Simulacija porarizacijskih mjerenja u elektrotvorbi kaona Monte Carlo metodom

Kaon electro-production experiments with polarized electron beam are planed at the Thomas Jefferson National Accelerator Facility (Virginia, USA) in order to complete the information on polarization response functions for the kaon electro-production reactions. The experiment uses the self analyzing property of the Λ recoil. The scattered electrons will be detected in coincidence with the kaons and the decay protons. This paper presents the simulation of this experiment which takes into account the spectrometer acceptances, multiple scattering and radiative corrections. The phase space distribution of the decay protons in the Λ center-of-mass system are generated in order to extract information on the polarization on the three directions. An experimental test with an unpolarized beam has been performed to estimate the efficiency of the method.U Thomas Jefferson National Accelerator Facility (Virginia, USA) predlažu se mjerenja elektrotvorbi s polariziranim elektronima radi cjelovitosti podataka o polarizacijskim funkcijama odziva u elektrotvorbi kaona. Mjerenje rabi samoanalizacijsko svojstvo odboja Λ čestice. Raspršeni elektroni opažat će se sudesno s kaonima i protonima. Ovaj rad predstavlja simulaciju tog eksperimenta u kojoj se uzimaju u obzir prihvati spektrometara, višestruko raspršenje i radijativne popravke. Izvodi se fazna raspodjela protona u centru mase Λ čestice radi dobivanja podataka o polarizaciji u trima smjerovima. Mjerenjem pomoću nepolariziranog snopa ocijenili smo učinkovitost metode

Absence of Embedded Mass Shells: Cerenkov Radiation and Quantum Friction

We show that, in a model where a non-relativistic particle is coupled to a quantized relativistic scalar Bose field, the embedded mass shell of the particle dissolves in the continuum when the interaction is turned on, provided the coupling constant is sufficiently small. More precisely, under the assumption that the fiber eigenvectors corresponding to the putative mass shell are differentiable as functions of the total momentum of the system, we show that a mass shell could exist only at a strictly positive distance from the unperturbed embedded mass shell near the boundary of the energy-momentum spectrum.Comment: Revised version: a remark added at the end of Section

Collective motional resonances and instabilities of an electron cloud stored in a Penning trap

We have experimentally investigated the behavior of an electron cloud confined in a Penning trap at weak superimposed magnetic fields. Exciting the motional frequencies of the electrons by an external drive field we found the axial mode split into two components which were identified as center-of-mass and individual electron oscillations. When the trapping potential was varied, rapid electron loss appeared at numerous values of the applied voltage. They are determined by the relation n z ω z + n m ω m =ω c . ω z ,ω m ,ω c are the axial, magnetron, and cyclotron frequency of the trapped electrons, respectively. The reason for this loss is attributed to higher order contributions to the ideal quadrupole trapping potential

Large deviations for ideal quantum systems

We consider a general d-dimensional quantum system of non-interacting particles, with suitable statistics, in a very large (formally infinite) container. We prove that, in equilibrium, the fluctuations in the density of particles in a subdomain of the container are described by a large deviation function related to the pressure of the system. That is, untypical densities occur with a probability exponentially small in the volume of the subdomain, with the coefficient in the exponent given by the appropriate thermodynamic potential. Furthermore, small fluctuations satisfy the central limit theorem.Comment: 28 pages, LaTeX 2

Diamagnetism of quantum gases with singular potentials

We consider a gas of quasi-free quantum particles confined to a finite box, subjected to singular magnetic and electric fields. We prove in great generality that the finite volume grand-canonical pressure is jointly analytic in the chemical potential ant the intensity of the external magnetic field. We also discuss the thermodynamic limit

Elastic Wave Transmission at an Abrupt Junction in a Thin Plate, with Application to Heat Transport and Vibrations in Mesoscopic Systems

The transmission coefficient for vibrational waves crossing an abrupt junction between two thin elastic plates of different widths is calculated. These calculations are relevant to ballistic phonon thermal transport at low temperatures in mesoscopic systems and the Q for vibrations in mesoscopic oscillators. Complete results are calculated in a simple scalar model of the elastic waves, and results for long wavelength modes are calculated using the full elasticity theory calculation. We suggest that thin plate elasticty theory provide a useful and tractable approximation to the full three dimensional geometry.Comment: 35 pages, including 12 figure

Measurements of the Separated Longitudinal Structure Function FL From Hydrogen and Deuterium Targets at Low Q2

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the partonic dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available in particular for the longitudinal structure function. Here, we present separated structure functions for hydrogen and deuterium at low four-momentum transfer squared, Q2 \u3c 1GeV2, and compare them with parton distribution parametrization and kT factorization approaches. While differences are found, the parametrizations generally agree with the data, even at the very low-Q2 scale of the data. The deuterium data show a smaller longitudinal structure function and a smaller ratio of longitudinal to transverse cross section, R, than the proton. This suggests either an unexpected difference in R for the proton and the neutron or a suppression of the gluonic distribution in nuclei

Bound Magnetic Polaron Interactions in Insulating Doped Diluted Magnetic Semiconductors

The magnetic behavior of insulating doped diluted magnetic semiconductors (DMS) is characterized by the interaction of large collective spins known as bound magnetic polarons. Experimental measurements of the susceptibility of these materials have suggested that the polaron-polaron interaction is ferromagnetic, in contrast to the antiferromagnetic carrier-carrier interactions that are characteristic of nonmagnetic semiconductors. To explain this behavior, a model has been developed in which polarons interact via both the standard direct carrier-carrier exchange interaction (due to virtual carrier hopping) and an indirect carrier-ion-carrier exchange interaction (due to the interactions of polarons with magnetic ions in an interstitial region). Using a variational procedure, the optimal values of the model parameters were determined as a function of temperature. At temperatures of interest, the parameters describing polaron-polaron interactions were found to be nearly temperature-independent. For reasonable values of these constant parameters, we find that indirect ferromagnetic interactions can dominate the direct antiferromagnetic interactions and cause the polarons to align. This result supports the experimental evidence for ferromagnetism in insulating doped DMS.Comment: 11 pages, 7 figure