Results 1 - 10 of 2090
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[en] Beam halo is a challenging issue for intense beams since it can cause beam loss, emittance growth, nuclear activation and secondary electron emission. Because of the potentially low number of particles in the halo compared with beam core, traditional imaging methods may not have sufficient contrast to detect faint halos. We have developed a high dynamic range, adaptive masking method to measure halo using a digital micro-mirror array device and demonstrated its effectiveness experimentally on the University of Maryland Electron Ring (UMER). We also report on similar experiments currently in progress at the Jefferson Lab Free Electron Laser (FEL) using this method.
[en] Dark matter halos of subsolar mass are the first bound objects to form in cold dark matter theories. In this paper, I discuss the present understanding of 'microhalos', their role in structure formation and the implications of their potential presence, in the interpretation of dark matter experiments.
[en] This report summarizes the presentations and discussions over a wide range of topics in Working Group I at the Second ICFA Advanced Accelerator Workshop on Physics of High-Brightness Beams held at the University of California at Los Angeles (UCLA), November 9-12, 1999. Latest developments towards to a better understanding of high-brightness photoinjectors were reported. The design and commissioning of the Los Alamos National Laboratory (LANL) Low-Energy Demonstration Accelerator (LEDA) Radio-Frequency Quadrupole (RFQ) were reported. The problem of beam halo formation was discussed in both beam transport systems and the SLAC 50 MW 11.4 GHz periodic permanent magnet (PPM) focusing klystron amplifier. A new class of corkscrewing elliptic beam equilibria was reported, and applications of such novel beam equilibria in controlling of charge-density and velocity fluctuations, beam halo formation and emittance growth were discussed. Pattern formation in proton rings was also discussed
[en] The DAMA/Libra experiment at the Gran Sasso National Laboratory of the INFN. has confirmed with higher sensitivity the model independent evidence for Dark Matter (D M) particles in the galactic halo obtained by the former DAMA/NaI experiment by investigating the D M annual modulation signature. Considering these data together with those of former DAMA/NaI a confidence level of 8.2 σ is achieved for a cumulative exposure of 0.82 ton x y. Recently a first upgrading of the set-up has been carried up and a second one is in preparation: this latter one has the main aim to decrease the energy threshold of the experiment. Moreover, investigations on other rare processes are also in progress.
[en] The theory of Faddev/AGS few body reaction frameworks is presented. A comparison with other reaction formalisms (DWBA, CDCC) is made. Sucesses and shortcomings of the scattering approaches for breakup are analysed. Some set of calculated reaction observales for resonant and nonresonant breakup are presented to obtain insight into the physics incorporated on the scattering approaches.
[en] The neutral atomic hydrogen data of the Very Large Array for the spiral galaxy NGC 5921 with z = 0.0045 at the distance of 22.4 Mpc, has been used to investigate the nature of dark matter. The investigation was based on two theories, namely, dark matter and Modified Newtonian Dynamics (MOND). Presented in this study is the kinematic analysis of the rotation curve with two models of dark matter, namely, the Burkert and NFW profiles. The results revealed that the NFW halo model can reproduce the observed rotation curve, with χ2red≈1, while the Burkert model is unable to fit the observation data. Therefore, the dark matter density profile of NGC 5921 can be presented as a cuspy halo. The observed rotation curve of NGC 5921 with MOND, has been investigated along with the possible assumption on baryonic matter and distance. It has been noted that MOND is still incapable of mimicking the rotation curve with the observed data of the galaxy. (author)
[en] The present DAMA/LIBRA experiment and the former DAMA/NaI have cumulatively released so far the results obtained with the data collected over 13 annual cycles (total exposure: 1.17 ton per year). They give a model independent evidence of the presence of dark matter particles in the galactic halo on the basis of the dark matter annual modulation signature at 8.9 σ C.L. for the cumulative exposure.
[en] The nuclear shell structure that has served as a fundamental framework for understanding the arrangement of nucleons exhibits dramatic changes as the neutron to proton ratio in nuclei increases. This paper describes how reaction spectroscopy of the neutron- and proton-rich nuclei has brought about a new revolution towards a more global view of nuclear shells. The relationship between changes in shell structure and the discovery of exotic forms of nuclei such as nuclear halo and skin is discussed. It is shown that the well-known shell gaps (magic numbers) N = 8 and 20 disappear. The discovery of a new magic number at N = 16 at the limit of nuclear binding is discussed. (paper)