Search

16 pp. (1995)., A comparison of the inclusive photon energy spectrum in the radiative decay B → XS + γ, measured recently by the CLEO Collaboration, with the standard model is presented, using a B-meson wave function model and improving earlier perturbative QCD-based computations of the same. The dependence of the photon energy spectrum on the non-perturbative model parameters, pF, the b-quark Fermi momentum in the B hadron, and mq, the spectator quark mass, is explicitly shown, allowing a comparison of these parameters with the ones obtained from the analysis of the lepton energy spectrum in semileptonic B decays. Taking into account present uncertainties, we estimate BR(B → Xs + γ) = (2.55 ± 1.28) × 10−4 in the standard model, assuming . Comparing this with the CLEO measurement BR(B → Xs + γ) = (2.32±0.67) × 10−4 implies , in agreement with the CKM unitarity.

12 pp. (1995)., A precise measurement of the spectrum of the photons fromep bremsstrahlung with the ZEUS luminosity monitor at HERA is reported. The measurement shows a reduced rate compared to the Bethe-Heitler spectrum for photon energies below 5 GeV. This suppression, called the beam-size effect, is explained by the finite transverse size of the beam overlap relative to the typical impact parameter in the process ofep bremsstrahlung at HERA energies.

27 pp. (1993)., Implications of the recent CLEO observation [1] of the rare decay mode $B→K^*+γ$ having a combined branching ratio BR($B→K^*+γ$)=(4.5±1.5±0.9)×10−5 and an improved upper limit on the inclusive branching ratio BR(B→Xs+γ)-108 GeV. Within the SM, we show that the resulting experimental upper limit can be interpreted as a corresponding limit on the CKM-matrix element ratio yielding $|V_{ts} |/|V_{cb} |$1.6×10−5 [1,2]. Combining the exclusive and inclusive decay rates, we determine 0.50≤|Vts|/|Vcb|≤1.67 (at 95% C.L.).

7 pp. (1990)., We have searched for axion and light Higgs boson production in the channel $ϒ (1S)$ → $(a^0 or h^0) + γ$, where the non-interacting axion a0 and the Higgs boson $h^0$ do not decay in the detector. We find no evidence for an axion and give an upper limit,$ Br(ϒ (1S) → a^0γ) < 4.0 × 10^{−5} (90% CL)$, for long-lived axions. Combining our limit with the previous search in J/ψ decays, we are able to rule out the axion in the standard model with first order QCD corrections. Our $ϒ (1S)$ data also rule out a Higgs boson with mass mh < 86 MeV.

133 pp. (1986)., The cascade reaction $e^+e^- \to \Upsilon' \to \gamma X_b \to \gamma \gamma \Upsilon \to \gamma \gamma (\mu^+ \mu^-$ or $e^+e^-)$ has been studied with the Crystal Ball detector at the $e^+e^-$ storage ring DORIS-II. Two $x_b$ states are observed by monoenergetic photon lines at 107.7 ± 1.1 ± 1.0 MeV and 132.4 ± 0.9 ± 1.0 MeV, with amplitudes of 56 ± 6 and 82 ± 10 events correspondingly. Upper limits for full widths of those states at 90 % confidence level are < 6.2 MeV and < 6.9 MeV respectively...

91 pp. (1985).

88 pp. (1987).

Angular correlations in the cascade reaction e+e−→Υ(2S)→γχb, χb→γΥ, Υ→μ+μ− or Υ→e+e−, have been used for the first time to investigate the spins of the χb states. The results support the χb spins predicted by the potential models of heavy quarkonia.

7 pp. (1985).

29 pp. (1985).

128 pp. (1984)., The production of photons, neutral pions and $\eta$ - mesons in multihadronic events is investigated with the JADE detector at the electron - positron storage ring PETRA.The production properties of photons are in good agreement with theore- tical expectations from fragmentation models and quantum electrodynamics. The energy spectra scale with the centre of mass energy. Photon multiplicities as well as the photonic energy fraction are measured.Neutral pions are reconstructed by their decay into two photons. The corresponding energy spectra show scaling and agree with those of charged pions in the covered range.$\eta$ - mesons are observed in the two photon mass spectrum. Their energy spectrum is softer than the spectra of other mesons. The study of $\eta$ - meson production in special event - and jet- topologies suggests enhanced production rates in gluon fragmentation.A comparison of all measured photon sources dem onstrates the dominant production of inclusive photons from decays of neutral pions.

106 pp. (1986).

34 pp. (1996).