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.

KEDR is a general-purpose detector for experiments at the VEPP-4M e+e−-collider in the energy range 2E=2.0–12GeV. All detector subsystems (except the aerogel Cherenkov counters) have been installed into the detector at VEPP-4M. Some preliminary data have been taken in the energy region of the J/Ψ meson. The tuning of the detector and the VEPP-4M collider is in progress. Preliminary results on the detector performance are presented. The future experimental program for the KEDR detector is discussed.

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(1S) and Ψ(2S) mass measurements.

The differential cross section of Delbrück scattering is measured on a bismuth germanate $Bi_4Ge_3O_{12}$ target at photon energies $140 - 450 MeV$ and scattering angles $2.6 - 16.6 mrad$. A good agreement with the theoretical results, obtained exactly in a Coulomb field, is found.

The new experimental results with a prototype of the liquid krypton calorimeter (LKr) for the KEDR detector are presented. The prototype (0.4 t of LKr) has the strip structure with a strip width of 1.0 cm. The signals from the strips are used for measuring the coordinates of the photon conversion point. The experiment was carried out at VEPP-4M collider on a tagged photon beam with an energy of 100–1700 MeV. Spatial resolution of the order of 1.0 mm in the whole energy region was obtained which is much better than that for crystal calorimeters. The results are in good agreement with the Monte-Carlo simulation.

Experiments with the MD-1 detector at the VEPP-4 collider in the energy region of Upsilon masons were carried out in 1980-1985. Some of the MD-1's results are still among the most accurate: precise measurement of Upsilon(1S), Upsilon(2S) and Upsilon(3S) meson masses; leptonic widths of Upsilon(1S) and Upsilon(2S); R ratio in the energy region root s=7.2-10.3 GeV; upper limits on the Upsilon(1S) decays to p (p) over bar, K+K-, pi(+)pi(-); upper limit on the electron width of new resonances in the energy region 7.2-10.3 GeV. New values of Upsilon(1S), Upsilon(2S), and Upsilon(3S) masses corrected to change of the electron mass are given.

The experiment with the prototype of liquid krypton electromagnetic calorimeter for the KEDR detector is described. The experiment was carried out at the VEPP-4M collider at the tagged photon beam. The tagged photons were obtained in the energy region 50–625 MeV using the ROKK-1M facility. The edges of the bremsstrahlung spectra were used for the energy resolution measurement in the high-energy region up to 4500 MeV. The energy resolution comparable with the resolution of the best crystal calorimeters and the excellent spatial resolution (∼1 mm) have been obtained. The results are in good agreement with the Monte-Carlo simulation.

A new type of gaseous photodetector has been suggested. It is a proportional counter consisting of a glass tube with a photocathode at its inner surface, an anode wire, and a set of gate wires to suppress the positive photon and ion feedback. The detector is intended for the detection of photons in the visible wavelength region and is able to work in a magnetic field. The photocathode covers a significant part of the total surface of the counter. Properties of the multi-alkali photocathode in methane at different gas pressures were investigated. The decrease of a photo-current in 0.7 bar methane was 15% of that in vaccum. The obtained results show the possibility of construction of such photodetectors.

This paper reviews physical results obtained at the e+e− collider VEPP-4 with the MD-1 detector. The results of experiments on the ϒ meson physics and study of the hadron production in continuum in the energy region 7.2–10.3 GeV as well as the results of study of the two photon reactions are presented. Among results obtained in the upsilon physics: the precise measurement of the ϒ(1S), ϒ(2S), ϒ(3S) masses and the precise determination of the ϒ(1S) and ϒ(2S) electronic widths. In the experiments on study of the hadron production in continuum the precise measurement of the R was carried out. The peculiarity of the detector is the magnetic field transverse to the orbit plane which provided the possibility to study two photon reactions with tagging one or both scattered electrons even at zero emission angle. Among results on the γγ reactions is the measurement of the two photon total hadronic cross section performed in the double-tag mode. In the QED experiments a new QED effect — the impact parameter cut-off in single bremsstrahlung was discovered.

A description of the liquid krypton calorimeter for the KEDR detector and experimental results on energy and position resolution obtained with prototypes are presented.

The total cross section of the processe + e − →hadrons has been measured in the center-of-mass energy range between 7.25 and 10.34 GeV using the MD-1 detector at the VEPP-4 collider. The ratioR=σ(e + e − →hadrons)/σ(e + e − →μ + μ −) was found to be constant in this energy range with the average value of 3.58±0.02±0.14.

