0000000000191828
AUTHOR
V Lapin
showing 13 related works from this author
B* production in Z decays
1995
The decay B*→Bγ has been observed with the DELPHI detector at LEP, where the B* meson is produced in Z boson decays. The combination of inclusively reconstructed B mesons with well-measured converted photons yields a measurement of the flavour-averaged B*-B mass difference of 45.5±0.3 (stat.) ±0.8 (syst.) MeV/c2. 95% confidence level upper limits at 6 MeV/c2 are placed on both the isospin (i.e. B+-B0) and the Bs-Bud splitting of the mass difference. The production ratio of B* to B mesons in Z decays is measured to be 0.72±0.03 (stat.) ±0.06 (syst.). Limits on the production cross-section of other hypothetical excited B hadron states decaying radiatively are established. The differential B* …
Measurements of the Lineshape of the $Z^{0}$ and Determination of Electroweak Parameters from its Hadronic and Leptonic Decays
1994
Abstract: During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450000 Z0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z0 resonance. Model independent fits to the cross sections and leptonic forward-backward asymmetries yield the following Z0 parameters: the mass and total width M(Z) = 91.187 +/- 0.009 GeV, GAMMA(Z) = 2.486 +/- 0.012 GeV, the hadronic and leptonic partial widths GAMMA(had) = 1.725 +/- 0.012GeV, GAMMA(l) = 83.01 +/- 0.52 MeV, the invisible width GAMMA(inv) = 51…
DETERMINATION OF ALPHA(S) FOR B-QUARKS AT THE Z(0) RESONANCE
1993
The strong coupling constant for b quarks has been determined, and its flavour independence, as predicted by QCD, investigated. The analysis involved events with lepton candidates selected from approximately 356 000 hadronic decays of the Z0, collected by the DELPHI detector at LEP in 1990 and 199 1. A method based on a direct comparison of the three-jet fraction in a b enriched sample, selected by requiring leptons with large momenta and transverse momenta, to that of the entire hadronic sample, illustrated the significant effect of the b quark mass on the multi-jet cross section, and verified the flavour independence of the strong coupling constant to an accuracy of +/- 6%. A second proce…
Photon events with missing energy at root s=183 to 189 GeV
2000
The production of single photons has been studied in the reaction e+e- -> gamma + invisible particles at centre-of-mass energies of 183 GeV and 189 GeV. A previously published analysis of events with multi-photon final states accompanied by missing energy has been updated with 189 GeV data. The data were collected with the DELPHI detector and correspond to integrated luminosities of about 51 pb^{-1} and 158 pb^{-1} at the two energies. The number of light neutrino families is measured to be 2.84 +/- 0.15(stat) +/- 0.14(syst). The absence of an excess of events beyond that expected from Standard Model processes is used to set limits on new physics as described by supersymmetric and compos…
Measurement of inclusive pi(0) production in hadronic Z(0) decays
1996
An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \…
DETERMINATION OF ALPHA-S FROM THE SCALING VIOLATION IN THE FRAGMENTATION FUNCTIONS IN E+E- ANNIHILATION
1993
A determination of the hadronic fragmentation functions of the Z0 boson is presented from a study of the inclusive hadron production with the DELPHI detector at LEP. These fragmentation functions were compared with the ones at lower energies, thus covering data in a large kinematic range: 196 less-than-or-equal-to Q2 less-than-or-equal-to 8312 GeV2 and x (= p(h)/E(beam)) > 0.08. A large scaling violation was observed, which was used to extract the strong coupling constant in second order QCD: alpha(s)(M(Z)) = 0.118 +/- 0.005. The corresponding QCD scale for five quark flavours is: LAMBDA(MS)(5)BAR = 230 +/- 60 MeV.
W pair production cross-section and W branching fractions in $e^{+}e^{-}$ interactions at 189 GeV
2000
The cross-section for the process e+e- -> W+W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 189 GeV and corresponding to an integrated luminosity of 155 pb^{-1}. Based on the 2392 events selected as WW candidates, the cross-section for the doubly resonant process e+e- -> W+W- has been measured to be 15.83 +- 0.38 (stat) +- 0.20 (syst) pb. The branching fractions of the W decay were also measured and found to be in good agreement with the Standard Model expectation. From these a value of the CKM mixing matrix element |V_{cs}| = 1.001 +- 0.040 (stat) +- 0.020 (syst) was derived.
The Scale Dependence of the Hadron Multiplicity in Quark and Gluon Jets and a Precise Determination of $C_{A}/C_{F}$
1999
\frac{C_A}{C_F} = 2.246 \pm 0.062~(stat.) \pm 0.080~(syst.) \pm 0.095~(theo.) Data collected at the Z resonance using the DELPHI detector at LEP are used to determine the charged hadron multiplicity in gluon and quark jets as a function of a transverse momentum-like scale. The colour factor ratio, \cacf, is directly observed in the increase of multiplicities with that scale. The smaller than expected multiplicity ratio in gluon to quark jets is understood by differences in the hadronization of the leading quark or gluon. From the dependence of the charged hadron multiplicity on the opening angle in symmetric three-jet events the colour factor ratio is measured to be: C_A/C_F = 2.246 \pm 0.0…
Measurement of Event Shape and Inclusive Distributions at $\sqrt{s} =$ 130 and 136 GeV
1997
Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine $\alpha_s$ from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: % %\alpha_s…
Hadronic Shower Development in Iron-Scintillator Tile Calorimetry
2000
The lateral and longitudinal profiles of hadronic showers detected by a prototype of the ATLAS Iron-Scintillator Tile Hadron Calorimeter have been investigated. This calorimeter uses a unique longitudinal configuration of scintillator tiles. Using a fine-grained pion beam scan at 100 GeV, a detailed picture of transverse shower behavior is obtained. The underlying radial energy densities for four depth segments and for the entire calorimeter have been reconstructed. A three-dimensional hadronic shower parametrization has been developed. The results presented here are useful for understanding the performance of iron-scintillator calorimeters, for developing fast simulations of hadronic showe…
Measurement of the charged particle multiplicity of weakly decaying B hadrons
1998
From the Z decays recorded in 1994 and 1995 by the DELPHI detector at LEP, the charged particle multiplicity of weakly decaying B hadrons was measured to be: 4.97 +/- 0.03 +/- 0.06 excluding the K-o and Lambda decay products. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
Multiplicity fluctuations in one- And two-dimensional angular intervals compared with analytic QCD calculations
1999
Multiplicity fluctuations in rings around the jet axis and in off-axis cones have been measured by the DELPHI collaboration in $e^+e^-$ annihilations into hadrons at LEP energies. The measurements are compared with analytical perturbative QCD calculations for the corresponding multiparton system, using the concept of Local Parton Hadron Duality. Some qualitative features are confirmed by the data but substantial quantitative deviations are observed.
Measurement and Interpretation of Fermion-Pair Production at LEP Energies of 183 and 189 GeV
2000
An analysis of the data collected in 1997 and 1998 with the DELPHI detector at e+e- collision energies close to 183 and 189 GeV was performed in order to extract the hadronic and leptonic fermion-pair cross-sections, as well as the leptonic forward-backward asymmetries and angular distributions. The data are used to put limit on contact interactions between fermions, the exchange of R-parity violating SUSY sneutrinos, Z' bosons and the existence of gravity in extra dimensions.