8 research outputs found
Magnetic and electric field effect on the photoelectron emission from prototype LHC bean screen material.
This paper describes experimental studies of the effect of a dipole field on the photoelectron emission and on the photon reflectivities from LHC beam screen material. These studies were performed using synchrotron radiation from the VEPP-2M storage ring at BINP (Novosibirsk). The particular surface roughness and geometry of the prototype LHC beam screen material requires dedicated experimental measurements. The experiments were performed under conditions close to those expected in the LHC. An important result obtained is that a dipole magnetic field attenuates the photoelectron emission from surface by more than two orders of magnitude with the magnetic field aligned parallel to the surface. The measurements of photon reflectivities, forward scattered and diffuse, and the azimuthal distribution of emitted photoelectrons from the same material are reported. These experimental results are important input for the final design of the LHC beam screen
Experimental study of the e+e- -> pi0 gamma process in the energy region sqrt(s)=0.60-0.97 GeV
Results of the study of the e+e-->pi0 gamma process with SND detector at
VEPP-2M collider in the c.m.s. energy range sqrt(s)=0.60-0.97 GeV are
presented. Using 36513 selected events corresponding to a total integrated
luminosity of 3.4 pb^-1 the e+e-->pi0 gamma cross section was measured. The
energy dependence of the cross section was analyzed in the framework of the
vector meson dominance model. The data are well described by a sum of
phi,omega,rho0->pi0 gamma decay contributions with measured decay
probabilities: Br(omega->pi0 gamma)=(9.34+-0.15+-0.31)% and Br(rho0->pi0
gamma)=(5.15+-1.16+-0.73)*10^-4 . The rho-omega relative interference phase is
phi(rho,omega}=(-10.2+-6.5+-2.5) degree
Search for direct production of a2(1320) and f2(1270) mesons in e+e- annihilation
A search for direct production of C-even resonances a2(1320) and f2(1270) in
e+e- annihilation was performed with SND detector at VEPP-2M e+e- collider. The
upper limits of electronic widths of these mesons were obtained at 90%
confidence level:
Gamma(a2(1320) \to e+e-) < 0.56 eV,
Gamma(f2(1270) \to e+e-) < 0.11 eV.Comment: 6 pages, 5 figures, 1 table. Submitted to Phys. Lett.
The beam energy measurement system for the Beijing electron-positron collider
The beam energy measurement system (BEMS) for the upgraded Beijing
electron-positron collider BEPC-II is described. The system is based on
measuring the energies of Compton back-scattered photons. The relative
systematic uncertainty of the electron and positron beam energy determination
is estimated as 2 \cdot 10^{-5}. The relative uncertainty of the beam's energy
spread is about 6 %
Status of a radio-frequency-based streak camera with subpicosecond time resolution
Usage of a cavity with a high quality factor in a streak
camera (SC) allows us to increase the energy of electrons
up to 100 keV and therefore to reduce the influence of
some of the effects that limit the SC time resolution. Time
resolution up to 1.4 ps on a prototype of a radio-frequency-based
SC (RFC) with circular scanning was demonstrated earlier.
Following this, the new RFC was produced. The possibility
of achieving a time resolution of 0.6 ps for a 350-ps single
light signal is demonstrated. Preparation for experiments
with spiral scanning (sub-ps time resolution for 10-ns
process duration) is in progress