Results of the test of the BELLE barrel calorimeter prototype using a tagged photon beam are presented. The prototype consisted of 36 CsI(Tl) counters with the same preamplifiers and shapers as in the BELLE calorimeter. The measurements were carried out at the VEPP-4M collider with the tagged photon beam provided by the ROKK-1M facility. The energy resolution for photons was measured in the energy range 40–800MeV. The achieved energy resolution was 3% for 40MeV and 1.5% for 800MeV photons. The results are consistent with the Monte Carlo simulation taking into account effects of the electronics noise.

Bose-Einstein correlations in direct γ(1S) decays and continuum in the energy region √s=7.2−10.3 GeV have been studied using data taken with the MD-1 detector at VEPP-4 storage ring. Assuming gaussian density of the pion source the data indicate the radius of the sourceπ=0.73±0.10±0.04 fm for direct γ (1S) decays andπ=0.83±0.22±0.05 fm for the continuum. The correlation strengthsλ for both data samples also are similar. Thus Bose-Einstein correlations do not reveal a noticeable difference between quark and gluon fragmentation.

Using the MD-1 detector at the VEPP-4 e+e- strorage ring we have measured the inclusive LAMBDA and XI-production rates in direct UPSILON (1 S) decays [n(LAMBDA)(UPSILON(1S)dir)] = 0.194 +/- 0.018 +/- 0.017, [n(XI)-(UPSILON(1S)dir)] = 0.038 +/- 0.015 +/- 0.009.The LAMBDA momentum spectrum in direct UPSILON(1S) decays was obtained.We have measured also the -inclusive A production rate in the continuum at center of mass energies between 7.2 and 10.0 GeV [n(LAMBDA)(cont.)] = 0.076 +/- 0.018 +/- 0.015.In the range of cms energies between 7.2 and 9.4 GeV this measurement was performed for the first time.

A calorimeter using 30 tons of liquid krypton for the KEDR detector is being constructed. The main effects which determine the energy and space resolution have been studied. An energy resolution of 1.7% at 1.2 GeV was obtained with the prototype. A space resolution of 0.4 mm for relativistic particles has been reached with the prototype.

In the experiment with e+ e--beams performed at the VEPP-4 storage ring with the MD-1 detector we have measured B(mu-mu), the branching ratio for the decay of UPSILON (1S) state into mu+ mu-. We obtained B(mu-mu) = (2.12 + 0.20 + 0.10)%. It is shown that the continuum and resonance interference should be taken into account. For the first time the upper limits on the branching ratio for the decays UPSILON --> pi+ pi-, K+ K-, ppBAR have been measured: Br(UPSILON --> pi+ pi-) < 5.10(-4), Br(UPSILON --> K+ K-) < 5.10(-4)Br(UPSILON --> ppBAR) < 9.10(-4) (90% CL).

The total cross section for γγ→hadrons was measured as a function of the invariant massW of the system (1.25 to 4.25 GeV) at thee+e−-collider VEPP-4 with the detector MD-1. For the first time the data were obtained by detecting both scattered leptons with almost zero emission angles. The mean squared four momentum transfer 〈q2〉 is −0.005 GeV2, the rmsW resolution is 100–250 MeV. The data on the mean charged multiplicity 〈n C 〉 are well described by the function 〈n C 〉=(1.62 ±0.37)+(1.83±0.45)·ln(W(GeV)). TheW dependence of the total cross section is consistent with the theoretical prediction σ(nb)=240+270/W(GeV).

In the experiment withe+e−-beams performed at the VEPP-4 storage ring with the MD-1 detector we have measuredBμμ, the branching ratio for the decay of Υ(1S) state intoμ+μ−. We obtainedBμμ=(2.12+0.20+0.10)%. It is shown that the continuum and resonance interference should be taken into account. For the first time the upper limits on the branching ratio for the decaysΥ→π+π−,K+K−,p\(\bar p\) have been measured: Br(Υ→π+π−)<5·10−4, Br(Υ→K+K−)<5·10−4, Br(Υ→p\(\bar p\)<9·10−4 (90% CL).

The process γγ→π+π− was measured using the detector MD-1 at VEPP-4. The two-photon reactionse+e−, μ+ μ− and π+ π− pair production were separated using scintillation counters, Cherenkov counters and shower-range chambers. A radiation widthГγγ(f2(1270))=3.1±0.35±0.35 keV was obtained.

Analyzing the data recorded with the MD-1 detector operated at the VEPP-4 storage ring we have determined the UPSILON(1S) resonance leptonic partial width and mass. We find GAMMA(ee) = 1.29+/-0.03+/-0.03 keV, M = 9460.59+/-0.09+/-0.05 MeV/c2.This new value of the UPSILON(1S) mass should supersede the previously published value [11] based on almost the same statistics.