Phys.Lett.B

Using the D0 detector, we have observed events produced in pbar-p collisions that contain W or Z bosons in conjunction with very little energy deposition (``rapidity gaps'') in large forward regions of the detector. The fraction of W boson events with a rapidity gap (a signature for diffraction) is 0.89\pm^{0.19}_{0.17}%, and the probability that the non-diffractive background fluctuated to yield the observed diffractive signal is 3 x 10^{-14}, corresponding to a significance of 7.5 sigma. The Z boson sample has a gap fraction of 1.44 \pm^{0.61}_{0.52}%, with a significance of 4.4 sigma. The diffractive events have very similar properties to the more common non-diffractive component.

Phys.Lett.B

A search for events containing isolated tau leptons and large missing transverse momentum, not originating from the tau decay, has been performed with the ZEUS detector at the electron-proton collider HERA, using 130 pb^-1 of integrated luminosity. A search was made for isolated tracks coming from hadronic tau decays. Observables based on the internal jet structure were exploited to discriminate between tau decays and quark- or gluon-induced jets. Three tau candidates were found, while 0.40 +0.12 -0.13 were expected from Standard Model processes, such as charged current deep inelastic scattering and single W-boson production. To search for heavy-particle decays, a more restrictive selection was applied to isolate tau leptons produced together with a hadronic final state with high transverse momentum. Two candidate events survive, while 0.20 +-0.05 events are expected from Standard Model processes.

Phys. Rev. D

The results based on 1992-95 data (Run 1) from the CDF and DO experiments on the measurements of the W boson mass and width are presented, along with the combined results. We report a Tevatron collider average M_W = 80.456 +- 0.059 GeV. We also report the Tevatron collider average of the directly measured W boson width Gamma_W = 2.115 +- 0.105 GeV. We describe a new joint analysis of the direct W mass and width measurements. Assuming the validity of the standard model, we combine the directly measured W boson width with the width extracted from the ratio of W and Z boson leptonic partial cross sections. This combined result for the Tevatron is Gamma_W = 2.135 +- 0.050 GeV. Finally, we use the measurements of the direct total W width and the leptonic branching ratio to extract the leptonic partial width Gamma(W -> e nu) = 224 +- 13 MeV.

Phys. Rev. Lett.

We report a study of $\bar p+p\to \bar p+X+Y$ at $\sqrt s=1800$ GeV, where $Y$ is a proton or system of mass-squared $M_Y^2\lesssim 8$ GeV$^2$. In a sample of events with a leading $\bar p$ of fractional momentum loss $0.035<\xi_{\bar p}<0.095$ and 4-momentum transfer squared $|t_{\bar p}|<1.0$ GeV$^2$, the proton fractional momentum loss $\xi_p^X$ to the system $X$ was evaluated from the momenta of the particles comprising $X$. In the region $\xi_p^X<0.02$, the $\xi_p^X$ distribution behaves as $\sim 1/(\xi_p^X)^{1.1}$, as expected for double Pomeron exchange. The fraction of events with $\xi_p^X<0.02$ is found to be $0.194\pm 0.001 {\rm (stat)}\pm 0.012 {\rm (syst)}$.

Phys.Rev.D

We present a measurement of the coefficient alpha_2 of the leptonic polar-angle distribution from W boson decays, as a function of the W transverse momentum. The measurement uses an 80+/-4 pb^{-1} sample of proton-antiproton collisions at sqrt{s}=1.8 TeV collected by the CDF detector and includes data from both the W->e+nu and W->mu+nu decay channels. We fit the W boson transverse mass distribution to a set of templates from a Monte Carlo event generator and detector simulation in several ranges of the W transverse momentum. The measurement agrees with the Standard Model expectation, whereby the ratio of longitudinally to transversely polarized W bosons, in the Collins-Soper W rest frame, increases with the W transverse momentum at a rate of approximately 15% per 10 GeV/c.

Phys.Rev.D

We present a detailed examination of the heavy flavor properties of jets produced at the Fermilab Tevatron collider. The data set, collected with the Collider Detector at Fermilab, consists of events with two or more jets with transverse energy $E_T \geq 15$ GeV and pseudo-rapidity $|\eta| \leq 1.5$. The heavy flavor content of the data set is enriched by requiring that at least one of the jets (lepton-jet) contains a lepton with transverse momentum larger than 8 GeV/c. Jets containing hadrons with heavy flavor are selected via the identification of secondary vertices. The parton-level cross sections predicted by the {\sc herwig} Monte Carlo generator program are tuned within theoretical and experimental uncertainties to reproduce the secondary-vertex rates in the data. The tuned simulation provides new information on the origin of the discrepancy between the $b\bar{b}$ cross section measurements at the Tevatron and the next-to-leading order QCD prediction. We also compare the rate of away-jets (jets recoiling against the lepton-jet) containing a soft lepton ($p_T \geq 2$ GeV/c) in the data to that in the tuned simulation. We find that this rate is larger than what is expected for the conventional production and semileptonic decay of pairs of hadrons with heavy flavor.

