Phys. Rev. D

We present measurements of the B+ meson total cross section and differential cross section $d\sigma/ dp_T$. The measurements use a $98\pm 4$ pb^{-1} sample of $p \bar p$ collisions at $\sqrt{s}=1.8$ TeV collected by the CDF detector. Charged $B$ meson candidates are reconstructed through the decay $B^{\pm} \to J/\psi K^{\pm}$ with $J/\psi\to \mu^+ \mu^-$. The total cross section, measured in the central rapidity region $|y|<1.0$ for $p_T(B)>6.0$ GeV/$c$, is $3.6 \pm 0.6 ({\rm stat} \oplus {\rm syst)} \mu$b. The measured differential cross section is substantially larger than typical QCD predictions calculated to next-to-leading order.

Phys. Rev. Lett.

We report on measurements of the ϒ(1S), ϒ(2S), and ϒ(3S) differential cross sections (d2σ/dpTdy)|y|<0.4, as well as on the ϒ(1S) polarization in pp¯ collisions at s=1.8TeV using a sample of 77±3pb−1 collected by the collider detector at Fermilab. The three resonances were reconstructed through the decay ϒ→μ+μ−. The measured angular distribution of the muons in the ϒ(1S) rest frame is consistent with unpolarized meson production.

Nucl. Phys. B

A study of strange particle production in ν μ charged current interactions has been performed using the data from the NOMAD experiment. Yields of neutral strange particles ( K 0 s ,Λ, Λ ̄ ) have been measured. Mean multiplicities are reported as a function of the event kinematic variables E ν , W 2 and Q 2 as well as of the variables describing particle behaviour within a hadronic jet: x F , z and p T 2 . Decays of resonances and heavy hyperons with identified K 0 s and Λ in the final state have been analyzed. Clear signals corresponding to K ★± , Σ ★± , Ξ − and Σ 0 have been observed.

Phys.Lett.B

A search was made among ν μ charged current events collected in the NOMAD experiment for the reaction: ν μ +N→μ − +D ★+ + hadrons ↪ D 0 +π + ↪ K − +π + . A high purity D ★+ sample composed of 35 events was extracted. The D ★+ yield in ν μ charged current interactions was measured to be T =(0.79±0.17(stat.)±0.10(syst.))%. The mean fraction of the hadronic jet energy taken by the D ★+ is 0.67±0.02(stat.)±0.02(syst.). The distributions of the fragmentation variables z, P T 2 and x F for D ★+ are also presented.

Phys. Rev. Lett.

We present the results of a search for leptoquark (LQ) pairs in (85.2 +- 3.7) pb^{-1} of p anti-p collider data collected by the D0 experiment at the Fermilab Tevatron. We observe no evidence for leptoquark production and set a limit on sigma(p anti-p -> LQ anti-LQ -> neutrino neutrino + jets) as a function of the mass of the leptoquark (m_{LQ}). Assuming the decay LQ -> neutrino q, we exclude scalar leptoquarks for m_{LQ} < 98 GeV/c^2, and vector leptoquarks for m_{LQ} < 200 GeV/c^2 and coupling which produces the minimum cross section, at a 95% confidence level.

Phys. Rev. Lett.

We present results of a search for R-parity-violating decay of the neutralino chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that this decay proceeds through one of the lepton-number violating couplings lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data, collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at a center of mass energy of 1.8 TeV in 1992-1995.

Eur.Phys.J.C

Neutral Higgs bosons of the Standard Model (SM) and the Minimal Supersymmetric Standard Model (MSSM) were searched for in the data collected in 1999 by the DELPHI experiment at centre-of-mass energies between 191.6 and 201.7 GeV with a total integrated luminosity of 228 pb^{-1}. These analyses, in combination with our results at lower energies, set 95% confidence level lower mass bounds on the Standard Model Higgs boson (107.3 GeV/c^2) and on the lightest neutral scalar (85.9 GeV/c^2) and neutral pseudoscalar (86.5 GeV/c^2) Higgs bosons in representative scans of the MSSM parameter space. An extended scan of the MSSM parameter space was also performed to test the robustness of these limits.

