Ageing and performance studies of drift chamber prototypes for the MEG II experiment

We present the tests aimed at verifying the proper functioning of the tracking systems of MEG II on small prototypes, estimating the achievable resolutions and evaluating the gain loss experienced by the chamber during its operation

Results and perspectives of the MEG and MEG II experiments

Charged-lepton-flavour–violating decays are prohibited in the framework of the Standard Model of elementary particles, but many of its extensions predict measurable values for such decays. Several experiments are running or being designed to measure (or to set a limit on) such processes. Among these, the MEG experiment has recently set a new upper limit on the μ → eγ branching ratio B < 5.7 × 10 −13 at 90% CL. The process has a simple kinematics but very good resolutions are needed for discarding the huge background. In order to improve its sensitivity, an upgrade of the experiment is under development, and will start taking data in 2016. The foreseen sensitivity of the upgraded apparatus will be about 5 × 10−14 on the branching ratio of the process

Longitudinal Single-Bunch Instability in the ILC Damping Rings: Estimate of Current Threshold

Characterization of single-bunch instabilities in the International Linear Collider (ILC) damping rings (DRs) has been indicated as a high-priority activity toward completion of an engineering design. In this paper we report on a first estimate ofthe current thresholds for the instability using numerical and analytical models of the wake potentials associated with the various machine components. The numerical models were derived (upon appropriate scaling) from designs of the correspondingcomponents installed in existing machines. The current thresholds for instabilities were determined by numerical solution of the Vlasov equation for the longitudinal dynamics. For the DR baseline lattice as of Feb. 2007 we find the critical current forinstability to be safely above the design specifications leaving room for further optimization of the choice of the momentum compaction

Treatment of HER-2 positive breast cancer

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Equilibrium of an Arbitrary Bunch Train in Presence of a Passive Harmonic Cavity: Solution through Coupled Ha\" issinski Equations

We study the effect of a passive harmonic cavity, introduced to cause bunch lengthening, in an electron storage ring. We derive a formula for the induced voltage from such a cavity with high $Q$, excited by a a sequence of bunches, allowing for arbitrary gaps in the sequence and arbitrary currents. Except for a minor term that can be determined iteratively, the voltage is given in terms of a single mode of the Fourier transforms of the bunch forms, namely the mode at the resonant frequency of the cavity. Supposing that the only wake field is from the harmonic cavity, we derive a system of coupled Ha\"issinski equations which determine the bunch positions and profiles in the equilibrium state. The number of unknowns in the system is only twice the number of bunches, and it can be solved quickly by a Newton iteration, starting with a guess determined by path-following from a solution at weak current. We explore the effect of the fill pattern on the bunch lengthening, and also the dependence on the shunt impedance and detuning of the cavity away from the third harmonic of the main accelerating cavity. We consider two measures to reduce the effects of gaps: 1) distribution of the gaps around the ring to the greatest extent allowed, and 2) "guard bunches" with higher charges adjacent to the gaps, compensating for the charge missing in gaps. Results for parameters of the forthcoming ALS-U light source are presented

Modeling Microbunching from Shot Noise Using Vlasov Solvers

Unlike macroparticle simulations, which are sensitive to unphysical statistical fluctuations when the number of macroparticles is smaller than the bunch population, direct methods for solving the Vlasov equation are free from sampling noise and are ideally suited for studying microbunching instabilities evolving from shot noise. We review a 2D (longitudinal dynamics) Vlasov solver we have recently developed to study the microbunching instability in the beam delivery systems for x-ray FELs and present an application to FERMI{at}Elettra. We discuss, in particular, the impact of the spreader design on microbunching

Ageing and performance studies of drift chamber prototypes for the MEG experiment upgrade.

