Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets

In the CERN NA63 collaboration we have addressed the question of the potential inadequacy of the commonly used Migdal formulation of the Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20 and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference target, Ta. For each target and energy, a comparison between simulated values based on the LPM suppression of incoherent bremsstrahlung is shown, taking multi-photon effects into account. For these targets and energies, we find that Migdal's theoretical formulation is adequate to a precision of better than about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure

Monografie di Agathòn. Atti del Symposium East-West Artistic and Technological Contaminations/Oriente-Occidente. Contaminazioni Artistiche e Tecnologiche

AgAthón, the Ph.D.’s journal collecting together the best of the works about the renovation and the enhancement of ancient contexts, has had increasing success among institutions and both Italian and foreign researchers. The choral pattern chosen in the four sectors, which alludes to the Greek city, has certainly contributed to create this appreciation: the Agorá, like the central space in the pólis, for guest contributions; the Stoá, the covered portico under which the philosopher Zeno used to teach his disciples, for the Ph.D. teachers’ contributions; the gymnásion, the place of endeavour for young Greeks training their bodies and minds, is the section meant for the doctoral candidates; lastly, the Sekós, i.e. the part of the house where the young people used to dwell, as described by Plato in his Republic, is assigned to young graduates. In this way, we have created a common approach to the topics dealt with and the related disciplines; this shared and plural approach is borne out by the large number of applications with articles to be published in the various issues. Hence the need for the editorial staff to ensure a monographic and multi-disciplinary area: a syllogé, meant as an anthological collection of scientific writings, concerning an author’s or a group of authors’ production, as a cultural and literary gleaning of the stubble left over in a field after the harvest and, therefore, as a collection of topics not entirely and not always of secondary relevance

A water-based sequential preparatory approach vs. conventional aquatic training in stroke patients: a randomized controlled trial with a 1-month follow-up

Background: Many studies hypothesize that people who have suffered stroke could benefit from water-based exercises to improve their strength and ability to perform the activities of daily living. Objective: The study aim was to compare the effects of a water-based sequential preparatory approach (SPA) and conventional aquatic therapy in improving motor functions and quality of life in patients with chronic stroke. Methods: Thirty-three chronic stroke outpatients diagnosed with hemiplegia were recruited and randomly assigned to the experimental or control group. Subjects in the experimental group underwent a trial water-based SPA balance training, and patients in the control group were given traditional water balance training. Both groups of participants underwent 45 min of therapy twice a week for 4 weeks. All patients were evaluated before treatment (T0), after 4 weeks of training (T1), and 4 weeks after the end of training (T2) using the Berg balance scale (BBS), the modified Barthel index (MBI), the Tinetti balance and gait scale (TBG), the Stroke Specific Quality Of Life Scale (SS-QOL), and the modified Ashworth scale (MAS). Results: After the training, statistically significant differences (p < 0.05) were found between the groups in their score averages on the BBS (p = 0.01) and the SS-QOL scale (p = 0.03). Furthermore, the SPAg showed a significantly greater percentage of improvement on the BBS (p = 0.02) and the SS-QOL (p = 0.03). Both groups obtained a significantly improved MAS score (p < 0.01). Conclusion: Results indicate that water training based on an SPA is more effective than traditional aquatic training for balance rehabilitation of chronic poststroke patients

Experimental investigations of synchrotron radiation at the onset of the quantum regime

The classical description of synchrotron radiation fails at large Lorentz factors, $\gamma$, for relativistic electrons crossing strong transverse magnetic fields $B$. In the rest frame of the electron this field is comparable to the so-called critical field $B_0 = 4.414\cdot10^9$ T. For $\chi = \gamma B/B_0 \simeq 1$ quantum corrections are essential for the description of synchrotron radiation to conserve energy. With electrons of energies 10-150 GeV penetrating a germanium single crystal along the $$ axis, we have experimentally investigated the transition from the regime where classical synchrotron radiation is an adequate description, to the regime where the emission drastically changes character; not only in magnitude, but also in spectral shape. The spectrum can only be described by quantum synchrotron radiation formulas. Apart from being a test of strong-field quantum electrodynamics, the experimental results are also relevant for the design of future linear colliders where beamstrahlung - a closely related process - may limit the achievable luminosity.Comment: 11 pages, 18 figures, submitted to PR

