Vector meson photoproduction in ultra-peripheral heavy ion collisions with ALICE at the LHC

Ultra-relativistic heavy ions generate strong electromagnetic fields which offer the possibility to study γ-γ and γ-nucleus processes at the LHC in the so called ultra-peripheral collisions (UPC). The photoproduction of J/ψ vector mesons in UPC is sensitive to the gluon distribution of the interacting nuclei. In this thesis the study of coherent and incoherent J/ψ production in Pb-Pb collisions at √sNN = 2.76 TeV is described. The J/ψ has been measured via its leptonic decay in the rapidity range -0.9 < y < 0.9. The cross section for coherent and incoherent J/ψ are given. The results are compared to theoretical models for J/ψ production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process γ γ→ e+e− has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions. The analysis has been published by the ALICE Collaboration in the European Physical Journal C, with one of its main plot depicted on the cover-front of the November 2013 issue.

Measurements of ttbar Differential Cross Section at the ATLAS Experiment in pp Collisions at sqrt(s)=7TeV and sqrt(s)=8TeV

This PhD thesis presents two measurements of differential production cross section of top and anti-top pairs tt ̅ decaying in a lepton+jets final state. The normalize cross section is measured as a function of the top transverse momentum and the tt ̅ mass, transverse momentum and rapidity using the full 2011 proton-proton (pp) ATLAS data taking at a center of mass energy of √s=7 TeV and corresponding to an integrated luminosity of L=4.6 〖fb〗^(-1). The cross section is also measured at the particle level as a function of the hadronic top transverse momentum for highly energetic events using the full 2012 data taking at √s=8 TeV and with L=20 〖fb〗^(-1). The measured spectra are fully corrected for detector efficiency and resolution effects and are compared to several theoretical predictions showing a quite good agreement, depending on different spectra.

The new Beam Halo Monitor for the CMS experiment at the LHC

In the context of increasing beam energy and luminosity of the LHC accelerator at CERN, it will be important to accurately measure the Machine Induced Background. A new monitoring system will be installed in the CMS cavern for measuring the beam background at high radius. This detector, called the Beam Halo Monitor, will provide an online, bunch-by-bunch measurement of background induced by beam halo interactions, separately for each beam. The detector is composed of synthetic quartz Cherenkov radiators, coupled to fast UV sensitive photomultiplier tubes. The directional and fast response of the system allows the discrimination of the background particles from the dominant flux in the cavern induced by pp collision debris, produced within the 25 ns bunch spacing. The readout electronics of this detector will make use of many components developed for the upgrade of the CMS Hadron Calorimeter electronics, with a dedicated firmware and readout adapted to the beam monitoring requirements. The PMT signal will be digitized by a charge integrating ASIC, providing both the signal rise time and the charge integrated over one bunch crossing. The backend electronics will record bunch-by-bunch histograms, which will be published to CMS and the LHC using the newly designed CMS beam instrumentation specific DAQ. A calibration and monitoring system has been designed to generate triggered pulses of UV light to monitor the efficiency of the system. The experimental results validating the design of the detector, the calibration system and the electronics will be presented.

Measurement of the $B^0$ - $\bar{B}^0$ and $B^0_s$ - $\bar{B}^0_s$ production asymmetries in pp collisions at $\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV with the LHCb experiment

The production rate of $b$ and $\bar{b}$ hadrons in $pp$ collisions are not expected to be strictly identical, due to imbalance between quarks and anti-quarks in the initial state. This phenomenon can be naively related to the fact that the $\bar{b}$ quark produced in the hard scattering might combine with a $u$ or $d$ valence quark from the colliding protons, whereas the same cannot happen for a $b$ quark. This thesis presents the analysis performed to determine the production asymmetries of $B^0$ and $B^0_s$. The analysis relies on data samples collected by the LHCb detector at the Large Hadron Collider (LHC) during the 2011 and 2012 data takings at two different values of the centre of mass energy $\sqrt{s}=7$ TeV and at $\sqrt{s}=8$ TeV, corresponding respectively to an integrated luminosity of 1 fb$^{-1}$ and of 2 fb$^{-1}$. The production asymmetry is one of the key ingredients to perform measurements of $CP$ violation in b-hadron decays at the LHC, since $CP$ asymmetries must be disentangled from other sources. The measurements of the production asymmetries are performed in bins of $p_\mathrm{T}$ and $\eta$ of the $B$-meson. The values of the production asymmetries, integrated in the ranges $4 < p_\mathrm{T} < 30$ GeV/c and $2.5<\eta<4.5$, are determined to be: \begin{equation} A_\mathrm{P}(\B^0)= (-1.00\pm0.48\pm0.29)\%,\nonumber \end{equation} \begin{equation} A_\mathrm{P}(\B^0_s)= (\phantom{-}1.09\pm2.61\pm0.61)\%,\nonumber \end{equation} where the first uncertainty is statistical and the second is systematic. The measurement of $A_\mathrm{P}(B^0)$ is performed using the full statistics collected by LHCb so far, corresponding to an integrated luminosity of 3 fb$^{-1}$, while the measurement of $A_\mathrm{P}(B^0_s)$ is realized with the first 1 fb$^{-1}$, leaving room for improvement. No clear evidence of dependences on the values of $p_\mathrm{T}$ and $\eta$ is observed. The results presented in this thesis are the most precise measurements available up to date.

