Measurement of the neutral to charged current cross section ratio in neutrino and antineutrino interactions

We report on the analysis of inclusive neutral current events produced in neutrino and antineutrino narrow band beams. We find for incident neutrino energies in the range 12–200 GeV and for hadron energies above 12 GeV a neutral to charged current cross-section ratio of R_v = 0.293 ± 0.010 for incident neutrinos, and $\text{R}{}_{\mathrm{<mtext>v</mtext>}}\text{= 0.35 ± 0.03}$ for antineutrinos. These ratios are consistent with the Weinberg-Salam model, with sin²θ_w = 0.24 ± 0.02.     

The number of lattice points in alcoves and the exponents of the finite Weyl groups

We count lattice points in certain rational simplices associated with an irreducible finite Weyl group and observe that these numbers are linked to the exponents of .

     

Predissociation via conformational change: photodissociation of N,N-dimethylnitrosamine in the S(1) state

We investigated the photodissociation mechanism of N,N-dimethylnitrosamine (CH(3))(2)NNO (DMN) by ab intio quantum chemical methods. Inspired by an earlier study we calculated two-dimensional potential energy surfaces of the S(1) state of DMN in its planar and pyramidal conformations. While the planar molecular geometry appears to possess no direct dissociation channel, the pyramidal configuration is dissociative yielding the products NO + (CH(3))(2)N. Using wave packet dynamics on the planar S(1) potential energy surface the experimental absorption spectrum was well reproduced which gives indirect but strong support for the nondissociative nature of this surface. The transition from the planar to the pyramidal conformation of DMN was then investigated by an ab initio molecular dynamics method which revealed the time evolution of the geometrical parameters of the molecule up to the dissociation of the N-N bond. This occurs about 90 fs after photon excitation. The calculated minimum energy path along the N-N coordinate and the structural changes of the molecule along this coordinate provided a detailed picture of this indirect dissociation or, more specific, predissociation process via conformational change.