Current bearing wire compensators were successfully used in the 2005-2006 run of the DA{Phi}NE collider to mitigate the detrimental effects of parasitic beam-beam interactions. A marked improvement of the positron beam lifetime was observed in machin
e operation with the KLOE detector. In view of the possible application of wire beam-beam compensators for the High Luminosity LHC upgrade, we revisit the DA{Phi}NE experiments. We use an improved model of the accelerator with the goal to validate the modern simulation tools and provide valuable input for the LHC upgrade project.
Reflection of light from surfaces is a very common, but complex phenomenon not only in science and technology, but in every day life. The underlying basic optical principles have been developed within the last five centuries using visible light avail
able from the sun or other laboratory light sources. X-rays were detected in 1895, and the full potential of soft- and hard-x ray radiation as a probe for the electronic and geometric properties of matter, for material analysis and its characterisation is available only since the advent of synchrotron radiation sources some 50 years ago. On the other hand high-brilliance and high power synchrotron radiation of present-days 3rd and 4th generation light sources is not always beneficial. Highenergy machines and accelerator-based light sources can suffer from a serious performance drop or limitations due to interaction of the synchrotron radiation with the accelerator walls, thus producing clouds of photoelectrons (e-cloud) which in turn interact with the accelerated beam. Thus the suitable choice of accelerator materials and their surface coating, which determines the x-ray optical behaviour is of utmost importance to achieve ultimate emittance. Basic optical principles and examples on reflectivity for selected materials are given here.
The secondary emission yield (SEY) properties of colaminated Cu samples for LHC beam screens are correlated to the surface chemical composition determined by X-ray photoelectron spectroscopy. The surface of the as received samples is characterized by
the presence of significant quantities of contaminating adsorbates and by the maximum of the SEY curve (dmax) being as high as 2.2. After extended electron scrubbing at kinetic energy of 10 and 500 eV, the dmax value drops to the ultimate values of 1.35 and 1.1, respectively. In both cases the surface oxidized phases are significantly reduced, whereas only in the sample scrubbed at 500 eV the formation of a graphitic-like C layer is observed. We find that the electron scrubbing of technical Cu surfaces can be described as occurring in two steps, where the first step consists in the electron induced desorption of weakly bound contaminants that occurs indifferently at 10 and at 500 eV and corresponds to a partial decrease of dmax, and the second step, activated by more energetic electrons and becoming evident at high doses, which increases the number of graphitic-like C-C bonds via the dissociation of adsorbates already contaminating the as received surface or accumulating on this surface during irradiation. Our results demonstrate how the kinetic energy of impinging electrons is a crucial parameter when conditioning technical surfaces of Cu and other metals by means of electron induced chemical processing.
The Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides for a quick look and review of the gamma-ray sky observed daily by the Fermi Large Area Telescope (LAT). The FA-GSW service provides alerts and communicates to th
e external scientific community potentially new gamma-ray sources, interesting transients and source flares. A weekly digest containing the highlights about the variable LAT gamma-ray sky at E>100 MeV is published in the web (Fermi Sky Blog). Other news items are occasionally posted through the Fermi multiwavelength mailing list, Astronomers Telegrams (ATels) and Gamma-ray Coordination Network notes (GCNs). From July 2008 to January 2013 about 230 ATels and some GCNs have been published by the Fermi LAT Collaboration, more than 40 target of opportunity observing programs have been triggered by the LAT Collaboration and performed though the Swift satellite, and individual observing alerts have been addressed to ground-based Cherenkov telescopes. This is helping the Fermi mission to catch opportunities offered by the variable high-energy sky, increasing the rate of simultaneous multifrequency observations and the level of international scientific cooperation.
The FOCUS photoproduction experiment took data in the ninenties and produced a wealth of results in charm physics. Some of the studies were seminal for contemporary experiments, and even paved the way for the technology of many charm and beauty analysis tools.
To settle the question whether the growth with energy is universal for different hadronic total cross-sections, we present results from theoretical models for pion-proton, proton-proton and proton-antiproton total cross-sections. We show that present
and planned experiments at LHC can differentiate between different models, all of which are consistent with presently available (lower energy) data. This study is also relevant for the analysis of those very high energy cosmic ray data which require reliable pion-proton total cross-sections as seeds. A preliminary study of the total pion-pion cross-sections is also made.
Recently the BaBar Collaboration published new data on the cross section for the annihilation e+e- -> phi pi0, obtained using the initial state radiation technique at a center of mass energy of 10.6 GeV. Such a process represents an interesting test
bed for the quark model. Indeed, since the phi-pi0 production via e+e- annihilation proceeds through a mechanism which violates the Okubo-Zweig-Iizuka rule, the corresponding cross section could be characterized by contributions from non-qqbar bound states, like hybrids or tetraquarks. The phi-pi0 cross section is analyzed in connection with other data coming from different processes, that involve the same mesons, using a method which implements the analyticity in the phi-pi0 transition form factor by means of a dispersion relation procedure.
A method to determine masses, widths and coupling constants of vector mesons, like phi(1020), omega(782) and rho0(770) recurrences is defined. Starting from data on decay rates and cross sections for the processes: phi -> M_I gamma, phi -> M_I e+e- a
nd e+e- -> M_I phi, where M_I is a pseudoscalar or scalar meson with isospin I=0,1, the time-like transition form factors, which describe the vertex phi-gamma-M_I, are parametrized using a vector meson-propagators description in the low energy region <3-4 GeV, the quark-counting rule prescription for the high energy behavior, and the analyticity imposed by means of the dispersion relations.
