Measurement of the W boson properties in the forward region in pp collisions at $\sqrt{s}= 5.02$ TeV

This thesis primarily presents a detailed study of the fiducial cross--sections for $W^+$ and $W^-$ boson production at $\sqrt{s}= 5.02$ TeV, using data from the LHCb experiment at the Large Hadron Collider at CERN. The dataset corresponds to an integrated luminosity of $99.86 \pm 2.00 \ \text{pb}^{-1}$, recorded during 2017. The research focusses on muonic decays of W bosons. The cross--sections are measured differentially in intervals of the muon transverse momentum between 25 and 55 GeV, with the pseudorapidity ranging from 2.2 to 2.4. Integrated over this 2D fiducial sub--volume, the cross--sections are measured to be: \begin{align*} \sigma_{W^+ \to \mu^+ \nu} &= 301.62 \pm 3.00 \pm 3.74 \pm 6.03 \ \text{pb}, \\ \sigma_{W^- \to \mu^- \bar{\nu}_\mu} &= 237.80 \pm 2.72 \pm 2.67 \pm 4.76 \ \text{pb}, \end{align*} where the first uncertainty is statistical, the second systematic, and the third is attributed to the luminosity determination. A fit to the differential cross--sections yields the following determination of the \W boson mass: \begin{align*} m_W = 80355 \pm 128 \pm 21 \ \text{MeV}, \end{align*} where the first error is experimental (statistical and systematic errors combined) and the second error is theory systematic errors for measuring $m_W$. It is important to note that the $m_W$ result is currently blinded, and the analysis is in internal review within the international LHCb collaboration. This analysis serves as a proof--of--principle for determining the W boson mass with intermediate measurements of the differential cross--sections in intervals of the muon transverse momentum. The method of investigation involves novel techniques to extract the W boson mass using differential cross--sections in bins of transverse momentum. By eventually applying this approach to the full Run 2 dataset at $\sqrt{s}$ = 13 TeV, we expect a precision of around 15 MeV, which would be a competitive measurement that enriches the findings of ATLAS and CMS. Furthermore, the thesis covers the author's role in the Real--Time Analysis (RTA) project at the LHCb experiment. This involves developing data processing software and optimising workflows for the Run 3 data collection phase.