The phase-1 upgrade of the CMS vertex detector

The operation of the present pixel detector has started in 2010 with LHC operating at a center of mass (CM) energy of 7\,TeV. At the beginning of 2012 the CM energy was increased to 8\,TeV and within December 2012 a total of 19\,fb$^{-1}$ integrated luminosity has been delivered, with instantaneous peak luminosities approaching $7\times 10^{33}$\,cm$^{-2}$s$^{-1}$. The present pixel detector was originally designed for a luminosity of $1\times 10^{34}$\,cm$^{-2}$s$^{-1}$ and a pileup (number of inelastic interaction per bunch crossing) of 25 for 25\,ns bunch spacing. These beam parameters will be reached in the middle of the data taking period 2015-2017 (with an additional increase in the center of mass energy up to the value of 13-14\,TeV) and then the peak luminosity will keep increasing until 2017, when it will reach the value of $1.5\times 10^{34}$\,cm$^{-2}$s$^{-1}$. The present detector will remain operative until the end of 2016 and will be replaced with an upgraded detector before Long Shutdown 2 (LS2). After LS2 the beam parameters will change again, around 2021 a peak luminosity reaching at least $2\times 10^{34}$\,cm$^{-2}$s$^{-1}$ is foreseen, consequently pile-up will increase up to 50 if the bunch spacing will be kept at 25\,ns, or to 100 if the bunch spacing will be brought to 50\,ns. In this context the present pixel detector will be unable to perform adequately and this is the reason why a new detector needs to be built and installed before LS2. The new upgraded detector will have higher tracking efficiency and lower mass with four barrel layers and three forward/backward disks to provide a hit pixel coverage up to absolute pseudorapidities of 2.5. The new pixel detector will be described focusing mostly on the barrel detector design, construction and expected performances. Preliminary tests on detector module production will also be presented.