Phys. Rev. D

We update our exploration of the MSSM parameter space at the weak scale where new accelerator and cosmological constraints are respected. The dependence of WIMP-nucleon cross sections on parameters of the MSSM, uncertainties of the nucleon structure and other theoretical assumptions like universality and co-annihilation are considered. In particular, we find that the coannihilation does not have a significant effect in our analysis in certain regions which are allowed even with coannihilation. The new cosmological constraint on the relic neutralino density used in the form $0.1 < \Omega_\chi h^2_0<0.3$ does also not significantly affect the regions of allowed neutralino-nucleon cross sections. We notice that for nuclear targets with spin the spin-dependent interaction may determine the lower bound for the direct detection rate when the cross section of the scalar interaction drops below about $10^{-12}$pb.

Eur. Phys. J. C

The production and semi-leptonic decay of heavy quarks have been studied in the photoproduction process $e^+p -> e^+ + {dijet} + e^- + X with the ZEUS detector at HERA using an integrated luminosity of 38.5${\rm pb^{-1}}$. Events with photon-proton centre-of-mass energies,$W_{\gamma p}$, between 134 and 269 GeV and a photon virtuality, Q^2, less than 1${\rm GeV^2}$were selected requiring at least two jets of transverse energy$E_T^{\rm jet1(2)} >7(6)$GeV and an electron in the final state. The electrons were identified by employing the ionisation energy loss measurement. The contribution of beauty quarks was determined using the transverse momentum of the electron relative to the axis of the closest jet,$p_T^{\rm rel}$. The data, after background subtraction, were fit with a Monte Carlo simulation including beauty and charm decays. The measured beauty cross section was extrapolated to the parton level with the b quark restricted to the region of transverse momentum$p_T^{b} > p_T^{\rm min} =$5 GeV and pseudorapidity$|\eta^{b}| <$2. The extrapolated cross section is$1.6 \pm 0.4 (stat.)^{+0.3}_{-0.5} (syst.) ^{+0.2}_{-0.4} (ext.) {nb}$. The result is compared to a perturbative QCD calculation performed to next-to-leading order.$

Phys.Rev.D

We report on a search for the supersymmetric partner of the top quark (stop) produced in t \bar{t}$events using$110 {\rm pb}^{-1}$of$p \bar{p}$collisions at$\sqrt{s} = 1.8 {\rm TeV}$recorded with the Collider Detector at Fermilab. In the case of a light stop squark, the decay of the top quark into stop plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with Standard Model$t \bar{t}$production and decay. Hence, we set limits on the branching ratio of the top quark decaying into stop plus LSP, excluding branching ratios above 45$^{2}$.$

Phys.Rev.D

We apply a quasi-model-independent strategy ("Sleuth") to search for new high p_T physics in approximately 100 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV collected by the DZero experiment during 1992-1996 at the Fermilab Tevatron. Over thirty-two e mu X, W+jets-like, Z+jets-like, and 3(lepton/photon)X exclusive final states are systematically analyzed for hints of physics beyond the standard model. Simultaneous sensitivity to a variety of models predicting new phenomena at the electroweak scale is demonstrated by testing the method on a particular signature in each set of final states. No evidence of new high p_T physics is observed in the course of this search, and we find that 89% of an ensemble of hypothetical similar experimental runs would have produced a final state with a candidate signal more interesting than the most interesting observed in these data.

Phys.Lett.B

The n$-th moments of the nuclear structure function$F_2^A(x,Q^2)$are analyzed using the off-shell kinematics appropriate to describe deep inelastic electron-nucleus scattering within the impulse approximation. It is shown that off-shell effects are sensitive to the form of both the nuclear spectral function and the nucleon structure function$F_2^N(x,Q^2)$, and can be as large as$\sim 10%$at Q$^2~\sim~2$~(GeV/c)$^2$.$