Nucl. Phys. B Proc. Suppl.

One IGEX 76 Ge 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. A new exclusion plot, σ(m), has been derived for WIMP-nucleon spin-independent interactions. To obtain this result, 40 days of data from the IGEX detector (energy threshold E thr ∼ 4 keV), recently collected, have been analyzed. These data improve the exclusion limits derived from all the other ionization germanium detectors in the mass region from 20 GeV to 200 GeV, where a WIMP supposedly responsible for the annual modulation effect reported by the DAMA experiment would be located. The new IGEX exclusion contour enters, by the first time, the DAMA region by using only raw data, with no background discrimination, and excludes its upper left part. It is also shown that with a moderate improvement of the detector performances, the DAMA region could be fully explored.

Phys.Lett.B

The production of pions emitted backward in inelastic neutrino-nucleus interactions is analyzed within the impulse approximation in the framework of the dual parton model. We focus on the $Q^2$-dependence of the multiplicity of negative pions, normalized to the total cross section of the reaction $\nu + A \to \mu + X$. The inclusion of planar (one-Reggeon exchange) and cylindrical (one-Pomeron exchange) graphs leads to a multiplicity that decreases as $Q^2$ increases, in agreement with recent measurements carried out at CERN by the NOMAD collaboration. A realistic treatment of the high momentum tail of the nucleon distribution in a nucleus also allows for a satisfactory description of the semi-inclusive spectrum of backward pions.

JETP Lett.

Available data on large-angle nucleon-deuteron elastic scattering $Nd\to dN$ below the pion threshold give a signal for three-body forces. There is a problem of separation of possible subtle aspects of these forces from off-shell effects in two-nucleon potentials. By considering the main mechanisms of the process, we show qualitatively that in the quasi-binary reaction $N+d\to (NN)+N$ with the final spin singlet NN-pair in the S-state the relative contribution of the 3N forces differs substantially from the elastic channel. It gives a new testing ground for the problem in question.

J. Phys. G

Quasi-binary reaction of the deuteron breakup $p+d\to (pp)+n$ with the final proton-proton pair $(pp)$ in the $^1S_0$ state is analyzed at initial energies $0.5 - 2$ GeV in the kinematics of backward elastic pd-scattering $pd\to dp$. On the basis of the main mechanisms of the $pd\to dp$ process, including initial and final state interaction, we show that unpolarized cross section and spin observables of this reaction exhibit important properties of the half-off-shell $pp(^1S_0)$-scattering amplitude, which are relevant to the nucleon-nucleon interaction at short distances.

Phys.Lett.B

Available experimental data on the exclusive $pd\to pnp$ reaction at 585 MeV show a narrow peak in the proton-neutron final-state interaction region. It was supposed previously, on the basis of a phenomenological analysis of the shape of this peak, that the final spin-singlet $pn$ state provided about one third of the observed cross section. By comparing the absolute value of the measured cross section with that of $pd$ elastic scattering using the F\"aldt-Wilkin extrapolation theorem, it is shown here that the $pd\to pnp$ data can be explained mainly by the spin-triplet final state with a singlet admixture of a few percent. The smallness of the singlet contribution is compatible with existing $pN\to pN\pi$ data and the one-pion exchange mechanism of the $pd\to pnp$ reaction.

Phys. Rev. D

We present the results of a search in proton-antiproton collisions at sqrt(s) = 1.8 TeV for anomalous production of events containing a photon with large transverse energy and a lepton (e or mu) with large transverse energy, using 86 pb^{-1} of data collected with the Collider Detector at Fermilab during the 1994-95 collider run at the Fermilab Tevatron. The presence of large missing transverse energy, additional photons, or additional leptons in these events is also analyzed. The results are consistent with standard model expectations, with the possible exception of photon-lepton events with large missing transverse energy, for which the observed total is 16 events and the expected mean total is 7.6+/-0.7 events.

