Publications (620)1192.33 Total impact
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ABSTRACT: The hadronic part of the Electron Structure Function (ESF) has been measured for the first time, using e+e data collected by the DELPHI experiment at LEP, at centreofmass energies sqrt(s) = 91.2209.5 GeV. The data analysis is simpler than that of the measurement of the photon structure function. The ESF data are compared to predictions of phenomenological models based on the photon structure function. It is shown that the quasireal photon virtuality contribution is significant. The presented data can serve as a crosscheck of the photon structure function analyses and help in refining existing parametrizations.Physics Letters B 10/2014; 737(7):39. · 4.57 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The nature of bquark jet hadronisation has been investigated using data taken at the Z peak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying bhadrons, E^weak_B. The average value of x^weak_B = E^weak_B/E_beam is measured to be 0.699 +/ 0.011. The resulting x^weak_B distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the nonperturbative contribution to be used in studies of bhadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA~6.156 from DELPHI data: a= 1.84^{+0.23}_{0.21} and b=0.642^{+0.073}_{0.063} GeV^2, with a correlation factor rho = 92.2%. Combining the data on the bquark fragmentation distributions with those obtained at the Z peak by ALEPH, OPAL and SLD, the average value of x^weak_B is found to be 0.7092 +/ 0.0025 and the nonperturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a= 1.48^{+0.11}_{0.10} and b=0.509^{+0.024}_{0.023} GeV^2, with a correlation factor rho = 92.6%.European Physical Journal C 10/2011; 71(2). · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The nature of bquark jet hadronisation has been investigated using data taken at the Zpeak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying bhadrons, EBweakE_{\mathrm{B}}^{\mathrm{weak}}. The average value of xweakB = EBweak/Ebeamx^{\mathrm{weak}}_{\mathrm{B}} = E_{\mathrm{B}}^{\mathrm{weak}}/E_{\mathrm{beam}} is measured to be 0.699±0.011. The resulting xweakBx^{\mathrm{weak}}_{\mathrm{B}} distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the nonperturbative contribution to be used in studies of bhadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA6.156 from DELPHI data: a = 1.84+0.230.21and b=0.642+0.0730.063GeV2,a= 1.84^{+0.23}_{0.21}\quad\mbox{and}\quad b=0.642^{+0.073}_{0.063}~\mathrm{GeV}^{2}, with a correlation factor ρ=92.2%. Combining the data on the bquark fragmentation distributions with those obtained at the Zpeak by ALEPH, OPAL and SLD, the average value of xweakBx^{\mathrm{weak}}_{\mathrm{B}} is found to be 0.7092±0.0025 and the nonperturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a = 1.48+0.110.10and b=0.509+0.0240.023GeV2,a= 1.48^{+0.11}_{0.10}\quad\mbox{and}\quad b=0.509^{+0.024}_{0.023}~\mathrm{GeV}^{2}, with a correlation factor ρ=92.6%.European Physical Journal C 02/2011; 71(2):129. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Single top quark production via fourfermion contact interactions associated to flavourchanging neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centreofmass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1pb−1. No evidence for a signal was found. Limits on the energy scale Λ, were set for scalar, vector and tensorlike coupling scenarios.European Physical Journal C 02/2011; 71(2):113. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.European Physical Journal C 06/2010; 67(3):343366. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The data taken by DELPHI at centreofmass energies between 189 and 209 GeV are used to place limits on the CPconserving trilinear gauge boson couplings Delta_g1z, lambda_gamma and Delta_kappag associated to W+W and single W production at LEP2. Using data from the jjlv, jjjj, jjX and lX final states, where j, l and X represent a jet, a lepton and missing fourmomentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Delta_g1z = 0.025^{+0.033}_{0.030}, lambda_gamma = 0.002^{+0.035}_{0.035} and Delta_kappag = 0.024^{+0.077}_{0.081} . Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by DELPHI.European Physical Journal C 03/2010; 66(12):35. · 5.25 Impact Factor 
Article: Measurements of CPconserving trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at LEP2
