HERA (, ) was a

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel electric charge, charged particles to very high speeds and energies to contain them in well-defined particle beam, beams. Small accelerators are used for fundamental ...

DESY DESY, short for Deutsches Elektronen-Synchrotron (English: ''German Electron Synchrotron''), is a national research centre for fundamental science located in Hamburg and Zeuthen near Berlin in Germany. It operates particle accelerators used to ...

Hamburg Hamburg (, ; ), officially the Free and Hanseatic City of Hamburg,. is the List of cities in Germany by population, second-largest city in Germany after Berlin and List of cities in the European Union by population within city limits, 7th-lar ...

. It was operated from 1992 to 30 June 2007. At HERA,

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

s or

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

s were brought to collision with

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

s at a center-of-mass

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

of 320 GeV. HERA was used mainly to study the structure of

s and the properties of

quarks A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly o ...

, laying the foundation for much of the science done at the

Large Hadron Collider The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the CERN, European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, ...

(LHC) at the

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

particle physics laboratory today. HERA is the only

lepton In particle physics, a lepton is an elementary particle of half-integer spin (Spin (physics), spin ) that does not undergo strong interactions. Two main classes of leptons exist: electric charge, charged leptons (also known as the electron-li ...

–proton collider in the world to date and was on the energy frontier in certain regions of the kinematic range. HERA-EWcurrents

To collide protons with either electrons or positrons, HERA used mainly

superconducting magnets A superconducting magnet is an electromagnet made from coils of superconducting wire. They must be cooled to cryogenic temperatures during operation. In its superconducting state the wire has no electrical resistance and therefore can conduct much ...

, which was also a world first. At HERA, it was possible to study the structure of protons up to 30 times more accurately than before. The resolution covered structures 1/1000 of the proton in size, facilitating many discoveries concerning the composition of protons from quarks and

gluon A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...

s. The HERA tunnel runs 10 to 25 m below ground level and has a

circumference In geometry, the circumference () is the perimeter of a circle or ellipse. The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. More generally, the perimeter is the curve length arou ...

of 6.3 km and an inner diameter of 5.2 m. For the construction, the same technology was used as for the construction of subway tunnels. Two

storage ring A storage ring is a type of circular particle accelerator in which a continuous or pulsed particle beam may be kept circulating, typically for many hours. Storage of a particular particle depends upon the mass, momentum, and usually the charge o ...

s were located on top of each other inside the tube. One accelerated electrons to energies of 27.5 GeV, the other one protons to energies of 920 GeV in the opposite direction. Both beams completed their circle nearly at the speed of light, making approximately revolutions per second. There are four interaction regions around the ring, which were used by the experiments H1,

ZEUS Zeus (, ) is the chief deity of the List of Greek deities, Greek pantheon. He is a sky father, sky and thunder god in ancient Greek religion and Greek mythology, mythology, who rules as king of the gods on Mount Olympus. Zeus is the child ...

HERMES Hermes (; ) is an Olympian deity in ancient Greek religion and mythology considered the herald of the gods. He is also widely considered the protector of human heralds, travelers, thieves, merchants, and orators. He is able to move quic ...

and

HERA-B The HERA-B detector was a particle physics experiment at the HERA accelerator at the German national laboratory DESY that collected data from 1993 to 2003. It measured 8 m × 20 m × 9 m and weighed 1000 tons. The HERA-B collaborati ...

. All these experiments were

particle detector In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing elementary particle, particles, such as t ...

s run by international groups of researchers. These groups developed, constructed and ran the multi-storey, complex measurement devices in many years of cooperative work and evaluated enormous amounts of data.

HERA accelerators

Lepton In particle physics, a lepton is an elementary particle of half-integer spin (Spin (physics), spin ) that does not undergo strong interactions. Two main classes of leptons exist: electric charge, charged leptons (also known as the electron-li ...

s (electrons or positrons) were pre-accelerated to 450 MeV in the linear accelerator LINAC II. From there, they were injected into the storage ring DESY II and accelerated further to 7.5 GeV before their transfer into the storage ring

PETRA Petra (; "Rock"), originally known to its inhabitants as Raqmu (Nabataean Aramaic, Nabataean: or , *''Raqēmō''), is an ancient city and archaeological site in southern Jordan. Famous for its rock-cut architecture and water conduit systems, P ...

