A.A. Semenov

Measurements of the K+→π0e+ν form factors

Abstract The q2 dependence of the vector form factor has been investigated using 3.2 × 104 K+ → π0e+ν decays. The usual linear parametrization. ƒ + (q 2 ) = ƒ(0)(1+λ + q 2 /m π 0 0 ) gives λ+ = 0.0284±0.0027. An analysis of the Dalitz plot density distribution for Ke3+ decays yields the values for the scalar and tensor couplings ƒs and ƒt, and their relative phase angle ost.

Multi-hit drift time digitizer with one-nanosecond resolution

Abstract A multi-hit drift time digitizer is described (in the 16 μs range). It measures the time position of signals with an accuracy of 1 ns from a wide-gap drift chamber. A fast MECL memory (256 × 7 bits) in each information channel allows one to register up to 256 signals with a ⩾ 64 ns interval between pulses.

Measurement of the Dalitz plot slope parameters for K+→ π+π0π0 decay

We have measured the Dalitz plot slope parameters for the K+ → π+π0π0 decay with an accuracy higher than in previous experiments. The values obtained are substantially different from the world averages. The experiment was performed at the Serpukhov PS with the HYPERON-2 spectrometer at the beam energy 10 GeV We have collected about 33000 events with energies and momenta measured for all involved particles.

Tensor analyzing power T20 for cumulative pion production from deuterons in the GeV energy region

Abstract The tensor analyzing power T 20 for the reaction d ↑ + 12 C → π ± (0°) + X has been measured with a polarized deuteron beam from 6.2 to 9.0 GeV/ c at a pion momentum3.0 GeV/ c . This experiment is focused on “cumulatively produced pions”, which are produced beyond the kinematically allowed limit for free nucleon-nucleon collisions. The measured values of T 20 turn out to be close to zero. They are in disagreement with the results of our impulse approximation calculation which is based on a single NN → πNN interaction and takes into account the internal motion of nucleons in the deuteron. Possible explanations of the result are discussed.

A time projection chamber for double-beta-decay experiments

Abstract A large-volume time projection chamber (TPC) designed for double-beta-decay experiments with solid samples of 2.5 m 2 total surface is described. The TPC will operate in a weak magnetic field of ≲ 0.05 T with He+20% CH 4 gas filling at atmospheric pressure. A prototype TPC operating in the 10 GeV proton beam of the IHEP Serpukhov accelerator had shown ≈100% efficiency and a spatial resolution of ≲ 0.45 mm in the direction of the drift of electrons and ≈ 1.6 mm along the delay lines. A limit on half-life of ∼ 10 24 years should be reached with the large TPC operating in the deep underground laboratory.

A new upper limit for the branching ratio of the decay K0S → e+e−

Abstract A new value of the upper limit for the branching ratio of the decay of K 0 S into e + e − has been experimentally obtained using a lead glass detector. The value is BR (K 0 S → e + e − ) −4 (90% CL).

Electrodeless drift chamber in a flux of more than 105 particles per second per wire

Abstract Electrodeless drift chambers with drift lengths of 50 and 100 mm have been tested at a particle flux from 10 3 to 1.5 × 10 5 /s per wire. The efficiency remains high (>99%) up to a flux of 7 × 10 4 /s, but at a rate 1.5 × 10 5 /s it drops to 70%. The space-time linearity and spatial resolution do not change with the count rate. The recovery time after a high particle intensity is about 20 min. The characteristics do not change within many days of operation, even after large changes in the particle flux.

Upper limit for the branching ratio of Ks0→e+e− decay

Abstract A search for K s 0 → e + e − decay was performed by means of a 624-channel lead glass shower hodoscope and a set of proportional chambers. Neutral kaons were obtained in the quasibinary charge exchange reaction. A new upper limit of 2.8×10−6 at 90% C.L. for the branching ratio is obtained.

A-dependence of η-meson inclusive production at 10.5 GeV/c

Abstract The experimental results are presented for ratios of ν-meson inclusive differential cross sections in 10.5 GeV/c π+p, π+D and π+A collisions, RD/p=(dσ/dxF)(π+D→ηX)/ (dσ/dxF)π+p→ηX), RA=(dσ/dxF)(π+D→ηX) in the beam fragmentation region. The results are based on the statistics of ≈ 5 × 104 detected η → 2γ decays. It is shown that the power α in the parametrisation RA ≈ Aα(xf) does not change significantly with xF and its mean value is 0.50±0.02. The lower limit is obtained for the effective coefficient with string tension in the colour string model, κ ⩾ 3 GeV/fm. The observed growth of RA with xF can be explained by an assumption of a neutron halo with the factor H ≈ 4 in the nuclei.

Measurement of electromagnetic shower position with an electrodeless drift chamber

Abstract Spatial resolution of a lead-glass shower detector was considerably improved by means of a converter and an electrodeless drift chamber as a coordinate detector. The coordinate of an electromagnetic shower was measured without a flash ADC; only a multi-hit TDC was used. A spatial resolution of 1.95 mm (r.m.s.) at an energy of 3 GeV was achieved. The efficiency in a relatively high shower count rate was checked.