The H1 particle detector at HERA, Hamburg. The detector itself is hidden behind the dark red concrete wall behind the electronics trailer.

H1 is a particle detector in operation at HERA (Hadron Elektron Ring Anlage) in DESY, Hamburg. It began operating together with HERA in 1992. Leptons (electrons or positrons) are collided with protons by HERA in the interaction point of H1. H1 is operated by an international collaboration of about 400 physicists from 42 institutes in 15 countries. The detector is about 12 x 15 x 10 meters big and weighs 2800 tons. It is accompanied by an electronics trailer 3 stories high.

While H1 is a general purpose detector its main design feature is an asymmetric construction to cope with the boosted center of mass in the laboratory frame due to the large energy imbalance of the colliding beams. In the forward (incident proton) direction the instrumentation has higher granularity to give a better resolution for refined measurement of the proton remnant left after the collision with the incident lepton. The reaction products, often including the proton remnant and the scattered lepton, are detected by several subdetectors. Combination of their information allows the identification of particles from the reaction, or a least the reconstruction of the overall reaction kinematics. This in turn allows the classification of the reaction. From the center outwards, H1's most important systems are:

• Silicon trackers for the determination of primary and secondary vertices.
• Jet chambers for the measurement of charged particle tracks.
• Liquid Argon (LAr) calorimeter for the measurement of electromagnetic and hadronic showers.
• Lead/scintillating fibre calorimeter (SpaCal) in the backward direction for the measurement of the scattered lepton.
• Muon detectors in the iron magnet yoke surrounding H1 and in the forward direction.

In addition to these systems, H1 has several helper systems, such as a luminosity system, ToF (time of flight) detectors and radiation monitors. Also in the course of time additional detector systems have been added as the focus on special physics processes has become bigger. For example, forward instrumentation for diffractive physics has been added far down the HERA tunnel.

The most interesting physics topics treated at H1 include

• Cross section measurements of reactions with charged and neutral electroweak currents
• Studies of proton structure and determination of quark and gluon parton distribution functions
• Tests of QCD in jet and particle production
• Production of heavy quarks (charm and bottom)
• Diffraction (physics with the exchange of a pomeron)
• Search for physics beyond the Standard Model (For example the substructure of quarks / contact interactions, Leptoquarks, magnetic monopole)

The H1 detector took data until the shutdown of HERA in June 2007.

[edit] External links

• H1 Homepage