Search results for "SCOPE"
showing 10 items of 2420 documents
Peculiarities in fragment mass distribution in the 238U + 40Ar (243 MeV) reaction
2001
A pronounced fine structure (FS) in the form of distinct peaks was observed in neutron gated mass spectra from the decay of the 278110 composite system produced in the reaction 238U + 40Ar (243 MeV) at an initial excitation energy E * > 70 MeV. The FS peaks are located in the vicinity of mass numbers 70-80, 100, and 130, which correspond to those of magic nuclei (clusters). In the data there is also evidence for a new type of decay -- collinear cluster tripartition of an excited nucleus.
Theoretical study of incoherent phi photoproduction on a deuteron target
2012
We study the photoproduction of phi mesons in deuteron, paying attention to the modification of the cross section from bound protons to the free ones with the aim of comparing with recent results at LEPS. For this purpose we take into account Fermi motion in single scattering and rescattering of the phi to account for phi absorption on a second nucleon as well as the rescattering of the proton. We find that the contribution of the double scattering is much smaller than the typical cross section of gamma p to phi p in free space, which implies a very small screening of the phi production in deuteron. The contribution from the proton rescattering, on the other hand, is found to be not negligi…
Einzelnachweis von Elektronen (15 bis 50 keV) in Kernphotoplatten
1960
Nuclear track emulsions (Ilford G 5) were used for counting of single slow electrons. They had to be accelerated by high voltage of about 30 kV and were incident vertically. The pulsed electron-beam was measured in a cage, single pulses were shot on the emulsion. The developed plates were photographed under the microscope and the tracks counted on the enlarged copies. The results are: about 40% of incoming electrons can be found as tracks in the emulsions. This number varies between different emulsions (of same type G 5), within one plate the number of tracks is better proportional to the number of electrons than between different plates. With a counting resultx one may expect the true resu…
Time-of-flight photoelectron emission microscopy TOF-PEEM: first results
1998
The time structure of the synchrotron radiation at BESSY (Berlin) is used to operate a photoemission electron microscope in a time-of-flight (TOF) mode. The electrons which are emitted from the sample surface with different energies are dispersed in a drift tube subsequent to the imaging optics. The screen of the microscope was replaced by a fast scintillator (tau = 1.4 ns) and the light is detected by an ultra fast gated intensified CCD camera (800 ps gate 1 MHz repetition rate). The resolving power in the energy domain is demonstrated and possible implications on the spatial resolution (chromatic correction) are discussed. Additionally, an improved contrast at very low emission energies i…
Conservative upper limits on WIMP annihilation cross section from Fermi-LAT γ rays
2012
The spectrum of an isotropic extragalactic {\gamma}-ray background (EGB) has been measured by the Fermi-LAT telescope at high latitudes. Two new models for the EGB are derived from the subraction of unresolved point sources and extragalactic diffuse processes, which could explain from 30% to 70% of the Fermi-LAT EGB. Within the hypothesis that the two residual EGBs are entirely due to the annihilation of dark matter (DM) particles in the Galactic halo, we obtain stringent upper limits on their annihilation cross section. Severe bounds on a possible Sommerfeld enhancement of the annihilation cross section are set as well. Finally, we consider models for DM annihilation depending on the inver…
Scalar isoscalar pion pairs in nuclei and theA(π,ππ)Xreaction
1999
The reaction A(pi,pi pi)X has been studied at low energies, paying particular attention to the interaction of the two final pions in the scalar isoscalar (I=J=0) channel. We have developed a microscopic model for the pion production, and then implemented the two pion final state interaction by using the results of a non-perturbative unitary coupled-channels method based in the standard chiral Lagrangians. The resulting model, describes well the reaction on the nucleon for all different isospin channels. Finally, we have considered the reaction in nuclei. Our calculation takes into account Fermi motion, Pauli blocking, pion absorption, and also the strong modification of the pi-pi interactio…
Ultra-long-lived particles searches with MATHUSLA
2018
Abstract There are many theoretical motivations for long-lived particle (LLP) signals at the LHC in a comprehensive survey of Standard Model (SM) extensions. LLPs are a common prediction of a wide range of theories that address unsolved fundamental mysteries such as naturalness, dark matter, baryogenesis and neutrino masses, and represent a natural and generic possibility for physics beyond the SM (BSM). MATHUSLA (MAssive Timing Hodoscope for Ultra Stable neutraL pArticles) is a proposal for a minimally instrumented, large-volume surface detector to detect such LLPs. The MATHUSLA surface detector will consist of an air-filled decay volume surrounded by charged particles detectors (top, bott…
The COMPASS trigger system for muon scattering
2005
Abstract The trigger system of the COMPASS experiment at the CERN polarized muon beam is presented. It detects muon scattering events on (polarized) nucleons with a relative energy loss exceeding a selectable value y min independent of the four-momentum transfer. The requirement of a minimum energy deposit in a hadron calorimeter rejects background events like scattering on electrons, elastic and quasi-elastic radiative events as well as events from beam halo tracks. The trigger system which can be considered as a tagger for quasi-real photon events is now, along with larger trigger hodoscope system for deep inelastic scattering events, in regular use for the measurement of the gluon polari…
Quasielastic neutrino (antineutrino) reactions in nuclei and the axial-vector form factor of the nucleon
1992
Abstract Quasielastic neutrino and antineutrino reactions in nuclei are studied to investigate the effect of the nuclear medium on the determination of axial dipole mass M A in nuclei. The calculations are done in the local density approximation and various nuclear effects like Pauli blocking, Fermi motion of nucleons and strong renormalization effects in the spin-isospin channel are taken into account. The nuclear effects are found to be quite large at low q 2 , but the data in this region are too meagre to influence the determination of M A . The experimental data on differential and total cross sections are found to be consistent with M A as determined from deuterium experiments and no c…
Mesonic and binding contributions to the EMC effect in a relativistic many-body approach
1996
We revise the conventional nuclear effects of Fermi motion, binding and pionic effects in deep inelastic lepton scattering using a relativistic formalism for an interacting Fermi sea and the local density approximation to translate results from nuclear matter to finite nuclei. In addition we also consider effects from rho-meson renormalization in the nucleus. The use of nucleon Green's functions in terms of their spectral functions offers a precise way to account for Fermi motion and binding. On the other hand the use of many body Feynman diagrams in a relativistic framework allows one to avoid using prescriptions given in the past to introduce relativistic corrections in a non relativistic…