Study of a new method for high energy top tagging at the ATLAS experiment

Since its discovery, top quark has represented one of the most investigated field in particle physics. The aim of this thesis is the reconstruction of hadronic top with high transverse momentum (boosted) with the Template Overlap Method (TOM). Because of the high energy, the decay products of boosted tops are partially or totally overlapped and thus they are contained in a single large radius jet (fat-jet). TOM compares the internal energy distributions of the candidate fat-jet to a sample of tops obtained by a MC simulation (template). The algorithm is based on the definition of an overlap function, which quantifies the level of agreement between the fat-jet and the template, allowing an efficient discrimination of signal from the background contributions. A working point has been decided in order to obtain a signal efficiency close to 90% and a corresponding background rejection at 70%. TOM performances have been tested on MC samples in the muon channel and compared with the previous methods present in literature. All the methods will be merged in a multivariate analysis to give a global top tagging which will be included in ttbar production differential cross section performed on the data acquired in 2012 at sqrt(s)=8 TeV in high phase space region, where new physics processes could be possible. Due to its peculiarity to increase the pT, the Template Overlap Method will play a crucial role in the next data taking at sqrt(s)=13 TeV, where the almost totality of the tops will be produced at high energy, making the standard reconstruction methods inefficient.

Stacked searches for high-energy neutrinos from blazars with IceCube

In the year 2013, the detection of a diffuse astrophysical neutrino flux with the IceCube neutrino telescope – constructed at the geographic South Pole – was announced by the IceCube collaboration. However, the origin of these neutrinos is still unknown as no sources have been identified to this day. Promising neutrino source candidates are blazars, which are a subclass of active galactic nuclei with radio jets pointing towards the Earth. In this thesis, the neutrino flux from blazars is tested with a maximum likelihood stacking approach, analyzing the combined emission from uniform groups of objects. The stacking enhances the sensitivity w.r.t. the still unsuccessful single source searches. The analysis utilizes four years of IceCube data including one year from the completed detector. As all results presented in this work are compatible with background, upper limits on the neutrino flux are given. It is shown that, under certain conditions, some hadronic blazar models can be challenged or even rejected. Moreover, the sensitivity of this analysis – and any other future IceCube point source search – was enhanced by the development of a new angular reconstruction method. It is based on a detailed simulation of the photon propagation in the Antarctic ice. The median resolution for muon tracks, induced by high-energy neutrinos, is improved for all neutrino energies above IceCube’s lower threshold at 0.1TeV. By reprocessing the detector data and simulation from the year 2010, it is shown that the new method improves IceCube’s discovery potential by 20% to 30% depending on the declination.

High-energy view of radio galaxies: prospects for the new generation of Cherenkov telescopes

I Nuclei Galattici Attivi (AGN) sono sorgenti luminose e compatte alimentate dall'accrescimento di materia sul buco nero supermassiccio al centro di una galassia. Una frazione di AGN, detta "radio-loud", emette fortemente nel radio grazie a getti relativistici accelerati dal buco nero. I Misaligned AGN (MAGN) sono sorgenti radio-loud il cui getto non è allineato con la nostra linea di vista (radiogalassie e SSRQ). La grande maggioranza delle sorgenti extragalattiche osservate in banda gamma sono blazar, mentre, in particolare in banda TeV, abbiamo solo 4 MAGN osservati. Lo scopo di questa tesi è valutare l'impatto del Cherenkov Telescope Array (CTA), il nuovo strumento TeV, sugli studi di MAGN. Dopo aver studiato le proprietà dei 4 MAGN TeV usando dati MeV-GeV dal telescopio Fermi e dati TeV dalla letteratura, abbiamo assunto come candidati TeV i MAGN osservati da Fermi. Abbiamo quindi simulato 50 ore di osservazioni CTA per ogni sorgente e calcolato la loro significatività. Assumendo una estrapolazione diretta dello spettro Fermi, prevediamo la scoperta di 9 nuovi MAGN TeV con il CTA, tutte sorgenti locali di tipo FR I. Applicando un cutoff esponenziale a 100 GeV, come forma spettrale più realistica secondo i dati osservativi, prevediamo la scoperta di 2-3 nuovi MAGN TeV. Per quanto riguarda l'analisi spettrale con il CTA, secondo i nostri studi sarà possibile ottenere uno spettro per 5 nuove sorgenti con tempi osservativi dell'ordine di 250 ore. In entrambi i casi, i candidati migliori risultano essere sempre sorgenti locali (z<0.1) e con spettro Fermi piatto (Gamma<2.2). La migliore strategia osservativa per ottenere questi risultati non corrisponde con i piani attuali per il CTA che prevedono una survey non puntata, in quanto queste sorgenti sono deboli, e necessitano di lunghe osservazioni puntate per essere rilevate (almeno 50 ore per studi di flusso integrato e 250 per studi spettrali).

