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Showing papers by "Jalal Abdallah published in 2005"


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +373 moreInstitutions (44)
TL;DR: In this article, the DELPHI data was combined with earlier data to search for phenomena beyond the Standard Model and the measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the standard model processes was used to set limits on new physics.
Abstract: The production of single- and multi-photon events has been studied in the reaction e+e- -> gamma (gamma) + invisible particles. The data collected with the DELPHI detector during the years 1999 and 2000 at centre-of-mass energies between 191 GeV and 209 GeV was combined with earlier data to search for phenomena beyond the Standard Model. The measured number of light neutrino families was consistent with three and the absence of an excess of events beyond that predicted by the Standard Model processes was used to set limits on new physics. Both model-independent searches and searches for new processes predicted by supersymmetric and extra-dimensional models have been made. Limits on new non-standard model interactions between neutrinos and electrons were also determined.

182 citations


Journal ArticleDOI
TL;DR: In this paper, the first moments of the hadronic invariant mass and the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP.
Abstract: Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: m_b(1 GeV) = 4.591 +/- 0.062 +/- 0.039 +/- 0.005 GeV/c^2 m_c(1 GeV) = 1.170 +/- 0.093 +/- 0.055 +/- 0.005 GeV/c^2 mu_{pi}^2(1 GeV) = 0.399 +/- 0.048 +/- 0.034 +/- 0.087 GeV^2 \tilde{\rho}_D^3 = 0.053 +/- 0.017 +/- 0.011 +/- 0.026 GeV^3, and include corrections at order 1/m_b^3. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: |V_cb| = 0.0421 x (1 +/- 0.014 (meas.) +/- 0.014 (fit) +/- 0.015 (th.)).

33 citations


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +372 moreInstitutions (45)
TL;DR: In this article, a novel high precision method was proposed to measure the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000.
Abstract: A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b-quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b-quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: A_{FB}^b (89.449 GeV) = 0.0637 \pm 0.0143(stat.) \pm 0.0017(syst.) A_{FB}^b (91.231 GeV) = 0.0958 \pm 0.0032(stat.) \pm 0.0014(syst.) A_{FB}^b (92.990 GeV) = 0.1041 \pm 0.0115(stat.) \pm 0.0024(syst.) Combining these results yields the b-quark pole asymmetry A_{FB}^{b,0} = 0.0972 \pm 0.0030(stat.) \pm 0.0014(syst.)

25 citations


Journal ArticleDOI
TL;DR: In this paper, DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -> ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider.
Abstract: This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -> ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study a variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering and several models which include physics beyond the Standard Model: the exchange of Z' bosons, contact interactions between fermions, the exchange of gravitons in large extra dimensions and the exchange of sneutrino in R-parity violating supersymmetry.

24 citations


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +371 moreInstitutions (45)
TL;DR: In this paper, flavour independent searches for hadronically decaying neutral Higgs bosons in the DELPHI experiment at LEP, at centre-of-mass energies between 189 and 209 GeV, are described.
Abstract: This paper describes flavour independent searches for hadronically decaying neutral Higgs bosons in the data collected by the DELPHI experiment at LEP, at centre-of-mass energies between 189 and 209 GeV. The collected data-set corresponds to an integrated luminosity of around 610 pb(-1). The e(+)e(-) -> hA and e(+)e(-) -> hZand processes are considered, with direct Higgs boson decays into hadrons. No evidence for Higgs boson production is found, and cross-section limits are set as a function of the Higgs boson masses. No explicit assumptions are made on the underlying physics beyond the Standard Model, allowing interpretation of the data in a large class of models.

14 citations


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +373 moreInstitutions (45)
TL;DR: In this paper, Bose-Einstein correlations between final state particles in the reaction e(+)e(-) -> W+ W- -> q(1)(q(2)) over barq(3)(q (4)over bar>) over bar) have been studied.
Abstract: Bose-Einstein correlations (BEC) between final state particles in the reaction e(+)e(-) -> W+ W- -> q(1)(q(2)) over barq(3)(q(4)over bar>) over bar) have been studied. Data corresponding to a total integrated luminosity of 550 pb(-1), recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.

