LHCb

Abstract:

Analysis of the rapidity structure of charge correlations in hadronic events from Z0 decays gives evidence for chain-like charge-ordering of particle production along the thrust axis, as predicted by 'QCD-motivated string-like fragmentation models. © 1997 Published by Elsevier Science B.V.

Abstract:

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.

Abstract:

An inclusive measurement of the average multiplicity of bb̄ pairs from gluons, gbb̄, in hadronic Z⁰ events collected by the DELPHI experiment at LEP, is presented. A counting technique, based on jet b-tagging in 4-jet events, has been used. Looking for secondary bottom production in events with production of any primary flavour, by requiring two b-tagged jets in well defined topological configurations, gave gbb̄ = (0.21 ± 0.11(stat) ± 0.09(syst))%. This result was checked with a different method designed to select events with four b quarks in the final state. Agreement within the errors was found.© 1997 Elsevier Science B.V.

Abstract:

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.

Abstract:

Diffractive dissociation of quasi-real photons at a photon-proton centre of mass energy of W ≈ 200 GeV is studied with the ZEUS detector at HERA. The process under consideration is γp → XN, where X is the diffractively dissociated photon system of mass MX and N is either a proton or a nucleonic system with mass MN < 2 GeV. The cross section for this process in the interval 3 < MX < 24 GeV relative to the total photoproduction cross section was measured to be σDpartial/σtot = 6.2 ± 0.2(stat) ± 1.4(syst)%. After extrapolating this result to the mass interval of mφ2 < MX2 < 0.05W2 and correcting it for proton dissociation, the fraction of the total cross section attributed to single diffractive photon dissociation, γp → Xp, is found to be σSD/σtot = 13.3 ± 0.5(stat) ± 3.6(syst)%. The mass spectrum of the dissociated photon system in the interval 8 < MX < 24 GeV can be described by the triple pomeron (IP IP IP) diagram with an effective pomeron intercept of αIP(0) = 1.12 ± 0.04(stat) ± 0.08(syst). The cross section for photon dissociation in the range 3 < MX < 8 GeV is significantly higher than that expected from the triple pomeron amplitude describing the region 8 < MX < 24 GeV. Assuming that this discrepancy is due to a pomeron-pomeron-reggeon (IP IP IR) term, its contribution to the diffractive cross section in the interval 3 < MX < 24 GeV is estimated to be fIP IP IR = 26 ± 3(stat) ± 12(syst)%. © Springer-Verlag 1997.