Experimental results on a search for charmed particle production in proton-proton collisions at the center of mass energy (.sqrt.s) of 53 GeV are presented. Evidence of cidences, a signature of charmed particle production, was sought. The inclusive e/.pi. ratio was measured with a magnetic spectrometer located at 32° from Beam 1 of Intersection I6 of the CERN Intersecting Storage Rings (ISR). The e/.pi. ratio from direct (unknown) sources was found to rise from 1.06 x 10−4 at p/sub perpendicular to/ = 1.5 GeV/c to 5.53 x 10−4 at p/sub perpendicular to/ = 0.25 GeV/c. One possible source for this signal is the semi-leptonic decay of charmed particles (e.g., D .-->. K° e.nu.). If so, then electron-strange particle (e.g., .lambda.°, K°) coincidences are expected. The charged decay products of .lambda.° and K° were detected in a multiparticle spectrometer surrounding Beam 1 downstream of the intersection. To determine if there is an electron-strange particle correlation, the number of .lambda.°'s (K°'s) in coincidence with an electron in the 32° spectrometer was compared with the number of .lambda.'s (K°'s) in coincidence with a hadron in the same kinematic range. No evidence for an enhanced production of strange particles with electrons relative to hadrons was found. However, given the acceptance of the apparatus, the absence of a signal is consistent with current models of charmed particle production and decay. 40 references, 51 figures, 20 tables.

The associated production of a W boson and a single charm quark (W+c) is the only process in proton-proton collisions that directly probes the strange quark content of the proton. In this thesis, W+charm production is measured in proton-proton collisions at the LHC at 13 TeV, as recorded by the Compact Muon Solenoid (CMS) experiment. The analysis focuses on the identification of W bosons in their leptonic decay to a muon and a neutrino and charm quarks are tagged via the full reconstruction of D*-Mesons. The measured cross sections of W+c production are used, in combination with other relevant CMS results and the most precise HERA DIS data, in a QCD analysis to determine the strange quark content of the proton. The resulting strange quark distribution and suppression, with respect to the other light sea quarks, are in good agreement with those obtained in neutrino scattering experiments and extend their kinematic reach.

^ 74 GeV and |y| 2.4; the b jets must contain a B hadron. The measurement has significant statistics up to p T ∼ O(TeV). Advanced methods of unfolding are performed to extract the signal. It is found that fixed-order calculations with underlying event describe the measurement well.

There has been much recent discussion of the possibility of the existence of 'charmed' particles, hadrons which possess non-zero values of 'charm', a further additive quantum number. These particles may be generated either in the three triplet model of Han and Nambu or by the postulate of a fourth, charm-bearing quark. On the assumption that charm, like strangeness, is conserved in strong and electromagnetic interactions (the opposite assumption would necessitate charmed particles coupling strongly to ordinary hadrons and the existence of yet undiscovered states, e.g. Z*s) but not conserved in weak interactions one might expect their production either singly in neutrino interactions or in pairs in associated production in high energy hadron collisions, to be followed by their subsequent, relatively slow, decay into 'uncharmed' particles. Various estimates as to mass, lifetime, production cross-sections and decay modes have been made for these particles. However their failure to appear as di-lepton events among the neutrino interactions of the Brookhaven A.G.S. and CERN P.S. experiments might suggest that their masses are in excess of 2 GeV/c2 the other hand, such particles would have been expected to have been observed directly in bubble chamber studies at FNAL had their lifetimes been greater than 10−11s as suggested by some authors. This proposal, which may be thought of as complementary to that of Burhop et al, is for a straightforward exposure of a stack of emulsions to a 400 GeV/c proton beam to look for evidence of the pair production of charmed particles. The spatial resolution of the emulsion technique is about one micron with the consequence that the decays of particles of mean lives in the range 10−11 to 10−14 s should be readily observable.

This thesis provides a comprehensive view of the physics of charmed hadrons in high-energy proton-proton and heavy-ion collisions. Given their large masses, charm quarks are produced in the early stage of a heavy-ion collision and they subsequently experience the full system evolution probing the colour-deconfined medium called quark-gluon plasma (QGP) created in such collisions. In this thesis, the mechanisms of charm-quark in-medium energy loss and hadronisation are discussed via the measurements of the production of charm mesons with (Ds+) and without (D+) strange-quark content in different colliding systems, using data collected by the ALICE experiment at the CERN LHC. The participation of the charm quark and its possible thermalisation in the QGP are studied via measurements of azimuthal anisotropies in the production of D+ mesons. Finally, the prospects for future measurements with the upgraded ALICE experimental apparatus and with more refined machine learning techniques are presented.