D. Schinzel

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.

A high statistics measurement of the nucleon structure function F2(x,Q2) from deep inelastic muon-carbon scattering at high Q2

Abstract We present results from a high statistics study of the nucleon structure function F 2 ( x , Q 2 ) measured in deep inelastic scattering of muons on carbon in the kinematic range 0.25⩽ x ⩽0.80 and Q 2 ⩾25 GeV 2 . The analysis is based on 1.5×10 6 reconstructed events recorded at beam energies of 120, 200 and 280 GeV. R = σ L / σ T is found to be independent of x in the range 0.25⩽ x ⩽0.07 and 40 GeV 2 ⩽ Q 2 ⩽200 GeV 2 with a mean value R =0.015±0.013 ( stat ) ±0.026 (syst.).

Reaction π−p→ηn in the 15 to 40 GeV/c momentum range

A high statistics measurement of the reaction π−p → π0n has been performed at the Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. More than 3 million charge-exchange events have been recorded in total. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small |t|, as exponentials with the same slopes to within a few percent. Also the behaviour of the differential cross section for small and medium |t| agrees with the prediction of a geometrical s-channel model which describes binary reactions in terms of a complex pole b0(s). The imaginary part of this universal pole, Im b0(s), has been determined and found to be growing logarithmically with s.

Electroweak asymmetry in deep inelastic muon-nucleon scattering

At the CERN SPS we have measured a deep inelastic μ± cross section asymmetry at momentum transfers Q2 ranging from 15 to 180GeV2. The result is in quantitative agreement with the WS/GIM standard electroweak model and allows to determine the muon neutral current couplings.

Diffractive production of the charmed baryon Λ+c at the CERN ISR☆

Abstract In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c2 in the K−pπ+ mass distribution and, although with less statistical strength, at the same mass in the Λ0π+π+π− channel. These signals are identified as being due to the decay of the charmed baryon Λ+c which is produced with a cross section times branching ratio σcB in the range 0.7−1.8 μb for the K−π+p decay and 0.3−0.7 μb for the Λ-π+π+ π− system.

Reaction π− p → η′n in the 15–40 GeV/c momentum range☆

Abstract Measurements were made of the cross section of the reactions π−p → ν′(958)n, η′ → 2γ at momenta at 15, 20, 25, 30 and 40 GeV/c. The experiment was carried out on the IHEP 70 GeV accelerator using the 648 channel hodoscope spectrometer NICE for γ-ray detection. A total of 6000 η′ mesons were recorded. A sharp drop is seen in the differential cross section for t → 0. The dependences of the differential cross sections for the π−p → η′n and π−p → η n on t are identical. On the basis of the ratio of the cross sections for these reactions at t = 0, i.e. R( η′ n ) t=0 = 0.55 ± 0.06 , the singlet-octet mixing angle for pseudoscalar mesons was determined to be β = −(18.2 ± 1.4)°.

Experimental observation of a copious yield of electrons with small transverse momenta in pp collisions at high energies

Abstract Inclusive electron and positron emission have been observed for θcm = 30° and s = 2800 GeV2 at the CERN Intersecting Storage Rings (ISR). Over the transverse momentum interval 0.2 GeV/c

Observation of the UV scintillation light from high energy electron showers in liquid xenon

Abstract The UV scintillation light in liquid xenon has been observed using silicon drift photodiodes. Measurements were carried out in a rectangular light cell of dimentions 7.4 × 7.4 × 60 cm3 using 5 GeV electrons. The photodiodes and the preamplifiers were immersed in the liquid. A high quantum efficiency for 175 nm UV light has been measured. The scintillation light yield is found to be (1.5 ± 0.6) × 104 photons per MeV of energy deposited in liquid xenon. A light attenuation lenght of ≈ 40 cm has been measured.