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

A search for events with one jet and at most one isolated lepton used data taken at LEP-2 by the DELPHI detector.These data were accumulated at a center-of-mass energy of 183 GeV and correspond to an integrated luminosity of 47.7 1/pb. Production of single scalar and vector leptoquarks was searched for. Limits at 95% confidence level were derived on the masses (ranging from $134 GeV/c^2$ to $171 GeV/c^2$ for electromagnetic type couplings) and couplings of the leptoquark states.A search for top-charm flavour changing neutral currents($e^+ e^- \to \bar t c$ or charge conjugate) used the semileptonic decay channel. A limit on the flavour changing cross-section via neutral currents was set at 0.55pb (95% confidence level).

Phys.Lett.B

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb −1 recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/ c 2 higher than those obtained at a centre-of-mass energy of 172 GeV. The ( μ ,M 2 ) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/ c 2 for tan β ≥ 1.

Eur. Phys. J. C

The partial decay width of the Z to ${\rm b \bar b}$ quark pairs has been measured by the DELPHI detector at LEP using data taken in the years 1992 to 1995. Decays

Eur. Phys. J. C

Results of the SND experiment at the VEPP-2M $e^+e^-$ collider on the QED processes $e^+e^-\rightarrow e^+e^-\gamma$ and

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.

Phys. Lett. B

A search for the production of the η ′ c meson, the first radial excitation of the ground state of charmonium η c (2980), in the photon–photon fusion reaction at LEP has been performed using the data collected by the DELPHI detector during 1992–1996. No evidence of η ′ c production is found in the mass region 3520–3800 MeV/c 2 . An upper limit for the ratio of the two-photon widths of the η ′ c and η c is obtained.

10.2172/1861363

Eur.Phys.J.C

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermion

Phys.Lett.B

A search for stable and long-lived heavy charged particles used the data taken by the DELPHI experiment at energies from 130 to 183 GeV. The Cherenkov light detected in the Ring Imaging Cherenkov Detector and the ionization loss measured in the Time Projection Chamber identify heavy particles from masses of 2 to nearly 89 GeV/c^2. Upper limits are given on the production cross-section and masses of sleptons, free squarks with a charge of $q = \pm 2/3e$ and hadronizing squarks.

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.

Eur. Phys. J. C

Promptly decaying lightest neutralinos and long-lived staus are searched for in the context of light gravitino scenarios. It is assumed that the stau is the next to lightest supersymmetric particle (NLSP) and that the lightest neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of the production of these particles is found. Hence, lower mass limits for both kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is found to be greater than 71.5 GeV/c^2. In the search for long-lived stau, masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10 to 150 \eVcc . Combining this search with the searches for stable heavy leptons and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc may be set for the stau mass

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

Two-particle angular correlations in jet cones have been measured in e + e − annihilation into hadrons at LEP energies ( s = 91 and 183 GeV) and are compared with QCD predictions using the LPHD hypothesis. Two different functions have been tested. While the differentially normalized correlation function shows substantial deviations from the predictions, a globally normalized correlation function agrees well. The size of α S eff (and other QCD parameters) and its running with the relevant angular scale, the validity of LPHD, and problems due to non-perturbative effects are discussed critically.

Eur.Phys.J.C

The events with two photons and missing (transverse) energy collected by the DELPHI detector at centre-of-mass energies between 130 GeV and 183 GeV have been studied to search for processes of the type e+e- → YY with the subsequent decay Y → X7, where X is an undetectable neutral particle. Reactions of this kind are expected in supersymmetric models, where the Y particle can be either the lightest neutralino, decaying to a photon and a gravitino, or the next-to-lightest neutralino, decaying to a photon and the lightest neutralino. To study the case of long-lived Y particles, a search for single-photon events with the reconstructed photon axis pointing far from the beam interaction region has also been performed. No evidence for a deviation from Standard Model expectations has been observed in the data and upper limits have been derived on the signal cross-section as a function of the the X and Y masses and of the Y mean decay path.

Nucl.Phys.B Proc.Suppl.

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 and an antiquark 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 2.5 ppm order, which means order of 7% for the analyzing power. This makes us hope to use certain effects in polarized DIS experiments for transversity measurement.

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.