<p>Quantum chromodynamics has interesting limits both in the low and the high-energy region. In the low energy region one has phenomenology of meson interactions which are still not clearly understood. In the high-energy region one wants to find a new theory which will envelope gravity and the standard model in the quantum framework, possibly via some kind of string theory.</p><p>In this thesis some aspects are touched upon including both these limits. On the one hand we look at meson scattering close to threshold and try to describe cross sections via phenomenological models such as the two-step model. We then go on and dwell upon noncommutative geometry, a framework which has been successful in describing certain aspects of the theory of strings.</p><p>The low-energy calculations gave some insight into the need for finding better understanding of the theories of mesons. The work on noncommutative geometry was on the other hand fruitful in gaining understanding of certain connections between different star products and their relations on a local level.</p>

<p> Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important parts of the analysis include the identification of neutral pions from the invariant mass of the decay gammas, the identification of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp®ppπ⁺π^-, the pp®ppπ⁰π⁰ and the pp®pnπ⁺π⁰ reactions are presented at beam energies ranging from 650 to 775 MeV. </p><p>The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the δ and the <i>N</i>^* resonances in either one or both of the participating nucleons. </p><p>The <i>N</i>^*(1440)®N(πp)^T=0_S−<i>wave</i> transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions. </p>

Two-pion production reactions in proton-proton collisions have been studied using the PROMICE/WASA detector and an internal cluster gas-jet target at the CELSIUS storage ring in Uppsala. Three out of the four isospin-independent reaction channels have been measured at several energies in the intermediate and near threshold energy region. Important parts of the analysis include the identification of neutral pions from the invariant mass of the decay gammas, the identification of positive pions with the delayed pulse technique and the use of Monte Carlo simulations to understand the detector response. The total cross sections for the pp®ppπ+π-, the pp®ppπ0π0 and the pp®pnπ+π0 reactions are presented at beam energies ranging from 650 to 775 MeV. The production mechanism for two-pion production near threshold seems to be dominated by resonance production. The contribution from the non-resonant terms alone can not reproduce the total cross sections. In most models, two-pion production is governed by the δ and the N* resonances in either one or both of the participating nucleons. The N*(1440)®N(πp)T=0S−wave transition has been suggested as the dominating production mechanism for two-pion production in proton-proton collisions. However, the total cross sections presented in this thesis show that other production mechanisms also must give large contributions.

Quantum chromodynamics has interesting limits both in the low and the high-energy region. In the low energy region one has phenomenology of meson interactions which are still not clearly understood. In the high-energy region one wants to find a new theory which will envelope gravity and the standard model in the quantum framework, possibly via some kind of string theory. In this thesis some aspects are touched upon including both these limits. On the one hand we look at meson scattering close to threshold and try to describe cross sections via phenomenological models such as the two-step model. We then go on and dwell upon noncommutative geometry, a framework which has been successful in describing certain aspects of the theory of strings. The low-energy calculations gave some insight into the need for finding better understanding of the theories of mesons. The work on noncommutative geometry was on the other hand fruitful in gaining understanding of certain connections between different star products and their relations on a local level.

Meson production in proton-deuteron collisions has been studied using the WASA detector facility at the CELSIUS storage ring in Uppsala. Data were obtained at two different beam energies, 1360 MeV and 1450 MeV, slightly above threshold for η and ω mesons. The differential cross sections of pd → 3He ω constitute the first measurements of this reaction covering the whole angular range. The ω angular distributions are isotropic at 1360 MeV but have strong forward and backward enhancements at 1450 MeV. Theoretical calculations using a two-step model fail to reproduce the shapes of the angular distributions and underestimate the total cross sections. The tensor polarisation of the ω meson has been derived from the measured angular distributions of the ω decay products. The π+ π- π0 and the π0 γ decay channels gave consistent results, showing that the ω meson is produced unpolarised at both energies. This is in contrast to a recent MOMO measurement which showed that the Φ meson is produced almost completely polarised in the pd → 3HeΦ reaction. Different production dynamics of ω and Φ mesons close to threshold raises the question whether the Okubo-Zweig-Iizuka (OZI) rule is applicable in low-energy nucleon-nucleon reactions. The angular distributions of the η meson produced in the pd → 3He η reaction are strongly enhanced for forward going η mesons at both energies. The σ(pd → 3He π+ π- π0 )/σ(pd → 3He π0 π0 π0 ) ratio has been measured and discussed in terms of isospin amplitudes. A rough estimate of the pd → 3He π0 π0 π0 π0 cross sections has also been obtained and the pd → 3He η π0 reaction has been studied for the first time near threshold.

No description available.

