Search

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 A, a lepton and an oppositely charged pion; the impact parameter distribution of 441 muons with high transverse momentum accompanied by a A in the same jet; and the proper decay time distribution of 125 A0-lepton decay vertices with the A, exclusively reconstructed through its pKπ, pK0 and A3π decay modes. The combined result is: 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 T (b-baryon) = (1.255+0.115-0.102(stat)0102 ± 0.05) ps. © Springer-Verlag 1996., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Semileptonic decays B→ D*-ℓ+νX were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*-π+ states was performed and the ratio of the branching fractions: Br(B → D*-ℓ+νX)/Br(B → D*-+νX) + Br(B0 → + D*-ℓ+ν) = 0.19 ± 0.10(stat) ± 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B0 → D*-ℓ+ν was measured as a function of the momentum transfer from the B to the D*- in two separate analyses, using exclusive and inclusive methods of D*- reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of {pipe}Vcb{pipe} times the normalization of the decay form factor F(q2max): F(q2max){pipe}Vcb{pipe} = (35.4 ± 1.9(stat) ± 2.4(syst)) · 10-3. The value of {pipe}Vcb{pipe} was computed using theoretical calculations of F(q2max), giving: {pipe}Vcb{pipe} = (38.9 ± 2.0(stat) ± 2.6(syst) ± 1.7(theory)) · 10-3. The total branching fraction Br(B0 → D*-ℓ+ν) was determined to be: Br(130, D*-ℓ+v) = (5.52 ± 0.17(stat) ± 0.68(syst))%. © Springer-Verlag 1996., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A partial wave analysis of the π0π0 system produced centrally in pp collisions at 450 GeV/c shows evidence for the f0(980), f0(1300) and f0(1500) resonances. f2(1270) is observed dominantly in the D-0 wave. A broad enhancement is seen in the D-waves below 1 GeV. © 1999 Published by Elsevier Science B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

The π0π0 system produced in charge-exchange π-p interactions at a primary momentum of 100 GeV/c has been studied. The data employed come from the experiment that was performed at the CERN SPS accelerator and which recorded photons from π0 decays with the aid of the hodoscopic multiphoton GAMS-4000 spectrometer. A partial-wave analysis of the π0π0 system in the mass interval between 0.8 and 3 GeV has been performed with allowance for the S, D, G, and J waves. The S wave has a rather complicated structure, displaying a series of four bumps separated by three dips at about 1, 1.5, and 2 GeV. This suggests the existence of several scalar resonances. The higher waves show clear peaks corresponding to the f2(1270), f4(2050), and f6(2510) mesons, which are produced predominantly via one-pion exchange. The parameters of these mesons and their production cross sections have been determined., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The reaction π-p → ηπ0n at primary π- meson momenta of 32, 38, and 100 GeV/c has been studied by using the GAMS facilities. A partial-wave analysis has been performed in the effective-mass range 0.77 ≤ Mηπ0 < 182 GeV/c2. A peak associated with the a2 meson is clearly seen in the D+-wave. The difference of the D+-and P+-wave phases changes abruptly in the region of the a2 mass. A significant contribution of the P+ wave is observed at the a2-mass value and above, but this wave does not show a clear-cut resonance behavior. No significant contribution from exchanges of unnatural spin-parity are observed with the exception of the S-wave contribution in the region of the a0 mass and the D0-wave contribution in the region of the a2 mass., SCOPUS: ar.j, info:eu-repo/semantics/published

In an analysis of multihadronic events recorded at LEP by DELPHI in the years 1992 through 1994, rapidity correlations of A-A, proton-proton, and A-proton pairs are compared with each other and with the predictions of the string fragmentation model. For Ap̄ pairs, the additional correlation with respect to charged kaons is also analysed. © 1998 Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The π0π0-system produced in the charge exchange π-p-reaction at 100 GeV/c has been studied. The experiment was performed at the GERN SPS accelerator with the multiphoton hodoscope spectrometer GAMS-4000. A partial wave analysis was carried out in the mass range from 0.8 GeV to 3.0 GeV at -t < 0.2 (GeV/c)2 with the S, D, G and J waves. The S-wave exhibits rather complicated behaviour with a series of four bumps separated by three dips, at 1 GeV, 1.5 GeV and 2 GeV, which give the evidence for several scalar resonances. Clear peaks corresponding to the f2(1270), f4(2050) and f6(2510) mesons are seen in the higher waves. All the three mesons are produced via a dominating one pion t-channel exchange. The parameters and production cross sections of these mesons are measured., SCOPUS: ar.j, info:eu-repo/semantics/published

