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 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 × 10³³ cm^-2s^-1. The present pixel detector was originally designed for a luminosity of 1 × 10³⁴ cm^-2 s^-1 and a pileup (number of inelastic interactions per bunch crossing) of 25 in 25 ns bunch spacing. These beam parameters will be reached in the middle of the data taking period 2015-2018 (with an additional increase in the center of mass energy up to the value of 13 TeV) and then the peak luminosity will keep increasing until 2017 when it will reach the value of 1.5 × 10³⁴ cm^-2 s^-1. The present detector will remain operative until the end of 2016 and will be replaced with an upgraded detector that will be described in this work before Long Shutdown 2 (LS2). After LS2 the beam parameters will change again, around 2021 a peak luminosity reaching at least 2 × 10³⁴ cm^-2 s^-1 is foreseen, consequently pile-up will increase up to 50 with 25 ns bunch spacing. 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. In this paper the new pixel detector will be described focusing mostly on the barrel detector design, construction and expected performances. Test procedures for detector module production will also be presented.