Phys. Lett. B

This paper presents results on charged Higgs boson production, based on LEP data collected at s =172 GeV, that complement the previous DELPHI results obtained at centre of mass energies up to 161 GeV. The charged Higgs bosons are assumed to be pair produced and to decay either into a quark pair or into τν τ . The three different possible final states are included in the analysis. Data from ring imaging Cherenkov and microvertex detectors are used to identify the quarks as a cs pair. The number of candidates found is compatible with the background expected from standard processes. Combining the results of the present analysis with those of the previous analysis at lower energies, a new lower mass limit for the charged Higgs boson is set at 54.5 GeV/ c 2 .

Nucl.Phys.A

The NEMO-2 tracking detector located in the Fréjus Underground Laboratory was designed as a prototype of the NEMO-3 detector to study neutrinoless (Oν) and two neutrino (2ν) double-beta decay (ββ) physics. After 10357 h of running with an isotopically enriched selenium source (2.17 mol yr of 82 Se) a ββ2ν decay half-life of T 1 2 = (0.83 ± 0.10( stat ) ± 0.07 ( syst )) × 10 20 yr was measured. Limits with a 90% C.L. on the 82 Se half-lives of 9.5 × 10 21 yr for ββ0ν decay to the ground state, 2.8 × 10 21 yr to the (2 + ) excited state and 2.4 × 10 21 yr for ββ 0 νχ 0 decay with a Majoron ( χ 0 ) were also obtained.

Phys.Usp.

The density of states for the Schroedinger equation with a Gaussian random potential is determined by the functional integral corresponding to the phi^4 theory with a `wrong' sign of the interaction constant. The special role of the dimension d=4 for such a problem can be seen from different viewpoints but is fundamentally determined by the renormalizability of the theory. The construction of an epsilon-expansion in direct analogy with the phase-transition theory gives rise to the problem of a `spurious' pole. To solve this problem, a proper treatment of the factorial divergency of the perturbation series is necessary. Simplifications arising in high dimensions can be used for the development of a (4-epsilon)-dimensional theory, but this requires successive consideration of four types of theories: a nonrenormalizable theory for d>4, nonrenormalizable and renormalizable theories in the logarithmic situation (d=4), and a super-renormalizable theory for d<4. An approximation is found for each type of theory giving asymptotically exact results. The qualitative effect is the same in all four cases and consists in a shifting of the phase transition point in the complex plane. This results in the elimination of the `spurious' pole and in regularity of the density of states for all energies. A discussion is given of the calculation of high orders of perturbation theory and a perspective of the epsilon-expansion for the problem of conductivity near the Anderson transition.

IEEE Trans. Nucl. Sci.

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multi-particle final states produced in $pp$ scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the $\vec{p} p \to p K^{+} \vec{Y}$ ($Y = \Lambda, \Sigma^{0}$ or $Y^{*}$) reaction and vector meson production ($\phi, \omega$ and $\rho$) in $pp$ collisions. The common signature of such events is the multiplicity of four charged particles in the final state. A flexible 1st level trigger which uses topological information from fast detectors (scintillating fibers and hodoscope) has been built. It is completely software programmable through a menu-driven user interface and allows switching between production and monitor triggers on successive beam spills.

IEEE Trans. Nucl. Sci.

The DISTO collaboration has built a large-acceptance magnetic spectrometer designed to provide broad kinematic coverage of multi-particle final states produced in $pp$ scattering. The spectrometer has been installed in the polarized proton beam of the Saturne accelerator in Saclay to study polarization observables in the $\vec{p} p \to p K^{+} \vec{Y}$ ($Y = \Lambda, \Sigma^{0}$ or $Y^{*}$) reaction and vector meson production ($\phi, \omega$ and $\rho$) in $pp$ collisions. The data acquisition system is based on a VME 68030 CPU running the OS/9 operating system, housed in a single VME crate together with the CAMAC interface, the triple port ECL memories, and four RISC R3000 CPU. The digitization of signals from the detectors is made by PCOS III and FERA front-end electronics. Data of several events belonging to a single Saturne extraction are stored in VME triple-port ECL memories using a hardwired fast sequencer. The buffer, optionally filtered by the RISC R3000 CPU, is recorded on a DLT cassette by DAQ CPU using the on-board SCSI interface during the acceleration cycle. Two UNIX workstations are connected to the VME CPUs through a fast parallel bus and the Local Area Network. They analyze a subset of events for on-line monitoring. The data acquisition system is able to read and record 3500 ev/burst in the present configuration with a dead time of 15%.

Nucl. Instrum. Meth. A

Prototypes of the FERMI system have been used to read out a prototype of the ATLAS hadron calorimeter in a beam test at the CERN SPS. The FERMI read-out system, using a compressor and a sampling ADC, is compared to a standard charge integrating read-out by measuring the energy resolution of the calorimeter separately with the two systems on the same events. Signal processing techniques have been designed to optimize the treatment of FERMI data. The resulting energy resolution is better than the one obtained with the standard read-out.

Yad.Fiz.