Phys. Rev. C

The exclusive production cross sections for \omega$and$\phi$mesons have been measured in proton-proton reactions at$p_{lab}=3.67$GeV/c. The observed$\phi/\omega$cross section ratio is$(3.8\pm0.2^{+1.2}_{-0.9})\times 10^{-3}$. After phase space corrections, this ratio is enhanced by about an order of magnitude relative to naive predictions based upon the Okubo-Zweig-Iizuka (OZI) rule, in comparison to an enhancement by a factor$\sim 3$previously observed at higher beam momenta. The modest increase of this enhancement near the production threshold is compared to the much larger increase of the$\phi/\omega$ratio observed in specific channels of$\bar pp$annihilation experiments. Furthermore, differential cross section results are also presented which indicate that although the$\phi$meson is predominantly produced from a$^3P_1$proton-proton entrance channel, other partial waves contribute significantly to the production mechanism at this beam momentum.$

Nucl.Phys.B

Differential cross sections for dijet photoproduction in association with a leading neutron using the reaction e + + p → e + + n +jet+jet+ X r have been measured with the ZEUS detector at HERA using an integrated luminosity of 6.4 pb −1 . The fraction of dijet events with a leading neutron in the final state was studied as a function of the jet kinematic variables. The cross sections were measured for jet transverse energies E T jet >6 GeV, neutron energy E n >400 GeV, and neutron production angle θ n <0.8 mrad. The data are broadly consistent with factorization of the lepton and hadron vertices and with a simple one-pion-exchange model.

Phys.Rev.Lett.

We present the results of a search for neutral Higgs bosons produced in association with b$quarks in$p\bar{p}\to b\bar{b} \phi\to b\bar{b}b\bar{b}$final states with$91 \pm 7$pb$^{-1}$of$p\bar{p}$collisions at$\sqrt{s}=1.8$TeV recorded by the Collider Detector at Fermilab. We find no evidence of such a signal and the data is interpreted in the context of the neutral Higgs sector of the Minimal Supersymmetric extension of the Standard Model. With basic parameter choices for the supersymmetric scale and the stop quark mixing, we derive 95$\tb$values in excess of 35.$

Nucl. Instrum. Meth. A

Real time pattern recognition is becoming a key issue in many position sensitive detector applications. The CDF collaboration is building SVT: a specialized electronic device designed to perform real time track reconstruction using the Silicon VerteX detector (SVX II). This will strongly improve the CDF capability of triggering on events containing b quarks, usually characterized by the presence of a secondary vertex.

Eur. Phys. J. C

Data taken by the DELPHI experiment at centre-of-mass energies of 183 GeV and 189 GeV with a total integrated luminosity of 212 pb^{-1} have been used to search for the supersymmetric partners of the electrons, muons, and taus in the context of the Minimal Supersymmetric Standard Model (MSSM). The decay topologies searched for were the direct decay ({\tilde \ell} -> \ell {\tilde \chi_1^0}), producing acoplanar lepton pairs plus missing energy, and the cascade decay ({\tilde \ell} -> \ell {\tilde \chi_2^0} -> \ell \gamma {\tilde \chi_1^0}), producing acoplanar lepton and photon pairs plus missing energy. The observed number of events is in agreement with Standard Model predictions. The 95% CL excluded mass limits for selectrons, smuons and staus are m_{\tilde {e}} \leq 87 GeV/c^2, m_{\tilde {\mu}} \leq 80 GeV/c^2 and m_{\tilde {\tau}} \leq 75 GeV/c^2, respectively, for values of \mu=-200 GeV/c^2 and tan(beta)=1.5.

Phys.Rev.D

A study of the antineutrino-jet mass spectrum in e^+p -> antineutrino+X events at center-of-mass energy 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb^-1. The mass spectrum is in good agreement with that expected from Standard Model processes over the antineutrino -jet mass range studied. No significant excess attributable to the decay of a narrow resonance is observed. By using both e^+p -> e^+ X and e^+p -> antineutrino X data, mass-dependent limits are set on the s-channel production of scalar and vector resonant states. Couplings to first-generation quarks are considered and limits are presented as a function of the e^+q and antineutrino-q branching ratios. These limits are used to constrain the production of leptoquarks and R-parity violating squarks.

