Eur. Phys. J. A

The data from the first measurement, performed at ANKE/COSY, of the unpolarized cross section of the reaction $pd\to (pp)n$ in the kinematics of backward elastic $pd\to dp$ scattering at proton-beam energies between 0.6 and 1.9 GeV are analyzed in a phenomenological approach. The $pd\to (pp)n$ data and the triplet cross section of the reaction $pd\to (pn)p$, calculated from the $pd\to dp$ data on the basis of the F\aldt-Wilkin extrapolation, are used here to derive the ratio $\zeta$ of the singlet production matrix element squared to the triplet one. This ratio, defined in our earlier analysis of $pd\to (pn)p$ data in a largely model-independent way, depends on the dynamics of the $pd$ interaction. We find here $\zeta\approx 0.02$ and show that the smallness of this value may point toward softness of the deuteron at short NN distances.

Phys.Rev.Lett.

We report a search for production of long-lived charged massive particles in a data sample of 90 $pb{-1}$ of $\sqrt{s}$ = 1.8 TeV $p\bar{p}$ collisions recorded by the Collider Detector at Fermilab (CDF). The search uses the muon-like penetration and anomalously high ionization energy loss signature expected for such a particle to discriminate it from backgrounds. The data is found to agree with background expectations, and cross section limits of $\cal{O} (1) pb$ are derived using two reference models, a stable quark and a stable scalar lepton.

Phys. Rev. D

The inclusive cross section for J/ψ production times the branching ratio B(J/ψ→μ+μ−) has been measured in the forward pseudorapidity region: B×dσ[p¯+p→J/ψ(pT>10GeV/c,2.1<|η|<2.6)+X]/dη=192±9(stat)±29(syst)pb. The results are based on 74.1±5.2pb−1 of data collected by the CDF Collaboration at the Fermilab Tevatron Collider. The measurements extend earlier measurements of the D0 Collaboration to higher pTJ/ψ. In the kinematic range where the experiments partially overlap, these data are in good agreement with previous measurements.

Phys.Lett.B

The production of wrong sign charmed mesons b→ D (s) X , D ( s ) =( D 0 , D + , D s ), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z→b b ̄  events are exclusively reconstructed by searching for the decays  D 0 → K − π + , D + → K − π + π + and D s + → φπ + → K + K − π + . The wrong sign contribution is extracted by using two discriminant variables: the charge of the b -quark at decay time, estimated from the charges of identified particles, and the momentum of the charmed meson in the rest frame of the b -hadron. The inclusive branching fractions of b -hadrons into wrong sign charm mesons are measured to be: B (b→ D 0 X)+ B (b→D − X)=(9.3±1.7( stat )±1.3( syst )±0.4( B ))% , B (b→D s − X)=(10.1±1.0( stat )±0.6( syst )±2.8( B ))% where the first error is statistical, the second and third errors are systematic.

arXiv

One IGEX 76Ge double-beta decay detector is currently operating in the Canfranc Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic scattering. In this talk we report on the on-going efforts to understand and eventually reject the background at low energy. These efforts have led to the improvement of the neutron shielding and to partial reduction of the background, but still the remaining events are not totally identified. A tritium contamination or muon-induced neutrons are considered as possible sources, simulations and experimental test being still under progress. According to the success of this study we comment the prospects of the experiment as well as those of its future extension, the GEDEON dark matter experiment.

Nucl.Phys.A

We give reasons for the existence of the NN decoupled dibaryon resonance $d^*_1$(1956). Strong evidence for its presence has first been found in the energy spectrum of coincident photons emitted at $\pm 90^0$ from the $pp \to \gamma\gamma X$ process at 216 MeV measured by the DIB2$\gamma$ collaboration at JINR. As further experimental indications of the $d^*_1$(1956) existence we present those found in the available photon energy spectra of $np\gamma$, $pd\gamma$, and $pA\gamma$ reactions below the pion threshold. It is noted that serious discrepancies between the $np\gamma$ and $pd\gamma$ experimental cross sections and theoretical calculations can reasonably be explained by the fact that latter did not take into account the $d^*_1$ effect.

