Phys.Rev.Lett.

We have performed magnetic compression experiments with the two-dimensional gas of hydrogen atoms on liquid 4He at T=120–200mK. For 2D phase-space densities higher than 3, the probability of three-body dipole recombination is observed to decrease gradually by an order of magnitude in comparison to its low-density value Kbbb=8.4(3.5)×10−25cm4s−1. This is attributed to local coherence developing in a 2D quasicondensate. We have also determined the value U/k=5.1(5)×10−15Kcm2 for the mean-field energy of the gas.

Phys.Rev.Lett.

The excited states of the “halo” nucleus, 11Li, have been investigated by means of the pion capture reaction, C14(π−,pd)11Li. Excited states have been identified at 1.02±0.07, 2.07±0.12, and 3.63±0.13MeV. The continuum part of the 11Li missing mass spectrum is found to contain a major component which is consistent with 11Li breakup into one of the 9Li excited states and two strongly correlated neutrons.

Phys.Lett.B

We report the first precision measurements of the scaled momentum, the charge multiplicity, and the thrust of hadronic jets in the Breit frame in Deep Inelastic Scattering ν μ N and ν ̄ μ N charged current events over the Q 2 range from 1 to 100 GeV 2 . The neutrino data, obtained in the NOMAD experiment at the CERN SPS, extend the Q 2 -evolution of these parameters by two orders of magnitude, and with commensurate precision, when compared to those reported by the ep and e + e − experiments.

Nucl. Instrum. Meth. A

On the basis of the ideas, proposed by one of the authors (I.N. Silin), a suitable software has been developed for constrained data fitting. Constraints may be of arbitrary type; i.e. equalities and inequalities. The simplest possible way has been used. The widely known program FUMILI was re-written in the C++ language. Constraints in the form of inequalities φ( θ )≥a were taken into account by changing them into equalities φ( θ )=t and simple inequalities of type t ≥ a . The equalities were taken into account by means of quadratic penalty functions. The suitable software was tested on the model data for the ANKE setup (COSY accelerator, Forschungszentrum Jülich, Germany).

Eur. Phys. J. A

The extrapolation of the nuclear spectral function at large nucleon three-momentum and removal energy is suggested.

Eur. Phys. J. A

We calculate the elastic and inelastic $\omega N\to \omega N, \to \pi N, \to \rho N, \to \rho \pi N, \to \pi \pi N, \to \sigma N$ reactions within a boson exchange approximation where the $\omega\rho\pi$ coupling constant and form factor are fixed by the reaction $\pi N \to \omega N$ in comparison to the experimental data. We find rather large $\omega N$ cross sections at low relative momenta of the $\omega$-meson which leads to a substantial broadening of the $\omega$-meson width in nuclear matter. The implications of the ${\omega}N$ final state interactions are studied for $\omega$ production in $^{12}C{+}^{12}C, ^{40}Ca{+}^{40}Ca$ and $^{58}Ni{+}^{58}Ni$ reactions at about 2 A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative to a general m_T-scaling (for $\pi^0$ and $\eta$ mesons) might be controlled experimentally by the TAPS Collaboration.

Phys.Lett.B

The production of pions by antiproton-deuteron annihilation at rest is analyzed. Assuming the possible existence of two delta-isobars in a deuteron some enhancement in the distribution over the invariant mass of two negative charged pions is predicted.

10.2172/1861363

Phys. Lett. B

The ratio of productions of pi+pi- atoms to free pi+pi- pairs is calculated with account of the strong interaction in final states. It is shown that this ratio is expressed via a squared ratio of the well-known Coulomb wave functions and thus can be calculated with a high accuracy.

Math. Res. Lett.

We give a summary of the results from Parts I-V (math.RT/9804086, math.RT/9804087, math.RT/9804088, math.RT/9810013, math.RT/9810014). Our work originated from harmonic analysis on the infinite symmetric group. The problem of spectral decomposition for certain representations of this group leads to a family of probability measures on an infinite-dimensional simplex, which is a kind of dual object for the infinite symmetric group. To understand the nature of these measures we interpret them as stochastic point processes on the punctured real line and compute their correlation functions. The correlation functions are given by multidimensional integrals which can be expressed in terms of a multivariate hypergeometric series (the Lauricella function of type B). It turns out that after a slight modification (`lifting') of the processes the correlation functions take a common in Random Matrix Theory (RMT) determinantal form with a certain kernel. The kernel is expressed through the classical Whittaker functions. It depends on two parameters and admits a variety of degenerations. They include the well-known in RMT sine and Bessel kernels as well as some other Bessel-type kernels which, to our best knowledge, are new. The explicit knowledge of the correlation functions enables us to derive a number of conclusions about the initial probability measures. We also study the structure of our kernel: this finally leads to a constructive description of the initial measures. We believe that this work provides a new promising connection between RMT and Representation Theory.