Eur.Phys.J.C

These final results on e+e- -> W+W- production cross-section measurements at LEP2 use data collected by the DELPHI detector at centre-of-mass energies up to 209 GeV. Measurements of total cross-sections, W angular differential distributions and decay branching fractions, and the value of the CKM element |V_{cs}| are compared to the expectations of the Standard Model. These results supersede all values previously published by DELPHI.

Phys. Rev. C

As part of a measurement of the cross section of $\phi$ meson photoproduction to high momentum transfer, we measured the polar angular decay distribution of the outgoing $K^+$ in the channel $\phi \to K^+K^-$ in the $\phi$ center-of-mass frame (the helicity frame). We find that s-channel helicity conservation (SCHC) holds in the kinematical range where $t$-channel exchange dominates (up to $-t \sim 2.5$ GeV$^2$ for $E_{\gamma}$=3.6 GeV). Above this momentum, $u$-channel production of a $\phi$ meson dominates and induces a violation of SCHC. The deduced value of the $\phi NN$ coupling constant lies in the upper range of previously reported values.

Nucl.Phys.B Proc.Suppl.

Nucl.Phys.B Proc.Suppl.

Yad.Fiz.

The Weakly Interacting Massive Particle (WIMP) is the main candidate for the relic dark matter. A set of exclusion curves currently obtained for cross sections of the spin-dependent WIMP-proton and WIMP-neutron interaction is given. A two-orders-of-magnitude improvement of the sensitivity of the dark matter experiment is needed to reach the SUSY predictions for relic neutralinos. It is noted that near-future experiments with the high-spin isotope Ge-73 can yield a new important constraint on the neutralino-neutron effective coupling and the SUSY parameter space.

Phys.Lett.B

Bose-Einstein correlations in one and two dimensions have been studied in deep inelastic EP scattering events measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The correlations are independent of the virtuality of the exchanged photon, Q2, in the range 0.1100 GeV2. The two-dimensional shape of the particle-production source was investigated, and a significant difference between the transverse and the longitudinal dimensions of the source is observed.This difference also shows no Q2 dependence.The results demonstrate that Bose-Einstein interference, and hence the size of the particle-production source, is insensitive to the hard subprocess.

Phys.Rev.D

We present a measurement of the mass difference m(D+_s) - m(D+), where both the D+_s and D+ are reconstructed in the phi pi+ decay channel. This measurement uses 11.6 pb-1 of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be: 99.41 +- 0.38 (stat) +- 0.21 (syst) MeV/c^2.

Eur.Phys.J.C

The forward-backward asymmetries of the processes e+e- -> Z -> b bbar and e+e- -> Z -> c cbar were measured from a sample of hadronic Z decays collected by the DELPHI experiment between 1993 and 1995. Enriched samples of b bbar and c cbar events were obtained using lifetime information. The tagging of b and c quarks in these samples was based on the semileptonic decay channels b/c -> X + mu and b/c -> X + e combined with charge flow information from the hemisphere opposite to the lepton. Combining the A_{FB}^{b bbar} and A_{FB}^{c cbar} measurements presented in this paper with published results based on 1991 and 1992 DELPHI data samples, the following pole asymmetries were obtained: A_{FB}^{0,b} = 0.1021 +/- 0.0052 (stat) +/- 0.0024 (syst) A_{FB}^{0,c} = 0.0728 +/- 0.0086 (stat) +/- 0.0063 (syst) The effective value of the weak mixing angle derived from these measurements is sin^2 theta_{W,eff}^{lept} = 0.23170 +/- 0.00097 .

Eur. Phys. J. C

Oscillations in the B0_s - anti-B0_s system were studied in events selected from about 4.3 million hadronic Z^0 decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses ([11,12]). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes D_s-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of B0_s oscillations was observed and limits on the mass difference between the physical B0_s states were obtained to be: \Delta m_s > 8.0 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 9.1 ps^{-1} in the high p_t lepton analysis and \Delta m_s > 4.9 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 8.6 ps^{-1} in the D_s-lepton analysis. Previously published results on these analyses are superseed. The combination of these results with those obtained in other independent analyses previously performed in DELPHI (D_s-hadron, exclusive B0_s, inclusive vertex) gives: \Delta m_s > 8.5 ps^{-1} at the 95% C.L. with a sensitivity of \Delta m_s = 12.0 ps^{-1}.

Instrum. Exp. Tech.

The stands for testing mini drift tubes at the workshop of the Joint Institute for Nuclear Research are described. The test stands are used to perform persistent and effective quality control of detectors under conditions of mass production. Detectors manufactured for the D0 and COMPASS experiments have been tested on these stands.