Phys. Rev. D

We present a search for the flavor-changing neutral current decay Bs→μ+μ−φ in pp¯ collisions at s=1.8 TeV, using 91 pb−1 of data collected at the Collider Detector at Fermilab (CDF). We find two candidate events for this decay, which are consistent with the background estimate of one event, and set an upper limit on the branching fraction of B(Bs→μ+μ−φ)<6.7×10−5 at a 95% confidence level. This is the first limit on the branching fraction of this decay.

Phys.Rev.D

We search for standard model single-top-quark production in the W-gluon fusion and W* channels using 106 pb^-1 of data from p-pbar collisions at sqrt(s)=1.8 TeV collected with the Collider Detector at Fermilab. We set an upper limit at 95% C.L. on the combined W-gluon fusion and W* single-top cross section of 14 pb, roughly six times larger than the standard model prediction. Separate 95% C.L. upper limits in the W-gluon fusion and W* channels are also determined and are found to be 13 and 18 pb, respectively.

Phys. Rev. D

We present a study of pp¯ collisions at s=1800 and 630 GeV collected using a minimum bias trigger by the CDF experiment in which the data set is divided into two classes corresponding to “soft” and “hard” interactions. For each subsample, the analysis includes measurements of the multiplicity, transverse momentum (pT) spectrum, and the average pT and event-by-event pT dispersion as a function of multiplicity. A comparison of results shows distinct differences in the behavior of the two samples as a function of the center of mass (c.m.) energy. We find evidence that the properties of the soft sample are invariant as a function of c.m. energy.

Phys. Rev. Lett.

The dominant one-loop radiative corrections to atomic wave functions, those associated with vacuum polarization in the nuclear Coulomb field, are evaluated for the 6s-7s parity-nonconserving (PNC) transition amplitude in 133Cs. These corrections increase the size of the PNC amplitude by 0.4% and, correspondingly, increase the difference between the experimental value of the weak charge Q_W(133Cs) and the value predicted by the standard model.

Phys.Lett.B

One IGEX 76 Ge 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. A new exclusion plot, σ (m), has been derived for WIMP-nucleon spin-independent interactions. To obtain this result, 40 days of data from the IGEX detector (energy threshold E thr ∼4 keV), recently collected, have been analyzed. These data improve the exclusion limits derived from all the other ionization germanium detectors in the mass region from 20 to 200 GeV, where a WIMP supposedly responsible for the annual modulation effect reported by the DAMA experiment would be located. The new IGEX exclusion contour enters, by the first time, the DAMA region by using only raw data, with no background discrimination, and excludes its upper left part. It is also shown that with a moderate improvement of the detector performances, the DAMA region could be fully explored.

AIP Conf.Proc.

The energy spectrum for high energy $\gamma$-rays ($E_\gamma \geq 10$ MeV) from the process $pp \to \gamma \gamma X$ emitted at $90^0$ in the laboratory frame has been measured at 216 MeV. The resulting photon energy spectrum extracted from $\gamma-\gamma$ coincidence events consists of a narrow peak (5.3$\sigma$) at a photon energy of about 24 MeV and a relatively broad peak (3.5$\sigma$) in the energy range of (50 - 70) MeV. This behavior of the photon energy spectrum is interpreted as a signature of the exotic dibaryon resonance $d^\star_1$ with a mass of about 1956 MeV which is assumed to be formed in the radiative process $pp \to \gamma d^\star_1$ followed by its electromagnetic decay via the $d^\star_1 \to pp \gamma$ mode. The experimental spectrum is compared with those obtained by means of Monte Carlo simulations.

AIP Conf. Proc.

