Inclusive Particle Production at LEP

New results on inclusive production of Sigma^- and Lambda(1520) and on proton production in quark and gluon jets are presented. These results are based on 2 million hadronic Z decays collected with the DELPHI detector at LEP. They are compared with the results of other LEP experiments and with models. It has been shown that the total production rates of all light-flavour hadrons measured so far at LEP 1 follow phenomenological laws related to the spin, isospin, strangeness and mass of the particles. A significant proton enhancement in gluon jets is observed, indicating that baryon production proceeds directly from colour objects.Comment: LaTeX with moriond.sty; 4 pages with 2 eps-figures. Talk given at the 35th Rencontres de Moriond on QCD and High Energy Hadronic Interactions, Les Arcs, France, March 18-25, 2000. To be published in the Proceeding

Determination of the strangeness contents of light-flavour isoscalars from its production rates in hadronic Z decays measured at LEP

A new phenomenological approach is suggested to determine the strangeness contents of light-flavour isoscalars. This approach is based on phenomenological laws of hadron production related to the spin, isospin, strangeness content and mass of the particles. The ``effective'' numbers of s and \bar{s} quarks in the isoscalar partners i_1 and i_2 are given by the nonstrange-strange mixing angle \phi: k(i_1)=2\sin^2\phi and k(i_2)=2\cos^2\phi. From the total production rates per hadronic Z decay of all light-flavour hadrons measured so far at LEP the values for k are found to be: k(\eta) \equiv 2-k(\eta^{\prime}) = 0.91 \pm 0.12, k(\phi) \equiv 2-k(\omega) = 1.94 \pm 0.09, k(f_2^{\prime}) \equiv 2-k(f_2) = 1.84 \pm 0.21 and k(f_0) = 0.09 \pm 0.13. Our results on the \eta--\eta^{\prime}, \omega--\phi and f_2--f_2^{\prime} isoscalar mixing are consistent with the present experimental evidence. Quite remarkably, our value for k(\eta) corresponds to the singlet-octet mixing angle \theta_P = -12.4^{\circ} \pm 3.5^{\circ}. The obtained strangeness content of the f_0(980) scalar/isoscalar is not consistent with the values supported by different model studies. However, taking the f_0(980) in our analysis with the mass of the bare state (K-matrix pole) f_0^{bare}(720 \pm 100), the mixing angle is found to be: |\phi_S^{bare}| = 73^{\circ} \pm 7^{\circ} \pm 24^{\circ}, in good agreement with the prediction of the K-matrix analysis.Comment: 12 pages, 2 figure

Massless spinning particle and null-string on AdSdAdS_d: projective-space approach

Massless spinning particle and tensionless string models on $AdS_d$ background in the projective-space realization are proposed as constrained Hamiltonian systems. Various forms of particle and string Lagrangians are derived and classical mechanics is studied including the Lax-type representation of the equations of motion. After that transition to the quantum theory is discussed. Analysis of potential anomalies in the tensionless string model necessitates introduction of ghosts and BRST charge. It is shown that quantum BRST charge is nilpotent for any $d$ if coordinate-momentum ordering for the phase-space bosonic variables, Weyl ordering for the fermions and $cb$ ($\gamma\beta$) ordering for ghosts is chosen, while conformal reparametrizations and space-time dilatations turn out to be anomalous for the ordering in terms of positive and negative Fourier modes of the phase-space variables and ghosts.Comment: 23 pages, v4: In the title and abstract added adjective 'Massless'. In subsection 2.2 the material has been rearranged to streamline the presentation and also a comment added to explain the notation. Minor improvements of the text and further typos corrected. Version accepted for publicatio

Determination of the strangeness content of light-flavour isoscalars from their production rates in hadronic Z decays at LEP

A new phenomenological approach is suggested for determining the strangeness content of light-flavour isoscalars. This approach is based on phenomenological laws of hadron production related to the spin, isospin, strangeness content and mass of the particles. From the total production rates per hadronic Z decay of all light-flavour hadrons, measured so far at LEP, the values of the nonstrange-strange mixing angles are found to be |\phi_P| = 42.3^{\circ} \pm 3.5^{\circ}, |\phi_V| = 10^{\circ} \pm 8^{\circ}, |\phi_T| = 16^{\circ} \pm 11^{\circ} and |\phi_S| = 13^{\circ} \pm 9^{\circ}. Our results on the \eta-\eta^{\prime}, \omega-\phi and f_2-f_2^{\prime} isoscalar mixing are consistent with the present experimental evidence. The strangeness content obtained for the f_0(980) scalar/isoscalar is not consistent with the values supported by recent model studies and is discussed further in the framework of our approach and the K-matrix analysis.Comment: Talk given at the 9th International Conference on Hadron Spectroscopy (Protvino, 2001), 4 pages with 2 figure

Study of charge multiplicity in hadronic three-jet Z decays at LEP

The mean charge multiplicity in hadronic three-jet Z decays has been measured with the DELPHI detector as a function of the event topology and compared with recent theoretical calculations. The QCD colour factor ratio C_A/C_F was determined, and the gluon contribution to this multiplicity was extracted giving a measurement of the mean charge multiplicity of a two-gluon colour-singlet system as a function of the effective c.m. energy covering the range from 16 to 52 GeV.Comment: Talk given at the 32nd International Symposium on Multiparticle Dynamics (ISMD 2002), Alushta, Ukraine, September 7 - 13, 2002; 4 pages with 2 eps-figure