13 citations


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +376 moreInstitutions (47)
TL;DR: In this paper, the four-jet rate was used to measure alpha-s in the next-to-leading-order approximation, yielding alpha s(M_Z^2) = 0.1175 +/- 0.0030.
Abstract: Hadronic events from the data collected with the DELPHI detector at LEP within the energy range from 89 GeV to 209 GeV are selected, their jet rates are determined and compared to predictions of four different event generators. One of them is the recently developed APACIC++ generator which performs a massive matrix element calculation matched to a parton shower followed by string fragmentation. The four-jet rate is used to measure alpha_s in the next-to-leading-order approximation yielding alpha_s(M_Z^2) = 0.1175 +/- 0.0030. The running of alpha_s determined by using four-jet events has been tested. The logarithmic energy slope is measured to be d\alpha_s^{-1} / d\log E_{cm} = 1.14 +/- 0.36. Since the analysis is based on four-jet final states it represents an alternative approach to previous DELPHI alpha_s measurements using event shape distributions.

11 citations


Journal ArticleDOI
TL;DR: In this article, the topology dependence of the hadron production ratio is found to agree with a leading-order QCD prediction and the need for the presence of a destructive interference term gives evidence for the coherent nature of gluon radiation.

10 citations


Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +365 moreInstitutions (45)
TL;DR: In this article, the topology dependence of the event multiplicity is described by a modified leading logarithmic prediction, which yields a measurement of the colour factor ratio with the result C_A/C_F = 2.261 +/- 0.014.
Abstract: The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio C_A/C_F with the result C_A/C_F = 2.261 +/- 0.014 (stat.) +/- 0.036 (exp.) +/- 0.066 (theo.) in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios r=N_{gg}(s)/N_{q qbar}(s) of the gluon and quark multiplicities and r^{(1)}=N_{gg}'(s)/N_{q qbar}'(s) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r^{(1)}, larger deviations are found for r indicating that non-perturbative effects are more important for r than for r^{(1)}.

8 citations


Journal ArticleDOI
TL;DR: In this article, flavour independent searches for hadronically decaying neutral Higgs bosons in the data collected by the DELPHI experiment at LEP, at centre-of-mass energies between 189 and 209 GeV, are described.
Abstract: This paper describes flavour independent searches for hadronically decaying neutral Higgs bosons in the data collected by the DELPHI experiment at LEP, at centre-of-mass energies between 189 and 209 GeV. The collected data-set corresponds to an integrated luminosity of around 610 pb^{-1}. The e+e- -> hA and e+e- -> hZ processes are considered, with direct Higgs boson decays into hadrons. No evidence for Higgs boson production is found, and cross-section limits are set as a function of the Higgs boson masses. No explicit assumptions are made on the underlying physics beyond the Standard Model, allowing interpretation of the data in a large class of models.

8 citations


Journal ArticleDOI
TL;DR: In this paper, Bose-Einstein correlations between final state particles in the reaction e+e- -> W+W- -> q_1 anti-q_2 q_3 anti-Q_4 have been studied.
Abstract: Bose-Einstein correlations (BEC) between final state particles in the reaction e+e- -> W+W- -> q_1 anti-q_2 q_3 anti-q_4 have been studied. Data corresponding to a total integrated luminosity of 550 pb^{-1}, recorded by the DELPHI detector at centre-of-mass energies ranging from 189 to 209 GeV, were analysed. An indication for inter-W BEC between like-sign particles has been found at the level of 2.4 standard deviations of the combined statistical and systematic uncertainties.