The effect of high-energy extracorporeal shock waves on hyaline cartilage of adult rats in vivo

The aim of this study was to determine if extracorporeal shock wave therapy (ESWT) in vivo affects the structural integrity of articular cartilage. A single bout of ESWT (1500 shock waves of 0.5 mJ/mm(2)) was applied to femoral heads of 18 adult Sprague-Dawley rats. Two sham-treated animals served as controls. Cartilage of each femoral head was harvested at 1, 4, or 10 weeks after ESWT (n = 6 per treatment group) and scored on safranin-O-stained sections. Expression of tenascin-C and chitinase 3-like protein 1 (Chi3L1) was analyzed by immunohistochemistry. Quantitative real-time polymerase chain reaction (PCR) was used to examine collagen (II)alpha(1) (COL2A1) expression and chondrocyte morphology was investigated by transmission electron microscopy no changes in Mankin scores were observed after ESWT. Positive immunostaining for tenascin-C and Chi3L1 was found up to 10 weeks after ESWT in experimental but not in control cartilage. COL2A1 mRNA was increased in samples 1 and 4 weeks after ESWT. Alterations found on the ultrastructural level showed expansion of the rough-surfaced endoplasmatic reticulum, detachment of the cell membrane and necrotic chondrocytes. Extracorporeal shock waves caused alterations of hyaline cartilage on a molecular and ultrastructural level that were distinctly different from control. Similar changes were described before in the very early phase of osteoarthritis (OA). High-energy ESWT might therefore cause degenerative changes in hyaline cartilage as they are found in initial OA.

Proteomic changes in the rat brain induced by homogenous irradiation and by the bystander effect resulting from high energy synchrotron X-ray microbeams

Abstract Purpose: To further evaluate the use of microbeam irradiation (MBI) as a potential means of non-invasive brain tumor treatment by investigating the induction of a bystander effect in non-irradiated tissue. Methods: Adult rats were irradiated with 35 or 350 Gy at the European Synchotron Research Facility (ESRF), using homogenous (broad beam) irradiation (HI) or a high energy microbeam delivered to the right brain hemisphere only. The proteome of the frontal lobes were then analyzed using two-dimensional electrophoresis (2-DE) and mass spectrometry. Results: HI resulted in proteomic responses indicative of tumourigenesis; increased albumin, aconitase and triosphosphate isomerase (TPI), and decreased dihydrolipoyldehydrogenase (DLD). The MBI bystander effect proteomic changes were indicative of reactive oxygen species mediated apoptosis; reduced TPI, prohibitin and tubulin and increased glial fibrillary acidic protein (GFAP). These potentially anti-tumourigenic apoptotic proteomic changes are also associated with neurodegeneration. However the bystander effect also increased heat shock protein (HSP) 71 turnover. HSP 71 is known to protect against all of the neurological disorders characterized by the bystander effect proteome changes. Conclusions: These results indicate that the collective interaction of these MBI-induced bystander effect proteins and their mediation by HSP 71, may confer a protective effect which now warrants additional experimental attention.

