The CMS Magnetic Field Map Performance

TL;DR

This paper details the measurement, modeling, and analysis of the CMS detector's magnetic field, ensuring precise characterization for accurate particle detection at the LHC.

Contribution

It presents a comprehensive magnetic field map of the CMS detector using measurements and 3D modeling, enhancing the accuracy of magnetic field representation for physics analyses.

Findings

Magnetic flux density measured inside the CMS magnet with specialized sensors.

A TOSCA 3-D model accurately describes the magnetic field outside the tracking volume.

Comparison between measurements and model shows good agreement.

Abstract

The Compact Muon Solenoid (CMS) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive featuresinclude a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10000-ton return yoke made of construction steel. Accurate characterization of the magnetic field everywhere in the CMS detector is required. During two major tests of the CMS magnet the magnetic flux density was measured inside the coil in a cylinder of 3.448 m diameter and 7 m length with a specially designed field-mapping pneumatic machine as well as in 140 discrete regions of the CMS yoke with NMR probes, 3-D Hall sensors and flux-loops. A TOSCA 3-D model of the CMS magnet has been developed to describe the magnetic field everywhere outside the tracking volume measured with the field-mapping machine. A volume based representation of the magnetic field is used to provide the CMS simulation and reconstruction software with the magnetic field values. The value of the field at a given point of a volume is obtained by interpolation from a regular grid of values resulting from a TOSCA calculation or, when available, from a parameterization. The results of the measurements and calculations are presented, compared and discussed.