A new generation of semi-conducting pixel sensors for detecting minimum ionising particles (m.i.p.) was designed and first prototypes were fabricated in a standard CMOS technology, guided by the very high vertex detector performances demanded in future collider experiments. The device architecture resembles CMOS cameras, a recent alternative to CCD sensors for visible light imaging. The performances of the first prototype of Monolithic Active Pixel Sensors (MAPS), called MIMOSA, were evaluated with high energy π − beams at CERN. Preliminary test results demonstrate that the sensors detect m.i.p.s with very high efficiency and signal-to-noise ratio and provide excellent spatial resolution.

Phys.Rev.Lett.

We report a measurement of the diffractive structure function $F_{jj}^D$ of the antiproton obtained from a study of dijet events produced in association with a leading antiproton in $\bar pp$ collisions at $\sqrt s=630$ GeV at the Fermilab Tevatron. The ratio of $F_{jj}^D$ at $\sqrt s=630$ GeV to $F_{jj}^D$ obtained from a similar measurement at $\sqrt s=1800$ GeV is compared with expectations from QCD factorization and with theoretical predictions. We also report a measurement of the $\xi$ ($x$-Pomeron) and $\beta$ ($x$ of parton in Pomeron) dependence of $F_{jj}^D$ at $\sqrt s=1800$ GeV. In the region $0.035<\xi<0.095$, $|t|<1$ GeV$^2$ and $\beta<0.5$, $F_{jj}^D(\beta,\xi)$ is found to be of the form $\beta^{-1.0\pm 0.1} \xi^{-0.9\pm 0.1}$, which obeys $\beta$-$\xi$ factorization.

Phys. Rev. D

We present a detailed examination of the heavy flavor content of the $W $ + jet data sample collected with the CDF detector during the 1992-1995 collider run at the Fermilab Tevatron. Jets containing heavy flavor quarks are selected via the identification of secondary vertices or semileptonic decays of $b$ and $c$ quarks. There is generally good agreement between the rates of secondary vertices and soft leptons in the data and in the standard model simulation including single and pair production of top quarks. An exception is the number of events in which a single jet has both a soft lepton and a secondary vertex tag. In $W +$ 2,3 jet data, we find 13 such events where we expected 4.4 $\pm$ 0.6 events. The kinematic properties of this small sample of events are statistically difficult to reconcile with the simulation of standard model processes.

Phys.Lett.B

The central inclusive jet cross section has been measured using a successive-combination algorithm for reconstruction of jets. The measurement uses 87.3 pb −1 of data collected with the DØ detector at the Fermilab Tevatron p p Collider during 1994–1995. The cross section, reported as a function of transverse momentum ( p T >60 GeV) in the central region of pseudorapidity (| η |<0.5), exhibits reasonable agreement with next-to-leading order QCD predictions, except at low p T where the agreement is marginal.

Phys.Rev.D

It is shown that the corrections of $\alpha^2$ order to the total cross sections for interaction of elementary hydrogen-like atoms with target atoms, reported in the previously published paper [S.Mrowczynski, Phys.Rev. D36, 1520 (1987)], do not include some terms of the same order of magnitude. That results in a significant contribution of these corrections in particular cases. The full $\alpha^2$-corrections have been derived and it is shown that they are really small and could be omitted for most practical applications.

AIP Conf. Proc.

There is an interest in the problem of polarized fusion with the neutron-free d3He reaction. Up to now, the experimental data on the cross sections of two dd reactions, which produce neutrons at once or through secondary dt reaction, are absent for polarized deuterons. There is a relatively cheap way to carry out the experiments with polarized deuterons at the Charles University in Prague. A polarized deuteron beam with energy from 100 keV up to approximately 1 MeV may be produced on the Van de Graaff accelerator by the channeling of a deuteron beam through magnetized Ni single crystal foil, according M. Kaminsky [Phys. Rev. Lett. 23, 819 (1969)]. This method permits to produce a polarized deuteron beam of an energy ⩽1 MeV with a current of ∼1 nA, vector polarization P3 up to 2/3 and tensor polarization P33=0. It will be necessary to modify the existing polarized target at Charles University for work with a low energy deuteron beam [N. S. Borisov et al., Nucl. Instr. & Meth. A 345, 421 (1994)].