<p>During operation of heavy ion accelerators a significant pressure rise has been observed when the intensity of the high energy beam was increased. The cause for this pressure rise is ion induced desorption, which is the result when beam ions collide with residual gas molecules in the accelerator, whereby they undergo charge exchange. Since the change in charge state will affect the bending radius of the particles after they have passed a bending magnet, they will not follow the required trajectory but instead collide with the vacuum chamber wall and gas are released. For the Future GSI project FAIR (Facility for Antiproton and Ion Research) there is a need to upgrade the SIS18 synchrotron in order to meet the requirements of the increased intensity. The aim of this work was to measure the desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, Etched Cu, gold coated Cu, Ta and TiZrV coated stainless steel with argon and uranium beams at the energies 5-100 MeV/u. The measurements were performed at GSI and at The Svedberg Laboratory where a new dedicated teststand was built. It was found that the desorption yield scales with the electronic energy loss to the second power, decreasing for increasing impact energy above the Bragg Maximum. A feasibility study on the possibility to use laser refractometry to improve the accuracy of a specific throughput system was performed. The result was an improvement by up to 3 orders of magnitude, depending on pressure range.</p>

During operation of heavy ion accelerators a significant pressure rise has been observed when the intensity of the high energy beam was increased. The cause for this pressure rise is ion induced desorption, which is the result when beam ions collide with residual gas molecules in the accelerator, whereby they undergo charge exchange. Since the change in charge state will affect the bending radius of the particles after they have passed a bending magnet, they will not follow the required trajectory but instead collide with the vacuum chamber wall and gas are released. For the Future GSI project FAIR (Facility for Antiproton and Ion Research) there is a need to upgrade the SIS18 synchrotron in order to meet the requirements of the increased intensity. The aim of this work was to measure the desorption yields, η, (released molecules per incident ion) from materials commonly used in accelerators: 316LN stainless steel, Cu, Etched Cu, gold coated Cu, Ta and TiZrV coated stainless steel with argon and uranium beams at the energies 5-100 MeV/u. The measurements were performed at GSI and at The Svedberg Laboratory where a new dedicated teststand was built. It was found that the desorption yield scales with the electronic energy loss to the second power, decreasing for increasing impact energy above the Bragg Maximum. A feasibility study on the possibility to use laser refractometry to improve the accuracy of a specific throughput system was performed. The result was an improvement by up to 3 orders of magnitude, depending on pressure range.

No description available.

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / Hanbury Brown-Twiss interferometry is a correlation technique by which the size and shape of the emission function of identical particles created during collisions of high-energy leptons, hadrons or nuclei can be determined. Accurate experimental datasets of three-dimensional correlation functions in momentum space now exist; these are sometimes almost Gaussian in form, but may also show strong deviations from Gaussian shapes. We investigate the suitability of expressing these correlation functions in terms of statistical quantities beyond the normal Gaussian description. Beyond means and the covariance matrix, higher-order moments and cumulants describe the form and di erence between the measured correlation function and a Gaussian distribution. The corresponding series expansion is the Gram- Charlier series and in particular the Gram-Charlier Type A expansion found in the literature, which is based on a Gaussian reference distribution. We investigate both the Gram-Charlier Type A series as well as generalised forms based on non-Gaussian reference distributions, as well as the related Edgeworth expansion. For testing purposes, experimental data is initially represented by a suite of one-dimensional analytic non-Gaussian distributions. We conclude that the accuracy of these expansions can be improved dramatically through a better choice of reference distribution, suggested by the sign and size of the kurtosis of the experimental distribution. We further extend our investigation to simulated samples of such test distributions and simplify the theoretical expressions for unbiased estimators (k-statistics) for the case of symmetric distributions.

No description available.

