page_title: ALICE experiment
section_title: High Momentum Particle Identification Detector
hierarchical_section_title: ALICE experiment / The ALICE detectors / Particle identification with ALICE / High Momentum Particle Identification Detector
caption_attribution_description: English: The HMPID detector before final installation inside the ALICE magnet.
context_page_description: ALICE is one of eight detector experiments at the Large Hadron Collider at CERN. The other seven are: ATLAS, CMS, TOTEM, LHCb, LHCf, MoEDAL and FASER.
context_section_description: The High Momentum Particle Identification Detector (HMPID) is a RICH detector to determine the speed of particles beyond the momentum range available through energy loss (in ITS and TPC, p = 600 MeV) and through time-of-flight measurements (in TOF, p = 1.2–1.4 GeV).
  Cherenkov radiation is a shock wave resulting from charged particles moving through a material faster than the velocity of light in that material. The radiation propagates with a characteristic angle with respect to the particle track, which depends on the particle velocity. Cherenkov detectors make use of this effect and in general consist of two main elements: a radiator in which Cherenkov radiation is produced and a photon detector. Ring imaging Cherenkov (RICH) detectors resolve the ring-shaped image of the focused Cherenkov radiation, enabling a measurement of the Cherenkov angle and thus the particle velocity. This in turn is sufficient to determine the mass of the charged particle.
  If a dense medium (large refractive index) is used, only a thin radiator layer of the order of a few centimetres is required to emit a sufficient number of Cherenkov photons. The photon detector is then located at some distance (usually about 10 cm) behind the radiator, allowing the cone of light to expand and form the characteristic ring-shaped image. Such a proximity-focusing RICH is installed in the ALICE experiment.
  ALICE HMPID's momentum range is up to 3 GeV for pion/kaon discrimination and up to 5 GeV for kaon/proton discrimination.  It is the world's largest caesium iodide RICH detector, with an active area of 11 m². A prototype was successfully tested at CERN in 1997 and currently takes data at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratory in the US.
caption: The HMPID detector before final installation inside the ALICE magnet.
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