L’esperimento MEG, attualmente in presa dati presso il Paul Scherrer Institut di Zurigo (Svizzera), ha come scopo la ricerca del decadimento μ → eγ, proibito all’interno del Modello Standard, ma previsto da molte delle sue estensioni. La collaborazione ha appena pubblicato l’analisi dei dati 2009–2011, che porta il limite sul rapporto di decadimento di questo processo a BR(μ → eγ) < 5.7 × 10–13 , un fattore 20 rispetto al limite posto dall’esperimento precedente. La ricerca sperimentale del decadimento si basa sulla misura del quadrimpulso di fotoni e positroni provenienti da decadimenti di muoni fermi. Il quadrimpulso del fotone è misurato da un calorimetro a xenon liquido, mentre l’impulso del positrone è misurato da un insieme di camere a deriva poste in campo magnetico, seguito da barre scintillanti per una precisa determinazione del tempo. L’analisi dei dati raccolti nel 2012 è in corso, mentre un’ultima campagna di presa dati, prevista terminare a fine agosto 2013, permetterà di saturare la sensibilità raggiungibile con il presente apparato sperimentale. La collaborazione ha di recente proposto un upgrade dell’esperimento in cui alla stessa linea del fascio e allo stesso magnete verranno accoppiate una nuova camera a fili e un calorimetro a xenon con maggiore accettanza e granularità. Mediante tale upgrade si vuole migliorare la sensibilità alla ricerca del decadimento di un ulteriore fattore 10 (fino a qualche unità in 10–14 ) dove la maggior parte delle estensioni del Modello Standard prevedono l’esistenza del decadimento. Elemento chiave del nuovo apparato è la nuova camera a deriva, responsabilità dei gruppi italiani che partecipano all’esperimento. Essa è progettata per migliorare l’accettanza del segnale, mantenendo il materiale sulla traiettoria del positrone al minimo, dato che alle energie in gioco la diffusione coulombiana multipla è l’elemento di maggior disturbo per una precisa determinazione dell’impulso della particella. Tale camera, composta da più di 2000 fili con configurazione stereo, ` e riempita di una miscela molto leggera di elio e isobutano, e dovrà sostenere un flusso di particelle tre volte superiore a quella dell’esperimento attuale. In presenza di un così alto flusso di particelle le molecole del gas si scindono e tendono a formare depositi sui fili, riducendo le prestazioni della camera e arrivando a provocare, in casi estremi, danni macroscopici. Diventa di fondamentale importanza, nel momento in cui si va a costruire una nuova camera, studiare nel dettaglio quali siano le sue prestazioni su vari prototipi, e come le prestazioni siano modificate dall’invecchiamento della camera stessa, dato che la carica accumulata sui fili più caldi sarà dell’ordine di una frazione di Coulomb al centimetro. In questa tesi viene affrontato lo studio sperimentale del funzionamento dei primi prototipi, a partire dalla loro progettazione e simulazione (configurazione dei fili e dei campi elettrici, risposta al passaggio di particelle). I prototipi, realizzati all’interno dei laboratori della sezione di Pisa dell’Istituto Nazionale di Fisica Nucleare, sono stati caratterizzati per quanto riguarda le condizioni di lavoro e la risposta a diversi tipi di radiazione (particelle α, elettroni, raggi-X). Dall’analisi dei dati accumulati e da una semplice ricostruzione delle tracce ` e stato possibilie ricavare una stima delle risoluzioni ottenibili nell’apparato in diverse condizioni di lavoro, per orientare il disegno dell’apparato finale. Per lo svolgimento delle misure di invecchiamento è stato necessario allestire un nuovo laboratorio dove è stato possibile accelerare l’accumulo di radiazione mediante irraggiamento da una sorgente intensa di raggi-X, scelta e caratterizzata in base alle esigenze di misura. Si mostrer` a come i prototipi sono effettivamente in grado di misurare le tracce di particelle ionizzanti, e di sostenere un alto flusso di carica, e se ne evidenzieranno le modificazioni indotte dall’invecchiamento. Le misure effettuate per questa tesi hanno permesso di finalizzare il disegno della camera a deriva per l’upgrade dell’esperimento MEG, e di verificare in maniera preliminare le sue prestazioni

Shot-Noise Seeded Microbunching Instability: Second-Order Correction to the Gain Function

We determine the second-order correction to the gain function of the microbunching instability in single-pass systems of interest for the next generation of light sources. The calculation applies to the case where the instability is seeded by shot noise. We examine an analytically treatable model of beam dynamics where collective forces are active only in non-dispersive sections of the linac. We find that the second order term can augment the linear gain significantly while affecting the spectrum of the overall gain only marginally. The weight of the second-order correction relative to the linear gain is found to scale quadratically with respect to R56. The qualitative behavior predicted by the model is consistent with exact numerical solutions of the Vlasov equations for realistic lattices

Taxane-containing chemotherapy in the treatment of early breast cancer patients

In primary breast cancer, taxane-based compared with anthracycline-based adjuvant chemotherapy significantly reduces the relative risk of recurrence (ranging from 17% to 36%) and sometimes improves overall survival. Different dosages and schedules of anthracyclines and taxanes have been tested. Randomized studies comparing sequential versus concurrent administrations are in progress and no data about efficacy are available. However, based on a single randomized trial and on indirect comparisons, safety and tolerability seem to be better with sequential schema. A formal comparison between weekly and every 3 weeks administration of taxanes reported no substantial difference in terms of efficacy. However, taking into account a subgroup analysis of this study, and results coming from metastatic disease, the best way to give taxanes seems to be either weekly paclitaxel or docetaxel every 3 weeks. In the majority of the study, taxane efficacy seems to be independent of hormonal receptor status, i.e. active in both hormonal receptor positive and negative disease. In conclusion, taxane-based adjuvant chemotherapy is a standard option for most early breast cancer patients with node-positive disease. No sufficient and dedicated data are available in node-negative disease

Experimental qualification of new instrumentation for lead-Lithium eutectic in IELLLO facility

The experimental facility IELLLO was installed in ENEA Brasimone R.C. in 2007, aiming to support the design of liquid Test Blanket Modules that will be installed in ITER and to contribute to the development of Lead-Lithium Eutectic (LLE) technologies. IELLLO has been recently upgraded by installing instrumentation relevant for ITER application. Differential pressure transducers, a Coriolis and a thermal mass flow meters were installed in the facility. An experimental campaign was planned, setting two objectives. The first objective was to qualify the instrumentation for flowing LLE The installation of a differential pressure transducer across each flow meter made also possible to characterize the pressure drops across these instruments. The second objective of this activity was to improve the knowledge on the performances of the main components of the loop at lower mass flow rates (namely 0.5-1.2 kg/s) and to quantify their pressure drops. The investigated flow rates were chosen to be relevant for the LLE loop of the WCLL TBS (Water Cooled Lead-Lithium Test Blanket System). This work presents the results of the experimental campaign, paying particular attention to underline the lessons learned on how to correctly operate instrumentation for LLE