We perform an event-by-event hydrodynamic analysis for Pb-Pb collisions at the incident energy of sqrt(sNN) = 2.76TeV, also studying the effects of two equations of state under the same initial conditions and freeze-out scenario: one characterized by a critical point and the other based on Lattice QCD (Quantum Chromodynamics) calculations. The observables of interest are particle spectra in terms of pseudorapidity and transverse momentum, as well as flow harmonics, which are coefficients that carry information on the initial anisotropies of the system throughout its evolution. Those are computed and compared with experimental Large Hadron Collider (LHC) data. There are slight differences in the results for each equation of state, caused by their distinct features. Lastly, the LHC-based calculations are compared with previous works related to the Relativistic Heavy-Ion Collider (RHIC) experimental data. The main techniques of the latter are performed in this work, which results in differences between some aspects in the outcome for each collision type, from initial energy distributions to freeze-out temperatures. / É feita uma análise de hidrodinâmica evento-por-evento para colisões de Pb-Pb à energia incidente de sqrt(sNN) = 2.76TeV. Estudamos os efeitos de duas equações de estado sob as mesmas condições iniciais e desacoplamento: uma é caracterizada por um ponto crítico e a outra é baseada em cálculos de Lattice QCD (Cromodinâmica Quântica). Os observáveis de interesse são os espectros de partículas em termos da pseudo rapidez e momento transversal, assim como os coeficientes harmônicos de Fourier que, por sua vez, carregam as anisotropias iniciais do sistema durante toda a sua evolução. Tais observáveis são calculados e comparados com dados experimentais do Large Hadron Collider (LHC). Por fim, os cálculos baseados em parâmetros referentes às energias do LHC são comparados com trabalhos anteriores feitos com base em dados experimentais do Relativistic Heavy-Ion Collider (RHIC). Os principais métodos usados no caso anterior são aplicados a este trabalho, o que resulta em algumas diferenças entre os resultados dos dois tipos de colisão, desde a distribuição de energia inicial a temperaturas de freeze-out.

O advento dos colisores modernos tem proporcionado novas possibilidades de estudo em física de partículas como, por exemplo, a busca por nova física e o estudo de novos estados da matéria hadrônica. Em particular, em colisões de íons pesados em altas energias, acredita-se que um novo estado da matéria seja formado antes da colisão, o chamado condensado de vidros de cor. Tal estado seria a condição inicial de um plasma de quarks e glúons e é caracterizado por altas densidades de pártons (quarks e glúons). De fato, as equações de evolução da Cromodinâmica Quântica predizem que, para virtualidades moderadas e altas energias, os hádrons se tornam sistemas extremamente densos devido ao crescimento das distribuições de glúons nessas condições. Um crescimento indefinido das distribuições de glúons poderia levar à violação do vínculo de unitariedade. Para evitar essa violação, existe um mecanismo chamado de saturação de pártons o qual contém o crescimento das distribuições de quarks e glúons de forma a respeitar o vínculo de unitariedade. Teoricamente, no limite de altas energias, observa-se que os hádrons são populados especialmente por glúons. Experimentalmente, existem indícios da saturação em colisões ep, pp, pA e AA, contudo, isso ainda é uma questão em aberto. Portanto, no limite de altas densidades, espera- se que a física não linear, a qual leva em conta efeitos de recombinações de glúon, passe a se manifestar. Uma alternativa para o estudo da saturação em colisores hadrônicos são os processos foto-induzidos, os quais ocorrem em interações ultraperiféricas. Em uma colisão ultraperiférica entre dois hádrons, o parâmetro de impacto é maior do que a soma dos raios dos hádrons, de forma que interações fortes são suprimidas. Dessa forma os hádrons atuam como fontes de fótons (quase reais) podendo ocorrer interações fóton-hádron e fóton-fóton. Nesse trabalho estudamos a fotoprodução difrativa de mésons vetoriais em energias do LHC para colisões ultraperiféricas próton-próton, próton-núcleo e núcleo-núcleo e a produção dupla de mésons vetoriais em colisões fóton-fóton e devido ao mecanismo de duplo espalhamento fóton-p(A). Mostramos como esses processos podem ser usados para estudar a física de altas energias e os efeitos de saturação. Os efeitos de saturação em nossos cálculos são levados em conta através do formalismo de dipolo de cor, que é uma das ferramentas básicas usadas nessa tese. O tratamento de colisões ultraperiféricas hádron-hádron foi feito com a aproximação de fótons equivalentes que assim como o formalismo de dipolo, foi extensamente usada. Nossos resultados apontam que o estudo fenomenológico e experimental dos tipos de processos citados acima são factíveis e podem ser usados para vincular a dinâmica da QCD em altas energias. / The advent of the modern colliders has provided new possibilities of study in particle physics as, for example, the search for new physics and the study of new states of the hadronic matter. In particular, in high energy heavy ion collisions is expected that a new state can be formed before the collision, the so called Color Glass Condensate. This state would be the initial condition of the Quark Gluon Plasma and is characterized by high parton (quarks and gluons) densities. Indeed, the Quantum Chromodynamics evolution equations predict that, for moderate virtualities and high energies, the hadrons become extremely dense systems due to the growth of the parton distribution in these conditions. An indefinite growth of the parton distributions could lead to the violation of the unitarity bound. To avoid this violation, there is a mechanism called parton saturation which tames the growth of the parton distributions to satisfy the unitarity bound. Theoretically, in the high energy limit, one can see that the hadrons are populated mainly by gluons. Experimentally, there are indications of the saturation in ep, pp, pA and AA collisions, however, this is an open question. So, in the high density limit, we expect that the nonlinear physics, which takes into account gluon recombination effects start to manifest itself. An alternative for the study of the saturation at hadronic colliders are the photon-induced processes, which occurs in ultra-peripheral collisions. In a ultra-peripheral collision between two hadrons the impact parameter is greater than the sum of the radii of the hadrons, so the strong interaction is suppressed. Thus, the hadrons act as sources of (almost real) photons and may occur photon-hadron and photon-photon interactions. In this work we study the diffractive photoproduction of vector mesons at LHC and future colliders energies in ultra-peripheral proton-proton, proton-nucleus and nucleus-nucleus collisions and the double vector meson production in photon-photon collisions and due to the double photon-p(A) scattering mechanism. We show how these processes can be used to study the high energy physics and the saturation effects. These effects are considered in our calculations through the color dipole formalism, which is one of the basic tools used in this thesis. The treatment of the ultra-peripheral hadron-hadron collisions was done through the equivalent photon approximation that just as in the dipole formalism, was widely used. Our results point that the phenomenological and experimental studies of the processes cited above are feasible and can be used to constraint the QCD dynamics in high energies.

