Main directions of scientific activity.
Historically the laboratory has two basic directions:
µSR - studies in solid state physic.
Near threshold and "Subthreshold" meson production in proton-nuclear interaction.
Up to 1977 both activities were realized at pion and muon-channels of the 1 GeV PNPI synchrocyclotron.
After 1997 the prolongation of the
meson-production studies started at COSY (Juelich, Germany).
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µSR - studies in solid state physics.
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Within last 15 year several problem were under study. They are:
a) measurements of local magnetic field distributions in ceramic and textured high
temperature superconductivity materials such as YBaCuO or BiSrCaCuO, search for a
transition of these sample to a spinglass state at low temperatures, study of a
coexistence of magnetism and supercondyctivity, dynamics of the magnetic structure in
the condition of the "gigantic crip" and influence of the technology on all these phenomena.
b) Study of magnetic phase transitions in concentrated disordered magnetics (for example
FeNiCr) near triple points. In particular the difference of the transition into the
spin-glass state from the paramagnetic states directely or via the state of a collinear
magnetic. These study were done in these alloys.
c) Study of materials with "Shape-memory" (Cu1-xMnx - alloys) to understand the influence
of magnetism on the effect of the "Shape-memory".
In the region of 0.25 < x < 0.5 close to the percolation region and unusyal magnetic phase
was found before transition to the spin-glass state. In this phase the complete muon
spin depolarization is observed.
d) Study of Colossal Magnetoresistive manganites LaCaMnO3 an LaSrMnO3. For these
materials from the measured frequencies the critical exponents were obtained. At
temperatures below 150K the second freguency has been found which indicated on the
splitting of the magnetic phase in this temperature region.
e) Study of magnetic transitions into asperromagnetic states which can happen after
magnetic transition from the paramagnetic state to the collinear magnetic state and
before a magnetic transition from the collinear state to a spin-glass state.
This phenomena has been observed in several alloys but most serious studies were done
by both polarized neuterons and polarized muons methods for structure-ordered alloys
PtFeMn. For these alloys not only transition to the asperromagnetic state has been
studied but its dynamics in the external magnetic field was measured. The measured
magnetic field dependens follows the Gabey-Tuluse approach.
f) Recently, neutron depolarization measurement of the alloys PdFeMn indicated on the
some phenomena as in PtFeMn and it is under studies now at PNPI muon-beams.
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Meson production in proton-nucleon and proton-nuclear reactions.
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This activity started in the middle of 70-ties. There were measured:
a) p-n charge exchange from different nuclei in forward direction, double differential
cross section of p+and p -
production, procise measurements of p+ and K+ - mesons life time and total cross sections for "deeply subthreshold" K+ -mesons production in
proton-nuclei interactions at proton energies in the range 800 -
1000 MeV. The goal of that measurement was to see a cluster mechanism and to study short-range nucleon-nucleon.
Finally a two-step mechanism was proposed when at the first step a p - meson in pn -
interactions and than at the second step this p - meson produces K+ -meson on another
nuclear nucleon. This simple mechanism was sufficient to explain our data within
(10 - 20)% and is widely used nowdays by many other groups.
b) In 1997 these studies started at COSY, Juelich, Germany at the magnetic spectrometer
ANKE . There were measured already not total but double differention cross sections of
K+ -mesons production in pA interactions in proton energy range 1000 - 2300 MeV. To
explain all the data of the K+ -mesons production several parallelel processes has
been strudied such as : K+N rescattering in the nuclear matter, influence of the
Coulomb and K+ nuclear potentials and K+ -mesons production from protons and neutrons.
c) In the frame of COSY activity the unique K+p, K+d and K+t correlation experiment has
been started. From these measurements at 1200 MeV, first, the two-step mechanism was
experimentally confirmed and, second, at-last the 2N-cluster mechanism was identified.
It appeared that at 1.2 GeV this mechanism is very weak, only few percents of the total
process. But in the future a more ambicious experiment: K+p, K+d and K+t correlations
at the proton energy of 1000 MeV is planned. 10 times stronge 2N - clusters mechanism is
expected at this energy and 3N - cluster mechanism must be also visabbe.
d) Perfect K+ -meson selection permitted the ANKE collaboration to start other mesons
studies such as phi and ao+ in pp, pd and dd interactions. These program is under running now.
e) Recent studies at ANKE showed that the ANKE spectrometer can effectively detect Ko -
mesons to perform high statistics studies of pp®KoppL,
pp®KopS, pn®KopL, reactions to confirm an existence of narrow exotic resonances in K0p system.
