detectors, meaning that they are able to study a wide range of phenomena in high-energy physics. More specialised detectors do not necessarily have a hermetic construction; for example, LHCb covers only the forward (high-pseudorapidity) region, because this corresponds to the phase space region of greatest interest to its physics program. Components There are three main components of a hermetic detector. From the inside out, the first is a tracker, which measures the momentum of charged particles as they curve in a magnetic field. Next there are one or more calorimeters, which measure the energy of most charged and neutral particles by absorbing them in dense material, and a muon system which measures the one type of particle that is not stopped through the calorimeters and can still be detected. Each component may have several different specialized sub-components. Trackers The detector's magnetic field causes the particle to rotate by accelerating it in a direction perpendicular to its motion via the Lorentz force. The tracking system plots the helix traced by such a charged particle as it travels through a magnetic field by localizing it in space in finely-segmented layers of detecting material, usually silicon. The particle's radius of curvature is proportional to its momentum perpendicular to the beam (i.e. transverse momentum or ) according to the formula (where is the particle's charge and is the magnetic induction), while the degree to which it drifts in the direction of the beam axis gives its momentum in that direction. Calorimeters Calorimeters slow particles down and absorb their energy into a material, allowing that energy to be measured. They are often divided into two types: the electromagnetic calorimeter that specializes in absorbing particles that interact electromagnetically, and the hadronic calorimeter that can detect hadrons, which interact via the strong nuclear force. A hadronic detector is required in particular to detect heavy neutral particles. Muon system Of all the known stable particles, only muons and neutrinos pass through the calorimeter without losing most or all of their energy. Neutrinos cannot be directly observed at collider experiments owing to their extremely small interaction cross section with hadronic matter (such as the detector is made of), and their existence must be inferred from the so-called "missing" (transverse) energy which is computed once all other particles in the event are accounted for. However muons (which are charged) can be measured by an additional tracking system outside the calorimeters.