arXiv subjects

J. Abdallah

Publications and source records attributed to J. Abdallah.

83 records · Page 5Linked to original sources

arXiv2003

Inclusive b Decays to Wrong Sign Charmed Mesons

The production of wrong sign charmed mesons b -> \bar D_{(s)} X, D_{(s)}=(D0,D+,D_s), is studied using the data collected by the DELPHI experiment in the years 1994 and 1995. Charmed mesons in Z -> b bbar events are exclusively reconstructed by searching for the decays D0 -> K- pi+, D+ -> K- pi+ pi+ and D_s^+ -> phi pi+ -> K+ K- pi+. 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: Br(b -> \bar D0 X) + Br(b -> D- X) = (9.3 +/- 1.7(stat) +/- 1.3(syst) +/- 0.4(Br))%, Br(b -> D_s^- X) = (10.1 +/- 1.0(stat) +/- 0.6(syst) +/- 2.8(Br))% where the first error is statistical, the second and third errors are systematic.

hep-ex↗

arXiv2003

Search for resonant sneutrino production at sqrt(s) = 183 to 208 GeV

Searches for resonant sneutrino production in e+e- collisions under the assumption that R-parity is not conserved and that the dominant R-parity violating coupling is lambda_{121} or lambda_{131} used data recorded by DELPHI in 1997 to 2000 at centre-of-mass energies of 183 to 208 GeV. No deviation from the Standard Model was observed. Upper limits are given for the lambda_{121} and lambda_{131} couplings as a function of the sneutrino mass and total width. The limits are especially stringent for sneutrino masses equal to the centre-of-mass energies with the highest integrated luminosities recorded.

hep-ex↗

arXiv2003

Search for Doubly Charged Higgs Bosons at LEP2

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.

hep-ex↗

arXiv2003

Search for supersymmetric particles in light gravitino scenarios and sleptons NLSP

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.

hep-ex↗

arXiv2003

Search for an LSP gluino at LEP with the DELPHI detector

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 \tildeχ_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.

hep-ex↗

arXiv2002

Rapidity-Alignment and p_T Compensation of Particle Pairs in Hadronic Z0 Decays

Observation is made of rapidity-alignment of K+K- and ppbar pairs which results from their asymmetric orientation in rapidity, with respect to the direction from primary quark to antiquark. The K+K- and ppbar data are consistent with predictions from the fragmentation string model. However, the ppbar data strongly disagree with the conventional implementation of the cluster model. The non-perturbative process of `gluon splitting to diquarks' has to be incorporated into the cluster model for it to agree with the data. Local conservation of p_T between particles nearby in rapidity (i.e., p_T compensation) is analysed with respect to the thrust direction for pi+pi-, K+K-, and ppbar pairs. In this case, the string model provides fair agreement with the data. The cluster model is incompatible with the data for all three particle pairs. The model with its central premiss of isotropically-decaying clusters predicts a p_T correlation not seen in the data.

hep-ex↗

arXiv2002

Search for Charged Higgs Bosons in e+e- Collisions at sqrt(s)=189-202 GeV

A search for pair-produced charged Higgs bosons was performed in the high energy data collected by the DELPHI detector at LEP II at centre-of-mass energies from 189 GeV to 202 GeV. The three different final states, τντν, c \bar s \bar c s and c \bar s τνwere considered. New methods were applied to reject wrong hadronic jet pairings and for the tau identification, where a discriminator based on tau polarisation and polar angles was used. No excess of data compared to the expected Standard Model processes was observed and the existence of a charged Higgs boson with mass lower than 71.5 GeV/c^2 is excluded at the 95% confidence level.

hep-ex↗

arXiv2002

Searches for neutral Higgs bosons in e+e- collisions from sqrt(s) = 191.6 to 201.7 GeV

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.

hep-ex↗

arXiv2001

Search for Technicolor with DELPHI

Technicolor represents a viable alternative to the Higgs mechanism for generating gauge boson masses. Searches for technicolor particles rho_T and pi_T have been performed in the data collected by the DELPHI experiment at LEP at centre-of-mass energies between 192 and 208 GeV corresponding to an integrated luminosity of 452 pb^{-1}. Good agreement is observed with the SM expectation in all channels studied. This is translated into an excluded region in the (M_{pi_T},M_{rho_T}) plane. The rho_T production is excluded for all 90 < M_{rho_T} < 206.7 GeV/c^2. Assuming a point-like interaction of the pi_T with gauge bosons, an absolute lower limit on the charged pi_T mass at 95% CL is set at 79.8 GeV/c^2, independently of other parameters of the technicolor model.

hep-ex↗

arXiv1995

Radiation Rates for Low Z Impurities in Edge Plasmas

The role of impurity radiation in the reduction of heat loads on divertor plates in present experiments such as DIII-D, JET, JT-60, ASDEX, and Alcator C-Mod, and in planned experiments such as ITER and TPX places a new degree of importance on the accuracy of impurity radiation emission rates for electron temperatures below 250 eV for ITER and below 150 eV for present experiments. We have calculated the radiated power loss using a collisional radiative model for Be, B, C, Ne and Ar using a multiple configuration interaction model which includes density dependent effects, as well as a very detailed treatment of the energy levels and meta-stable levels. The "collisional radiative" effects are very important for Be at temperatures below 10 eV. The same effects are present for higher Z impurities, but not as strongly. For some of the lower Z elements, the new rates are about a factor of two lower than those from a widely used, simpler average-ion package (ADPAK) developed for high Z ions and for higher temperatures. Following the approach of Lengyel for the case where electron heat conduction is the dominant mechanism for heat transport along field lines, our analysis indicates that significant enhancements of the radiation losses above collisional radiative model rates due to such effects as rapid recycling and charge exchange recombination will be necessary for impurity radiation to reduce the peak heat loads on divertor plates for high heat flux experiments such as ITER.

plasm-ph↗

arXiv1995

Calculations of Energy Losses due to Atomic Processes in Tokamaks with Applications to the ITER Divertor

Reduction of the peak heat loads on the plasma facing components is essential for the success of the next generation of high fusion power tokamaks such as the International Thermonuclear Experimental Reactor (ITER) 1 . Many present concepts for accomplishing this involve the use of atomic processes to transfer the heat from the plasma to the main chamber and divertor chamber walls and much of the experimental and theoretical physics research in the fusion program is directed toward this issue. The results of these experiments and calculations are the result of a complex interplay of many processes. In order to identify the key features of these experiments and calculations and the relative role of the primary atomic processes, simple quasi-analytic models and the latest atomic physics rate coefficients and cross sections have been used to assess the relative roles of central radiation losses through bremsstrahlung, impurity radiation losses from the plasma edge, charge exchange and hydrogen radiation losses from the scrape-off layer and divertor plasma and impurity radiation losses from the divertor plasma. This anaysis indicates that bremsstrahlung from the plasma center and impurity radiation from the plasma edge and divertor plasma can each play a significant role in reducing the power to the divertor plates, and identifies many of the factors which determine the relative role of each process. For instance, for radiation losses in the divertor to be large enough to radiate the power in the divertor for high power experiments, a neutral fraction of 10-3 to 10-2 and an impurity recycling rate of netrecycle of ~ 10^16 s m^-3 will be required in the divertor.

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