Phys.Lett.B

A study of the deuteron breakup reaction $pd \to (pp)n$ with forward emission of a fast proton pair with small excitation energy $E_{pp}<$ 3 MeV has been performed at the ANKE spectrometer at COSY--J\ulich. An exclusive measurement was carried out at six proton--beam energies $T_p=$~0.6,~0.7,~0.8,~0.95,~1.35, and 1.9 GeV by reconstructing the momenta of the two protons. The differential cross section of the breakup reaction, averaged up to $8^{\circ}$ over the cm polar angle of the total momentum of the $pp$ pairs, has been obtained. Since the kinematics of this process is quite similar to that of backward elastic $pd \to dp$ scattering, the results are compared to calculations based on a theoretical model previously applied to the $pd \to dp$ process.

Pisma Zh.Eksp.Teor.Fiz.

The Gell-Mann - Low function \beta(g) in QCD (g=g0^2/16\pi^2 where g0 is the coupling constant in the Lagrangian) is shown to behave in the strong-coupling region as \beta_\infty g^\alpha with \alpha\approx -13, \beta_\infty\sim 10^5.

Eur.Phys.J.C

Neutral B meson oscillations in the B0_s - anti-B0_s and B0_d - anti-B0_d systems were studied using a sample of about 4.0 million hadronic Z decays recorded by the DELPHI detector between 1992 and 2000. Events with a high transverse momentum lepton were removed and a sample of 770 k events with an inclusively reconstructed vertex was selected. The mass difference between the two physical states in the B0_d - anti-B0_d system was measured to be: \Delta m_d = (0.531 +/- 0.025 (stat.) +/- 0.007 (syst.)) ps^{-1}. The following limit on the width difference of these states was also obtained: |\Delta\Gamma_{B_d}| / \Gamma_{B_d} < 0.18 at 95% CL. As no evidence for B0_s - anti-B0_s oscillations was found, a limit on the mass difference of the two physical states was given: \Delta m_s > 5.0 ps^{-1} at 95% CL. The corresponding sensitivity of this analysis is equal to 6.6 ps^{-1}.

Phys. Lett. B

A search for pair-produced doubly charged Higgs bosons has been performed using the data collected by the DELPHI detector at LEP at centre-of-mass energies between 189 and 209 GeV. No excess is observed in the data with respect to the Standard Model background. A lower limit for the mass of 97.3 GeV/c^2 at the 95% confidence level has been set for doubly charged Higgs bosons in left-right symmetric models for any value of the Yukawa coupling between the Higgs bosons and the tau leptons.

Eur.Phys.J.C

A search for sleptons, neutralinos, charginos, sgoldstinos and heavy stable charged sleptons in the context of scenarios where the lightest supersymmetric particle is the gravitino, is presented. Data collected during 2000 with the DELPHI detector at centre-of-mass energies from 204 to 208 GeV were analysed and combined with all the data collected from 1995 to 1999 at lower energies. No evidence for the production of sleptons, neutralinos and charginos has been found, therefore new limits on the mass of these supersymmetric particles and on the model parameter space are set. The search for heavy stable charged sleptons also updates the stable sleptons mass limit. The absence of evidence for sgoldstino production allows limits to be set on its mass and on the scale of supersymmetry breaking.

Eur. Phys. J. C

The standard method used for tagging b-hadrons in the DELPHI experiment at the CERN LEP Collider is discussed in detail. The main ingredient of b-tagging is the impact parameters of tracks, which relies mostly on the vertex detector. Additional information, such as the mass of particles associated to a secondary vertex, significantly improves the selection efficiency and the background suppression. The paper describes various discriminating variables used for the tagging and the procedure of their combination. In addition, applications of b-tagging to some physics analyses, which depend crucially on the performance and reliability of b-tagging, are described briefly.

