\chapter{Conclusion}
\label{ch:conclusion}

The \lhcbexperiment{} at the LHC is a specialised detector that probes the Standard Model of particle physics and theories beyond it by performing precision measurements of \textit{CP} violation and studying rare decays in the $b$ and $c$ quark sector.
During the first years of operation between 2010 and 2018, huge samples of processes involving these quarks were collected and enabled the publication of key results in the field of flavour physics.
Although the detector was already operating at twice the design luminosity towards the end of this period, many measurements are still limited by the statistical sensitivity of the data samples.
To overcome this, LHCb has undergone a major upgrade in preparation for another fivefold increase in instantaneous luminosity starting from the next data taking period in the course of 2022.
The complete tracking system has been replaced in the process, along with the front-end electronics of all sub-detectors.
The latter was required in order to enable a trigger-less readout of the complete detector at the LHC bunch crossing rate of \qty{40}{\mega\hertz}, which will in particular benefit analyses with hadronic final states.

The Scintillating Fibre (SciFi) Tracker is an essential component in the upgraded tracking system of the \lhcbexperiment{}.
With a fibre diameter of \qty{250}{\micro\meter}, sufficient granularity is provided for the increasing track multiplicities.
In addition, the SciFi front-end electronics have been developed and optimised to enable the readout of the detector at \qty{40}{\mega\hertz}.

During the three-year upgrade period, the 12 \cframes{} that make up the \scifitracker{} have been assembled.
While the overall (tracking) performance was already verified in previous test beam campaigns for individual fibre modules and Readout Boxes (ROBs), the following challenge was to ensure that the same quality could be maintained for the entire detector.
In case of the front-end electronics, this means that a total of \num{256} ROBs need to be thoroughly examined in their final environment.

In the scope of this thesis, the complex system was put into operation for the first time at the level of individual \cframes{}.
It consists of up to \num{24} ROBs that need to be operated in conjunction with the surrounding infrastructure and the upgraded LHCb DAQ system.
A key challenge in this context was to establish the readout of the detector at \qty{40}{\mega\hertz}.
With several hundred optical data links per \cframe{}, data rates of up to \qty{2}{\tera\bit/\second} are generated and need to be processed.
To ensure an error-free transmission along the path of the data, this requires a careful tuning of half a dozen clock phases per connection.

After overcoming the initial challenges, a detailed test sequence has been defined, developed and implemented.
The so-called commissioning procedure ranges from a series of basic functional tests to taking measurements that involve the complete data chain.
It is performed on each individual \cframe{} before it is released for installation in the LHCb cavern.
After a slow start and despite multiple interruptions due to the COVID-19 pandemic, the commissioning quickly became a routine operation.

The results from the first 9 commissioned \cframes{} corresponding to \num{196} ROBs and 400k channels were presented.
Critical failures occurred in \qty{5}{\percent} of the cases and required the replacement of the corresponding ROBs.
Since the commissioning takes place in a dedicated hall on the LHCb site, this operation is significantly easier and safer than performing it after the installation of the detector in the cavern.
The most common error concerned the communication between the control system and the front-end electronics via the optical links.
At a total of \num{6} ROBs, temporary losses of the acquired frame-locks were observed.
These typically only last for a few milliseconds, but can potentially lead to unwanted resets of the front-end electronics.

Apart from the critical errors, minor issues such as broken sensors were encountered that did not require further interventions.
This also includes a total of 3 dead and 7 malfunctioning detector channels, which were identified in the course of the commissioning.
However, in view of more than 400k channels,  this translates to a rate of functional channels well above \qty{99.99}{\percent}.

The performance studies that have been conducted alongside the commissioning confirmed the high quality of the front-end electronics.
It was demonstrated that they behave consistently and stably even with slight variations in conditions.
However, it was found that at least one additional retrimming iteration of the internal integrator baselines is required after the installation of the \cframes{} in order to achieve a uniform performance between the two PACIFIC integrators in each channel.

Overall, the commissioning of the SciFi front-end electronics has been a great success and demonstrated its flawless functionality on a large scale.
No unsolvable issues have been encountered along the way allowing the detector to be installed in the LHCb cavern and ready to take data.
The commissioning procedure has been developed using the same software and tools as will be used in the final system.
In addition, it has been conducted in conjunction with the same hardware that implements the control and DAQ system in the upgraded \lhcbexperiment{}.
Thereby, a lot of experience has been gained that will be invaluable for the operation of the detector in the course of the next years.








%\begin{figure}[b!]
%  \centering
%  \includegraphics[width=1.0\textwidth]{figures/conclusion/TS_Transport}
%  \caption{
%    TS-Cage with the first four commissioned \cframes{} being lowered into the LHCb cavern.
%    Photo taken from Ref.~\autocite{cern-photos}.
%  }
%  \label{fig:ts-transport}
%\end{figure}