Search

We have started a new series of experiments on a precise measurement of J/Ψ-, Ψ′- mesons and τ-lepton masses at VEPP-4M collider with KEDR detector. Features of the method used for an absolute particle energy calibration based on the resonance depolarization are described.

The goal of this work is an evaluation of utmost precision and analysis of any possible errors and corrections in planned experiment of new mass measurement of J/ψ and ψ′ mesons on VEPP-4M collider with absolute energy calibration by the spin precession frequency measurements.

An experiment, using the new detector Kedr, on the precise measurement of the τ-lepton mass is being readied on the VEPP-4M. The resonance depolarization method is used for absolute calibration of the particle energy. The main difficulty in using a polarized beam at the τ-lepton production threshold (1777 MeV) is the closeness of an integral spin resonance (1763 MeV). Experiments observing the polarization of particles in VEPP-4M after injection of the polarized beam from the VEPP-3 storage booster with different detunings from resonance have been performed. For comparison, the depolarization time of a beam due to quantum fluctuations in the presence of characteristic disturbances of the guiding field is calculated. The temporal stability of the energy indications is studied.

The VEPP-4M storage ring system of SR front ends is described. SR is released by means of 14 front ends. Eleven of them are intended for beamlines of experimental stations. One front end is technical. For the permanent stabilization of an orbit of a beam with respect to a coordinate and angle in the vertical direction, two monitoring front ends are used. They take out SR from emission regions, which are at a large distance from one another.

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.

Quasi-monochromatic photon beams of 108 MeV Compton-edge energy produced in the ROKK-1M facility at the storage ring VEPP-4M (BINP, Novosibirsk) and makrofol sheets as fission track detectors were used to measure the photofission yield of 27 Al. The fission yield was found to be .160 55 /b. From this result and previously measured 27 Al photofission yield at79 MeV end-point energy with the LADON apparatus, the trends of fission cross section and fissility have been obtained in the incident photon energy range 40-110 MeV. The present results and data for other intermediate-mass nuclei obtained with the same methodology indicate an increase of fissility with decreasing Z 2 =A as predicted by the liquid drop model for fissioning

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 40–800 MeV. The achieved energy resolution was 3% for 40 MeV and 1.5% for 800 MeV photons. The results are consistent with the Monte Carlo simulation taking into account effects of the electronics noise.

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.

Tagged photons produced by the ROKK-2 facility have been used to measure the photofission cross section of in the energy range 60 - 270 MeV. Fission events were detected by using a nuclear fragment detector based on multiwire spark counters. Fissility values have been deduced and compared with available data obtained with monochromatic photons in other laboratories. These data have been analysed in the framework of a two-step model which considers the primary photointeraction occurring via the quasi-deuteron and/or photomesonic processes, followed by a mechanism of evaporation - fission competition for the excited residual nucleus. The model was found to reproduce the main experimental features of photofissility up to 300 MeV.

The results of the BELLE barrel calorimeter prototype test with the tagged photon beam are presented. The prototype consisted of 36 CsI(Tl) counters with the same readout system as the BELLE calorimeter. The measurements were carried out at the VEPP-4 collider with the tagged photon beam provided by the ROKK-1M facility. The energy resolution for photons was measured in the energy range 40–800 MeV. The results are in good agreement with the Monte-Carlo simulation.

Photofission cross sections of and nuclei have been measured at an incident photon energy of 100 MeV using monochromatic photons produced by Compton backscattering at the ROKK-1M facility (BINP, Novosibirsk). Detection of fission fragments has been performed by means of Makrofol track-etch detectors in close contact with metallic foils of the target elements. The values of fissility at 100 MeV deduced for the targets under investigation are found to range between and . The present results show consistency with the fissility trends calculated for 69 and 600 MeV monoenergetic photons using a formalism based on the current two-step model for intermediate-energy photofission reactions.

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.

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-4e+e− strorage ring we have measured the inclusive Λ and370-1 production rates in direct Γ(1S) decays $$\begin{gathered} \left\langle {n_\Lambda (\Upsilon (1S)_{dir} )} \right\rangle = 0.194 \pm 0.018 \pm 0.017, \hfill \\ \left\langle {n_\Xi - (\Upsilon (1S)_{dir} )} \right\rangle = 0.038 \pm 0.015 \pm 0.009. \hfill \\ \end{gathered} $$ The Λ momentum spectrum in direct Γ(1S) decays was obtained.

Analyzing the data recorded with the MD-1 detector operated at the VEPP-4 storage ring we have determined the ϒ(1S) resonance leptonic partial width and mass. We find $$\begin{gathered} \Gamma _{ee} = 1.29 \pm 0.03 \pm 0.03keV, \hfill \\ M = 9460.59 \pm 0.09 \pm 0.05MeV/c^2 \hfill \\ \end{gathered} $$ M=9460.59±0.09±0.05 MeV/c2. This new value of the ϒ(1S) mass should supersede the previously published value [11] based on almost the same statistics.

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 〈nC〉 are well described by the function 〈nC〉=(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 experiments with e+e− beams performed at the VEPP-4 storage ring with the MD-1 detector we have measured Γee, the leptonic width, and Bμμ, the muon-pair branching ration, for the decay of γ(1s). We obtain Γee = (1.266 ± 0.023 ± 0.038) keV, Bμμ = (2.12 ± 0.20 ± 0.10)% and Γtot = (59.7 ± 5.7 ± 3.7) keV.

