G.Ya. Kezerashvili

Experimental investigation of high-energy photon splitting in atomic fields

Data analysis of an experiment in which photon splitting in atomic fields was observed is presented. The experiment was performed at the tagged photon beam of the ROKK-1M facility at the VEPP-4M collider. In the energy region of 120-450 MeV, statistics of 1.6x10(9) photons incident on the BGO target was collected. About 400 candidate photon-splitting events were reconstructed. Within the attained experimental accuracy, the experimental results are consistent with the calculated exact atomic-field cross section. The predictions obtained in the Born approximation differ significantly from the experimental results.

A detailed test of the CsI(Tℓ) calorimeter for BELLE with photon beams of energy between 20 MeV and 5.4 GeV

Abstract The results of a beam test of a prototype of the BELLE CsI(Tl) calorimeter are reported. The test used beams of photons with energies spanning the range from 20 MeV to 5.4 GeV, produced at ROKK-1M facility of the Budker Institute of Nuclear Physics. The single-counter energy-equivalent noise was measured to be ∼200 keV. The design goals for the energy resolution, e.g. 4% at 20 MeV and 1.7% at 5.4 GeV, were achieved using the sum of energy deposits in a 5×5 crystal matrices with a single crystal energy threshold of 0.5 MeV; the summed energy deposit measured in the array corresponds to 97±2% of the incident photon energy over the entire energy range. The average position resolution for 470 MeV energy photons was measured to be 8 mm.

Detector KEDR tagging system for two-photon physics

Abstract A special system to tag scattered electrons from γγ-processes is described. The system is intended for the experiments at the VEPP-4M storage ring. This system has a high detection efficiency and good invariant mass resolution.

Photofission of Heavy Nuclei at Energies up to 4 GeV

Total photofission cross sections for 238U, 235U, 233U, 237Np, 232Th, and natPb have been measured simultaneously, using tagged photons in the energy range Egamma=0.17-3.84 GeV. This was the first experiment performed using the Photon Tagging Facility in Hall B at Jefferson Lab. Our results show that the photofission cross section for 238U relative to that for 237Np is about 80% over the entire energy range, implying the presence of important processes which compete with fission. If we assume that for 237Np the photofission probability is equal to unity, we observe a significant shadowing effect, starting below 1.5 GeV.

The gamma ray energy tagging spectrometer of the ROKK-2 facility at the VEPP-3 storage ring

Abstract A tagging spectrometer for the gamma rays produced by Compton backscattering and bremsstrahlung processes is described. A storage ring bending magnet is used as an electron momentum separator for this spectrometer in the gamma ray energy range from 30 MeV up to 270 MeV. Factors determining the tagging efficiency and the energy resolution are discussed. The energy resolution is measured by the Compton backscattering process. The tagging spectrometer yields a resolution of 4 MeV and a tagging efficiency of 95%.

Comparison of the electron and positron anomalous magnetic moments: Experiment 1987

Abstract The anomalous magnetic moments of relativistic electrons and positrons have been compared by measuring the spin precession phase difference at a given time interval. The difference in the anomalous magnetic moments between the electron and the positron has been shown to lie within 1×10 −8 at 95% confidence level, which improves the accuracy of the previous measurements by an order of magnitude.

A Compton source of high energy polarized tagged γ-ray beams. The ROKK-1M facility

The ROKK-1M facility generates high energy polarized γ-ray beams by backscattering of laser light against the high energy electron and positron beams of the VEPP-4M collider. The facility design allows to obtain backscattering of laser light on electron and positron beams separately or simultaneously. Tagging and/or collimation is applied to select a narrow energy band from the γ-quanta spectrum. Operating in a laser polarimeter mode, the ROKK1-M facility is able to measure transverse and longitudinal polarization of the electron and positron beams in the VEPP-4M collider. A description of the facility and achieved γ-ray beam parameters are presented in this paper.

Liquid krypton calorimeter for KEDR detector and last prototype results

Abstract The liquid krypton calorimeter for the KEDR-VEPP-4M experiment is described. The experimental results with a prototype, obtained at the tagged photon beam of VEPP-4M in the photon energy region between 50 and 4500 MeV, are presented. The results on the energy resolution are in a good agreement with the Monte-Carlo expectations and are equal to 6% and 2% at 100 and 1000 MeV respectively. The spatial resolution is about 1–1.5 mm in a wide energy region and agrees with the expected spatial resolution.

ROKK‐1M is the Compton source of the high intensity polarized and tagged gamma beam at the VEPP‐4M collider

The Backward Scattered Compton Quanta light source (ROKK‐1M) developed for the high intensity polarized and tagged gamma beam at the Novosibirsk VEPP‐4M Collider is described. Energy calibration of the electron and positron beams, real‐time measurement of the beam polarization, and the electron‐positron beam emittance at the interaction point are discussed. (AIP)

High precision mass measurements in Ψ and ϒ families revisited

Abstract High precision mass measurements in Ψ and ϒ families performed in 1980–1984 at the VEPP-4 collider with OLYA and MD-1 detectors are revisited. The corrections for the new value of the electron mass are presented. The effect of the updated radiative corrections has been calculated for the J / Ψ (1 S ) and Ψ (2 S ) mass measurements.