Following a NEA high priority nuclear data request, an experimental campaign to measure the prompt Î3-ray emissions from 235 U has been performed. This has used the STEFF spectrometer at the new Experimental Area 2 (EAR2) within the neutron time- of-flight facility (n_TOF), a white neutron source facility at CERN with energies from thermal to approximately 1 GeV. Prior to the experimental campaign, STEFF has been optimised for the environment of EAR2. The experimental hall features a high background Î3-ray rate, due to the nature of the spallation neutron source. Thus an investigation into reduction of the background Î3-ray rate, encountered by the NaI(Tl) detector array of STEFF, has been carried out. This has been via simulations using the simulation package FLUKA. Various materials and shielding geometries have been investigated but the effects determined to be insufficient in reducing the background rate by a meaningful amount. The NaI(Tl) detectors have been modified to improve their performance in a high count rate environment, and their behaviour characterised to understand the response to higher count rates. Initial testing demonstrated that the modified detectors maintain a potential to measure Î3-ray multiplicities up to 3 counts per microsecond. However, the energy resolution fails somewhere below 1.75 counts per microsecond. The experimental campaign has produced a large amount of data. The preliminary analysis of phase one data has considered incoming neutron energies ranging from thermal to an upper limit of 1 eV, with a minimum Î3-ray energy threshold of 160 keV. Results have been achieved for the prompt fission Î3-ray multiplicity and total energy of M Î3 = 6.3 ± 0.2 and E S,Î3 = 9.0 ± 0.1 MeV respectively. Further work is ongoing by the STEFF team at Manchester to improve upon these results and analyse the remainder of the data set at higher incoming neutron energies.

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Title: Analysis of J/Psi + photon production in proton-proton collisions on ATLAS at LHC Author: Bc. Zuzana Vidláková Department: Institute of particle and nuclear physics Supervisor: prom. fyz. Václav Vrba, CSc. (Academy of Sciences of the Czech Republic) Abstract: The subject of this thesis is physics connected to quarkonia and their studies at the ATLAS detector situated at LHC in CERN, Geneva. In this thesis, following topics are cov- ered: ATLAS detector, history of physics connected to quarkonia, production mechanisms of quarkonia, software used at CERN for data analysis and cross-section measurement of J/Psi + photon continuum. The analysis was done on behalf of the B-physics working group at ATLAS. Keywords: CERN, LHC, ATLAS, B-fyzika, quarkonia

Dans les prochaines années, le complexe d'accélérateur du CERN va subir une profonde mise a jour dont le but est une augmentation de la luminosité du LHC. Le projet LIU ( LHC Injectors Upgrade) coordonne les mises a jour des différentes parties de la chaine d'injection. Le projet LINAC4 s'inscrit dans ce cadre et sera la première étape de la mise à jour. Cette thèse présente les différentes études conduites lors du développement de l'instrumentation nécessaire à la mesure du faisceau. Ce travail est limité aux instruments permettant la mesure des profils transverses (taille et emittance). La thèse se divise en quatre parties. La première partie, composée des trois premiers chapitres, est vue comme une partie d'introduction où il sera présenté le projet LINAC4 ainsi que les différents aperçus théoriques nécessaires à la conception de types d'instruments requis. Le chapitre 2 décrit brièvement la dynamique des faisceaux dans un accélérateur et présente également des rappels théoriques sur l'effet de charge d'espace induit par le faisceau. Le chapitre 3 est un rappel sur les interactions entre particules et matière. La seconde partie, comprenant les chapitres 4 a 6, décrit les différentes études menées lors de la conception des SEM grid, wire scanner et emittance mètre. Le lecteur trouvera dans cette partie une description des instruments mentionnés et qui seront déployés lors de la phase de test et pendant la phase d'opération du LINAC4. Le chapitre 4 s'attarde sur les effet de charge thermique induite sur les fils des SEM grid et wire beam scanner par le faisceau et leur conséquence sur la survit de ces fils. Le LINAC4 va produire un faisceau intense d'ion H-, avec un taille de faisceau de l'ordre du millimètre, cette densité de particule va, a basse énergie, induire un grand dépôt d'énergie dans la matière. La hausse de température qui en résulte peut dépasser les limites thermomécaniques des matériaux usuels employés pour ce type de mesure. Cette étude permet de déterminer le matériau idéal pour le fil et d'imposer certaines restrictions sur l'utilisation des différents moniteurs de profils. Au sein de ce chapitre il est aussi présente une estimation des signaux obtenus pour des géométries et des matériaux de fils différents. Les chapitres 5 et 6 sont une études de l'emittance mètre a moyenne énergie du LINAC4 (3 et 12 MeV), le système employé est un système dit "Slit & grid", ou une fente permet de sélectionner une faible partie du faisceau, le reste étant absorbé, le profil du faisceau non perturbé est mesuré par une grille. Le chapitre 5 présente une _étude sur les erreurs systématiques des mesures d'_emittance dû a la diffusion multiple et _a l'effet de charge d'espace du faisceau, ces deux phénomènes constituant les principale erreurs conduisant a une mauvaise reconstruction de l'emittance mesurée. le chapitre 6 quant a lui est dédié a l'_étude mécanique de la fente de l'emittance mètre. Comme pour les fils des moniteurs de profils, la charge thermique sur la partie supportant la slit est importante. Ce chapitre décrit les études effectuées pour le choix des matériaux et de la géométrie des pièces mécaniques. La troisième partie de la thèse, qui se résume au chapitre 7, est consacrée aux différents résultats expérimentaux obtenus dans la phase de test de la source de particule du LINAC4 ainsi que ceux obtenus lors d'une visite d'étude a SNS. Une partie de se chapitre décrira la mise au point de l'instrumentation aux banc test de la source, une autre présente l'effet de la diffusion multiple sur les mesures d'emittance a SNS et propose une mise a jour de l instrument. Le chapitre 8 constitue la dernière partie de cette thèse. Dans ce dernier chapitre, le lecteur pourra lire une étude préliminaire sur l'utilisation d'un faisceau laser pour la mesure d'emittance et de profil aux hautes énergies du linac.