Phys.Lett.B

It is shown that an alternative form of the parity-nonconserving (PNC) transition electromagnetic current resolves partly a puzzle with the Hara theorem. New formulation of it has allowed PNC weak radiative hyperon transitions of the charged hyperons $\Sigma^{+} \Rightarrow p + \gamma $ and $\Xi^{-} \Rightarrow \Sigma^{-} + \gamma $ revealing hitherto unseen transition toroid dipole moment.

Eur.Phys.J.A

The Compton scattering on a charged pion and the process \gamma\gamma \to \pi^0\pi^0 are studied using the dispersion relations. Unknown parameters of the S-wave \pi\pi interaction, represented as a board Breit-Wignar resonance, and a sum and a difference of the \pi^0 meson polarizabilities are found from a fit to the experimental data for the process \gamma+\gamma \to \pi^0+\pi^0. This fit gives \alpha+\beta=0.98\pm 0.03 and \alpha-\beta=-1.6\pm 2.2. The found parameters of the S-wave \pi\pi interaction are used for the calculation of the cross section of the Compton scattering on \pi^{\pm} meson. The analysis of the obtained results shows that the experimental data for the elastic \gamma\pi scattering in the energy region up to 1 GeV together with the data for the process \gamma+\gamma \to \pi^0+\pi^0 could be used both for a determination of the pion polarizability values with quite high accuracy and for study of the S-wave \pi\pi interaction.

Nucl.Phys.A

Backward elastic $p ^3He$-scattering at incident proton kinetic energies $T_p>1$ GeV is investigated in the framework of the np-pair transfer mechanism and triangular diagram of one-pion exchange with a subprocess $pd\to ^3He\pi^0$ using a realistic three-body wave function of the $^3He$ nucleus. It is found that the $np-$pair transfer mechanism dominates owing to a rich high momentum component of the $^3He$ wave function. We show that the experimental cross section of this process is defined mainly by the values of the Faddeev component of the $^3He$ wave function, $\phi ^{23}({\bf q}_{23}, {\bf p}_1)$, at high relative momenta $q_{23}> 0.6 GeV/c$ of the NN-pair in the $^1S_0$-state and at low spectator momenta $p_1\leq 0.1$ GeV/c. The spin-spin correlation parameter is calculated in the framework of the dominating mechanism for the case of polarized target and beam. Rescatterings in the initial and final states are taken into account. Comparison with the $pd\to dp$ process is performed.

Phys.Lett.B

We consider the neutrino oscillations within the minimal supersymmetric standard model with R-parity violation. The Super-Kamiokande atmospheric neutrino data are used to set limits on the bilinear R-parity violating terms. These very stringent limits are out of reach of the other experiments at present and in the near future.

Czech.J.Phys.

The first probe of the correlation of the T-odd one-particle fragmentation function responsible for the left--right asymmetry of fragmentation of a transversely polarized quark is done by using the 1991-95 DELPHI data for $Z\to 2$-jet decay. Integrated over the fraction of longitudinal and transversal momenta, this correlation is of 1.5% order, which means order of 13% for the analyzing power. A rather large ($\approx 10%$) handedness transversal to the production plane was observed in the diffractive production of ($\pi^-\pi^+\pi^-$) triples from nuclei by the $40 GeV/c \pi^-$--beam. It was shown that the phenomenon has a clear dynamic origin and resembles the single spin asymmetry behavior. All this makes us hope to use this effects in polarized DIS experiments for transversity measurement.

Phys.Rev.Lett.

A new upper limit for the probability of spontaneous muonium to antimuonium conversion was established at ${\rm P_{M\bar{M}}} \leq 8.2 \cdot 10^{-11}$ (90%C.L.) in 0.1~T magnetic field, which implies consequences for speculative extensions to the standard model. Coupling parameters in R-parity violating supersymmetry and the mass of a flavour diagonal bileptonic gauge boson can be significantly restricted. A Z$_8$ model with radiative mass generation through heavy lepton seed and the minimal version of 331-GUT models are ruled out.

