LHCb

Abstract:

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.

Abstract:

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.

Abstract:

The production of φ mesons in the reaction e⁺p → e⁺φp (φ → K⁺K^-), for 7 < Q² < 25 GeV² and for virtual photon-proton centre of mass energies (W) in the range 42-134 GeV, has been studied with the ZEUS detector at HERA. When compared to lower energy data at similar Q², the results show that the γp → p⁰p cross section rises strongly with W. This behaviour is similar to that previously found for the γ*p → p⁰p cross section. This strong dependence cannot be explained by production through soft pomeron exchange. It is, however, consistent with perturbative QCD expectations, where it reflects the rise of the gluon momentum density in the proton at small x. The ratio of σ(φ)/σ(p⁰), which has previously been determined by ZEUS to be 0.065 ± 0.013 (stat.) in photoproduction at a mean W of 70 GeV, is measured to be 0.18 ± 0.05 (stat.) ± 0.03 (syst.) at a mean Q² of 12.3 GeV2 and mean W of ≈ 100 GeV and is thus approaching at large Q² the value of 2/9 predicted from the quark charges of the vector mesons and a flavour independent production mechanism.

Abstract:

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.

Abstract:

The first measurement of like-sign charged kaon correlations in hadronic decays of the Z⁰ is presented, based on data collected by the DELPHI detector. The charged kaons are identified by means of ring imaging Cherenkov detectors. A significant enhancement at small values of the four-momentum difference is observed in the ratio of like-sign to unlike-sign KK pairs and in the ratio of like-sign pairs to a simulated reference sample. An update of the measurement of K⁰sK⁰s interference is also presented. An enhancement is found in the production of pairs of K⁰s of similar momenta, as compared with a simulated reference sample. The measured Bose-Einstein correlation parameters λ and r are similar for charged and neutral kaon pairs. The value of the Bose-Einstein correlation strength λ is consistent with unity.