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234 records were found.

We present fits to charmless strangeless hadronic B decay data for mean branching ratios and CP-violating asymmetries using the QCD factorization model of Beneke et al. Apart from one CP-violating parameter, the model gives a very good representation of 26 measured data. We find the CKM angle α=(93.5±8.4-1.3)° and to be quite stable to plausible "charming penguin" corrections.
We present fits to charmless strangeless hadronic B decay data for mean branching ratios and CP-violating asymmetries using the QCD factorization model of Beneke et al. Apart from one CP-violating parameter, the model gives a very good representation of 26 measured data. We find the CKM angle α=(93.5±8.4-1.3)° and to be quite stable to plausible "charming penguin" corrections.
A study of strange particle production in nu(mu) charged cur- rent interactions has been performed using the data from the NOMAD experiment. Yields of neutral strange particles (K-S(0), Lambda, (Λ) over bar) have been measured. Mean multiplicities are reported as a function of the event kinematic variables E-nu W-2 and Q(2) as well as of the variables describing particle behaviour within a hadronic jet: x(F), z and p(T)(2). Decays of resonances and heavy hyperons with identified K, and A in the final state have been analyzed. Clear signals corresponding to K*+/-, Sigma(*+/-), Xi(-) and Sigma(0) have been observed.
The inclusive production of the meson resonances ρ0(770), f0(980) and f2(1270) in neutrino–nucleus charged current interactions has been studied with the NOMAD detector exposed to the wide band neutrino beam generated by 450 GeV protons at the CERN SPS. For the first time the f0(980) meson is observed in neutrino interactions. The statistical significance of its observation is 6 standard deviations. The presence of f2(1270) in neutrino interactions is reliably established. The average multiplicity of these three resonances is measured as a function of several kinematic variables. The experimental results are compared to the multiplicities obtained from a simulation based on the Lund model. In addition, the average multiplicity of ρ0(770) in antineutrino–nucleus interacti...
Backward proton and pi (-) production has been studied in nu (mu) CC interactions with carbon nuclei. Detailed analyses of the momentum distributions, of the production rates, and of the general features of events with a backward going particle, have been carried out in order to understand the mechanism producing these particles. The backward proton data have been compared with the predictions of the reinteraction and the short range correlation models.
Results from the v, appearance search in a neutrino beam using the full NOMAD data sample are reported. A new analysis unifies all the hadronic tau decays, significantly improving the overall sensitivity of the experiment to oscillations. The "blind analysis" of all topologies yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90% CL allowed region in the sin(2)2 theta (mu tau)-Deltam(2) plane which includes sin(2)2 theta (mu tau) lt 3.3 x 10(-4) at large Deltam(2) and Deltam(2) lt 0.7 eV(2)/c(4) at sin(2) 2 theta (mu tau) = 1. The corresponding contour in the nu (e) → nu (tau) oscillation hypothesis results in sin(2) 2 theta (l tau) lt 1.5 x 10(-2) at large Deltam(2) and Deltam(2) lt 5.9 eV(2)/c(4) at sin(2) 2 theta (l tau) = 1. We also derive limits on effective couplings of the ...
We report on a search for heavy neutrinos ( nu /sub 4/) produced in the decay D/sub s/ to tau nu /sub 4/ at the SPS proton target followed by the decay nu /sub 4/ to nu /sub tau /e/sup +/e/sup -/ in the NOMAD detector. Both decays are expected to occur if nu /sub 4/ is a component of nu /sub tau /. From the analysis of the data collected during the 1996-1998 runs with 4.1*10/sup 19/ protons on target, a single candidate event consistent with background expectations was found. This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the nu /sub 4/ mass range from 10 to 190 MeV. Windows between the SN1987 A and big bang nucleosynthesis lower limits and our result are still open for future experimental searches. The results obtained are used to constrain an interpretation of the time a...
We carried out a model-independent search for light scalar or pseudoscalar particles a's (an example of which is the axion) that couple to two photons by using a photon-regeneration method at high energies allowing a substantial increase in the sensitivity to eV masses. The experimental set-up is based on elements of the CERN West Area Neutrino Facility (WANF) beam line and the NOMAD neutrino detector. The new particles, if they exist, could be produced through the Primakoff effect in interactions of high energy photons, generated by the 450 GeV protons in the CERN SPS neutrino target, with virtual photons from the WANF horn magnetic field. The particles would penetrate the downstream shielding and would be observed in the NOMAD neutrino detector through their re-conversion into real high energy photons by interacting with the virtual ...
Updated results from the appearance searches for nu(mu) → nu(tau) and nu(e) → nu(tau) oscillations in the full NOMAD data sample are reported. The increased data and the use of more refined kinematic schemes for the nu(tau) CC selection allow a significant improvement of the overall sensitivity. The "blind analysis" of both the deep-inelastic and the low multiplicity samples yields no evidence for an oscillation signal. In the two-family oscillation scenario, this sets a 90% C.L. region in the sin(2)2 theta(mu tau) - Delta m(2) plane which includes sin(2)2 theta(mu tau) lt 4.4 X 10(-4) at large Delta m(2) and Delta m(2) lt 0.8 eV(2)/c(4) at sin(2)2 theta(mu tau) = 1. The corresponding contour in the nu(e) → nu(tau) oscillation hypothesis results in sin(2)2 theta(e tau) lt 2.2 X 10(-2) at large Delta m(2) and Delta m(2) lt 6.5 e...
The Lambda polarization in upsilon (mu) charged current interactions has been measured in the NOMAD experiment. The event sample (8087 reconstructed Lambda 's) is more than an order of magnitude larger than that of previous bubble chamber experiments, while the quality of event reconstruction is comparable. We observe negative polarization along the W-boson direction which is enhanced in the target fragmentation region: P-x(x(F) lt 0) = -0.21 +/- 0.04(stat) +/- 0.02(sys). In the current fragmentation region we find P-x(x(F) gt 0) = -0.09 +/- 0.06(stat) +/- 0.03(sys). These results provide a test of different models describing the nucleon spin composition and the spin transfer mechanisms. A significant transverse polarization tin the direction orthogonal to the Lambda production plane! has been observed for the first time in a neutr...
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