iten
Home » Evento (page 31)

Tag Archives: Evento scientifico

Probabilities and signalling in quantum field theory

We present an approach to computing probabilities in quantum field theory for a wide class of source-detector models. The approach works directly with probabilities and not with squared matrix elements, and the resulting probabilities can be written in terms of expectation values of nested commutators and anticommutators. We present results that help in the evaluation of these, including an expression for the vacuum expectation values of general nestings of commutators and anticommutators in scalar field theory. This approach allows one to see clearly how faster-than-light signalling is prevented, because it leads to a diagrammatic expansion in which the retarded propagator plays a prominent role. We illustrate the formalism using the simple case of the much-studied Fermi two-atom problem.

Scopri di più »

Quality Assurance and radiation tolerance studies on double-sided silicon sensors of the CBM Silicon Tracking System.

The Silicon Tracking System (STS) is the main tracking detector of the upcoming fixed-target Compressed Baryonic Matter (CBM) experiment which aims to explore the phase diagram of the strongly interacting matter in a region of high net baryonic densities and moderate temperatures. The STS will be used for the reconstruction of tracks of charged particles and determination of their momenta. The system comprises 8 tracking stations located 30 cm downstream of the target. It will be mounted with approximately 1200 double-sided silicon microstrip sensors in three different sizes. A high level of radiation damage is expected to impact on the sensors. The maximum exposure of 1× 1014 in 1 MeV neutron equivalent will be reached after several years of running depending on the physics program. The Quality Assurance (QA) procedures for the STS sensors will be overviewed highlighting the automated QA testing procedure for a single strip defect identification. In addition to this, the radiation tolerance studies performed on STS sensor prototypes will be presented.

Scopri di più »

Going beyond traditional parton showers: amplitude-level evolution

I will explain how traditional parton showers, as implemented in the major general purpose monte carlo codes, are fundamentally limited in their accuracy and how that situation can be improved via a new amplitude-level algorithm that includes, amongst other things, Coulomb gluon exchanges between incoming and outgoing partons. Coulomb gluons are responsible for the breaking of soft-collinear factorization and they are what generates the underlying event and diffraction.

Scopri di più »

New perspectives in effective quantum gravity and cosmological perturbation theory

In this talk I will show how the general framework of effective quantum gravity proposed by Brunetti, Fredenhagen and myself can be used to study problems in quantum cosmology. This formulation allows to derive some known results in (first order) cosmological perturbation theory from first principles and it provides a robust tool for computing higher order corrections. Conceptually, it works as a test ground for new ideas concerning construction of gauge invariant observables in effective quantum gravity. The non-local character of these observables leads to new interesting combinatorial structures arising in renormalization.

Scopri di più »

Condensed Matter and Critical Phenomena

The workshop aims at presenting recent results in the mathematical theory of critical phenomena and effective theories in condensed matter physics and statistical mechanics, including: scaling limits of discrete spin systems, percolation models and interacting random walks; effective dynamics and phase transitions in interacting quantum many body systems; disordered electrons and localization phenomena. Invited speakers include:  M. Aizenman, R. Bauerschmidt, D. Chelkak, G. Gallavotti, K. Gawedzki, V. Mastropietro, B. Nachtergaele, A. Pizzo,  M. Porta, B. Schlein,  A. Vichi, S. Warzel Organizers: A. Giuliani, V. Mastropietro, A. Pizzo    

Scopri di più »

POSITRON SOURCES FOR FUTURE COLLIDERS

Except the radioactive sources, the positron sources are all based on photon materialization into electron-positron pairs in a target. After a rapid recall of the different methods to generate photons, underlining the corresponding photon characteristics , we shall concentrate on three kinds of radiation: bremsstrahlung in amorphous targets , channeling and coherent bremsstrahlung in oriented crystals. Applications to future linear e+e- and circular μ+ μ – colliders will be presented.