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−)

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.

The results of a search for narrow resonances ine+e− annihilation at centre-of-mass energies between 7.23 and 10.34 GeV are presented. The experiment was performed using the MD-1 detector at the VEPP-4 storage ring. The total luminosity integral of 16 pb−1 was taken. There is no evidence that new states exist. The upper limits on the leptonic widthΓee of possible resonances are less, by a factor of 10–80, than theΓee for the ϒ(1S) meson.

Results of a measurement of the two-photon widths of thea2, η′, η with the detector MD-1 at thee+e− collider VEPP-4 are presented. The specific feature of this experiment is tagging of at least one scattered electron. The following results have been obtained $$\begin{gathered} \Gamma _{\gamma \gamma } (a_2 ) = 1.26 \pm 0.26 \pm 0.18 keV, \hfill \\ \Gamma _{\gamma \gamma } (\eta ') = 4.6 \pm 1.1 \pm 0.6 keV, \hfill \\ \Gamma _{\gamma \gamma } (\eta ) = 0.51 \pm 0.12 \pm 0.05 keV. \hfill \\ \end{gathered} $$

A new high precision measurement of the $J/\psi$- and $\psi'$-meson masses has been performed at the VEPP-4M collider using the KEDR detector. The resonant depolarization method has been employed for the absolute calibration of the beam energy. The following mass values have been obtained: $M_{J/\psi} = 3096.917 \pm 0.010 \pm 0.007$ MeV, $M_{\psi'} = 3686.111 \pm 0.025 \pm 0.009$ MeV. The relative measurement accuracy has reached $4. 10^{-6}$ for $J/\psi$ and $7. 10^{-6}$ for $\psi'$, approximately 3 times better than in the previous precise experiments., Comment: 12 pages, 4 tables, 10 figures

KEDR is a general-purpose detector for experiments at the VEPP-4M e + e − -collider in the energy range 2 E =2.0– 12 GeV . 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.

First results on polarization measurement are presented. More sophisticated scheme of polarimeter is proposed. It is expected that the accuracy of the measurement of polarization of the circulated electron beam of about 20% will be achieved during 8 minutes of operation of this Moller polarimeter. The work was supported by Russian Foundation for Basic Researches, grants 98-02-17949 and 98-02-17993, INTAS, grant 96-0424 and State Scientific and Technical Programm (Nuclear Physics).

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

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)

The method of resonance depolarization has been used for the absolute energy calibration of storage ring VEPP-4. The beam polarization was measured by the up-down asymmetry of the synchrotron radiation back-scattered on the colliding beam. By scanning the ϒ resonance with the MD-1 detector, we obtained a massM=9460.59 ±0.12 MeV.

A high precision measurement of the υ-meson mass has been performed at the storage ring VEPP-4 using the MD-1 detector. The resonance depolarization method has been used for the absolute calibration of the beam energy that allowed to improve the accuracy of υ-mass measurement by a factor of ten. The following mass value has been obtained: M = 9459.7 ± 0.6 MeV.

A new method for measuring the polarization of e + e − in storage rings is described. It is based on the scattering of synchrotron radiation on the colliding beam. The method is simple in operation and allows a simultaneous measurement of the polarization of the electron and positron beam. This method was applied to the energy calibration of the storage ring VEPP-4 in the high precision measurements of the ϒ -mesons' masses with MD-1 detector.

In investigating the e + e − → e + e − γ process the radiation probability is oberved to be substantially less than that calculated in the standard QED. The effect is due to the fact that the characteristic impact parameters in the process are much greater than the transverse sizes of the colliding beams. The Compton scattering γ-spectrum of the synchrotron radiation by a colliding beam is measured.

An experiment has been performed at the storage ring VEPP-4 using the MD-1 detector. The resonance depolarization method has been employed for the absolute calibration of the beam energy. This has allowed the accuracy of the mass measurement to be improved by a factor of ten. The following mass values of ϒ, ϒ′ and ϒ″ -mesons have been obtained: M ( ϒ )=9460.6±0.4 MeV, M ( ϒ ′)=10023.8±0.5 MeV, M ( ϒ ″)=10355.5±0.5 MeV.

A high precision measurement of the Ψ- and Ψ′-resonance masses has been performed at the new storage ring VEPP-4. The resonance depolarization method has been used for the absolute calibration of the beam energy. Application of this technique allowed improvement of the accuracy of the Ψ- and Ψ′-mass measurements by a factor of more than ten. The following mass values have been obtained: mΨ = 3096.93 ± 0.09 MeV, mΨ′ = 3686.00 ± 0.10 MeV; the mass difference is thus mΨ′−mΨ = 589.07 ± 0.13 MeV.

The differential cross section of Delbr\"{u}ck 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., Comment: 6 pages, revtex, 12 figures, 2 tables

We plan to measure the mass of /spl tau/ lepton near the threshold of its production with an accuracy 10/sup -4/ or better in the experiment with the detector KEDR at the e/sup +/e/sup -/ collider VEPP-4M using the method of resonance depolarization for calibration of particle energy. The scenario of the experiment, the developed systems of polarimeters and the depolarizer are described. Some points regarding beam polarization and energy calibration accuracy are considered.

The description of the storage rings VEPP-2M, VEPP-3 and VEPP-4 is given, the main electron beam characteristics and the user's characteristics of the synchrotron radiation of these storage rigs are quoted. The prospects to improve the operation of the storage rings as the SR sources are discussed.