Eur.Phys.J.C

In the framework of k_T-factorization QCD approach and the colour singlet model we consider J/\psi inelastic photo- and leptoproduction processes at HERA. We investigate the dependences of the single differential and double differential cross section on different forms of the unintegrated gluon distribution. The z and p_T dependences of the spin aligment parameter \alpha are presented also. Our theoretical predictions agree well with recent data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/\psi mesons at low Q^2 < 1 GeV^2 is an additional test of BFKL gluon dynamics.

Phys.Rev.Lett.

We report the results of a search for a W' boson produced in p-pbar collisions at a center-of-mass energy of 1.8 TeV using a 106 pb-1 data sample recorded by the Collider Detector at Fermilab. We observe no significant excess of events above background for a W' boson decaying to a top and bottom quark pair, with the top quark subsequently decaying into a semileptonic final state. These data allow us to set limits on the rate of W' boson production and decay. In a model where this boson would mediate interactions involving a massive right-handed neutrino (nu_R) and has Standard Model strength couplings, we exclude a W' boson with mass between 225 and 536 GeV/c**2 at 95% confidence level for M_W' >> M_nu_R and between 225 and 566 GeV/c**2 at 95% confidence level for M_W' < M_nu_R.

Nucl.Phys.B Proc.Suppl.

The project, aimed at the theoretical support of experiments at modern and future accelerators -- TEVATRON, LHC, electron Linear Colliders (TESLA, NLC, CLIC) and muon factories, is presented. Within this project a four-level computer system is being created, which must automatically calculate, at the one-loop precision level the pseudo- and realistic observables (decay rates and event distributions) for more and more complicated processes of elementary particle interaction, using the principle of knowledge storing. It was already used for a recalculation of the EW radiative corrections for Atomic Parity Violation [1] and complete one-loop corrections for the process $e^+ e^-\to t\bar{t}$ [2-4]: for the latter an, agreement up to 11 digits with FeynArts and the other results is found. The version of {\tt SANC} that we describe here is capable of automatically computing the decay rates and the distributions for the decays $Z(H,W)\to f\bar{f}$ in the one-loop approximation.

Eur. Phys. J. A

The fragmentation of deuterons into pions emitted forward in the kinematic region forbidden for free nucleon-nucleon collisions is analyzed. It is shown that the inclusion of the non-nucleonic degrees of freedom in a deuteron results in a satisfactory description of the data for the inclusive pion spectrum and improves the description of the data about $T_{20}$. According to the data, $T_{20}$ has very small positive values, less than 0.2, which contradicts the theoretical calculations ignoring these degrees of freedom.

Phys.Rev.Lett.

Total and differential cross sections for the exclusive reaction pp->pp rho^0 observed via the pi+pi- decay channel have been measured at beam momentum=3.67 GeV/c. The observed total meson production cross section is determined to be 23.4 +- 0.8 +-8 microb and is significantly lower than typical cross sections used in model calculations for heavy ion collisions. The differential cross sections measured indicate a strong anisotropy cos^2(theta^{CM}) in the rho^0 meson production.

Phys. Rev. D

We have performed a search for radiative b-hadron decays using events produced in proton-antiproton collisions at sqrt(s) = 1.8 TeV and collected by the Collider Detector at Fermilab. The decays we considered were B_d -> K*0(-> K+ pi-) gamma, B_s -> phi(-> K+ K-) gamma, Lambda_b -> Lambda(-> p pi-) gamma, and their charge conjugates. Two independent methods to identify photons from such decays were employed. In the first method, the photon was detected in the electromagnetic calorimeter. In the second method, the photon was identified by an electron-positron pair produced through the external photon conversion before the tracking detector volume. By combining the two methods we obtain upper limits on the branching fractions for the B_d, B_s and Lambda_b radiative decays, which, at the 95% confidence level, are found to be B(B_d -> K*0 gamma) < 1.4 x 10^(-4), B(B_s -> phi gamma) < 1.6 x 10^(-4), and B(Lambda_b -> Lambda gamma) < 1.9 x 10^(-3).

