document: Each hit position inside the drift chambers was calculated from the drift time digitized by a flash analog-to-digital converter. The calculation was carried out based on a relation between the hit position and the drift time (x–t relation). The x–t relation was precisely calculated by a drift chamber simulation package, GARFIELD [20], and a gas property simulation package, MAGBOLTZ [21]. Although the chambers were constructed carefully with a tolerance of 100 μm, there was a small position deviation of wires and field-shaping patterns, which could locally modify the electric field. In order to take account of the limited accuracy in the chamber manufacturing, a correction was commonly applied to the calculated x–t relation throughout the experiments. The correction was obtained to minimize the χ2 in the fitting of straight tracks of clean muon events observed on the ground without magnetic field. The correction was as small as expected from the accuracy in the chamber manufacturing. During the observations, the x–t relation was affected by the variation in the pressure and temperature of the chamber gas. In order to take account of these time-dependent variations, the x–t relation was calibrated for each data-taking run. Especially in calibrating the x–t relation of ODCs, an absolute reference positions were provided by SciFi, which are not affected by the variation in the pressure nor temperature.
doc_bio_tags: O O O O O O B O O O O O O O O O O O O O O O O O O O O B I I I I I I I I B I O B I O O O O O O B O O B O O O B I I I B O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B O O O O O B I O O O O O O O O O O O O B O O O O O O O O O O O B I O O O O O O O O O O B I O B O O O O O O O O O O O O O O O O O O O O
extractive_keyphrases: chamber chambers garfield gas property simulation package magboltz magnetic field odcs relation between the hit position and the drift time x–t relation
abstractive_keyphrases: chamber gas chamber manufacturing drift chambers drift chamber simulation package flash analog-to-digital converter