Particle and light fragment emission in peripheral heavy ion collisions at Fermi energies

A systematic investigation of the average multiplicities of light charged particles and intermediate mass fragments emitted in peripheral and semiperipheral collisions is presented as a function of the beam energy, violence of the collision and mass of the system. The data have been collected with the "Fiasco" setup in the reactions 93Nb+93Nb at 17, 23, 30, 38AMeV and 116Sn+116Sn at 30, 38AMeV. The midvelocity emission has been separated from the emission of the projectile-like fragment. This last component appears to be compatible with an evaporation from an equilibrated source at normal density, as described by the statistical code Gemini at the appropriate excitation energy. On the contrary, the midvelocity emission presents remarkable differences for what concerns both the dependence of the multiplicities on the energy deposited in the midvelocity region and the isotopic composition of the emitted light charged particles.Comment: 18 pages, 17 figures, Revtex

Analysis of the exclusive final state npe+^+e−^- in quasi-free np reaction

We report on the investigation of dielectron production in tagged quasi-free neutron-proton collisions by using a deuteron beam of kinetic energy 1.25GeV/u impinging on a liquid hydrogen target. Our measurements with HADES confirm a significant excess of $e^{+}e^{-}$ pairs above the $\pi^{0}$ mass in the exclusive channel $dp \rightarrow npe^{+}e^{-}(p_{spect})$ as compared to the exclusive channel $ppe^{+}e^{-}$ measured in proton-proton collisions at the same energy. That excess points to different bremsstrahlung production mechanisms. Two models were evaluated for the role of the charged pion exchange between nucleons and double- $\Delta$ excitation combined with intermediate $\rho$ -meson production. Differential cross sections as a function of the $e^{+}e^{-}$ invariant mass and of the angles of the virtual photon, proton and electrons provide valuable constraints and encourage further investigations on both experimental and theoretical sides.Peer Reviewe

Centrality determination of Au + Au collisions at 1.23A GeV with HADES

The centrality determination for Au+Au collisions at 1.23A GeV, as measured with HADES at the GSI-SIS18, is described. In order to extract collision geometry related quantities, such as the average impact parameter or number of participating nucleons, a Glauber Monte Carlo approach is employed. For the application of this model to collisions at this relatively low centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}} = 2.42$ GeV special investigations were performed. As a result a well defined procedure to determine centrality classes for ongoing analyses of heavy-ion data is established.Peer Reviewe

Coherent Pair Production by Photons in the 20-170 GeV Energy Range Incident on Crystals and Birefringence

The cross section for coherent pair production by linearly polarised photons in the 20-170 GeV energy range was measured for photon aligned incidence on ultra-high quality diamond and germanium crystals. The theoretical description of coherent bremsstrahlung and coherent pair production phenomena is an area of active theoretical debate and development. However, under our experimental conditions, the theory predicted the combined cross section and polarisation experimental observables very well indeed. In macroscopic terms, our experiment measured a birefringence effect in pair production in a crystal. This study of this effect also constituted a measurement of the energy dependent linear polarisation of photons produced by coherent bremsstrahlung in aligned crystals. New technologies for manipulating high energy photon beams can be realised based on an improved understanding of QED phenomena at these energies. In particular, this experiment demonstrates an efficient new polarimetry technique. The pair production measurements were done using two independent methods simultaneously. The more complex method using a magnet spectrometer showed that the simpler method using a multiplicity detector was also viable.Comment: 10 pages, 13 figures, 1 table, REVTeX4 two column, Version for publicatio