Experimental constraints on weak mixing angles in the six quark scheme

Experimental results on charm production by neutrinos and onB meson decays are used to derive bounds on the quark mixing anglesθ ₂ andθ ₃ in the six quark model of Kobayashi and Maskawa.     

New far-infrared laser lines produced by resonant Q-branch-pumping of CH3F

Conclusion We showed that by pumping the ₃-Q-branch of CH₃F using the 9P-branch radiation produced by a continuously tunable 20 atmospheres CO₂ laser all Q-branch transitions with quantum number 5J28 can be pumped. From the 23 laser lines with frequencies from 10 cm^–1 to 47 cm^–1, 13 were detected for the first time. The optimum operating pressure for the FIR laser was 11 Torr.     

Beckmann-Umlagerung und Fragmentierung,IV. Teil. 5- und 7-Zentren-Fragmentierung von γ-Keto-ketoximen: Fragmentierungsreaktionen, 21. Mitteilung

A heterolytic 7-centre fragmentation reaction of the type a-b-c-d-e-f-X → a b + c = d + e = f + X has been demonstrated for the first time utilizing γ-keto-ketoximes. This system may also undergo a novel 5-centre fragmentation. With sodium hydroxide in aqueous ethanol and with sodium ethoxide in ethanol the p-toluene-sulfonate of 1-oxo-9-methyl-5-oximino-trans-decalin (7b) is converted quantitatively into 9-cyano-6-methyl-non-5-enoic acid (10b) and the corresponding ethyl ester, respectively. With lower concentrations of nucleophile normal Beckmann rearrangement to the lactam 13a and the lactimether 19b predominates. In the case of the p-toluenesulfonate of the 9-nor-derivative 7a a base-induced 5-centre fragmentation reaction to the α,β-unsaturated ketone 12 competes with 7-centre fragmentation to 9-cyano-non-5-enoic acid (10a), strong bases favouring the former reaction. In the absence of strong bases of nucleophiles Beckmann rearrangement again dominates.     

Quasioptical superconducting hot electron bolometer for submillmeter waves

We report on a superconducting hot electron bolometer coupled to radiation via a broadband antenna. The bolometer, a structured NbN film, was patterned on a thin dielectric membrane between terminals of a gold slotline antenna. We investigated the response to submillimeter radiation (wave-lengths 0.1 mm to 0.7 mm) in the fundamental Gaussian mode. We found that the directivity of the antenna was constant within a factor of 2.5 through the whole experimental range. The noise equivalent power of the bolometer at 119 µm was 3 · 10^–13 W/Hz^1/2; a time constant of 160 ps was estimated.     

Prompt neutrino production in a proton beam-dump experiment

In the interactions of 400 GeV/c protons with copper nuclei, a flux of prompt neutrinos is observed. The reactions produced by these neutrinos in our apparatus appear consistent with those of electron- and muon-neutrinos. The prompt neutrino fluxes are interpreted as being due to associated production and subsequent semileptonic decay of charmed hadrons. The prompt flux ratio \(\bar v_\mu /v_\mu = 0.46_{ - 0.16}^{ + 0.21} \) suggests a sizeable production of charmed baryons near the forward direction. The ratio of prompte ^?+e ⁺ toµ ^?+µ ⁺ event rates is 0.64 _?0.15 ^+0.22 , where unity is expected frome-μ universality.     

Determination of the gluon distribution in the nucleon from deep inelastic neutrino scattering

The observed scaling violations of the nucleon structure functionF ₂ and \(\bar q\) have been analysed in the framework of perturbative QCD to determine the shape and magnitude of the gluon distribution. The data are in good agreement with leading order QCD, and the simultaneous use ofF ₂ and \(\bar q\) structure functions permits, for the first time, a reliable determination of the gluon structure function.     

Frequency multiplication using induced dipole domains in a semiconductor superlattice

We theoretically studied the possibility of frequency multiplication using propagating dipole domains which are induced in a semiconductor superlattice by microwave radiation. We have investigated the dynamics of electrons in a superlattice submitted to both a static voltage and a microwave field by performing a simulation based on a drift-diffusion model and incorporating current-limiting boundary conditions. The motion of electrons in the superlattice was governed by an Esaki–Tsu drift velocity field characteristic with a negative differential mobility above a critical electrical field. The simulation delivered, for a static voltage larger than a critical voltage, the periodic formation and annihilation of propagating dipole domains and, as a consequence, a reduction of the direct current through the superlattice. Our simulation showed that an additional microwave field can periodically induce and subsequently quench domains giving rise to a strongly anharmonic current. The anharmonicity of the current is the origin for the generation of higher harmonics of the microwave field. Both the formation and annihilation of a domain can take place within a time of about 1 ps suggesting that the mechanism of domain induction and quenching can be used for generation of radiation up to almost 1 THz.     

Transient-Pulse Nonlinear Spectroscopy with the Radiation of a Multimode THz Gas Laser

We report on transient-pulse nonlinear spectroscopy with the radiation of a multimode THz gas laser. The method is demonstrated for studying the nonlinear response of a current-carrying superlattice to THz radiation; the current through a superlattice can be suppressed by a strong THz field. The method makes use of the pulses of a high power multimode THz gas laser. By splitting the laser beam for selected laser modes into a main beam and a reference beam we monitored with a reference detector the transient power in the main beam. The simultaneous measurement of both the instantaneous response and the instantaneous power allows to obtain the power dependence of the response within a single laser pulse. The method is suitable to study the nonlinear response of matter to THz radiation fields in a large dynamic range.     

Note on the impact parameter analysis of high-energy proton-proton collisions

Following a prior analysis of measured pp elastic differential cross-sections, the impact parameter representation in terms of profile functions is calculated from two different parametrizations of single diffractive dissociation data. The derivative of this quantity, with respect to the collision energy squared s, measures the growth rate of the reaction's blackness. Its distribution in impact parameter space allows detailed insight into the growth pattern of the total diffractive cross-section and the approaching unitarity limit. Comparing the results with the elastic case, the different mechanisms of unitarization of two parametrizations are discussed. Received: 19 January 2001 / Accepted: 11 July 2001