A. Gonidec

A STUDY OF IONIZATION ELECTRONS DRIFTING OVER LARGE DISTANCES IN LIQUID ARGON

Abstract We have measured the lifetime of electrons drifting in liquid argon using a gridded ionization chamber with a drift gap of 153 mm. The electrons were produced by the passage of cosmic rays through the chamber. We find a best fit for the electron lifetime τ at 5 V/cm of 9.2 ms (with 13.2 > τ > 7.1 ms at 95% CL). This value is consistent with all the data below 15 V/cm. This corresponds to an impurity concentration ρ = 0.03 ppb oxygen equivalent. The attenuation length calculated from the above lifetime is 18 m for a field of 1 kV/cm. The liquid remained in the chamber for 14 weeks with no recirculation system and suffered no noticeable deterioration with respect to the lifetime or the pulse height. The low field mobility μ 0 has been measured for fields up to 150 V/cm and we find a value of 545 ± 4 cm 2 V −1 s −1 which is consistent with measurements by other authors. The electron yield as a function of the electric field strength has been measured down to 3 V/cm. The results seem to indicate the need for a modification of the geminate recombination theory.

Performance of a uranium/tetramethylpentane electromagnetic calorimeter

Abstract A calorimeter, consisting of uranium plates and thin liquid ionization chambers filled with tetramethylpentane (TMP) at room temperature, has been tested using electrons between 10 and 70 GeV. The essential characteristics of the liquid are discussed, including measurements of the free electron lifetime. Results on uniformity, linearity and energy resolution are described and some information on the response to hadrons has been obtained. A single TMP box containing four electrodes and a TMP position detector for electromagnetic showers have also been tested.

Performance of an electromagnetic liquid krypton calorimeter based on a ribbon electrode tower structure

The NA48 collaboration is preparing a new experiment at CERN aiming to study CP violation in the K0-K0 system with an accuracy of 2 × 10−4 in the parameter Re(ϵ′/ϵ). Decays in two π0s will be recorded by a quasi-homogeneous liquid krypton calorimeter. A liquid krypton calorimeter has been chosen to combine good energy, position and time resolution with precise charge calibration and long-term stability. The prototype calorimeter incorporating the final design of the electrode read-out structure is presented in this paper. An energy resolution of ≃3.5%√E with a constant term smaller than 0.5% has been obtained. The time resolution was found to be better than 300 ps above 15 GeV.

Spin dependence of the inclusive reaction p + p (polarized) → π0 + X at 24 GeV/c for high-pT π0 produced in the central region

Abstract The spin dependence of π 0 inclusive production by 24 GeV/ c protons has been measured using a polarized target for Fhe Feynman x near 0 in the transverse momentum range 1.0 p T c . The results indicate a negative updown asymmetry growing strongly with p T and greater than 50% in absolute value for p T greater than 2 GeV/ c .

SPACE CHARGE IN IONIZATION DETECTORS AND THE NA48 ELECTROMAGNETIC CALORIMETER

Abstract The subject of space charge due to positive ions slowly moving in parallel plate ionization chambers is considered. A model for the degradation of the detector response is developed, with particular emphasis on electromagnetic calorimeters.The topics discussed include: (a) the stationary; (b) the time dependent cases; (c) the limit of very large space charge; (d) the electric field dependence of the electron drift velocity; (e) the effect of longitudinal development of showers; (f) the behaviour of the average reductions of response; (g) the non-uniformity of response for different positions of the shower axis inside the cell defined by the electrodes. The NA48 calorimeter is used as application and for comparison of results.

A study of the electron image due to ionizing events in a two-dimensional liquid argon TPC with a 24 cm drift gap

Abstract We have tested a liquid argon time projection chamber with a novel wire configuration based on electrostatic focussing which allows the realization of a nondestructive detection of the electron image produced by ionizing events. The chamber was tested in a 5 GeV pion beam at the CERN proton synchrotron. The measured pulse shapes at both 200 V/cm and 500 V/cm were in very good agreement with the expected shapes, calculated taking into account the electron lifetime, the response of the electronics and the longitudinal diffusion of the electron cloud. The measured electron drift velocity was in good agreement with the results of other workers as well as with our previous measurements. We have also analysed a sample of events containing delta rays in order to study the behaviour of low-energy electrons in the liquid argon. We find that for electron energies greater than 5 MeV the measured energy spectrum agrees very well with the predicted spectrum after corrections for acceptance and energy loss, hence demonstrating the feasibility of recognizing low-energy electrons in liquid argon.

Purity in room temperature liquid ionization chambers

Abstract Electron attaching impurities in the liquids TMS (tetramethylsilane) and TMP (2,2,4,4 tetramethylpentane) have been removed to a high degree with efficient and fast purification methods. Free electron lifetimes of 450 and 77 μs have been measured for the two liquids respectively.

Spin effects in the inclusive reactions π± + p(↑) → π± + anything at 8 GeV/c

Abstract The asymmetry in inclusive reactions of the type a + p (→) → a + anything at 8 GeV/ c a = π + , π − or p) have been measured at the CERN Proton Synchrotron using a polarized proton target. In the πp reactions and over a limited range of p T (0.17 ⩽ p T ⩽ 0.36) GeV / c the results indicate i) an asymmetry for x = p ‖ ∗ /p max > 0.7 which is mirror symmetric for the π + and π − reactions;ii) an asymmetry compatible with zero for 0.3

PERFORMANCE OF AN ELECTROMAGNETIC LIQUID KRYPTON CALORIMETER

Abstract A prototype electromagnetic calorimeter containing 180 litres of liquid krypton has been tested in electron and muon beams at the CERN SPS. The main features of this detector are its active shower medium, a granularity of 2 cm with tower readout, and the use of the initial current readout technique with an effective shaping time of about 60 ns. An energy resolution for electrons of 4.1% √E[ GeV ] with a constant term of 0.4% and a noise contribution of 50 MeV has been achieved. The calorimeter has a spatial resolution of 4.5 mm √E[ GeV ] with a constant term of 0.3 mm and a time resolution of about 0.5 ns for energies larger than 10 GeV.

Influence of the electric field on compensation in a uranium/tetramethylpentane hadronic calorimeter

Abstract A uranium tetramethylpentane hadronic calorimeter has been tested using electrons and pions of 7 GeV/ c momentum with electric fields varying from 0.8 to 16.0 kV/cm; the e/π charge collection ratio has been measured as a function of the electric field within this range. It is observed that the e/π ratio can be tuned acting on the electric field without spoiling the energy resolution for electrons. At the same time the energy resolution for pions is improved. The effect was cross-checked using a second module and 40 GeV/ c electron and pion beams.