The spin density matrix elements for the ρ0, K*0(892) and φ produced in hadronic Z0 decays are measured in the DELPHI detector. There is no evidence for spin alignment of the K*0(892) and φ in the region xp ≤ 0.3 (xp = p/pbeam), where ρ00 = 0.33 ± 0.05 and ρ00 = 0.30 ± 0.04, respectively. In the fragmentation region, xp ≥ 0.4, there is some indication for spin alignment of the ρ0 and K*0(892), since ρ00 = 0.43 ± 0.05 and ρ00 = 0.46 ± 0.08, respectively. These values are compared with those found in meson-induced hadronic reactions. For the φ, ρ00 = 0.30 ± 0.04 for xp ≥ 0.4 and 0.55 ± 0.10 for xp ≥ 0.7. The off-diagonal spin density matrix element ρ1 - 1 is consistent with zero in all cases.© 1997 Published by Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The measurement of the correlation between the transverse spin components of τ+ τ- pairs collected during 1992 to 1994 with the DELPHI detector at LEP1 is presented. A value CTT = 0.87 ± 0.20 (stat.) +0.10-0.12 (syst.) was obtained for the correlation parameter, in agreement with the Standard Model expectation. © 1997 Published by Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A search with the DELPHI detector at LEP for excited leptons (e*, μ*, τ* and v*) decaying through γ, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb-1 at an e+e- centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits me* > 79.6 GeV/c2, mμ* > 79.6 GeV/c2, mτ* > 79.4 GeV/c2 and mv* > 56.4 GeV/c2 at 95% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio λ/mℓ* of the coupling of the excited lepton to its mass., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