Scopri di più »

Direct dark matter search: the XENON project

Astronomical and cosmological observations indicate that a large fraction of the energy content of the Universe is composed of cold dark matter. One of the most favored particle candidates, under the generic name of WIMPs (Weakly Interacting Massive Particles), arises naturally in many theories beyond the Standard Model of particle physics. The XENON Project, hosted by the Laboratori Nazionali del Gran Sasso (LNGS), is dedicated to the direct search of dark matter particles. It consists of a double-phase time projection chamber (TPCs) using ultra-pure liquid xenon as both target and detection medium for dark matter particle interactions. The XENON100 detector, currently running since 2009 with 160 kg of liquid xenon, has reached in 2012 the sensitivity of 2×10-45 cm2 at 55 GeV/c2 on spin-independent WIMP-nucleon coupling. We will present also the results on the spin-dependent coupling, and the recent search for annual modulation and for leptophilic dark matter interactions with electrons. The next generation XENON1T detector, that will host 3.5 tonnes of xenon, is in its final stage of commissioning and will likely start taking data by 2016. The detector is designed to increase the sensitivity by two orders of magnitude. The status of the project and its physics reach will be presented in details.

Scopri di più »

Measurements of RF breakdowns in beam driven 200 GHz accelerating structure

We studied the physics and properties of rf breakdowns in high gradient traveling wave accelerating structures at 100 GHz and 200 GHz. The structures are open, made of two haves with a gap in between. The rf fields were excited in the structure by an ultra-relativistic electron beam generated by the FACET facility at the SLAC National Accelerator Laboratory. We observed rf breakdowns generated in the presence of GV/m scale electric fields. We varied the rf fields excited by the FACET bunch by moving structure relative to the beam and by changing the gap between structure halves. Reliable breakdowns detectors allowed us to measure the rf breakdown rate at these different rf parameters. We measured radiated rf energy with a pyro-detector and characterized the rf spectrum with an interferometer. When the beam was off-axis, we observed beam deflection in the beam position monitors and on the screen of a magnetic spectrometer. The measurements of the deflection allowed us to verify our calculation of the accelerating gradient. This talk will report results of 200 GHz experiments.

Scopri di più »

AWAKE: A Proton-driven Plasma Wakefield Experiment At CERN

High energy intense proton beams such as the in the 7 TeV x 7 TeV Large Hadron Collider at CERN have sufficient energy stored per proton bunch to power and accelerate an electron beam to an energy of 600 GeV if a suitable mechanism could be found to transform all the stored proton beam energy into the electrons. A suitably designed plasma column could be such a ‘transformer’, with the potential of being able to generate sufficiently high electromagnetic wakefields, upon excitation by the proton beams, to accelerate an electron beam to an energy of 600 GeV in a single pass through the plasma column. The idea will be tested experimentally in a “scaled-down” prototype proof-of-principle demonstration experiment at CERN known as AWAKE. Proton beams of 400 GeV energy will be extracted from the Super Proton Synchrotron and used to excite a specially dersigned plasma column and the generated wakefields will be sampled by specially prepared electrons from an injector for acceleration. The experiment has been approved by the CERN Scientific Program Committee for some years now and a global collaboration of institutions from across Europe and Russia (and potential Asian and North American collaborators) is busy preparing the experiment in the 2018-2020 time scale. The experimental cave previously used for the Gran Sasso long baseline neutrino experiment is being prepared by CERN to launch this demonstration experiment. I will describe the status of this experiment and its promise for future high energy electron-proton and electron-positron colliders.

Scopri di più »

Fractal aspects of hadronic interaction

A remarkable feature of high energy collisions is the power-law behavior of the transverse momentum distributions, p_T. Although at the high momentum sector this can be explained in terms of perturbative QCD, the low momentum sector can be described only by the assumption of a thermodynamically equilibrated system formed in the collision. It has been shown that when Tsallis statistics is used, the well-known Hagedorn self-consistent thermodynamics, now extended with the non extensive features, can describe the experimental data with only two free parameters that are independent of the collision energy and of the observed particle mass, namely, the critical temperature, T, and the entropic index, q, which appears in Tsallis statistics. Recently it was shown that the non extensive behavior of the hadronic systems can be related to a fractal structure in its thermodynamical functions. The fractal dimension is determined by those two parameters of the Tsallis statistics and, suprisingly, is in accordance with the fractal dimension obtained from the analysis of intermittance in the high energy distributions. In this talk we present an overview on the developments of the non extensive self-consistent thermodynamics applied for high energy collisions and discuss possible implications in the investigation of non-perturbative QCD.

Scopri di più »