Neste trabalho são reportadas medidas realizadas no detector PHENIX do RHIC sobre J/Psi em colisões p+p e Au+Au a s^(1/2) = 200 GeV na região de rapidez central e Psi\' em colisões p+p nas mesmas condições. As medidas incluem a dependência com o momento transverso da produção de charmônio e o fator de modificação nuclear de J/Psis para vários regimes de centralidade de colisão. / This work reports measurements done by the PHENIX detector at RHIC about J/Psi in p+p and Au+Au collisions at s^(1/2) = 200 GeV in the mid-rapidity range and Psi\' in p+p collisions in the same conditions. The measurements include the transverse momentum dependence of charmonium production and J/Psi nuclear modification factor in different centrality regimes.

We perform an event-by-event hydrodynamic analysis for Pb-Pb collisions at the incident energy of sqrt(sNN) = 2.76TeV, also studying the effects of two equations of state under the same initial conditions and freeze-out scenario: one characterized by a critical point and the other based on Lattice QCD (Quantum Chromodynamics) calculations. The observables of interest are particle spectra in terms of pseudorapidity and transverse momentum, as well as flow harmonics, which are coefficients that carry information on the initial anisotropies of the system throughout its evolution. Those are computed and compared with experimental Large Hadron Collider (LHC) data. There are slight differences in the results for each equation of state, caused by their distinct features. Lastly, the LHC-based calculations are compared with previous works related to the Relativistic Heavy-Ion Collider (RHIC) experimental data. The main techniques of the latter are performed in this work, which results in differences between some aspects in the outcome for each collision type, from initial energy distributions to freeze-out temperatures. / É feita uma análise de hidrodinâmica evento-por-evento para colisões de Pb-Pb à energia incidente de sqrt(sNN) = 2.76TeV. Estudamos os efeitos de duas equações de estado sob as mesmas condições iniciais e desacoplamento: uma é caracterizada por um ponto crítico e a outra é baseada em cálculos de Lattice QCD (Cromodinâmica Quântica). Os observáveis de interesse são os espectros de partículas em termos da pseudo rapidez e momento transversal, assim como os coeficientes harmônicos de Fourier que, por sua vez, carregam as anisotropias iniciais do sistema durante toda a sua evolução. Tais observáveis são calculados e comparados com dados experimentais do Large Hadron Collider (LHC). Por fim, os cálculos baseados em parâmetros referentes às energias do LHC são comparados com trabalhos anteriores feitos com base em dados experimentais do Relativistic Heavy-Ion Collider (RHIC). Os principais métodos usados no caso anterior são aplicados a este trabalho, o que resulta em algumas diferenças entre os resultados dos dois tipos de colisão, desde a distribuição de energia inicial a temperaturas de freeze-out.