Journal ArticleDOI
Jalal Abdallah, P. Abreu1, Wolfgang Adam2, Petar Adzic  +364 moreInstitutions (45)
TL;DR: In this paper, the DELPHI experiment was used to search for the charmed baryon Ξ0c and the beauty baryons Ξb in the hadronic Z decay channel.
Abstract: The charmed strange baryon Ξ0c was searched for in the decay channel Ξ0c → Ξ−π+, and the beauty strange baryon Ξb in the inclusive channel Ξb → Ξ−−¯νX, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992–1995. The Ξ− was reconstructed through the decay Ξ− → Λπ−, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Ξ0c and Ξb selection. The production rates were measured to be fΞ0c ×BR(Ξ0c → Ξ−π+) = (4.7 ± 1.4(stat.) ± 1.1(syst.)) × 10−4 per hadronic Z decay, and BR(b → Ξb)×BR(Ξb → Ξ−−X) = (3.0 ± 1.0(stat.) ± 0.3(syst.)) × 10−4 for each lepton species (electron or muon). The lifetime of the Ξb baryon was measured to be τΞb = 1.45+0.55 −0.43(stat.) ± 0.13(syst.) ps. A combination with the previous DELPHI lifetime measurement gives τΞb = 1.48+0.40 −0.31(stat.) ± 0.12(syst.) ps.

Journal ArticleDOI
TL;DR: In this paper, the topology dependence of the event multiplicity is described by a modified leading logarithmic prediction, which yields a measurement of the colour factor ratio with the result C_A/C_F = 2.261 +/- 0.014.
Abstract: The charged particle multiplicity in hadronic three-jet events from Z decays is investigated. The topology dependence of the event multiplicity is found to be well described by a modified leading logarithmic prediction. A parameter fit of the prediction to the data yields a measurement of the colour factor ratio C_A/C_F with the result C_A/C_F = 2.261 +/- 0.014 (stat.) +/- 0.036 (exp.) +/- 0.066 (theo.) in agreement with the SU(3) expectation of QCD. The quark-related contribution to the event multiplicity is subtracted from the three-jet event multiplicity resulting in a measurement of the multiplicity of two-gluon colour-singlet states over a wide energy range. The ratios r=N_{gg}(s)/N_{q qbar}(s) of the gluon and quark multiplicities and r^{(1)}=N_{gg}'(s)/N_{q qbar}'(s) of their derivatives are compared with perturbative calculations. While a good agreement between calculations and data is observed for r^{(1)}, larger deviations are found for r indicating that non-perturbative effects are more important for r than for r^{(1)}.

Journal ArticleDOI
TL;DR: In this paper, the charmed strange baryon Xi_c^0 was searched for in the decay channel Xi-c^ 0 -> Xi- pi+, and the beautiful baryons Xi_b in the inclusive channel Xi_ b → Xi- l- anti-nu X, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992--1995.
Abstract: The charmed strange baryon Xi_c^0 was searched for in the decay channel Xi_c^0 -> Xi- pi+, and the beauty strange baryon Xi_b in the inclusive channel Xi_b -> Xi- l- anti-nu X, using the 3.5 million hadronic Z events collected by the DELPHI experiment in the years 1992--1995. The Xi- was reconstructed through the decay Xi- -> Lambda pi-, using a constrained fit method for cascade decays. An iterative discriminant analysis was used for the Xi_c^0 and Xi_b selection. The production rates were measured to be f_{Xi_c^0} x BR(Xi_c^0 -> Xi- pi+)= (4.7 +/- 1.4 (stat.) +/- 1.1 (syst.))10^{-4} per hadronic Z decay, and BR(b -> Xi_b) x BR(Xi_b -> Xi- l- X)= (3.0 +/- 1.0 (stat.) +/- 0.3 (syst.))10^{-4} for each lepton species (electron or muon). The lifetime of the Xi_b baryon was measured to be tau_{Xi_b} = 1.45{^{+0.55}_{-0.43}} (stat.) +/- 0.13 (syst.) ps. A combination with the previous DELPHI lifetime measurement gives tau_{Xi_b} = 1.48{^{+0.40}_{-0.31}} (stat.) +/- 0.12 (syst.) ps.