Eur.Phys.J.C

In some supersymmetric models, the gluino is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino is not constrained by hadron collider results, which looked for the decay gluino -> q qbar \tilde{\chi}_1^0. Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for (q qbar gluino gluino) events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c^2 is excluded at the 95% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity of 609 pb^-1. The observed number of events is in agreement with the Standard Model predictions. Limits at 95% confidence level are derived on the squark masses from the excluded regions in the plane (m_\tilde{q_1},m_gluino): m_\tilde{t_1} > 90 GeV/c^2, and m_\tilde{b_1} > 96 GeV/c^2 for purely left squarks. m_\tilde{t_1} > 87 GeV/c^2, and m_\tilde{b_1} > 82 GeV/c^2 independent of the mixing angle.

Nucl. Instrum. Meth. A

A drift chamber readout system of the DIRAC experiment at CERN is presented. The system is intended to read out the signals from planar chambers operating in a high current mode. The sense wire signals are digitized in the 16-channel time-to-digital converter boards which are plugged in the signal plane connectors. This design results in a reduced number of modules, a small number of cables and high noise immunity. The system has been successfully operating in the experiment since 1999

Astrophys.J.

We present the final installment of an intensive 13-year study of variations of the optical continuum and broad H-beta emission line in the Seyfert 1 galaxy NGC 5548. The data base consists of 1530 optical continuum measurements and 1248 H-beta measurements. The H-beta variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction that the size of the broad-line region is proportional to the square root of the ionizing luminosity. Moreover, the apparently linear nature of the correlation between the H-beta response time and the nonstellar optical continuum arises as a consequence of the changing shape of the continuum as it varies, specifically with the optical (5100 A) continuum luminosity proportional to the ultraviolet (1350 A) continuum luminosity to the 0.56 power.

Lect.Notes Phys.

We consider J/Psi meson production in $ep$ deep inelastic scattering in the colour singlet model using the k_T-factorization QCD approach. We investigate the z-, Q^2-, p_T^2-, y^*- and W-dependences of inelastic J/Psi production on different forms of the unintegrated gluon distribution. The p_T^2- and Q^2-dependences of the J/Psi spin aligment parameter alpha are presented also. We compare the theoretical results with recent experimental data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/Psi mesons at Q^2 < 1 {GeV}^2 is an additional test of BFKL gluon dynamics.

NATO Sci. Ser. II

In the framework of k T -factorization QCD approach and the colour singlet model we consider J/ψ deep inelastic leptoproduction processes at HERA. We investigate the dependences of the single differential cross section on different forms of the unintegrated gluon distribution. The z and P T dependences of the spin aligment parameter α are presented also. Our theoretical predictions agree well with recent data taken by the H1 and ZEUS collaborations at HERA. It is shown that experimental study of the polarization J/ψ mesons at low Q 2 < 1 GeV2 is an additional test of BFKL gluon dynamics.

Phys.Rev.D

We present data on multiple production of jets with transverse energies near 20 GeV in p-pbar collisions at Root(s) = 1.8 TeV. QCD calculations in the parton-shower approximation of PYTHIA and HERWIG and the next-to-leading order approximation of JETRAD are compared to the data for one, two, three, and four jet inclusive production. Transverse energy spectra and multiple jet angular and summed transverse-energy distributions are adequately described by the shower approximation while next-to-leading order calculations describe the data poorly.

Phys.Rev.Lett.

We report the first search for supersymmetric particles via s-channel production and decay of smuons or muon sneutrinos at hadronic colliders. The data for the two-muon and two-jets final states were collected by the DO experiment, and correspond to an integrated luminosity of 94 +/- 5 pb^{-1}. Assuming that R-parity is violated via the single coupling lambda^{prime}_{211}, the number of candidate events is in agreement with expectation from the standard model. Exclusion contours are given in the (m_0,m_{1/2}) and (m_{tilde{chi}},m_{tilde{nu}}) planes for lambda^{prime}_{211}=0.09, 0.08 and 0.07.