Nessa tese serão apresentadas medidas de anisotropia azimutal elíptica de elétrons de decaimentos de quarks pesados feitas no perimento de colisão de íons pesados ALICE (A Large Ion Collider Experiment, em inglês). As medidas foram obtidas em colisões de Pb-Pb com energia de centro de massa por par de nucleons (psNN) igual a 2.76 TeV com o colisor de hadrons LHC (Large Hadron Collider, em inglês). Colisões ultrarelativísticas de íons pesados podem alcançar temperaturas e/ou densidades de energia suficientemente altas para formar o Plasma de Quarks e Gluons (QGP, na sigla em inglês), o estado da matéria onde os partons estão desconfinados dos hadrons. O parâmetro de anisotropia azimutal elíptica é um dos observáveis mais importantes utilizados no estudo da formação do QGP. Esse parâmetro é quantificado pelo segundo harmônico, denominado v2, da distribuição do ângulo azimutal das partículas em relação ao ângulo do plano de reação, o qual é definido pela direção do parâmetro de impacto e pela direção do feixe de partículas. Medidas de anisotropia azimutal elíptica de quarks pesados (charm e beauty) são interessantes, pois os quarks pesados são sondas sensíveis às propriedades do QGP, visto que eles são predominantemente produzidos em processos iniciais de espalhamento duro e interagem com o meio desconfinado. Medidas de v2 de elétrons de decaimentos de quarks pesados em baixos valores de momento transversal indicam movimento coletivo de quarks pesados e possível termalização no QGP. Por outro lado, medidas de v2 de elétrons de decaimentos de quarks pesados em altos valores de momento transversal são interpretadas como uma dependência da geometria do meio por onde os quarks pesados atravessam e perdem energia. Serão mostrados resultados de v2 de elétrons de decaimentos de quarks pesados em função do momento transversal em colisões de Pb-Pb a psNN = 2.76 TeV em eventos com centralidades 20-40% e 30-50%. O resultado é comparado com previsões teóricas e medida obtida em colisões de Au-Au a psNN = 0.2 TeV no experimento RHIC. Resultados preliminares de v2 de elétrons de decaimentos de charm e beauty, separadamente, também serão mostrados em colisões de Pb-Pb a psNN = 2.76 TeV em eventos com centralidade 30-50%. / This thesis presents measurements of the elliptic azimuthal anisotropy of electrons from heavy-flavour decays with the A Large Ion Collider Experiment (ALICE). The measurement is performed for the first time in Pb-Pb collisions at center-of-mass energy per colliding nucleon pair psNN = 2.76 TeV at the Large Hadron Collider (LHC). In heavy-ion collisions at ultrarelativistic energies sufficiently high temperature and/or energy density can be achieved to form the Quark-Gluon Plasma (QGP), the state of matter predicted by Quantum Chromodynamics (QCD) in which quarks and gluons are deconfined from hadrons. One of the most important probes of the QGP formation is the elliptic azimuthal anisotropy, which is quantified by the second harmonic v2 of the particle azimuthal angle distribution with respect to the angle of the reaction plane, which is defined by the impact parameter direction and the beam direction. In addition, heavy quarks (charm and beauty) serve as a sensitive probe of the QGP properties since they are predominantly produced in initial hard scattering processes and interact with the deconfined medium. The transverse momentum dependence of the heavy-flavour decay electron v2 can be used to investigate the QGP properties. The measurement of v2 of electrons from heavy-flavour decays at low transverse momentum provides a way to test whether heavy quarks take part in the collective motion in the medium. Whereas, v2 of electrons from heavy-flavour decays at high transverse momentum is interpreted as a path length dependence of heavy-quark energy loss within the created dense medium. Results of the elliptic azimuthal anisotropy of electrons from heavy-flavour decays as a function of tranverse momentum obtained in 20-40% and 30-50% central Pb-Pb collisions at psNN = 2.76 TeV will be shown. The measurement is compared with theoretical predictions and previous measurement at the RHIC experiment. Preliminary measurements of the elliptic azimuthal anisotropy of electrons from charm and beauty as a function of tranverse momentum in 30-50% central Pb-Pb collisions at psNN = 2.76 TeV will be shown as well.