Various exact solutions of two-particle eigenvalue problems for nonrelativistic contact four-fermion current-current interaction are obtained. Specifics of Goldstone mode is investigated. The connection between a renormalization procedure and construction of self-adjoint extensions is revealed.

Surveys High Energ.Phys.

On a nonrelativistic contact four-fermion model we have shown that the simple Lambda-cut-off prescription together with definite fine-tuning of the Lambda dependency of "bare"quantities lead to self-adjoint semi-bounded Hamiltonian in one-, two- and three-particle sectors. The fixed self-adjoint extension and exact solutions in two-particle sector completely define three-particle problem. The renormalized Faddeev equations for the bound states with Fredholm properties are obtained and analyzed.

Phys.Lett.B

The value of the b quark mass at the M Z scale defined in the MS renormalization scheme, m b ( M Z ), was determined using 2.8 million hadronic Z decays collected during 1992-1994 by the DELPHI detector to be m b (M Z )=2.67±0.25 ( stat. )±0.34 ( frag. )±0.27 ( theo. ) GeV/c 2 . The analysis considers NLO corrections to the three-jet production rate including mass effects, and the result obtained agrees with the QCD prediction of having a running b quark mass at an energy scale equal to M Z . This is the first time that such a measurement is performed far above the b b production threshold. The study also verifies the flavour independence of the strong coupling constant for b and light quarks within 1% accuracy.

Nucl.Phys.A

We reanalyse the production of $p\bar{p}$ pairs in proton-nucleus and nucleus-nucleus collisions employing novel elementary cross sections for baryon-baryon and pion-baryon production channels based on a boson-exchange model. In contrast to previous transport studies performed in the literature the secondary pion induced channel is found to be most important in both p+A and A+A collisions at subthreshold energies. A detailed comparison with the experimental data available indicates that sizeable attractive $\bar{p}$ potentials in the order of - 100 to - 150 MeV at normal nuclear matter density are needed to reproduce the size and shape of the experimental spectra.

Nucl. Phys. B Proc. Suppl.

We review the present status of the Baikal Underwater Neutrino Experiment and report on neutrino events recorded with the detector stages NT-36 and NT-96.

Prog.Part.Nucl.Phys.

We review the present status of the Baikal Underwater Neutrino Experiment and present results obtained with the various stages of the stepwise increasing detector: NT-36 (1993-95), NT-72 (1995-96) and NT-96 (1996-97). Results cover atmospheric muons, first clear neutrino events, search for neutrinos from WIMP annihilation in the center of the Earth, search for magnetic monopoles, and -- far from astroparticle physics -- limnology.

Eur.Phys.J.C

An update of the searches for charginos and neutralinos in DELPHI is presented, based mainly on recent data collected at centre-of-mass energies of 161 GeV and 172 GeV. No signal is found. For a sneutrino with mass above 300 GeV/c 2 and a mass difference between the chargino and the lightest neutralino above 10 GeV/c 2, the lower limit at 95% confidence level on the chargino mass ranges from 84.3 GeV/c 2 to the kinematical limit (86.0 GeV/c 2), depending on the mixing parameters. The limit decreases for lower chargino-neutralino mass differences. The limit in the case of a light sneutrino is 67.6 GeV/c 2, provided that that there is no light sneutrino with a mass within 10 GeV/c 2 below the chargino mass. Upper limits on neutralino pair production cross-sections of about a picobarn are derived. The (μ,M 2) domain excluded in the MSSM-GUT scenario is determined by combining the neutralino and chargino searches. These results imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino. imply a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 24.9 GeV/c 2 for tanß >- 1. The search has also been extended to the case where the lightest neutralino is unstable and decays into a photon and a gravitino.

Eur.Phys.J.C

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in$e^+e^-$collisi

Phys.Lett.B

The 4-jet events collected by the DELPHI experiment at LEP1 in 1992, 1993 and 1994 are analysed to determine the contribution of the triple-gluon vertex. Two of the four jets are tagged as jets from b - or c -quarks using lifetime and lepton transverse momentum information. The 4-jet contributions from double-gluon bremsstrahlung, the triple-gluon vertex, and secondary quark-antiquark pair production then yield significantly different two-dimensional distributions in the generalized Nachtmann Reiter angle versus the opening angle of the two secondary jets. These distributions are used to fit C A C F , the ratio of the coupling strength of the triple-gluon vertex to that of gluon bremsstrahlung, and N C N A , the ratio of the number of quark colours to the number of gluons, giving C A C F = 2.51 ± 0.28 and N C N A = 0.38 ± 0.10 in agreement with the values expected from QCD: C A C F = 9 4 = 2.25 and N C N A = 3 8 = 0.375 .

Phys. Lett. B

Oscillations of B s 0 mesons were studied in events with a large transverse momentum lepton selected from 3.2 million hadronic Z 0 decays registered by DELPHI between 1991 and 1994. A limit on the mass difference between the physical B s 0 states Δm s > 6.5 ps −1 at 95% C.L. was obtained by combining the results obtained in three channels.