Com o objetivo de investigar a fotoprodução de kaons na região de energias intermediarias, foram realizadas medidas de seção de choque de fotoprodução de híperons utilizando o deutério como alvo, entre 0,50 e 2,95GeV. Para obtenção das medidas foi utilizado o acelerador de elétrons do TJNAF (Thomas Jefferson National Accelerator Facility) localizado na Virginia, USA. Foram obtidas seções de choque de fotoprodução para as reações gama(p, K+)lambda, gama(p, K+)sigmaº, sigma(n, K+)lambda-. Observou-se a estrutura de interferência na proximidade do limiar de produção de \'lambdaº, previsto teoricamente. As seções de choque obtidas foram comparadas com o modelo teórico existente fornecendo informações fundamentais para uma elaboração teórica mais consistente. Foram ainda, observados lambda(1385) com grande resolução abrindo possibilidade de realizar um estudo muito interessante desta produção. / Kaon photoproduction on deuterium was investigated and the differential cross sections were determined using the data obtained in Hall B at TJNAF (Thomas Jefferson National Accelerator Facility). Real photons were produced in the range covered from 0.50 to 2.95GeV. The cross section for kaon production reactions gama(p, K+ ) lambda, gama(p, K+ ) \'sigmaº, sigma(n, K+)lambda- were obtained. The interference structure near the production of lambdaº, predicted theoretically, was revealed. Theoretical model was compared to the cross section obtained and fundamental informations became available in order to improve the consistence of the model existent. At last, lambda(1385) were identified with good resolution conducting to interesting investigation in the future.

This thesis reports two measurements performed using proton-proton collision data collected by the LHCb detector in 2011 and 2012, corresponding to an integrated luminosity of 3 inverse femtobarn and centre-of-mass energies of 7 and 8 TeV respectively. The first measures the CP asymmetry in Bs-anti-Bs oscillations, called asls. This is measured in inclusive Bs and anti-Bs to Ds mu nu X decays, where the Ds meson is reconstructed in the final state K K pi. The measurement is performed in three regions in the Dalitz phase space of the Ds decay, and corrected for detection and background asymmetries. A value of asls = (0.39 +/- 0.26(stat) +/- 0.20(syst))% is found, which is the world's most precise measurement of a CP asymmetry in B meson mixing and is consistent with the Standard Model prediction. The second measurement determines the production asymmetry of Ds mesons, and probes non-perturbative QCD models. It is performed in bins of transverse momentum and pseudorapidity in the kinematic region 2.5.

We investigate charmonium production in the hot medium created by heavy-ion collisions by setting up a framework in which in-medium charmonium properties are constrained by thermal lattice QCD (lQCD) and subsequently implemented into kinetic approaches. A Boltzmann transport equation is employed to describe the time evolution of the charmonium phase space distribution with the loss and gain term accounting for charmonium dissociation and regeneration (from charm quarks), respectively. The momentum dependence of the charmonium dissociation rate is worked out. The dominant process for in-medium charmonium regeneration is found to be a 3-to-2 process. Its corresponding regeneration rates from different input charmquark momentum spectra are evaluated. Experimental data on J/[psi] production at CERN-SPS and BNL-RHIC are compared with our numerical results in terms of both rapidity-dependent inclusive yields and transverse momentum (pt) spectra. Within current uncertainties from (interpreting) lQCD data and from input charm-quark spectra the centrality dependence of J/[psi] production at SPS and RHIC (for both mid-and forward rapidity) is reasonably well reproduced. The J/[psi] pt data are shown to have a discriminating power for in-medium charmonium properties as inferred from different interpretations of lQCD results.

Com o objetivo de investigar a fotoprodução de kaons na região de energias intermediarias, foram realizadas medidas de seção de choque de fotoprodução de híperons utilizando o deutério como alvo, entre 0,50 e 2,95GeV. Para obtenção das medidas foi utilizado o acelerador de elétrons do TJNAF (Thomas Jefferson National Accelerator Facility) localizado na Virginia, USA. Foram obtidas seções de choque de fotoprodução para as reações gama(p, K+)lambda, gama(p, K+)sigmaº, sigma(n, K+)lambda-. Observou-se a estrutura de interferência na proximidade do limiar de produção de \'lambdaº, previsto teoricamente. As seções de choque obtidas foram comparadas com o modelo teórico existente fornecendo informações fundamentais para uma elaboração teórica mais consistente. Foram ainda, observados lambda(1385) com grande resolução abrindo possibilidade de realizar um estudo muito interessante desta produção. / Kaon photoproduction on deuterium was investigated and the differential cross sections were determined using the data obtained in Hall B at TJNAF (Thomas Jefferson National Accelerator Facility). Real photons were produced in the range covered from 0.50 to 2.95GeV. The cross section for kaon production reactions gama(p, K+ ) lambda, gama(p, K+ ) \'sigmaº, sigma(n, K+)lambda- were obtained. The interference structure near the production of lambdaº, predicted theoretically, was revealed. Theoretical model was compared to the cross section obtained and fundamental informations became available in order to improve the consistence of the model existent. At last, lambda(1385) were identified with good resolution conducting to interesting investigation in the future.