, where they were accelerated to 14 GeV. Finally, they were injected into their storage ring in the HERA tunnel and reached a final energy of 27.5 GeV. This storage ring was equipped with warm (non-superconducting) magnets keeping the leptons on their circular track by a magnetic field of 0.17 tesla. Protons were obtained from originally negatively charged

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

s and pre-accelerated to 50 MeV in a linear accelerator. They were then injected into the proton synchrotron DESY III and accelerated further to 7 GeV. Then they were transferred to PETRA, where they were accelerated to 40 GeV. Finally, they were injected into their storage ring in the HERA tunnel and reached their final energy of 920 GeV. The proton storage ring used superconducting magnets to keep the protons on track. The lepton beam in HERA became naturally transversely polarised through the

Sokolov–Ternov effect The Sokolov–Ternov effect is the effect of self-polarization of relativistic electrons or positrons moving at high energy in a magnetic field. The self-polarization occurs through the emission of spin-flip synchrotron radiation. The effect was p ...

. The characteristic build-up time expected for the HERA accelerator was approximately 40 minutes. Spin rotators on either side of the experiments changed the transverse polarisation of the beam into longitudinal polarisation. The positron beam polarisation was measured using two independent polarimeters, the transverse polarimeter (TPOL) and the longitudinal polarimeter (LPOL). Both devices exploit the spin-dependent cross section for

Compton scattering Compton scattering (or the Compton effect) is the quantum theory of high frequency photons scattering following an interaction with a charged particle, usually an electron. Specifically, when the photon hits electrons, it releases loosely bound e ...

of circularly polarised photons off positrons to measure the beam polarisation. The transverse polarimeter was upgraded in 2001 to provide a fast measurement for every positron bunch, and position-sensitive silicon strip and scintillating-fibre detectors were added to investigate systematic effects. On 30 June 2007 at 11:23 pm, HERA was shut down, and dismantling of the four experiments started. HERA's main pre-accelerator PETRA was converted into a

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in some types ...

source, operated under the name PETRA III since 2009. Today, a section of the HERA tunnel and 24 former superconducting dipole magnets are being used for the new ALPS experiment, which looks for

axion An axion () is a hypothetical elementary particle originally theorized in 1978 independently by Frank Wilczek and Steven Weinberg as the Goldstone boson of Peccei–Quinn theory, which had been proposed in 1977 to solve the strong CP problem ...

-like particles.

International project HERA

The construction of HERA was one of the first truly internationally financed projects of this magnitude. Previously, the construction of scientific facilities was always financed by the country in which they were located. Only the costs for the experiments were borne by the conducting national or foreign institutes. Due to the enormous scope of the HERA project, many international institutions agreed to participate already in the construction. More than 45 institutes and 320 corporations participated in the construction of the facility with donations of money or materials, and more than 20% of the costs were borne by foreign institutions. Following the example of HERA, many large-scale scientific projects have since then been financed jointly by several countries. This model has become established and international cooperation is moderately common in the construction of those facilities.

HERA experiments

H1

H1 was a universal detector for the collision of electrons and protons, located in the HERA Hall North. It measured 12 m × 10 m × 15 m, weighed 2800 tons and was operated from 1992 to 2007. It was designed for probing the inner structure of the proton, the exploration of the strong interaction as well as the search for new kinds of matter and unexpected phenomena in particle physics.

ZEUS

Like H1, ZEUS was a detector for electron–proton collisions, located in the HERA Hall South. It measured 12 m × 11 m × 20 m, weighed 3600 tons and was operated from 1992 to 2007. Its tasks were similar to those of H1.

HERA-B

HERA-B was an experiment in the HERA Hall West, which collected data from 1999 to February 2003. By using HERA's proton beam, researchers at HERA-B conducted experiments on heavy quarks. The detector measured 8 m × 20 m × 9 m and weighed 1000 tons.

HERMES

The HERMES experiment in the HERA Hall East was operated from 1995 to 2007. HERA's longitudinally polarised electron beam was used to explore the spin structure of nucleons. For this purpose, the electrons were scattered at energies of 27.5 GeV at an internal gas target. This target and the detector itself were designed especially with a view to spin-polarised physics. The detector measured 3.5 m × 8 m × 5 m and weighed 400 tons.

References

External links

HERA website at DESY
{{coords , 53.581, 9.887, display=title Buildings and structures in Altona, Hamburg Education in Hamburg Particle physics facilities Particle accelerators