates that energy at the infinitesimal scale to obtain very high concentrations of energy close to those that existed just after the Big Bang. Luminosity is a key indicator of an accelerator’s performance: it indicates the number of potential collisions per surface unit over a given period of time. The instantaneous luminosity is expressed in cm-2s-1 and the integrated luminosity, corresponding to the number of collisions that can occur over a given period, is measured in inverse femtobarn. One inverse femtobarn corresponds to 100 million millions (potential) collisions. What type of accelerators are there at CERN?+ CERN operates a complex of nine accelerators and two decelerators. These accelerators supply experiments or are used as injectors, accelerating particles for larger accelerators. Some, such as the Proton Synchrotron (PS) or Super Proton Synchrotron (SPS) do both at once, preparing particles for experiments that they supply directly and injecting into larger accelerators. The Large Hadron Collider is supplied with protons by a chain of four accelerators that boost the particles and divide them into bunches. The accelerators are controlled by operators 24 hours a day from the CERN Control Centre. LHC experiments Nine experiments at the Large Hadron Collider (LHC) use detectors to analyse the myriad of particles produced by collisions in the accelerator. These experiments are run by collaborations of scientists from institutes all over the world. Each experiment is distinct and characterised by its detectors. The biggest of these experiments, ATLAS and CMS, use general-purpose detectors to investigate the largest range of physics possible. Having two independently d...

Experiments – Home | CERN