M. Losasso

Measurement of the ATLAS solenoid magnetic field

ATLAS is a general purpose detector designed to explore a wide range of physics at the Large Hadron Collider. At the centre of ATLAS is a tracking detector in a 2 T solenoidal magnetic field. This paper describes the machine built to map the field, the data analysis methods, the final results, and their estimated uncertainties. The remotely controlled mapping machine used pneumatic motors with feedback from optical encoders to scan an array of Hall probes over the field volume and log data at more than 20 000 points in a few hours. The data were analysed, making full use of the physical constraints on the field and of our knowledge of the solenoid coil geometry. After a series of small corrections derived from the data itself, the resulting maps were fitted with a function obeying Maxwells equations. The fit residuals had an r.m.s. less than 0.5 mT and the systematic error on the measurement of track sagitta due to the field uncertainty was estimated to be in the range 0.02% to 0.12% depending on the track rapidity.

A dedicated device for measuring the magnetic field of the ND280 magnet in the T2K experiment

This paper describes a dedicated device to map the magnetic field of the T2K near detector (ND280) magnet, which runs at a nominal field value of 0.2 T, with an accuracy of the order of a Gauss. A high accuracy mapping is a key ingredient in order to provide the required momentum accuracy in the ND280 time projection chambers (TPCs) allowing T2K to measure precisely the PMNS matrix parameters ?m232 and ?23. This paper describes the design and realization of the device as well as its performance during operation. The reported results show that the aimed at goals are reached.