Developing a Silicon Pixel Detector for the Next Generation LHCb Experiment

The second long shutdown of the LHC presents an opportunity for the LHCb experiment to upgrade its detector systems and switch to a fully software triggered readout. Its first tracking layer, the VELO detector, is no exception to this and is undergoing an upgrade increasing the number of sensitive channels from 180 thousand silicon microstrips to about 41 million pixels. The new system will operate with zero-suppressed readout at 40 MHz, while cooled down using evaporative liquid CO$_2$ in silicon microchannel plates. The VELO Upgrade will consist of 52 modules, placed around the beam-pipe, built at the University of Manchester and Nikhef. The construction of the modules is a complex process that consists of a number of tight tolerance steps, their results verified both in metrology and in the electrical and thermal performance testing. In order to store data and track the performance a database has been developed, used to automatically analyse the uploaded values as well as compute the grades and quality of the individual steps and final modules. By the end of August 2021, 42 modules have been produced in Manchester, 37 of them with high quality and no issues present. Due to the nature of the harsh radiation environment, the sensors have to withstand a fluence up to 1e16 1 MeV n$_\mathrm{eq} \mathrm{cm^{-2}}$ and still provide a good signal to noise ratio. A new method of a charge collection scan has been proposed, linking the commonly used voltage scan with a threshold scan and using the extrapolated tracking information to estimate the amount of collected charge. The simulation indicates that the scan of a subset of modules will take about 8 min, a feasible duration despite the impact on the physics data taking. A further upgrade of the LHCb is planned for Long Shutdown four of the LHC. This will operate at higher luminosities leading to a significant increase in the pile-up of the collisions from a single proton-proton bunch crossing. For this reason a precise time stamping $\mathcal{O}$(50 ps) is to be added. This could be achieved in silicon detectors by using $\mathcal{O}$(10) internal gain in the sensor. Simulations of the expected performance of a recently produced batch of sensors are presented. These characterise the anticipated performance of these $\mathcal{O}$(50 $\mu$m) segmented devices in a test beam, providing the impact of charge sharing and device response to an angular scan

A new macro-imager based on Tpx3Cam optical camera for PLIM applications

The recently designed Tpx3Cam camera based PLIM (Phosphorescence Lifetime IMaging) macro-imager was tested using an array of phosphorescent chemical and biological samples. A series of sensor materials prepared by incorporating the phosphorescent O2-sensitive dye, PtBP, into five polymers with different O2 permeability were imaged along with several commercial and non-commercial sensors based on PtBP and PtOEPK dyes. The PLIM images showed good lifetime contrast between the different materials, and phosphorescence lifetime values obtained were consistent with those measured by alternative methods. A panel of live tissues samples stained with PtBP based nanoparticle probe were also prepared and imaged under resting conditions and upon inhibition of respiration. The macro-imager showed promising results as a tool for PLIM of O2 in chemical and biological samples

Digital Pixel Test Structures implemented in a 65 nm CMOS process

The ALICE ITS3 (Inner Tracking System 3) upgrade project and the CERN EP R&D on monolithic pixel sensors are investigating the feasibility of the Tower Partners Semiconductor Co. 65 nm process for use in the next generation of vertex detectors. The ITS3 aims to employ wafer-scale Monolithic Active Pixel Sensors thinned down to 20 to 40 um and bent to form truly cylindrical half barrels. Among the first critical steps towards the realisation of this detector is to validate the sensor technology through extensive characterisation both in the laboratory and with in-beam measurements. The Digital Pixel Test Structure (DPTS) is one of the prototypes produced in the first sensor submission in this technology and has undergone a systematic measurement campaign whose details are presented in this article. The results confirm the goals of detection efficiency and non-ionising and ionising radiation hardness up to the expected levels for ALICE ITS3 and also demonstrate operation at +20 C and a detection efficiency of 99% for a DPTS irradiated with a dose of $10^{15}$ 1 MeV n$_{\mathrm{eq}}/$cm$^2$. Furthermore, spatial, timing and energy resolutions were measured at various settings and irradiation levels.Comment: Updated threshold calibration method. Implemented colorblind friendly color palette in all figures. Updated reference

Microchannel cooling for the LHCb VELO Upgrade I

The LHCb VELO Upgrade I, currently being installed for the 2022 start of LHC Run 3, uses silicon microchannel coolers with internally circulating bi-phase \cotwo for thermal control of hybrid pixel modules operating in vacuum. This is the largest scale application of this technology to date. Production of the microchannel coolers was completed in July 2019 and the assembly into cooling structures was completed in September 2021. This paper describes the R\&D path supporting the microchannel production and assembly and the motivation for the design choices. The microchannel coolers have excellent thermal peformance, low and uniform mass, no thermal expansion mismatch with the ASICs and are radiation hard. The fluidic and thermal performance is presented.Comment: 31 pages, 27 figure

LHCb - LHCb VELO Upgrade Module Production

The construction of the new LHCb Vertex Locator (VELO) detector is presented. The upgraded subsystem will play a crucial role in the tracking during data-taking runs starting in 2021, its main objective locating primary and secondary vertices. Compared to its predecessor, the main advantages are better resolution together with trigger-less readout at the maximal rate of 40 MHz. In total, VELO consists of 52 modules positioned in vacuum along the LHC beampipe, surrounding the interaction point. The modules are populated with 4 hybrid silicon pixel detectors with pixel pitch of 55 µm. Each of the sensors is read out by 3 VeloPix ASICs with 256x256 pixels. For experiment control and data propagation, sets of front-end hybrids and GBTx ASICs are utilized. The data are then sent through a vacuum feed-through board to an opto-and-power (OPB) board, which is connected to the rest of the experiment via optical fibres. Cooling of the whole module is achieved by phase transition of liquid CO2 using a custom-made silicon micro-channel substrate. The assembly of modules at both University of Manchester (Manchester, UK) and Nikhef (Amsterdam, NL) requires high precision in many aspects, therefore extensive procedures for the large-scale construction and its quality assurance have been deployed. The information during each step is uploaded to the online database and automatically analyzed, providing instantaneous information about quality of both components, performed tasks and whole modules. Final assembly of the whole system then takes place at University of Liverpool (Liverpool, UK) and is then transported to CERN (Geneva, CH)