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 αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: αs(133 GeV) = 0.116 ± 0.007exp-0.004theo+0.005 from the high energy data. © Springer-Verlag 1997., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The hadronic fragmentation functions of the various quark flavours and of gluons are measured in a study of the inclusive hadron production from Z0 decays with the DELPHI detector and are compared with the fragmentation functions measured elsewhere at energies between 14 GeV and 91 GeV. A large scaling violation is observed, which is used to extract the strong coupling constant from a fit using a numerical integration of the second order DGLAP evolution equations. The result is αs(Mz) = 0.1241+0.006-0.007(exp) ±0.009(theory) where the first error represents the experimental uncertainty and the second error is due to the factorization and renormalization scale dependence. © 1997 Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A study of the channel e+e- → μ+μ-γISR, where γISR is an initial state radiation photon, is presented using data collected by the DELPHI experiment from 1991 to 1994. The total cross-section at effective annihilation energies (√s′) below the Z0 peak is obtained by using the events with relatively hard initial state radiative photon(s) (Eγ > 1 GeV). The differential cross-section as a function of the muon polar production angle is also determined in order to extract the forward-backward asymmetries for the reaction e+e- → μ+μ- at energies √s′ between 20 and 87 GeV. The ratio of the helicity cross-sections σLL+σRR/σRL+σ LR, where the two subscripts stand for the helicities of the incoming e- and outgoing μ- respectively, is extracted from the differential cross-sections in order to test the Standard Model and to look for new physics near 80 GeV. No deviations from the Standard Model were found. © Springer-Verlag 1997., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The spin-parity of the ηπ0π0 system from the charge-exchange transition π-p → ηπ0π0n is analyzed for mass values up to 1.9 GeV. Data used in this analysis come from the GAMS-4000 multiphoton spectrometer irradiated by a 100-GeV/c π- beam of the SPS accelerator at CERN. Experimental mass spectra show distinct signals from the pseudoscalar mesons η(1295) and ι/η(1440) and from the axial-vector meson D/f1(1285). The values found for their masses and widths agree well with the world-average values. The cross sections for the production of the above mesons are measured, and the relative branching fractions for some of their decays are estimated. The decay η(1295) → ηπ0π is found to be dominated by the a0(980)π0 channel. On the other hand, the decay ι/η(1440) → a0(980)π0 is dominated by the η(π0π0)S channel, whereas the a0(980)π0 contribution is small. This suggests that t is an exotic meson with a significant component of valence gluons., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Correlations between pions from different Ws in e+e- → W+W- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four- momentum difference of the pions. © 1997 Published by Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A search for stable or long-lived heavy charged particles in e+e- interactions at energies of 130-136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e and ±2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c2. Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c2 for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/c2 can be excluded at 95% confidence level. © 1997 Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A search for stable or long-lived heavy charged particles in e+e- interactions at energies of 130-136, 161 and 172 GeV has been performed using the data taken by the DELPHI experiment at LEP. The search is based on particle identification provided by the Time Projection Chamber and the Ring Imaging Cherenkov detector. Upper limits at 95% confidence level are derived on the cross-section for heavy long-lived pair-produced charge ±e and ±2/3e particles in the range of 0.4-2.3 pb for masses from 45 to 84 GeV/c2. Within supersymmetric extensions of the Standard Model, long-lived charginos with masses from 45 to 84 (80) GeV/c2 for high (low) sneutrino masses can be excluded at 95% confidence level. Left-handed (right-handed) long-lived or stable smuons and staus with masses between 45 and 68 (65) GeV/c2 can be excluded at 95% confidence level. © 1997 Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Correlations between pions from different Ws in e+e- → W+W- events are studied using data collected by the DELPHI detector at LEP running at a centre-of-mass energy of 172 GeV in 1996. At the present level of statistics, no enhancement of the correlation function above that expected from a pair of uncorrelated W's is observed at small values of the four- momentum difference of the pions. © 1997 Published by Elsevier Science B.V., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A search for fully reconstructed Λ0b beauty baryons is performed using about 3 million Ζ 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 Λ+cπ- channel and one in the Λ+ca-1 channel over a small background. The Λ0b beauty baryon mass is measured to be (5668 ± 16 (stat.) ± 8 (syst.)) MeV/c2., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

This letter reports the results of the measurement of single photon production in the reaction e+e- → γ+ invisible particles at centre-of-mass energies √s = 130 and 136 GeV and an integrated luminosity of 5.83 pb-1, collected with the DELPHI detector at LEP. The signal is compatible with the prediction of the Standard Model for the process e+e- → vv̄γ, and the number of neutrino families has been determined to be Nv, = 3.1 ± 0.6. Limits have been derived on anomalous neutral gauge boson couplings and on compositeness in the framework of a specific model., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The inclusive production of the f′2(1525) in hadronic Z0 decays has been studied in data collected by the DELPHI detector at LEP. The Ring Imaging Cherenkov detectors were important tools in the identification of the decay f′2(1525) → K+K-. The average number of f′2(1525) produced per hadronic Z decay, 〈f′2〉 = 0.020 ± 0.005 (stat) ± 0.006 (syst), and the momentum distribution of the f′2(1525) have both been measured. The mass and width of the f′2(1525) are found to be 〈M f′2〉 = 1535 ± 5 (stat) ± 4 (syst) MeV/c2, 〈Γ f′2〉 = 60 ± 20 (stat) ± 19 (syst) MeV/c2., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