<p>The Large Hadron Collider (LHC) at CERN have a capacity to produce protonproton collisions with an energy of 14 TeV. Four particle detectors are included in the LHC with the purpose to detect all the particles that are created in the collisions. In one of these detectors are scintillating lead tungstate crystals used, to detect the energy of photons and electrons created in the collisions. The energy is detected by measuring of the emitted light from the scintillating crystals. As much knowledge as possible about the optical properties of the crystals are desired to be able to analyze the acquired data from the crystals.</p><p><p>This thesis work presents some techniques used for the characterization of the optical properties for the crystals. It also presents measurements done on the decay time of lead tungstate crystals and on the temperature influence to the light yield from the crystals. These measurement results are in addition used in an attempt to estimate how big influence the Cherenkov radiation has to the total amount of emitted light from the scintillating crystals.</p><p>The influence from the temperature to the light yield is around <em>−</em>2<em>.</em>02 %<em>/◦C </em>for BTCP and around <em>−</em>1<em>.</em>75 %<em>/◦C </em>for SIC¹. No conclusions could been drawn concerning the influence from the Cherenkov radiation to the total amount of emitted light from the temperature measurements.The decay time measurements showed an influence from the Cherenkov radiation to the total amount of emitted light of; 8 % for crystal 1003, 47 % for crystal 1002 and 19 % for crystal 1001.</p></p><p><p><p>¹BTCP (Bogoroditsk Technical Chemical Plant) and SIC (Shanghai Institute of Ceramics) are the two different crystal production facilities used for the production of the crystals.</p></p></p>

<p>At the ATLAS experiment at CERN’s Large Hadron Collider, bunches of protons will cross paths at a rate of 40 MHz, resulting in 14 TeV head-on collisions. During these interactions, calorimeters, spectrometers and tracking detectors will look for evidence that can confirm or disprove theories about the smallest constituents of matter and the forces that hold them together. In order for these sub-detectors to sample the signals from exotic particles correctly, they rely on a constant phase between a clock signal and the bunch crossings in the experiment.</p><p>On each side of the detector, 175 m away from the interaction point, electrostatic button pick-up detectors are installed along the accelerator ring to monitor the beam. A model describing how these detectors function as beam information transducers is constructed and analyzed in order to understand the signal.</p><p>The focus of this thesis is the design, implementation and testing of a system that uses this signal to monitor the phase between the clock signal and the arrival time of the bunches in the center of the detector. In addition, the system extracts information about the proton beam structure as well as the individual bunches. Given the interaction rate and the complexity of the processes the experiment wants to study, vast amounts of data will be generated by ATLAS. To filter out well-understood phenomena, a trigger system selects only the most interesting events to be saved for further offline analysis. A proposal for how the signals from the button pick-ups can be used as input to the trigger system is therefore also presented.</p>