J. Phys. A

We extend the notion of quasi-exactly solvable (QES) models from potential ones and differential equations to Bose systems. We obtain conditions under which algebraization of the part of the spectrum occurs. In some particular cases simple exact expressions for several energy levels of an anharmonic Bose oscillator are obtained explicitly. The corresponding results do not exploit perturbation theory and include strong coupling regime. A generic Hamiltonian under discussion cannot, in contrast to QES potential models, be expressed as a polynomial in generators of sl_{2}$algebra. The suggested approach is extendable to many-particle Bose systems with interaction.$

Phys. Rev. C

The elastic backward proton-deuteron scattering is analyzed within a fully covariant approach based on the invariant expansion of the reaction amplitude. The method of calculation of any observables for any reaction mechanism is developed. The cross section and spin observables, like tensor analyzing power and polarization transfer coefficient etc., are investigated in explicit form within framework of the impulse approximation using different kinds of the relativistic deuteron wave function (DWF) with P-wave components. Our results of numerical calculation for complete set of polarization observables are compared with the experimental data and other calculations performed within both the non-relativistic and relativistic approaches. An experimental verification of the reaction mechanism is suggested by constructing some combinations of different observables.

Phys.Rev.D

We present a study of events with W bosons and hadronic jets produced in p¯p collisions at a center of mass energy of 1.8 TeV. The data consist of 51400 W→eν decay candidates from 108 pb−1 of integrated luminosity collected using the CDF detector at the Fermilab Tevatron collider. Cross sections and jet production properties have been measured for W+>~1 to >~4 jet events. The data compare well to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation.

Phys.Lett.B

Searches for spontaneous R -parity-violating signals at s =183  GeV and s =189  GeV have been performed using the 1997 and 1998 DELPHI data, under the assumption of R -parity breaking in the third lepton family. The expected topology for the decay of a pair of charginos into two acoplanar taus plus missing energy was investigated and no evidence for a signal was found. The results were used to derive a limit on the chargino mass and to constrain the allowed domains of the MSSM parameter space.

Phys. Lett. B

Searches for pair production of gauginos and squarks in e + e − collisions at a centre-of-mass energy of 189 GeV have been performed on data corresponding to an integrated luminosity of 158 pb −1 collected by the DELPHI detector at LEP. The data were analyzed under the assumption of non-conservation of R -parity through a single dominant U ̄ D ̄ D ̄  coupling between squarks and quarks. Typical final states contain between 4 and 10 jets with or without additional leptons. No excess of data above Standard Model expectations was observed. The results were used to constrain domains of the MSSM parameter space and derive limits on the masses of supersymmetric particles. The following mass limits at 95% CL were obtained from these searches: neutralino mass: m χ ̃ 0 1 ⩾32 GeV; chargino mass: m χ ̃ + 1 ⩾94 GeV; stop and sbottom mass (indirect decay) with ΔM >5 GeV: m t ̃ 1 ⩾74 GeV for Φ mix =0 rad, m t ̃ 1 ⩾59 GeV for Φ mix =0.98 rad, m b ̃ 1 ⩾72 GeV for Φ mix =0 rad. The angle φ mix is the mixing angle between left and right handed quarks.

Phys.Lett.B

A search for the supersymmetric partner of the goldstino, the sgoldstino S , at LEP2 is presented. The production Sγ followed by S decay into two gluons or into two photons was studied at 189–202 GeV LEP centre-of-mass energies. No evidence for the S production was found and limits on the S mass corresponding to different theory parameters are given.

Mod.Phys.Lett.A

Processes of heavy quark photoproduction at HERA energies are considered using the semihard (k_T factorization) QCD approach with emphasis of the BFKL dynamics of gluon distributions. We investigate the dependences of the total cross section of heavy quark photoproduction and also p_T, and rapidity distributions on different forms of the unintegrated gluon distribution. We present a comparision of the theoretical results with available H1 and ZEUS experimental data for charm and beauty photoproductions.