During the last 1995 data acquisition period at LEP, the DELPHI experiment collected an integrated luminosity of 5.9 pb-1 at centre-of-mass energies of 130 GeV and 136 GeV. Radiative leptonic events (e, μ, τ) with high energy photons were studied and compared to Standard Model predictions. The data were used to search for charged excited leptons decaying through an electromagnetic transition. No significant signal was found. From the search for pair produced excited leptons, the limits me* > 62.5 GeV/c2, mμ* > 62.6 GeV/c2 and mτ* > 62.2 GeV/c2 at 95% confidence level were established. For single excited lepton production, upper limits on the ratio λ/mℓ* of the coupling of the excited charged lepton to its mass were derived., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be 〈nch〉 = 23.84 ± 0.51 (stat) ± 0.52(syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value αs(130 GeV) = 0.105 ± 0.003(stat) ± 0.008(syst)., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A measurement of the mass difference, Δmd, between the two physical Bd0 states has been obtained from the analysis of the impact parameter distribution of a lepton emitted at large transverse momentum (pt) relative to the jet axis and from the analysis of the flight distance distribution of secondary vertices tagged by either a high pt lepton or an identified kaon. In the opposite hemisphere of the event, the charge of the initial quark has been evaluated using a high pt lepton, a charged kaon or the mean jet charge. With 1.7 million hadronic Z0 decays recorded by DELPHI between 1991 and 1993, Δmd is found to be: {Mathematical expression}. © 1996 Springer-Verlag., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Semileptonic decays B → D*- ℓ+νX were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*- π+ states was performed and the ratio of the branching fractions: Br(B → D*- ℓ+νX)/Br(B → D*- ℓ+νX) + Br(B0 → D*- ℓ+ν) = 0.19 ± 0.10(stat) ± 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B0 → D*- ℓ+ν was measured as a function of the momentum transfer from the B to the D*- in two separate analyses, using exclusive and inclusive methods of D*- ℓ+ reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of, 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The inclusive production of the neutral vector mesons K*0(892) and φ(1020), and of the tensor meson K2*0(1430), in hadronic decays of the Z has been measured by the DELPHI detector at LEP. The average production rates per hadronic Z decay have been determined to be 0.77 ± 0.08 K*0(892), 0.104 ± 0.008 φ(1020) and 0.079 ± 0.040 K2*0(1430). The ratio of the tensor-to-vector meson production yields, 〈K2*0(1430)〉/〈K *0(892)〉 = 0.10± 0.05, is smaller than the 〈f2(1270)〉/〈ρ0(770)〉 and 〈f2′(1525)〉 /〈φ(1020)〉 ratios measured by DELPHI. The production rates and differential cross sections are compared with the predictions of JETSET 7.4 tuned to the DELPHI data and of HERWIG 5.8. The K*0(892) and φ(1020) data are compatible with model predictions, but a large disagreement is observed for the K2*0(1430)., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The partial decay width of the Z to bb̄ quark pairs has been measured by the DELPHI detector at LEP. B-hadrons, containing b-quarks, were tagged by several methods using tracks with large impact parameters to the primary vertex complemented sometimes by event shape variables or using leptons with high transverse momentum relative to the hadron. In order to reduce the systematic uncertainties, in all methods the b-tagging efficiency has been extracted directly from the data. Combining all methods, the value: Γbb̄/Γhad = 0.2216 ± 0.0016(stat.) ± 0.0021(syst.) was found, where the cc̄ production fraction was fixed to its Standard Model value. © Springer-Verlag 1996., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A mass-independent partial-wave analysis of the reaction π-p → ηπ0n is performed in the ηπ0 mass range above 1.6 GeV. The analysis employs the S, P, D, F, and G waves and is based on experimental data collected with the GAMS-2000 multiphoton spectrometer in a 38-GeV/c pion beam extracted from the 70-GeV accelerator of IHEP. A resonance with quantum numbers JPC = 4++ and IG = 1- is observed in the G wave. Its mass and width are measured to be M = 2010 ± 20 MeV and Γ = 370 ± 80 MeV. The mechanism of the observed a04-meson production is dominated by natural-spin-parity exchange in the t channel. The measured unnaturalto-natural cross-section ratio is 0.60 ± 0.16., SCOPUS: ar.j, info:eu-repo/semantics/published

