Tag Archives: Evento scientifico

Machine learning techniques are increasingly used for recognizing pattern and devising optimal strategies: situations in which the machine is taught (or teaches itself) to learn a known correct answer, or the best use of known rules. In particle physics, machine learning has been used now for several years  in order to determine an underlying physical law which is known to exist, but which is unknown. Furthermore, because elementary particles are quantum objects, this law is stochastic in nature: the machine has to learn a probability distribution, rather than a unique answer. I will discuss some classic results, used among others in the discovery of the Higgs boson, as well as recent developments, which raise the fundamental question of how to decide whether an answer is correct.

This informal meeting is the third of the Rome physics encounter series. It aims at bringing together young speakers working or collaborating with the research groups in the Rome area. In the spirit of workshops and conferences at LNF, talks will be presented in a pedagogical way and plenty of time is scheduled to allow discussions among participants. The encounters will be synchronised with a selected LNF General Seminar, held in the afternoon at 2.30pm. The lunch is offered to all registered participant at the LNF canteen.

The SHERPA project aim is to develop an efficient technique to extract a positron beam from one of the Frascati DAΦNE collider rings, setting up a new beam line able to deliver positron spills of O(ms) length. An excellent beam energy spread and emittance, with a strong reduction of the background and the pile-up for the user experiments, will be achieved. The most common approach to extract from a ring is to use a resonant technique, creating an unstable region in the phase space and then driving the tune towards the separatrix, in order to gradually eject particles from the circulating beam. SHERPA proposes instead to use coherent processes in bent crystals to kick out positrons from the ring, a cheaper and less complex alternative. This non-resonant technique, already successfully used and still developed mainly in hadron accelerators, will provide a continuous multi-turn extraction with high-efficiency. Realizing this for < GeV leptons is challenging, however will provide the first primary positron beam obtained with crystal extraction. At the DAΦNE Beam Test Facility, < GeV positrons have already been deflected using crystals, proving the technique feasibility.  An immediate application of this new extracted beam line would be the PADME experiment, already running at the BTF, but currently strongly limited by the duty cycle. Using the proposed extraction, PADME could increase the statistics by a factor 104 and its sensitivity by a factor 102, extending the discovery potential at the forefront level. SHERPA could provide a unique new beam test facility, very competitive …

The discovery of the Higgs boson at the Large Hadron Collider (LHC) has experimen-tally proven that charged fermions and gauge bosons get masses after spontaneous breaking of electroweak symmetry. However, one of the key questions that still remains unexplained is the origin of light neutrino masses and mixings. A number of neutrino oscillation experiments have observed non-zero solar and atmospheric neutrino mass splittings. Which implies that neutrinos have tinny but non-zero mass. Seesaw mechanism is one the profound theory to explain the smallness of neutrino mass. In this talk I will discuss about different types of seesaw model. Mainly I will focus on Type-II seesaw model and collider searches of charged scalars in this model.

General introduction to cosmology of modified gravity is given. It is shown that different forms of modified gravity are possible, many of them being consistent with Solar system tests and cosmological bounds. Special attention is paid to the so-called F(R) modified gravity. It is shown that such a theory may naturally describe the early-time inflation with late-time acceleration (dark energy epoch). Realistic versions of F(R) gravity are proposed and the inflationary indices are shown to be consistent with Planck experiment. New ghost-free versions of modified gravity are introduced and their cosmological evolution is studied. It is shown that it may naturally give the unification of inflation with dark energy, while the scalar field which appears there plays the role of dark matter. 

https://agenda.infn.it/event/21379/overview

We propose a model describing the evolution of free electron current density in graphene giving rise to bidimensional wormhole solutions. Based on analogue concepts of General Relativity, we perform the analysis using the difference between curvatures of parallel and antiparallel spins. In such a framework, effective “gravitons” emerges in the form of gauge fields exchanged between electrons. In a plain grapheme system, the curvatures produced by both kinds of spins neutralize each other giving rise to no conduction. However, in the presence of geometrical defects of the graphene sheets, the inequality between curvatures leads to the emergence of current densities and conductivity in a wormhole solution. Depending on the type of defects, the resulting current density can be negative or positive. Possible applications are discussed.

In order to characterize low absorbing materials, where UV-vis spectrophotometry does not provide enough sensitivity, other more sensitive methods are needed. Photothermal lens technique is a very sensitive method to detect and photothermal characterize of materials. The thermal lens technique measures the amount of heat generated followed by the absorption of light in a sample. The heat produces a temperature gradient in the medium which generates a spatial refractive index gradient called a thermal lens. The performance of this method and applications such as photocatalytical degradation of dyes as well as the photothermal characterization of plasmonic nanostructures, quantum dots and graphene are presented.

Semileptonic decays provide an excellent environment for testing the Standard Model. Tests of lepton flavour universality using b->clnu decays have shown hints of new physics. In this seminar, an overview of the status of these measurements is given, including the impact of radiative corrections on these types of measurement. Also CKM matrix elements, and in particular |Vcb|, can be measured using semileptonic B decays. There is a long-standing disagreement between values of |Vcb| measured inclusively or exclusively. The exclusive determination relies on the parametrisation of the form factors of the decay.  Measurements using Bs mesons instead of B mesons can shed a new light on lepton flavour universality,  |Vcb| and form factors. They suffer from less backgrounds from excited decays and are easier to compute on a lattice. In this seminar I will present a new measurement of |Vcb| using Bs decays, as well  as measurements of Bs->Ds(*)munu form factors, performed by the LHCb experiment. Future prospects for measurements of Vcb, R(Ds) and R(Ds*) are also discussed.

In relativistic heavy-ion collisions a “Little-Bang” is produced, in which the matter for a few fm/c experiences very similar (but not equal) conditions to the one occurred in the early universe, about one millionth of a second after the Big Bang. In particular one expects to produce a fireball of deconfined QCD matter in which the active degrees of freedom are quarks and gluons rather than hadrons. If this fireball lives for such a short amount of time, which are the experimental signatures of the onset of deconfinement and how can one extract information about its properties from the experimental data? In this connection I will show how heavy-flavour particles arising from the hadronization of charm and beauty quarks play a major role.