PARTICLE PHYSICS

The HERA experiments

HERA was the largest particle accelerator and research project in Germany. During 1992-2007, high energy electron (27 GeV) and proton (920 GeV) beams circulated in a 6.3 km long tunnel with experiments, known as HERA-B, HERMES, H1 and ZEUS, at four stations around the ring. Even today, HERA has been the only electron-proton collider in the world and allowed the most precise measurements of the structure of the proton to be made as well as the investigation of a wide range of other phenomena. The data from the experiments is still being analysed and high-profile papers being published in international scientific journals.

The H1 and ZEUS experiments

The H1 and ZEUS experiments collected data from the collisions of high energy electrons and protons using general-purpose detectors which, although measuring the same physical processes, were very different constructions. Highlights of the physics programme have been a precise mapping of the structure of the proton over a wide kinematic range, demonstration of the unification of the electromagnetic and weak forces, determination of the strong coupling constant, as well as various other phenomena investigating the hadronic final state and searches for new particles and physics signatures. The complementarity of the two detectors has allowed the collaborations to combine measurements and gain extra precision beyond a simple doubling of statistics. Both Collaborations continue to publish world-leading papers, particularly those using data combined from both experiments.

ZEUS is collaboration of about 450 physicists who are running a large particle detector at the electron-proton collider HERA at the DESY laboratory in Hamburg. The ZEUS detector is a sophisticated tool for studying the particle reactions provided by the high-energetic beams of the HERA accelerator. Thus the participating scientists are pushing forward our knowledge of the fundamental particles and forces of nature, gaining unsurpassed insight into the exciting laws of the microcosm.

The HERMES experiment

The HERMES experiment collected data from scattering of longitudinally polarised electrons on various polarised gas targets such as hydrogen, deuterium, or helium. The main goal of the HERMES experiment is to map out the spin structure of the nucleon, i.e. protons and neutrons. These nucleons are made up of quarks with spin-1/2, bound together by gluons with spin-1. The HERMES experiment is trying to answer how the constituents make up a nucleon, which has spin-1/2. The Collaboration continues to publish results delving deeper into the spin structure of the building blocks of matter.

The HERA-B experiment

The HERA-B experiment collected data during 1999-2003 from collisions of the proton beam on a stationary target of wires of different nuclei. A large-aperture, high-rate spectrometer detector was designed to measure the properties of the heavy quarks, bottom and charm. The Collaboration continued publishing results in this area until 2009.

The OLYMPUS Collaboration

The OLYMPUS Collaboration took data at the DORIS storage ring using the BLAST detector. For this purpose, the BLAST detector was shipped from MIT-Bates Linear Accelerator Center to DESY. Data were taken in 2012 and early 2013, until the DORIS operation ended. The aim of the experiment is to measure the two photon contribution to elastic electron scattering at high precision.