General aspects of the H1 detector at the electron-proton storage ring HERA as well as technical descriptions of the magnet, luminosity system, trigger, slow-control, data acquisition and off-line data handling are given. The three major components of the detector, the tracking, calorimeter and muon detectors, will be described in a forthcoming article. The present paper describes the detector that was used from 1992 to the end of 1994. After this a major upgrade of some components was undertaken. Some performance figures from luminosity runs at HERA during 1993 and 1994 are given.

The H1 detector at HERA

The backward region of the H1 detector has been upgraded in order to provide improved measurement of the scattered electron in deep inelastic scattering events. The centerpiece of the upgrade is a high-resolution lead/scintillating-fibre calorimeter. The main design goals of the calorimeter are: good coverage of the region close to the beam pipe, high angular resolution and energy resolution of better than 2% for 30 GeV electrons. The calorimeter should be capable of providing coarse hadronic energy measurement and precise time information to suppress out-of-time background events at the first trigger level. It must be compact due to space restrictions. These requirements were fulfilled by constructing two separate calorimeter sections. The inner electromagnetic section is made of 0.5 mm scintillating plastic fibres embedded in a lead matrix. Its lead-to-fibre ratio is 2.3:1 by volume. The outer hadronic section consists of 1.0 mm diameter fibres with a lead-to-fibre ratio of 3.4:1. The mechanical construction of the new calorimeter and its assembly in the H1 detector are described.

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The H1 lead/scintillating-fibre calorimeter

The hadronic cascade description developed in an earlierpaper is extended to the response of an idealized fine-sampling hadroncalorimeter. Calorimeter response is largely determined by the transferof energy E_e from the hadronic to the electromagnetic sector via \pi0production. Fluctuations in this quantity produce the "constant term" inhadron calorimeter resolution. The increase of its fractional mean, f_\rmem^0= \vevE_e/E, with increasing incident energy E causes the energydependence of the \pi/e ratio in a noncompensating calorimeter. The meanhadronic energy fraction, f_h0 = 1-f_\rm em0, was shown to scaleverynearly as a power law in E: f_h0 = (E/E_0)m-1, where E_0\approx1~;GeV forpions, and m\approx0.83. It follows that \pi/e=1-(1-h/e)(E/E_0)m-1, whereelectromagnetic and hadronic energy deposits are detected withefficiencies e and h, respectively. Fluctuations in these quantities,along with sampling fluctuations, are in corporated to give an overallunderstanding of resolution, which is different from the usual treatmentsin interesting ways. The conceptual framework is also extended to theresponse to jets and the difference between pi and presponse.

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Energy flow in a hadronic cascade: Application to hadron calorimetry

We present the results of beam tests with high-energy (8–375 GeV) electrons, pions, protons and muons of a sampling calorimeter based on the detection of Cherenkov light produced by shower particles. The detector, a prototype for the very forward calorimeters in the CMS experiment, consists of thin quartz fibers embedded in a copper matrix. Results are given on the light yield of this device, on its energy resolution for electron and hadron detection, and on the signal uniformity and linearity. The signal generation mechanism gives this type of detector unique properties, especially for the detection of hadron showers: narrow, shallow shower profiles and extremely fast signals. These specific properties were measured in detail. The implications for measurements in the high-rate, high-radiation Large Hadron Collider (LHC) environment are discussed.

Beam test results from a fine-sampling quartz fiber calorimeter for electron, photon and hadron detection

The lateral profile of the energy deposition in a prototype of a lead and scintillating fiber calorimeter, constructed in the framework of the LAA project at CERN, has been measured for both electromagnetic and hadronic showers in the energy range from 5 to 150 GeV. The distributions are well described by analytic functions whose parameters allow one to determine the radial scaling of the shower development. In the electromagnetic case, the data are compared to Monte Carlo calculations. Estimates of the lateral leakage outside of the detector are made as well as calculations of the average π 0 content of hadronic showers and event-to-event fluctuations in this electromagnetic component. A method is developed whereby knowledge of the hadronic shower profile can be used to determine the relative calibration constants of neighboring towers in such a calorimeter.

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Y. Wang

Papers

Lateral shower profiles in a lead/scintillating fiber calorimeter