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ABSTRACT: The data taken by Delphi at centreofmass energies between 189and 209GeV are used to place limits on the CPconserving trilinear gauge boson couplings DgZ1\Delta g^{Z}_{1}, λ γ and Δκ γ associated to W + W − and single W production at Lep2. Using data from the jj ℓ ν, jjjj, jjX and ℓ X final states, where j, ℓ and X represent a jet, a lepton and missing fourmomentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: ${l}\Delta g^Z_1=0.025^{+0.033}_{0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{0.081}.$\begin{array}{l}\Delta g^Z_1=0.025^{+0.033}_{0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{0.081}.\end{array} Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by Delphi.European Physical Journal C 03/2010; 66(1):3556. · 5.25 Impact Factor 
Article: Measurements of CPconserving trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at LEP2
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ABSTRACT: The data taken by Delphi at centreofmass energies between 189 and 209 GeV are used to place limits on the CPconserving trilinear gauge boson couplings , λ γ and Δκ γ associated to W + W − and single W production at Lep2. Using data from the jj ℓ ν, jjjj, jjX and ℓ X final states, where j, ℓ and X represent a jet, a lepton and missing fourmomentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by Delphi.European Physical Journal C 02/2010; 66(12):3556. · 5.25 Impact Factor 
Article: Inclusive single particle production in twophoton collisions at LEP II with the DELPHI detector
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ABSTRACT: A study of the inclusive charged hadron production in twophoton collisions is described. The data were collected with the DELPHI detector at LEP II. Results on the inclusive singleparticle pTpT distribution and the differential charged hadrons dσ/dpTdσ/dpT crosssection are presented and compared to the predictions of perturbative NLO QCD calculations and to published results.Physics Letters B 08/2009; 678(5):444. · 4.57 Impact Factor 
Article: A Study of $b\overline{b}$ Production in $e^{+}e^{}$ Collisions at $\sqrt{s}$ = 130207 GeV
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ABSTRACT: Measurements are presented of R_b, the ratio of the b bbar crosssection to the q qbar crosssection in e+e collisions, and the forwardbackward asymmetry A^b_FB at twelve energy points in the range sqrt(s) = 130207 GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.European Physical Journal C 03/2009; 60(1):1. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Single photons detected by the DELPHI experiment at LEP2 in the years 19972000 are reanalysed to investigate the existence of a single extra dimension in a modified ADD scenario with slightly warped large extra dimensions. The data collected at centreofmass energies between 180 and 209 GeV for an integrated luminosity of ~650 pb^{1} agree with the predictions of the Standard Model and allow a limit to be set on graviton emission in one large extra dimension. The limit obtained on the fundamental mass scale M_D is 1.69 TeV/c^2 at 95% CL, with an expected limit of 1.71 TeV/c^2.European Physical Journal C 03/2009; 60(1):1723. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The production of two highp_T jets in the interactions of quasireal photons in e+e collisions at sqrt{s_ee} from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e luminosity of 550 pb^{1}. The jets reconstructed by the k_T cluster algorithm are defined within the pseudorapidity range 1 < eta < 1 and with jet transverse momentum, p_T, above 3 GeV/c. The differential dijet crosssection is measured as a function of the mean transverse momentum ptmean of the jets and is compared to perturbative QCD calculations.European Physical Journal C 02/2009; 58(4):531541. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Measurements are presented of R b, the ratio of the b[`(b)]{\mathrm{b}}\bar{\mathrm{b}} crosssection to the q[`(q)]{\mathrm{q}}\bar{\mathrm{q}} crosssection in e+e− collisions, and the forwardbackward asymmetry A FBb at twelve energy points in the range Ös=130\sqrt{s}=130 –207GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.European Physical Journal C 01/2009; 60(1):115. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In a study of the reaction e − e +→W − W + with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse–transverse (TT), longitudinal–transverse plus transverse–longitudinal (LT) and longitudinal–longitudinal (LL) have been determined using the final states WW®lnq[`(q)]WW{\rightarrow}l\nu q\bar{q} (l=e,μ). The twoparticle joint polarisation probabilities, i.e. the spin density matrix elements ρ TT , ρ LT , ρ LL , are measured as functions of the W − production angle, qW\theta _{W^{}}, at an average reaction energy of 198.2GeV. Averaged over all cosqW\cos\theta_{W^{}}, the following joint probabilities are obtained: [`(r)]TT=(67±8)%,\bar{\rho}_{TT}=(67\pm8)\%, [`(r)]LT=(30±8)%,\bar{\rho}_{LT}=(30\pm8)\%, [`(r)]LL=(3±7)%.