Updated precision measurement of the average lifetime of B hadrons

The measurement of the average lifetime of B hadrons using inclusively reconstructed secondary vertices has been updated using both an improved processing of previous data and additional statistics from new data. This has reduced the statistical and systematic uncertainties and gives \tau_{\mathrm{B}} = 1.582 \pm 0.011\ \mathrm{(stat.)} \pm 0.027\ \mathrm{(syst.)}\ \mathrm{ps.} Combining this result with the previous result based on charged particle impact parameter distributions yields \tau_{\mathrm{B}} = 1.575 \pm 0.010\ \mathrm{(stat.)} \pm 0.026\ \mathrm{(syst.)}\ \mathrm{ps.

Measurement of the Quark and Gluon Fragmentation Functions in Z0 Hadronic Decays

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in e+e- collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse σΤ and longitudinal σL components of the total hadronic cross section σtot are evaluated from the measured fragmentation functions. They are found to be σΤ/σtot = 0.949 ± 0.001(stat.) ± 0.007(syst.) and σL/σtot = 0.051 ± 0.001(stat) ± 0.007(syst.) respectively. The strong coupling constant is calculated from σL/σtot in next-to-leading order of perturbative QCD, giving αs(Mz) = 0.120 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) .Including non-perturbative power corrections leads to αs(Mz) = 0.101 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) .The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, 〈nch〉 = 21.21 ± 0.01(stat.) ± 0.20(syst.) The fragmentation functions and multiplicities in bb̄ and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Measurement of the quark and gluon fragmentation functions in Z0 hadronic decays

The transverse, longitudinal and asymmetric components of the fragmentation function are measured from the inclusive charged particles produced in e+e- collisions at LEP. As in deep inelastic scattering, these data are important for tests of QCD. The transverse σΤ and longitudinal σL components of the total hadronic cross section σtot are evaluated from the measured fragmentation functions. They are found to be σΤ/σtot = 0.949 ± 0.001(stat.) ± 0.007(syst.) and σL/σtot = 0.051 ± 0.001(stat) ± 0.007(syst.) respectively. The strong coupling constant is calculated from σL/σtot in next-to-leading order of perturbative QCD, giving αs(Mz) = 0.120 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) . Including non-perturbative power corrections leads to αs(Mz) = 0.101 ± 0.002(stat.) ± 0.013(syst.) ± 0.007(scale) . The measured transverse and longitudinal components of the fragmentation function are used to estimate the mean charged multiplicity, 〈nch〉 = 21.21 ± 0.01(stat.) ± 0.20(syst.) The fragmentation functions and multiplicities in bb̄ and light quark events are compared. The measured transverse and longitudinal components of the fragmentation function allow the gluon fragmentation function to be evaluated

A measurement of the photon structure function F2 γ at an average Q2 of 12 GeV2/c4

The hadronic photon structure function F2 γ has been measured in the Q2 range from 4 to 30 GeV2/c4 and down to x values of order 0.001, using data taken with the DELPHI detector at LEP between 1991 and 1993. A comparison is made with several F2 γ parameterizations with special emphasis on their low x behaviour. A result on the Q2 evolution of F2 γ is presented. © Springer-Verlag 1996

Search for exclusive decays of the Lambda(b) baryon and measurement of its mass

A search for fully reconstructed Λb0 beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the Λc+π− channel and one in the Λc+a1− channel over a small background. The Λb0 beauty baryon mass is measured to be (5668 ± 16 (stat.) ± 8 (syst.)) MeV/c2

Determination of the average lifetime of b-baryons

The average lifetime of b-baryons has been studied using 3 × 106 hadronic Z0 decays collected by the DEL-PHI detector at LEP. Three methods have been used, based on the measurement of different observables: the proper decay time distribution of 206 vertices reconstructed with a Λ, a lepton and an oppositely charged pion; the impact parameter distribution of 441 muons with high transverse momentum accompanied by a Λ in the same jet; and the proper decay time distribution of 125 Λc-lepton decay vertices with the Λc exclusively reconstructed through its pKπ, pK0 and Λ3π decay modes. The combined result is: τ(b-baryon) = (1.254-0.109+0.121(stat) ±0.04(syst)-0.05+0.03(syst)) ps where the first systematic error is due to experimental uncertainties and the second to the uncertainties in the modelling of the b-baryon production and semi-leptonic decay. Including the measurement recently published by DELPHI based on a sample of proton-muon vertices, the average b-baryon lifetime is : τ(b-baryon) = (1.255-0.102+0.115(stat) ±0.05) ps. © Springer-Verlag 1996

Observation of short range three particle correlations in e+ e- annihilations at LEP energies

Measurements are presented of short range three-particle correlations in e+e- annihilations at LEP using data collected by the DELPHI detector. At small values of the four-momentum difference, strong three-particle correlations are observed for like-sign (+++ and ---) and for unlike-sign (++- and +--) pion combinations which are not a consequence of two-particle correlations. A possible explanation of the observed effects in like-sign combinations is the existence of higher order Bose-Einstein interference, which significantly changes the particle distributions in jets.0SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Strange baryon production in Z hadronic decays

A study of the production of strange octet and decuplet baryons in hadronic decays of the Z recorded by the DELPHI detector at LEP is presented. This includes the first measurement of the ∑± average multiplicity. The total and differential cross sections, the event topology and the baryon-antibaryon correlations are compared with current hadronization models. © 1995 Springer-Verlag