Phys.Lett.B

We have searched for the signature of 3- and 4-body decays of pair-produced scalar top quarks (stop) in the inclusive final state containing an electron, a muon, and significant missing transverse energy using a sample of p p ̄ events corresponding to 108.3 pb −1 of data collected with the DØ detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the neutralino ( χ ̃ 0 1 ) is the lightest supersymmetric particle and is stable. No evidence for a signal is found and we derive cross-section upper limits as a function of stop ( t̃ ) and neutralino masses in different decay scenarios leading to the bℓν χ ̃ 0 1 final state.

Czech.J.Phys.

Single Spin Asymmetries (SSA) $A_N$ measured in the two reactions at the Protvino 70 GeV accelerator are presented. $A_N$ in the reaction $p+p(pol)->\pi^0+X$ in the central region is close to zero within the error bars. SSA in the reaction $\pi^- +p(pol)->\pi^0+X$ in the polarized target fragmentation region is equal to $(-15 \pm 4)$ at $|x_F|>0.4$. There is an indication that the asymmetry arises at the same pion energy in the center of mass system.

Phys.Rev.D

The lowest order radiative corrections (RC) to width and spectra of radiative $\pi e2$ decay are calculated. We take into account virtual photon emission contribution as well as soft and hard real photon emission one. The result turns out to be consistent with the standard Drell-Yan picture for the width and spectra in the leading logarithmical approximation which permits us to generalize it to all orders of perturbation theory. Explicit expressions of nonleading contributions are obtained. The contribution of short distance is found to be in agreement with Standard Model predictions. It is presented as a general normalization factor. We check the validity of the Kinoshita-Lee-Nauenberg theorem about cancellation in the total width of the mass singularities at zero limit of electron mass. We discuss the results of the previous papers devoted to this problem. The Dalitz plot distribution is illustrated numerically.

Eur.Phys.J.A

We discuss multi-hadron production in both inelastic neutrino-nucleon interactions in the current fragmentation region and neutrino-nucleus collisions in the target fragmentation region. Our analysis, carried out within the framework of the quark-gluon string model, is mainly focused on the difference between these two processes. We show that the $Q^2$ dependence of hadron multiplicity in the current and target fragmentation regions is indeed completely different. The study of inelastic $\nu-A$ scattering in the target fragmentation region also provides new information on nuclear structure at small $N-N$ distances. The results of the proposed approach are in satisfactory agreement with the data recently obtained at CERN by the NOMAD Collaboration.

10.1142/9789812702708_0007

The project aims at the measurement of very rare processes of double-beta decay of ¹⁰⁶Cd and ⁴⁸Ca. The experimental facility TGV II (Telescope Germanium Vertical) makes use of 32 HPGe planar detectors mounted in one common cryostat. The detectors are interleaved with thin foils containing ββ sources. Besides passive shielding against background radiation made of pure copper, lead and boron dopped polyethylene additional techniques for background suppression based on digital pulse shape analysis are used. The experimental setup is located in Modane underground laboratory (France). A review of the TGV II facility, its performance parameters and capabilities are presented.

Phys. Rev. Lett.

Data corresponding to a KamLAND detector exposure of 0.28 kton-year has been used to search for $\bar{\nu}_e$'s in the energy range 8.3 MeV $<$ E$_{\bar{\nu}_e}$ $<$ 14.8 MeV. No candidates were found for an expected background of $1.1{\pm}0.4$ events. This result can be used to obtain a limit on $\bar{\nu}_{e}$ fluxes of any origin. Assuming that all $\bar{\nu}_e$ flux has its origin in the Sun and has the characteristic $^8$B solar $\nu_e$ energy spectrum, we obtain an upper limit of 3.7 \times 10$^2$ cm$^{-2}$ s$^{-1}$ (90% C.L.) on the $\bar{\nu}_e$ flux. We interpret this limit, corresponding to $2.8{\times}10^{-4}$ of the Standard Solar Model $^8$B $\nu_e$ flux, in the framework of spin--flavor precession and neutrino decay models.

AIP Conf. Proc.

We report a new measurement of analyzing powers for the reaction p⃗ + CH 2 → one charged particle +X, at proton momenta of 1.75, 3.8, 4.5 and 5.3 GeV/c. These results extend the existing data basis, necessary for proton polarimetry at intermediate energy, and confirm the feasibility of an extended polarimeter based on this process. The experiment is performed at the accelerator complex of the JINR‐LHE (Dubna).

AIP Conf. Proc.

The paper presents new experimental data on the spin rotation parameter A obtained recently by ITEP‐PNPI collaboration at the ITEP accelerator. The set of measurements was performed in carefully chosen critical points with precision sufficient for choosing the correct branches of partial wave analyses. The data for both π+ and π−‐scattering at 1.0, 1.43 and 1.62 GeV/c is included.

AIP Conf. Proc.

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