The Large Hadron Collider (LHC) at CERN have a capacity to produce protonproton collisions with an energy of 14 TeV. Four particle detectors are included in the LHC with the purpose to detect all the particles that are created in the collisions. In one of these detectors are scintillating lead tungstate crystals used, to detect the energy of photons and electrons created in the collisions. The energy is detected by measuring of the emitted light from the scintillating crystals. As much knowledge as possible about the optical properties of the crystals are desired to be able to analyze the acquired data from the crystals. This thesis work presents some techniques used for the characterization of the optical properties for the crystals. It also presents measurements done on the decay time of lead tungstate crystals and on the temperature influence to the light yield from the crystals. These measurement results are in addition used in an attempt to estimate how big influence the Cherenkov radiation has to the total amount of emitted light from the scintillating crystals. The influence from the temperature to the light yield is around −2.02 %/◦C for BTCP and around −1.75 %/◦C for SIC1. No conclusions could been drawn concerning the influence from the Cherenkov radiation to the total amount of emitted light from the temperature measurements.The decay time measurements showed an influence from the Cherenkov radiation to the total amount of emitted light of; 8 % for crystal 1003, 47 % for crystal 1002 and 19 % for crystal 1001. 1BTCP (Bogoroditsk Technical Chemical Plant) and SIC (Shanghai Institute of Ceramics) are the two different crystal production facilities used for the production of the crystals.

At the ATLAS experiment at CERN’s Large Hadron Collider, bunches of protons will cross paths at a rate of 40 MHz, resulting in 14 TeV head-on collisions. During these interactions, calorimeters, spectrometers and tracking detectors will look for evidence that can confirm or disprove theories about the smallest constituents of matter and the forces that hold them together. In order for these sub-detectors to sample the signals from exotic particles correctly, they rely on a constant phase between a clock signal and the bunch crossings in the experiment. On each side of the detector, 175 m away from the interaction point, electrostatic button pick-up detectors are installed along the accelerator ring to monitor the beam. A model describing how these detectors function as beam information transducers is constructed and analyzed in order to understand the signal. The focus of this thesis is the design, implementation and testing of a system that uses this signal to monitor the phase between the clock signal and the arrival time of the bunches in the center of the detector. In addition, the system extracts information about the proton beam structure as well as the individual bunches. Given the interaction rate and the complexity of the processes the experiment wants to study, vast amounts of data will be generated by ATLAS. To filter out well-understood phenomena, a trigger system selects only the most interesting events to be saved for further offline analysis. A proposal for how the signals from the button pick-ups can be used as input to the trigger system is therefore also presented.

LHC proton-proton collisions at a centre of mass energy of $\sqrt{s} = 7 TeV were observed in 2011. From a 1.68 fb$^{-1}$ sample of the data collected using the ATLAS detector, electron-positron pairs originating from the Drell-Yan process were selected using a cut based analysis. After the selection process, an estimate of the background was determined followed by the selection efficiency, detector resolution, reconstruction efficiency, and kinematic acceptance. Using these, the Drell-Yan differential cross section was calculated as a function of invariant mass between 26 and 66 GeV/c$^2$. This measurement has a precision between 12.4\% and 8.01\% from the lower invariant mass bins to the higher ones. The Drell-Yan cross section in proton-proton collisions depends on empirical quantities known as parton distribution functions which parametrize the structure of the proton. The measurement outlined in this thesis observes a region in parton distribution function phase space previously untouched by experiments. / Graduate

The search for the Higgs boson has been a cornerstone of the physics program at the Large Hadron Collider in Geneva Switzerland. The ATLAS experiment successfully discovered the Higgs using the so-called ‘Golden Channels’ of H0 -> gamma gamma and H0 -> ZZ(∗) using data samples collected during the 2011 and 2012 run periods. In order to check if the discovered Higgs is consistent with purely Standard Model behaviour, it is necessary to further confirm the existence of the Higgs in each production mode and decay channel predicted by the Standard Model. For this dissertation, a search for the Higgs was conducted using the H0 -> b bbar decay channel, where the Higgs is produced by the inverse pair decay of two weak bosons exchanged by a scattered quark pair, also known as Vector Boson Fusion (VBF). This analysis uses data samples collected during the 2011 run period by the ATLAS detector totalling 4.2 /fb of proton-proton collisions at sqrt(s) = 7 TeV. No excess of events above background expectation is observed and 95% confidence level upper limits on the Standard Model Higgs cross section times branching ratio, sigma(VBF) x BR(H0 -> b bbar), are derived for Higgs masses in the range 115 < mH < 130 GeV. An observed 95% confidence level upper limit of 18.7 times the Standard Model cross section is obtained for a Higgs boson mass of 125 GeV. / Graduate / 0798