CMS: Present status, limitations, and upgrade plans

An overview of the CMS upgrade plans will be presented. A brief status of the CMS detector will be given, covering some of the issues we have so far experienced. This will be followed by an overview of the various CMS upgrades planned, covering the main motivations for them, and the various R and D efforts for the possibilities under study. The CMS detector has been working extremely well since the start of data-taking at the LHC as is evidenced by the numerous excellent results published by CMS and presented at this workshop and recent conferences. Less well documented are the various issues that have been encountered with the detector. In the spirit of this workshop I will cover some of these issues with particular emphasis on problems that motivate some of the upgrades to the CMS detector for this decade of data-taking. Though the CMS detector has been working extremely well and expectations are great for making the most of the LHC luminosity, there have been a number of issues encountered so far. Some of these have been described and while none currently presents a problem for physics performance, some of them are expected to become more problematic, especially at the highest Phase 1 luminosities for which the majority of the integrated luminosity will be collected. These motivate upgrades for various parts of the CMS detector so that the current excellent physics performance can be maintained or even surpassed in the realm of the highest Phase 1 luminosities.