\bar{\rho}_{LL}=(3\pm7)\%. These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation crosssections σ TT , σ LT and σ LL are also presented.European Physical Journal C 01/2009; 63(4):611623. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The production of two highp T jets in the interactions of quasireal photons in e + e − collisions at Ö{see}\sqrt{s_{ee}} from 189GeV to 209GeV is studied with data corresponding to an integrated e + e − luminosity of 550pb−1. The jets reconstructed by the k ⊥ cluster algorithm are defined within the pseudorapidity range −1<η<1 and with jet transverse momentum, p T , above 3GeV/c. The differential dijet crosssection is measured as a function of the mean transverse momentum [`(pT)]\overline{p_{T}} of the jets and is compared to perturbative QCD calculations.European Physical Journal C 11/2008; 58(4):531541. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The production of two highp_T jets in the interactions of quasireal photons in e+e collisions at sqrt{s_ee} from 189 GeV to 209 GeV is studied with data corresponding to an integrated e+e luminosity of 550 pb^{1}. The jets reconstructed by the k_T cluster algorithm are defined within the pseudorapidity range 1 < eta < 1 and with jet transverse momentum, p_T, above 3 GeV/c. The differential dijet crosssection is measured as a function of the mean transverse momentum ptmean of the jets and is compared to perturbative QCD calculations.European Physical Journal C 11/2008; 58(4):531. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2 < E_gamma <= 1 GeV and transverse momentum with respect to the parent muon p_T < 40 MeV/c, and 1 < E_gamma <= 10 GeV and p_T < 80 MeV/c . A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z^0 decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06 +/ 0.12 +/ 0.07 in the photon energy range 0.2 < E_gamma <= 1 GeV and 1.04 +/ 0.09 +/ 0.12 in the photon energy range 1 < E_gamma <= 10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.European Physical Journal C 11/2008; 57(3):499. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2<E γ ≤1GeV and transverse momentum with respect to the parent muon p T <40MeV/c, and 1<E γ ≤10GeV and p T <80MeV/c. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z 0 decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06±0.12±0.07 in the photon energy range 0.2<E γ ≤1GeV and 1.04±0.09±0.12 in the photon energy range 1<E γ ≤10GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP.European Physical Journal C 09/2008; 57(3):499514. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The effect of the heavy bquark mass on the two, three and fourjet rates is studied using LEP data collected by the DELPHI experiment at the Z peak in 1994 and 1995. The rates of bquark jets and light quark jets (l = uds) in events with n = 2, 3, and 4 jets, together with the ratio of two and fourjet rates of bquarks with respect to lightquarks, R_n^bl, have been measured with a doubletag technique using the CAMBRIDGE jetclustering algorithm. A comparison between experimental results and theory (matrix element or Monte Carlo event generators such as PYTHIA, HERWIG and ARIADNE) is done after the hadronisation phase. Using the fourjet observable R_4^bl, a measurement of the bquark mass using massive leadingorder calculations gives: m_b(M_Z) = 3.76 +/ 0.32 (stat) +/ 0.17 (syst) +/ 0.22 (had) +/ 0.90 (theo) GeV/c^2 . This result is compatible with previous threejet determinations at the M_Z energy scale and with low energy mass measurements evolved to the M_Z scale using QCD Renormalisation Group Equations.European Physical Journal C 05/2008; 55(4):525. · 5.25 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996–2000). The data sample has an integrated luminosity of 660 pb1 and was collected over a range of centreofmass energies from 161 to 209 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W→ℓν̄ℓqq̄’ and W+W→qq̄’q̄q’ channels. The W mass result for the combined data set is MW=80.336±0.055(Stat.)±0.028(Syst.)±0.025(FSI)±0.009(LEP)GeV/c2, where FSI represents the uncertainty due to final state interaction effects in the qq̄’q̄q’ channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is ΓW=2.404±0.140(Stat.)±0.077(Syst.)±0.065(FSI)GeV/c2. These results supersede all values previously published by the DELPHI collaboration.European Physical Journal C 05/2008; 55(1):1. · 5.25 Impact Factor
Publication Stats
671  Citations  
1,192.33  Total Impact Points  
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Institutions

2007–2011

University of Ljubljana
 Department of Physics
Ljubljana, Ljubljana, Slovenia


2001–2011

Bergische Universität Wuppertal
Wuppertal, North RhineWestphalia, Germany