Phys. Lett. B

The data collected by DELPHI in 1996 have been used to measure the average charged particle multiplicities and dispersions in q q ̄ events at centre-of-mass energies of s =161 GeV and s =172 GeV, and the average charge multiplicity in WW events at s =172 GeV. The multiplicities in q q ̄ events are consistent with the evolution predicted by QCD. The dispersions in the multiplicity distributions are consistent with Koba-Nielsen-Olesen (KNO) scaling. The average multiplicity of charged particles in hadronic W decays has been measured for the first time; its value, 19.23±0.74(stat+syst), is consistent with that expected for an e + e − interaction at a centre-of-mass energy equal to the W mass. The charged particle multiplicity in W decays shows no evidence of effects of colour reconnection between partons from different W's at the present level of statistics.

Nucl. Instrum. Meth. A

The polarization of extracted SATURNE II proton beam as a function of different ion source configurations was studied. Two distinct experiments were necessary for this purpose. In the first one, the LEFT-RIGHT instrumental asymmetry of the beam polarimeter was determined using an unpolarized beam. In the second one this correction factor was applied to asymmetries measured with the beam from the polarized ion source in all polarization states. The measurements were carried out at the proton beam kinetic energy 0.80 GeV, where the pp-elastic scattering analyzing power is near its maximum. The results confirmed that the two so-called “unpolarized states” of the source were polarized to several percent, whereas the absolute values of the beam polarizations in the so-called “polarized states” were equal and opposite. It was observed that the hexapole lens of the ion source produced beam polarization in the absence of any transition. The beam polarization as a function of hexapole current, transition field attenuation, and spin rotation solenoid current was measured. It was also shown how to obtain a strictly unpolarized beam using the polarized source only. The results obtained with the SATURNE II ion source HYPERION may also be relevant to similar sources at other accelerators.

Phys. Rev. C

The 4He p→ 3H pnπ+ reaction channel has been investigated at an incident 4He momentum of 8.6 GeV/c in an exclusive approach. It has been shown that the reaction mainly proceeds via pp→pnπ+ interaction with (pπ+) from Δ++, while triton is a spectator. The anisotropic angular distribution of the nucleons causes the splitting of (3Hn) invariant mass and leads to a natural separation of the interactions occuring either in proton or 4He vertices. Effects such as the shift of peak position in the (pπ+) invariant mass distribution have not been observed.

Eur.Phys.J.C

A search for neutral and charged Higgs bosons has been performed in the data collected by the DELPHI detector at centre-of-mass energies of 161 GeV and 172 GeV. The analysis assumes either the pair-pr

Phys. Lett. B

We analize semi-inclusive electron-nucleus processes e+A->e'+h+X at moderate Q**2 and energy transfer nu. Our results show that nucleons bound in the nuclear medium are distributed according to a function f_A that reduces to the standard light-cone distribution in the Bjorken limit and exhibits a sizeable Q**2-dependence at lower Q**2, particular Q**2 is order of nu**2.

Nucl.Instrum.Meth.A

The NOMAD experiment includes a transition radiation detector that provides a 10 3 pion rejection factor, for a 90% electron identification efficiency. Such a rejection factor is required in the search for ν μ →ν τ oscillations in the τ electron decay channel and in the search for ν μ →ν e oscillations. Algorithms used for the electron–pion discrimination and results obtained on the data are described.

Phys.Lett.B

Analysis of the rapidity structure of charge correlations in hadronic events from Z 0 decays gives evidence for chain-like charge-ordering of particle production along the thrust axis, as predicted by ‘QCD-motivated’ string-like fragmentation models.

Teor. Mat. Fiz.

Complicated dynamic systems with several degrees of freedom are investigated with the inverse scattering method using an adiabatic approach based on a consistent statement of two adiabatic problems. An algebraic technique based on the parametric inverse problem in an adiabatic representation is developed for reconstructing two-dimensional (time-dependent and time-independent) potentials and the corresponding solutions. The calculated elements of the exchange interaction matrix determine the system of corresponding gauge equations. The main characteristics of the exchange interaction essentially depend on the statement of the parametric inverse problem. Namely, if the parametric problem is specified on the entire axis, then the constraint matrix elements are regular at degeneration points of two levels. The opposite occurs in the case of the radial parametric problem or the parametric problem specified on the semiaxis. The influence of the parametric spectral characteristics of the fast subsystem on the behavior of the slow subsystem is studied. In particular, it is shown that state transitions of a two-level system vanish for a special choice of the normalization functions.

Phys.Rev.C

Deep inelastic scattering of leptons off nuclear targets is analized within the convolution model taking into account nucleon-nucleon correlations. We show that in the nuclear medium nucleons are distributed according to a function that exhibits a sizeable Q**2-dependence and reduces to the ordinary light-cone distribution in the Bjorken limit. At Q**2 < 50 (GeV/c)**2 and x > 1 this Q**2-dependence turns out to be stronger than the one associated with the nucleon structure function, predicted by pertubative quantum chromodynamics.