Testing the GlaaS algorithm for dose measurements on low- and high-energy photon beams using an amorphous silicon portal imager

The GLAaS algorithm for pretreatment intensity modulation radiation therapy absolute dose verification based on the use of amorphous silicon detectors, as described in Nicolini et al. [G. Nicolini, A. Fogliata, E. Vanetti, A. Clivio, and L. Cozzi, Med. Phys. 33, 2839-2851 (2006)], was tested under a variety of experimental conditions to investigate its robustness, the possibility of using it in different clinics and its performance. GLAaS was therefore tested on a low-energy Varian Clinac (6 MV) equipped with an amorphous silicon Portal Vision PV-aS500 with electronic readout IAS2 and on a high-energy Clinac (6 and 15 MV) equipped with a PV-aS1000 and IAS3 electronics. Tests were performed for three calibration conditions: A: adding buildup on the top of the cassette such that SDD-SSD = d(max) and comparing measurements with corresponding doses computed at d(max), B: without adding any buildup on the top of the cassette and considering only the intrinsic water-equivalent thickness of the electronic portal imaging devices device (0.8 cm), and C: without adding any buildup on the top of the cassette but comparing measurements against doses computed at d(max). This procedure is similar to that usually applied when in vivo dosimetry is performed with solid state diodes without sufficient buildup material. Quantitatively, the gamma index (gamma), as described by Low et al. [D. A. Low, W. B. Harms, S. Mutic, and J. A. Purdy, Med. Phys. 25, 656-660 (1998)], was assessed. The gamma index was computed for a distance to agreement (DTA) of 3 mm. The dose difference deltaD was considered as 2%, 3%, and 4%. As a measure of the quality of results, the fraction of field area with gamma larger than 1 (%FA) was scored. Results over a set of 50 test samples (including fields from head and neck, breast, prostate, anal canal, and brain cases) and from the long-term routine usage, demonstrated the robustness and stability of GLAaS. In general, the mean values of %FA remain below 3% for deltaD equal or larger than 3%, while they are slightly larger for deltaD = 2% with %FA in the range from 3% to 8%. Since its introduction in routine practice, 1453 fields have been verified with GLAaS at the authors' institute (6 MV beam). Using a DTA of 3 mm and a deltaD of 4% the authors obtained %FA = 0.9 +/- 1.1 for the entire data set while, stratifying according to the dose calculation algorithm, they observed: %FA = 0.7 +/- 0.9 for fields computed with the analytical anisotropic algorithm and %FA = 2.4 +/- 1.3 for pencil-beam based fields with a statistically significant difference between the two groups. If data are stratified according to field splitting, they observed %FA = 0.8 +/- 1.0 for split fields and 1.0 +/- 1.2 for nonsplit fields without any significant difference.

Long Versus Short Feeding Period for Steer Calves of Three Frame Sizes Fed High Energy Finishing Diets

An experiment was conducted using Angus cross steer calves of three frame sizes (small, medium, and large) to compare performance of two different grow/finish feeding programs. Half of the cattle in each frame size group were fed a high energy ration through the growing period, similar to calves going directly into the feedlot. The other half was fed a low energy ration, similar to a backgrounding diet, for a period prior to the finishing phase. All cattle were fed a high energy ration through the finishing period. The data showed the cattle fed the low energy growing diet experienced some compensatory gains as shown by ultrasound backfat and average daily gains coupled with intakes greater than the increases seen in the high energy treatment. Carcass data and overall performance data showed no ill effects due to the low energy growing ration.

Quantitative depth profiling of Ce 3+ in Pt/CeO 2 by in situ high-energy XPS in a hydrogen atmosphere

The redox property of ceria is a key factor in the catalytic activity of ceria-based catalysts. The oxidation state of well-defined ceria nanocubes in gas environments was analysed in situ by a novel combination of near-ambient pressure X-ray Photoelectron Spectroscopy (XPS) and high-energy XPS at a synchrotron X-ray source. In situ high-energy XPS is a promising new tool to determine the electronic structure of matter under defined conditions. The aim was to quantitatively determine the degree of cerium reduction in a nano-structured ceria-supported platinum catalyst as a function of the gas environment. To obtain a non-destructive depth profile at near-ambient pressure, in situ high-energy XPS analysis was performed by varying the kinetic energy of photoelectrons from 1 to 5 keV, and, thus, the probing depth. In ceria nanocubes doped with platinum, oxygen vacancies formed only in the uppermost layers of ceria in an atmosphere of 1 mbar hydrogen and 403 K. For pristine ceria nanocubes, no change in the cerium oxidation state in various hydrogen or oxygen atmospheres was observed as a function of probing depth. In the absence of platinum, hydrogen does not dissociate and, thus, does not lead to reduction of ceria.