The LHCb VELO Upgrade

The upgrade of the LHCb experiment, scheduled for LHC Run-3, will transform the experiment to a triggerless system reading out the full detector at 40 MHz event rate. All data reduction algorithms will be executed in a high-level software farm, enabling the detector to run at luminosities of 2×1033 cm−2 s −1 . The Vertex Locator (VELO) is the silicon vertex detector surrounding the interaction region. The current strip detector will be replaced with a hybrid pixel system equipped with electronics capable of reading out at 40 MHz. The upgraded VELO will allow for fast pattern recognition and track reconstruction in the software trigger. The silicon pixel sensors have 55×55 µm2 pitch, and are read out by the VeloPix ASIC. The VeloPix builds on the currently available Timepix3, modified to deliver a radiation hard design capable of an order of magnitude increase in output rate. The hottest regions will have pixel hit rates of 900 Mhits/s, yielding a total data rate more than 3 Tbit/s for the upgraded VELO. The silicon pixel sensors must be radiation hard to a level of 8×1015 1MeV neq cm−2 , delivered non uniformly over the sensor surface. The R&D; focusses on designs capable of tolerating high voltage after irradiation and maintaining good efficiency and resolution. The detector modules are located in a secondary vacuum, separated from the beam vacuum by a thin custom made foil. The material budget will be minimised by the use of evaporative CO2 coolant, circulating in microchannels within 400 µm thick silicon substrates. The current status of the VELO upgrade is described and latest results from the design and prototyping are presented.