Phys.Lett.B

The ratio of the total exclusive production cross sections for \eta\prime$and$\eta$mesons has been measured in the$pp$reaction at$p_{beam}=3.67$GeV/c. The observed$\eta\prime/\eta$ratio is$(0.83\pm{0.11}^{+0.23}_{-0.18})\times 10^{-2}$from which the exclusive$\eta\prime$meson production cross section is determined to be$(1.12\pm{0.15}^{+0.42}_{-0.31})\mu b$. Differential cross section distributions have been measured. Their shape is consistent with isotropic$\eta\prime$meson production.$

Nucl. Instrum. Meth. A

A new combined test of an electromagnetic liquid argon accordion calorimeter and a hadronic scintillating-tile calorimeter was carried out at the CERN SPS. These devices are prototypes of the barrel calorimeter of the future ATLAS experiment at the LHC. The energy resolution of pions in the energy range from 10 to 300 GeV at an incident angle θ of about 12° is well described by the expression σ/E=((41.9±1.6)%/ E +(1.8±0.1)\)⊕(1.8±0.1)/E , where E is in GeV. The response to electrons and muons was evaluated. Shower profiles, shower leakage and the angular resolution of hadronic showers were also studied. Results are compared with those from the previous beam test.

Phys.Lett.B

A partial wave analysis of the centrally produced ηπ 0 and ηπ − channels has been performed in pp collisions using an incident beam momentum of 450 GeV/c. Clear a 0 (980) and a 2 (1320) signals have been observed in S and D + waves respectively. The dP T , φ and | t | distributions of these resonances are presented.

Phys.Rev.D

We investigated the contribution of the MSSM Higgs bosons produced in the neutralino annihilation in the Earth and Sun to the total WIMPs detection signals. We found that this contribution is very important and results in a lower bound for the muon flux from the Sun of 10^{-7} - 10^{-8} m^{-2} yr^{-1} for neutralinos heavier than 200 GeV. We noticed that due to the SUSY charged Higgs bosons one can expect an energetic tau neutrino flux from the Sun at a level of 10^2 m^{-2} yr^{-1}.

Phys.Rev.Lett.

A full angular analysis has been performed for the pseudo-scalar to vector-vector decays, B0 --> J/psi K* and B_s --> J/psi phi, to determine the amplitudes for decays with parity-even longitudinal and transverse polarization and parity-odd transverse polarization. The measurements are based on 190 B0 candidates and 40 B_s candidates collected from a data set corresponding to 89 inverse pb of pbarp collisions at root(s) = 1.8 TeV at the Fermilab Tevatron. In both decays the decay amplitude for longitudinal polarization dominates and the parity-odd amplitude is found to be small.

Phys. Rev. D

We present a measurement of the W boson mass using data collected with the CDF detector during the 1994-95 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 30,115 W -> enu events recorded in an integrated luminosity of 84 pb^(-1) gives a mass Mw = 80.473 +- 0.065(stat.) +- 0.092(syst.) GeV/c^2. A fit to the transverse mass spectrum of a sample of 14,740 W -> munu events from 80 pb^(-1) gives a mass Mw = 80.465 +- 0.100(stat.) +- 0.103(syst.) GeV/c^2. The dominant contributions to the systematic uncertainties are the uncertainties in the electron energy scale and the muon momentum scale, 0.075 GeV/c^2 and 0.085 GeV/c^2, respectively. The combined value for the electron and muon channel is Mw = 80.470 +- 0.089 GeV/c^2. When combined with previously published CDF measurements, we obtain Mw = 80.433 +- 0.079 GeV/c^2.

Phys. Lett. B

Searches for supersymmetric partners of top and bottom quarks are presented using data taken by the DELPHI experiment at LEP in 1997 and 1998. No deviations from standard model expectations are observed in these data sets, which are taken at centre-of-mass energies of 183 GeV and 189 GeV and correspond to integrated luminosities of 54 pb −1 and 158 pb −1 . These results are used in combination with those obtained by DELPHI at lower centre-of-mass energies to exclude regions in the squark–neutralino mass plane at 95% confidence level.