Search

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 ???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 2> is -0.005 GeV2, the rmsW resolution is 100–250 MeV. The data on the mean charged multiplicity C> are well described by the function 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 s(nb)=240+270/W(GeV).

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

The results of an experiment on the search for ξ(2.2) andX(2.2) in the radiative decays of the Υ-meson are presented. The experiment was carried out with the MD-1 detector at the VEPP-4 collider. An upper limitB(Υ→γξ)B(ξ→K+K−)<2·10−4 is obtained at 90% C.L. Results are presented on the search for the decay Υ→γX, X→ ϕϕ not previously investigated. For this decay the upper limitB(Υ→γX)B(X→ϕϕ)<3·10−3 is obtained at 90% C.L.

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.

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 have been measured: Br(Υ→π+π−)<5·10−4, Br(Υ→K+K−)<5·10−4, Br(Υ→p <9·10−4 (90% CL).

Using the MD-1 detector at the VEPP-4e+e- strorage ring we have measured the inclusive ? and370-1 production rates in direct G(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 ? momentum spectrum in direct G(1S) decays 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 $$\begin{gathered} \Gamma _{\gamma \gamma } (a_2 ) = 1.26 \pm 0.26 \pm 0.18 keV, \hfill \\ \Gamma _{\gamma \gamma } (\eta ') = 4.6 \pm 1.1 \pm 0.6 keV, \hfill \\ \Gamma _{\gamma \gamma } (\eta ) = 0.51 \pm 0.12 \pm 0.05 keV. \hfill \\ \end{gathered} $$

The total cross section of the processe+e−→hadronshas 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.