This thesis presents the measurement of the production cross section of a W boson with a single charm quark in 7 TeV proton-proton collisions using the ATLAS detector at the Large Hadron Collider. The data analysed correspond to an integrated luminosity of 4.6 fb 1 and were collected during 2011. This is the first time that ATLAS data has been used for this particular measurement. This cross section is of particular interest as a probe of the strange quark density of the proton. Typically, the strange quark density is considered to be suppressed relative to that of the other light-quarks in the proton sea. However, some analyses suggest a more symmetric composition of light-quarks in the proton sea. The results of this study aim to improve the precision of the determination of the strange quark density. The analysis uses events where the W boson decays to a muon and a neutrino. In such events, the charm quark is identified by its semileptonic decay to a soft muon within a hadronic jet. The charge correlation between the W boson and the soft muon is exploited to reduce the backgrounds substantially. The analysis results are combined with those obtained using additional decay channels. The measured cross section provides further constraint for the determination of the strange quark density, advancing the knowledge of the fundamental structure of the proton. The results are compared with predictions of next-to-leading-order QCD calculations obtained using various parton distribution function parameterisations. Additionally, the ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26 0.30 at Q2 = 1.9 GeV2. This supports the hypothesis of a symmetric composition of light-quarks in the proton sea. The cross section ratio (W+ + c)= (W + c) is also determined and compared with different predictions for the asymmetry of the strange and anti-strange quark distribution functions.

Decays of neutral D mesons to final states containing K + π's could provide evidence for CP-violation from a source not accounted for in the Standard Model. Due to the interference between Cabibbo-favored and Cabibbo-suppressed transitions, a decay rate asymmetry of D0 → K0S π0 compared to D0 → K0Lπ0 has been predicted to be non-zero. If New Physics interferes in doubly Cabibbo-suppressed D decays, the measurement of this asymmetry would differ from the predicted value and may provide evidence for CP-violation beyond the CKM mechanism. I present an analysis method to measure this branching fraction asymmetry, R(D0) ≡ B(D0→K0S π0)−B(D0→K0L π0)/(B(D0→K0Sπ0)+B(D0→K0Lπ0)), utilizing e+e− → cc events in the Belle dataset. / Doctor of Philosophy / The Universe appears to be made almost entirely of matter rather than antimatter; however, matter and antimatter should have been created in equal amounts in the Big Bang. We do not know exactly why we observe so much more matter as compared to antimatter. The Standard Model (SM) of particle physics accounts for some of the asymmetry through Charge-Parity (CP) symmetry violation, which explains how particles behave differently than their corresponding antiparticles. In the current state of the SM, some CP-violation is allowed in decays via the weak force, but the theory does not account for enough CP violation to explain the amount of matter-antimatter asymmetry observed in the Universe. Decays of a D meson to a kaon (K meson) plus one or more pions (π mesons) via a new mechanism beyond the weak force could provide evidence of a new source of CP-violation. In this analysis, I present a method for analyzing the decays of neutral D mesons to a neutral kaon and a neutral pion in the Belle dataset to test the SM.