Performance of the Muon MWPC in high luminosity runs

The LHCb detector was conceived to operate with an average luminosity of 2x10$^{32}$cm$^{-1}$s$^{-1}$. During the last year of the LHC run, the whole apparatus has shown to be able to perfectly acquire and manage data produced at a luminosity as high as 4x10$^{32}$cm$^{-2}$s$^{-1}$. In this condition, all subdetectors operated at average particle rates higher than the design ones and in particular the detectors equipping the Muon System had to sustain a particle rate as high as 100kHz/cm$^2$. In order to study the possibility of increasing the luminosity of operation several tests were performed. This paper reports detailed studies on the performance of the LHCb Muon System in runs with a luminosity between 4 x 10$^{32}$cm$^{-2}$s$^{-1}$ and 10$^{33}$ cm$^{-2}$s$^{-1}$.