Nucl.Instrum.Meth.A

A deep underwater Cherenkov telescope has been operating since 1993 in stages of growing size at 1.1 km depth in Lake Baikal. The key component of the telescope is the Optical Module (OM) which houses the highly sensitive phototube QUASAR-370. We describe design and parameters of the QUASAR-370, the layout of the optical module, the front-end electronics and the calibration procedures, and present selected results from the five-year operation underwater. Also, future developments with respect to a telescope consisting from several thousand OMs are discussed.

Phys. Lett. B

The proton-antiproton annihilation at rest into the $\phi\eta$ final state was measured for three different target densities: liquid hydrogen, gaseous hydrogen at NTP and at a low pressure of 5 mbar. The yield of this reaction in the liquid hydrogen target is smaller than in the low-pressure gas target. The branching ratios of the $\phi\eta$ channel were calculated on the basis of simultaneous analysis of the three data samples. The branching ratio for annihilation into $\phi\eta$ from the $^3S_1$ protonium state turns out to be about ten times smaller as compared to the one from the $^1P_1$ state.

Phys. Lett. B

We discuss the transition radiation of a neutrino induced by its toroid dipole moment ($\tau$) when crossing the interface between two different media with different refraction indices. A neutrino of 1 MeV energy emits approximately $10^{-40}$ keV at $\tau=e\sqrt{2}G_F/\pi^2$. This effect depends very slightly on the neutrino mass and has a finite value in the massless limit.

Phys. Rev. C

It is shown that owing to a dominance of $np-$pair transfer mechanism of backward elastic $p^3He$- scattering for incident proton kinetic energies $T_p>1$ GeV the cross section of this process is defined mainly by the values of the Faddeev component of the wave function of $^3He$ nucleus, $\phi ^{23}({\bf q}_{23}, {\bf p}_1)$, at high relative momenta $q_{23}> 0.6 GeV/c$ of the NN-pair in the $^1S_0-$ state and at low spectator momenta $p_1\sim 0-0.2$ GeV/c.

Nucl.Phys.B

One object of interest in random matrix theory is a family of point ensembles (ramdom point configurations) related to various systems of classical orthogonal polynomials. The paper deals with a one-parametric deformation of these ensembles, which is defined in terms of the biorthogonal polynomials of Jacobi, Laguerre and Hermite type.

Phys.Lett.B

NOMAD is a neutrino oscillation experiment designed to search for ν τ appearance in the CERN-SPS wide band ν μ beam. Signal detection relies on the identification of ν τ charged current interactions using kinematic criteria. The analysis of the 1995 data sample yields no oscillation signal. Combining all studied τ decay modes, a limit of sin 2 2θ μτ < 4.2×10 −3 is obtained for large Δm 2 at the 90% confidence level.

Nucl. Instrum. Meth. A

The two-body transfer amplitude for the rearrangement process i+(jkl) - j+(ikl) is constructed on the basis of technique of 4-dimensional covariant nonrelativistic graphs. The developed formalism is applied to describing backward elastic $p^3He$ scattering in the energy range 0.5 - 1.7 GeV. Numerical calculations performed using the 5- channel wave function of the $^3He$ nucleus show that the transfer of a noninteracting np- pair dominates and explains satisfactorily the energy and angular dependence of the differential cross section at energies 0.9 - 1.7$ GeV. A weak sensitivity to high momentum components of the $~^3He$ wave function in spite of large momentum transfer as well as a very important role of rescatterings in the initial and final states are established.

Eur.Phys.J.C

A polarized proton beam extracted from SATURNE II and the Saclay polarized proton target were used to measure the rescattering observables$K_{onno}$and

Phys. Lett. B

A search was made for a new light gauge boson $X$ which might be produced in $\pi^{0}\to\gamma + X$ decay from neutral pions generated by 450-GeV protons in the CERN SPS neutrino target. The X's would penetrate the downstream shielding and be observed in the NOMAD detector via the Primakoff effect, in the process of $X \to\pi^{0}$ conversion in the external Coulomb field of a nucleus. With $1.45\times10^{18}$ protons on target, 20 candidate events with energy between 8 and 140 GeV were found from the analysis of neutrino data. This number is in agreement with the expectation of 18.1$\pm$2.8 background events from standard neutrino processes. A new 90% C.L. upper limit on the branching ratio $Br(\pi^{0}\to\gamma + X)< (3.3 to 1.9) \times10^{-5}$ for $X$ masses ranging from 0 to 120 MeV/c^2 is obtained.