Particle Identification in Jets and High-Multiplicity pp Events with the ALICE TPC

The spectra of identified particles in a collision experiment comprise crucial information about the underlying physical processes. The ALICE experiment has powerful Particle IDentification (PID) capabilities, which are unique at the Large Hadron Collider (LHC). In this thesis, a statistical PID method based on the specific energy loss d$E$/d$x$ in the ALICE Time Projection Chamber (TPC) is developed: the TPC Multi-Template Fit (MTF). The MTF allows for the extraction of identified charged particle spectra in a wide momentum range, which extends from about 150 MeV/$c$ to above 20 GeV/$c$. The TPC PID requires a detailed modelling of the TPC d$E$/d$x$ response for momenta above 2-3 GeV/$c$. A framework is developed that allows for the determination of the model parameters and for evaluating the PID information of charged particles. With the MTF, the transverse momentum $p_{\mathrm{T}}$ spectra of charged pions, kaons and protons at mid-rapidity ($|\eta| < 0.9$) are measured for pp collisions at $\sqrt{s}$ = 7 TeV. It is studied how these spectra and the corresponding K/$\pi$ and p/$\pi$ ratios evolve as a function of the event multiplicity. The study is motivated by the recent observation that high-multiplicity pp collisions exhibit intriguing similarities to p-Pb and Pb-Pb collisions. For instance, long-range correlations were observed in all three systems and the K/$\pi$ and p/$\pi$ ratios in p-Pb and Pb-Pb collisions showed a similar evolution with multiplicity. It is found that the latter ratios in pp collisions evolve as a function of multiplicity in a very similar way as in the larger systems. While a hydrodynamical description can explain these effects and is justified in Pb-Pb collisions, its application to smaller systems seems questionable. The new results can help to distinguish between the variety of models that has been suggested to explain the observations. These ``soft'' phenomena are just one aspect of the physics at particle colliders. Another are ``hard'' probes like jets. Jets are objects that are defined for both experimental measurement and theoretical calculation, thus, allowing for directly comparing the two. The calculation of hadronic production cross-sections usually involves Fragmentation Functions (FFs), that need to be determined from experiment and currently exhibit large systematic uncertainties. The MTF is therefore also used to measure the charged hadron composition in charged jets from pp collisions. The spectra have been obtained as a function of the transverse momentum of the constituent, $p_{\mathrm{T}}^{\mathrm{track}}$, and as a function of the reduced momentum $z^{\mathrm{charged}} \equiv p_{\mathrm{T}}^{\mathrm{track}} / p_{\mathrm{T}}^{\mathrm{jet,charged}}$. An increase of the strangeness production with $z^{\mathrm{charged}}$ and the suppression of leading baryons ($z^{\mathrm{charged}} \rightarrow 1$) is visible in the K/$\pi$ and p/$\pi$ ratios. The results can be used to further constrain the FFs and to distinguish between theoretical models. A comparison to various PYTHIA Perugia tunes shows that all considered tunes roughly reproduce the observed trends, but none of them provides a perfect description of the data.