A search for pair production of the lightest chargino at √s = 130.4 and 136.3 GeV has been carried out using the data sample corresponding to the 5.92 pb-1 recorded by the DELPHI detector during the high energy run of LEP in the last period of 1995. The theoretical reference model has been the Minimal Supersymmetric Standard Model with R-parity conservation. The three topologies expected for the decay of a pair of charginos, namely two acoplanar leptons plus missing energy (ℓℓ), two jets and an isolated lepton plus missing energy (jjℓ) and missing energy in a hadronic environment (√s), were investigated. No evidence of a signal was found. Lower mass limits were derived for various scenarios, including the case of a low mass difference between the chargino and the neutralino and of a light sneutrino. The mass limits range between 56.3 GeV/c2 and the kinematic limit., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Using data accumulated by DELPHI during the November 1995 LEP run at 130-136 GeV, searches have been made for events with jets or leptons in conjunction with missing momentum. The results are interpreted in terms of limits on the production of neutralinos, scalar leptons, and scalar quarks., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

An upper limit for BR(Z0 -»3g) is obtained from a correlation method, which distinguishes statistically between quark and gluon jets by using the difference in their charged particle multiplicity distributions. From the sample of threefold symmetric three-jet events collected by the DELPHI experiment at LEP during 1991-1994, the 95% confidence level upper limit is deduced to be: BR(Zn -> 3g) < 1.6 x 10~2 for the JADE and BR(Z0 -> 3g) < 1.5 x 10~2 for the DURHAM jet-finder., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Results are presented of a search for pair production of heavy objects decaying into four hadronic jets, as expected for example from associated or pair production of MSSM Higgs bosons, hAor H+H-, using a data sample of 5.9 pb-1 of e+e- collisions at √s = 130-136 GeV collected with the DELPHI detector at LEP in November 1995. The data and expectations from standard processes agree after four-jet selections. An analysis based on b-tagging finds no hA candidate with high mass. A study optimized to search for H+H- events with mass in the 40-50 GeV/c2 range also finds no candidate. Finally a comparison is made with a recent ALEPH analysis which found an excess of four-jet events with high multiplicity and high mass. Such a signal is not observed in the DELPHI data, although a slight excess in the mass region around 105 GeV/c2 is seen., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

An upper limit for BR(Z0 -»3g) is obtained from a correlation method, which distinguishes statistically between quark and gluon jets by using the difference in their charged particle multiplicity distributions. From the sample of threefold symmetric three-jet events collected by the DELPHI experiment at LEP during 1991-1994, the 95% confidence level upper limit is deduced to be: BR(Zn -> 3g) < 1.6 x 10~2 for the JADE and BR(Z0 -> 3g) < 1.5 x 10~2 for the DURHAM jet-finder., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Using data accumulated by DELPHI during the November 1995 LEP run at 130-136 GeV, searches have been made for events with jets or leptons in conjunction with missing momentum. The results are interpreted in terms of limits on the production of neutralinos, scalar leptons, and scalar quarks., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A search for pair production of the lightest chargino at √s = 130.4 and 136.3 GeV has been carried out using the data sample corresponding to the 5.92 pb-1 recorded by the DELPHI detector during the high energy run of LEP in the last period of 1995. The theoretical reference model has been the Minimal Supersymmetric Standard Model with R-parity conservation. The three topologies expected for the decay of a pair of charginos, namely two acoplanar leptons plus missing energy (ℓℓ), two jets and an isolated lepton plus missing energy (jjℓ) and missing energy in a hadronic environment (√s), were investigated. No evidence of a signal was found. Lower mass limits were derived for various scenarios, including the case of a low mass difference between the chargino and the neutralino and of a light sneutrino. The mass limits range between 56.3 GeV/c2 and the kinematic limit., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

