Simonetta Cerdonio

A large liquid xenon time projection chamber for the study of the radiative pion decay

Abstract A 64 1 liquid xenon TPC has been operated for the detection and measurement of the low energy γ rays from the decay π + → μ + + υ + γ . We present a detailed description of the chamber, the readout electronics and data acquisition together with the measurement of the liquid xenon purity and time stability obtained during a period of about two months. The electron lifetime was always longer than 2.7 ms (95% C.L.) and no deterioration of the liquid purity has been observed. Such a purity level and stability have never been previously reported for a large volume liquid xenon chamber, making this technique mature for physical applications.

Performance of a liquid xenon time projection chamber for low-energy γ-rays detection

Abstract We detected the ionization charge and the scintillation light produced in liquid xenon by the interactions of γ-rays emitted by radioactive sources. We could distinguish the multiple interactions of the photons and, by using the prompt scintillation signal, determine the distance of the tracks from the anode. Applying an electric field of 0.4 kV/cm, we obtained an intrinsic energy resolution of (8.4 ± 0.9)% at 1 MeV and found that the free-ion yield is 4.24 ± 0.43 independent on the photon energy within few percent in the explored range between 500 keV and 2 MeV. The experimental spectra are the sum of the total energy peaks and the Compton continuum. By selecting the γ-rays with multiple interactions we could strongly reduce the Compton background and enhance the total energy peaks. All the spectra were consistent with a Monte Carlo simulation of the apparatus. With a sensitive volume of about 200 cm 3 we measured a peak-to-total ratio ranging from almost 100% (500–600 keV γ-rays) to more than 60% for 2 MeV photons.

New measurement of the π → μνγ decay

Abstract We have measured the branching ratio of the radiative decay π → μνγ . The energies of the gamma-ray and of the muon were both measured and the Dalitz-plot distribution of the decay was obtained. The data agree well with the theoretical prediction (QED internal bremsstrahlung) down to a γ-ray energy of 1 MeV. The discrepancy reported in a previous experiment is not confirmed.

Excess electron mobility in liquid Xe-Ar mixtures

The mobility and lifetime of excess electrons in high-purity liquid Ar-Xe mixtures were measured as a function of the electric field for several Xe concentrations x in Ar at T = 83.7 K. An unexpected dependence of mobility and lifetime on x was found. Cluster formation is considered as a possible mechanism explaining the data.

A New Measurement of the π → µvγ Decay

We measured the branching ratio of the radiative decay π → µvγ. The energies of the gamma-ray and of the muon were both measured and the Dalitz-plot distribution of the decay was obtained. The data agree well with the theoretical prediction (QED internal bremsstrahlung) down to a γ-ray energy of 1 MeV. The discrepancy reported in a previous experiment is not confirmed.

The LXe Calorimeter for π → μνγ Decay

A large Liquid Xenon ionization chamber was operated for the detection and measure of the low-energy gamma-rays from the decay π → μνγ. The scintillation light is successfully used for the trigger and the ionization charge for the energy measurement. The detector was calibrated with radioactive sources and its performances were compared to a Monte Carlo simulation.

Calibration of a liquid xenon gamma ray detector for the study of radiative pion decay

Abstract The performance of a liquid xenon time projection chamber as a detector for gamma rays between 0 and 30 MeV has been studied by comparing data collected with radioactive sources to a Monte Carlo simulation. The detector was designed for the study of the pion radiative decay. Both the scintillation light and the ionization charge signals were exploited. The light signals were used in the trigger logic and for the measurement of the chamber trigger acceptance. The minimum triggerable energy turned out to be 170 keV. The charge signals were used to measure the gamma ray energy. The noise introduced by the electronics was about 140 keV and the minimum measurable energy 230 keV with an electric drift field of 0.5 kV/cm. All the charge and light spectra were in good agreement with the simulation. The overall apparatus acceptance, taking into account geometry, trigger efficiency and offline reconstruction losses, was independent of the gamma ray energy above 2 MeV and equal to 10%.

60-liter liquid xenon time projection chamber (LXe-TPC) for study of radiative pion decay

We present measurements on purity and long-term stability of a 60 l liquid Xenon TPC, showing electron lifetimes in the liquid higher than some milliseconds for a period of one month. The electron lifetime is measured with a monitor chamber inside the TPC. The method is based on the measurement of the number of electrons extracted from a photocathode and collected on the anode after the drift through an electric field. We also report on preliminary results of the calibration of the TPC with gamma-ray sources.