Measurement of azimuthal correlations of D$^{+}$ mesons with charged particles in pp collisions at $\sqrt{s}$ = 7 TeV and p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV with ALICE at the LHC

ALICE (A Large Ion Collider Experiment) was designed for the study of heavy-ion collisions at the LHC. It is now established that in these collisions a state of matter consisting of deconfined quarks and gluons, Quark-Gluon Plasma (QGP), is formed. The QGP appears as the hottest and almost lowest-viscosity liquid ever observed. While the experiments at LHC and at RHIC have unravelled a lot of its properties, one still does not have a complete picture. One of the ways of exploring the properties of the QGP would be to perform Rutherford scattering experiments with well-defined probes. One can use hard scattering processes as sources of strongly-interacting probes. Then by comparing particle production rates in ion-ion collisions to that in proton-proton collisions, one can gain insight into the properties of the medium. There are several ways by which one can learn about medium properties, for example, measurement of two particle correlations distribution and their properties such as, yield $I_{\rm{AA}}$, defined as the ratio of per correlation yields $Y$, measured in heavy-ion to that observed in pp collisions. Two particle angular correlations have been extensively used to study the properties of the deconfined matter created in ultra-relativistic collisions at RHIC and LHC. Building correlations with heavy-flavour particle having a mass greater than $\Lambda_{QCD}$ has the advantage that their production is controlled by perturbative QCD and they are produced in the initial stages of the collision. Hence they experience the full evolution of the fireball and are therefore ideal probes to determine the properties of the medium formed in heavy-ion collisions. Further, they provide insight into the energy loss mechanism of heavy quarks a topic of current interest. In this thesis work, we have measured the angular correlations between D$^{+}$ meson (trigger particles) and associated charged particles in pp and p-Pb collisions with the ALICE detector. The measurements in pp collisions can provide insight into the production of heavy flavour particles and also provides a necessary reference for the heavy-ion measurements. To understand the complete picture of energy loss mechanism in heavy-ion collisions, one needs to understand cold nuclear matter (CNM) effects in the initial and final states of the collisions. Therefore, the study of D$^{+}$ meson angular correlations in p-Pb collisions may shed light on the underlying production mechanisms that give rise to the double-ridge structure observed in high multiplicity p-Pb collisions with di-hadron correlations (light-flavour sector). The correlations distribution have been studied using D$^+$ meson as trigger particle in three $p_{\rm{T}}$ ranges from 3-5 GeV/$c$, 5-8 GeV/$c$ and 8-16 GeV/$c$ and with associated charged particles having $p_{\rm{T}}$ greater than 0.3 GeV/$c$, between 0.3 to 1.0 GeV/$c$ and finally with $p_{\rm{T}}$ greater than 1 GeV/$c$. The similar correlation measurements using other D mesons (D$^{0}$ and D$^{*+}$) as trigger particles have also been performed by the ALICE collaboration and to improve the statistical precision on the results, average correlations from three (D$^{+}$, D$^{0}$ and D$^{*+}$) measurements have been evaluated. The correlation properties of the averaged distributions have been then extracted and studied as a function of trigger $p_{\rm{T}}^{D}$. Finally, correlation distributions are compared with simulations using different event generators and their tunes, e.g. PYTHIA, POWHEG+PYTHIA and EPOS. This thesis work is first measurement of azimuthal correlations between D mesons and charged particles performed using minimum bias proton-proton collisions at $\sqrt{s} = 7$ TeV and proton-lead collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV collected by ALICE experiment in 2010 and 2013 respectively.