An excess of events containing, in a jet, a samesign Ξ∓-ℓ∓ pair as compared to those with an oppositesign Ξ∓-ℓ± pair has been observed in an analysis of 1.7 million hadronic Z0 decays collected by the DELPHI detector at LEP between 1991 and 1993 inclusive. The probability for this signal to come from non B-baryon decays is less than 5×10-4. The measured production fraction corresponds to:[Figure not available: see fulltext.] per lepton species, averaged for electrons and muons and assuming that the two channels have an equal contribution. Semileptonic decays of Λb baryons can account for less than 10% of these events and the major part of the signal has to originate from Ξb semileptonic decays. Using the subsample of these events where the Ξ∓ trajectory has been measured in the Vertex Detector, the lifetime of B-baryons producing a Ξ∓ in their semileptonic decay final state is found to be: {Mathematical expression} © 1995 Springer-Verlag., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A high-statistics study of the π0π0-system produced in the π-p→π0π0n reaction at 38GeV/c has been carried out at the IHEP accelerator using the GAMS-2000 multiphoton spectrometer. A partial-wave analysis which includes S, D0, D- and D+ waves has been performed in the, SCOPUS: ar.j, info:eu-repo/semantics/published

A partial-wave analysis of the ω ωπ0-system produced in the π-p→ωπ0n reaction at 38 GeV/c beam momentum has been performed. A new 5-- meson state, ρ5(22350), with a mass M=2330±35 MeV and a width Γ=400±100 MeV, is observed. The analysis also confirms the 1-- ρ(2150) meson, a radial-orbital excitation of the ρ(770), observed earlier by the GAMS Collaboration. © 1995 Springer-Verlag., SCOPUS: ar.j, info:eu-repo/semantics/published

An analysis is presented of inclusive π 0 production in Z 0 decays measured with the DELPHI detector. At low energies, π 0 decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to {Mathematical expression}) 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 qq and bb events. The number of π 0's per hadronic Z 0 event is N(π 0)/Z had 0 =9.2±0.2(stat)±1.0(syst) and for bb events the number of π 0's is N(π 0)/bb=10.1±0.4(stat)±1.1(syst). The ratio of the number of π 0's in bb events to hadronic Z 0 events is less affected by the systematic errors and is found to be 1.09±0.05±0.01. The measured π 0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the ξ p=ln(1/xp) distribution is ξ* p =3.90 -0.14 +0.24 .The average number of π 0's from the decay of primary B hadrons is found to be N(B→π 0 X)/B hadron=2.78±0.15(stat)±0.60(syst). © 1996 Springer-Verlag., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

An analysis is reported on the channel e+e-→μ+μ- (nγ), n=1,2. using data taken with the DELPHI detector at LEP from 1990 to 1992. Differential cross sections of the radiative photons as a function of photon energy and of the angle between the photon and the muon are presented. No significant deviations from expectations are observed. The data are also used to extract the muon-pair cross section and asymmetry below the Z0 peak by using those events with relatively hard initial state radiative photon(s). The measured cross section and asymmetry show no significant deviation from the Standard Model expectations. These results together with the DELPHI cross section and asymmetry measurements at the LEP energies from the 1990 to 1992 running periods are used to determine limits on the Z0-Z′ gauge boson mixing angle θZ′ and on the Z′ mass. There is no indication of the existence of a Z′; the limits obtained on the mixing angle substantially improve upon existing limits. The 95% confidence level allowed ranges of θZ′ in various models are: {Mathematical expression} © 1995 Springer-Verlag., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

A sample of events enriched in bb̄ quark pairs was selected in the data recorded by the DELPHI experiment at LEP during 1992 and 1993, by the presence of secondary decay vertices from short-lived particles. Using this sample, the average multiplicities of Ks0, K±, p(p̄), Λ(Λ) and of charged particles in bb̄ events have been measured, distinguishing the component from fragmentation and the component coming from the decay of b-hadrons. The measurement of the average charge multiplicity in bb̄ events was used to compute the mean fractional beam energy carried by the primary b-hadron, and the difference in charged particle multiplicity between bb̄ events and light quark (uū, dd̄, ss̄) events. © 1995., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The hadronic photon structure function F 2 γ has been measured in the Q 2 range from 4 to 30 GeV2/c 4 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 F 2 γ parameterizations with special emphasis on their low x behaviour. A result on the Q 2 evolution of F 2 γ is presented. © 1996 Springer-Verlag., 0, SCOPUS: ar.j, info:eu-repo/semantics/published