Fast and accurate numerical solutions in some problems of particle and radiation transport: synthetic acceleration for the method of short characteristics, Doppler-broadened scattering kernel, remote sensing of the cryosphere

The aim of this work is to present various aspects of numerical simulation of particle and radiation transport for industrial and environmental protection applications, to enable the analysis of complex physical processes in a fast, reliable, and efficient way. In the first part we deal with speed-up of numerical simulation of neutron transport for nuclear reactor core analysis. The convergence properties of the source iteration scheme of the Method of Characteristics applied to be heterogeneous structured geometries has been enhanced by means of Boundary Projection Acceleration, enabling the study of 2D and 3D geometries with transport theory without spatial homogenization. The computational performances have been verified with the C5G7 2D and 3D benchmarks, showing a sensible reduction of iterations and CPU time. The second part is devoted to the study of temperature-dependent elastic scattering of neutrons for heavy isotopes near to the thermal zone. A numerical computation of the Doppler convolution of the elastic scattering kernel based on the gas model is presented, for a general energy dependent cross section and scattering law in the center of mass system. The range of integration has been optimized employing a numerical cutoff, allowing a faster numerical evaluation of the convolution integral. Legendre moments of the transfer kernel are subsequently obtained by direct quadrature and a numerical analysis of the convergence is presented. In the third part we focus our attention to remote sensing applications of radiative transfer employed to investigate the Earth's cryosphere. The photon transport equation is applied to simulate reflectivity of glaciers varying the age of the layer of snow or ice, its thickness, the presence or not other underlying layers, the degree of dust included in the snow, creating a framework able to decipher spectral signals collected by orbiting detectors.

Advanced aspects of radiation protection in the use of particle accelerators in the medical field

In this work, the well-known MC code FLUKA was used to simulate the GE PETrace cyclotron (16.5 MeV) installed at “S. Orsola-Malpighi” University Hospital (Bologna, IT) and routinely used in the production of positron emitting radionuclides. Simulations yielded estimates of various quantities of interest, including: the effective dose distribution around the equipment; the effective number of neutron produced per incident proton and their spectral distribution; the activation of the structure of the cyclotron and the vault walls; the activation of the ambient air, in particular the production of 41Ar, the assessment of the saturation yield of radionuclides used in nuclear medicine. The simulations were validated against experimental measurements in terms of physical and transport parameters to be used at the energy range of interest in the medical field. The validated model was also extensively used in several practical applications uncluding the direct cyclotron production of non-standard radionuclides such as 99mTc, the production of medical radionuclides at TRIUMF (Vancouver, CA) TR13 cyclotron (13 MeV), the complete design of the new PET facility of “Sacro Cuore – Don Calabria” Hospital (Negrar, IT), including the ACSI TR19 (19 MeV) cyclotron, the dose field around the energy selection system (degrader) of a proton therapy cyclotron, the design of plug-doors for a new cyclotron facility, in which a 70 MeV cyclotron will be installed, and the partial decommissioning of a PET facility, including the replacement of a Scanditronix MC17 cyclotron with a new TR19 cyclotron.

Valutazione in opera ed in laboratorio della trasmissione laterale nelle tipologie edilizie italiane

L’attività di ricerca del dottorando è stata rivolta allo studio della trasmissione del rumore per via strutturale negli edifici. Questo argomento e' di notevole interesse sia fondamentale che applicativo. Il fenomeno e le problematiche ad essa connesse contribuiscono alla diminuzione delle prestazioni fonoisolanti, sia per le strutture verticali (usualmente valutate rispetto al rumore aereo), sia per quelle orizzontali (valutate anche rispetto al rumore impattivo) ed è tipico degli edifici con struttura portante a telaio e tamponatura in laterizi. Si tratta delle tipiche tipologie edilizie italiane, per le quali il problema risulta amplificato rispetto ad altre tipologie. La metodologia di studio è stata di tipo sperimentale. La scelta è dettata sia dall’insufficiente avanzamento dello stato dell’arte dei metodi di calcolo teorici, o delle loro versioni numeriche, sia dalla necessità di disporre di dati certi da confrontare con i valori forniti dai metodi previsionali semplificati indicati nelle norme UNI (modello CEN); infatti queste ultime sono un recepimento letterale di quelle europee, sebbene esse si basino su tipologie costruttive, materiali e tecniche di realizzazione differenti da quelle comunemente in uso in Italia; da qui la difformità di risultati tra formule previsionali e misurazioni sperimentali. Al fine di realizzare uno studio completo delle principali casistiche della trasmissione laterale sono state utilizzate 6 configurazioni in scala reale, con elementi edilizi diversamente collegati fra loro in modo da simulare i nodi strutturali comunemente realizzati negli edifici. La parte sperimentale della ricerca è stata svolta presso le “Camere Acustiche di Prova” del Laboratorio del Lazzaretto “R. Alessi” del DIENCA. Oltre alle usuali misurazioni di isolamento acustico, sono state eseguite numerose misurazioni di vibrazione. Infatti, dal confronto dei livelli di velocità di vibrazione dei diversi elementi di una struttura, rigidamente connessi, è possibile determinare l’indice di riduzione delle vibrazioni Kij che è la grandezza chiave per modellizzare il fenomeno della trasmissione laterale. La possibilità di determinare sperimentalmente tali valori nel contesto di un lavoro di ricerca finalizzato a determinare i meccanismi di propagazione delle vibrazioni nelle strutture, permette di valutare la precisione delle formule previsionali del modello CEN e di proporne varianti e integrazioni. I valori di Kij così determinati assumono grande importanza anche in fase di progetto, fornendo dati attendibili da utilizzare per la progettazione acustica degli edifici.