CERN Accelerating science

By comparing the particle production in pp and p-Pb collisions, nuclear initial state effects can be studied. Measurements of the $\omega$ meson $p_\text{T}$-spectra in pp and p-Pb collisions not only allow for a determination of the nuclear modification factor $R_\text{pA}$, but also provide insight into the fragmentation process and serve as vital input for direct-photon cocktail simulations. The $\omega$ mesons can be reconstructed in ALICE via their primary decay channel into three pions ($\omega\rightarrow\pi^+\pi^-\pi^0$). While the two charged pions are being directly identified with the tracking detectors, i.e. the Time Projection Chamber and the Inner Tracking System, the $\pi^0$ is reconstructed from its two decay photons. These photons can either be detected in the calorimeters or via tracks in case they convert to an electron-positron pair in the detector material. This thesis describes the measurement of the $\omega$ meson production in pp and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02~$TeV. This includes the signal extraction and various corrections of the $\omega$ meson yields, leading to their production cross sections and the first measured nuclear modification factor $R_\text{pA}$ ($2.2\leq p_\text{T}<20~$GeV/$c$) of the $\omega$ meson at LHC energies.