Low-energy supersymmetry

We discuss the problem of constructing a model in which supersymmetry is unbroken down to low energies. It is suggested that the scalar partners of quarks and leptons may get their masses through radiative corrections and that the breaking of the weak interactions also occurs through radiative corrections. A toy model is constructed which illustrates these ideas.     

Explaining Tevatron leptons photons missing-E T events with supersymmetry

The CDF experiment reported a lepton photon missing transverse energy (ie651_01)signal 3σ in excess of the standard model prediction in Tevatron Run I data. The excess can be explained by the resonant production of a smuon, which subsequently decays to a muon, a photon and a gravitino. Here, we perform combined fits of this model to the CDF (ie651_02) excess, the DO measurement of the same channel and the CDF (ie651_03) channel. Although the rates of the latter two analyses are in agreement with the standard model prediction, our model is in good agreement with these data because their signal to background efficiency is low at the best-fit point. However, they help to constrain the model away from the best fit point.     

Low-energy measurement of the 7Be(p,gamma)8B cross section

We have measured the cross section of the 7Be(p,gamma)8B reaction for E(c.m.) = 185.8, 134.7, and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta+ and alpha particles from 8B and 8Be* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5+/-2.4 eV b and a weighted mean value of 18.8+/-1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies.     

On the scale variation of the total cross section for Higgs production at the LHC and at the Tevatron

We present a detailed study of the total pp cross section for scalar Higgs production to next-to-next-to-leading order in α_s at LHC energies, and of the pp̄ cross section at the Tevatron, combining an implementation of the solutions of the parton evolution equations at the three-loop order with the corresponding hard scatterings, evaluated at the same perturbative order. Our solutions of the DGLAP equations are implemented directly in x-space and allow for the study of the dependence of the results on the factorization (μ_F) and renormalization scales (μ_R) typical of a given process, together with the stability of the perturbative expansion. The input sets for the parton evolutions are those given by Martin, Roberts, Stirling and Thorne and by Alekhin. Results for K-factors are also presented. The NNLO corrections can be quite sizeable at typical collider energies. The stability region of the perturbative expansion is found when μ_R>m_H∼μ_F.     

Low-energy vibrational excitation cross section of multilayers of CO molecules on graphite using electron scattering

This paper presents a low-energy study of the vibrational excitation cross section of 50 layers of CO molecules on graphite at 23 K using the electron energy loss spectroscopy technique. The vibrational excitation cross section or the excitation curve is presented for two different scattering angles. The results show an energy dependence of the vibrational excitation cross section, at both angles, which indicates the formation of negative ion resonance in this adsorbed phase of CO on graphite. The data show an oscillatory structure in the region between 0.5 and 3 eV that is associated with the excitation of the ²Π state.     

Relationship between the cross section for deep-inelastic scattering and the cross section for inclusive annihilation

Arguments have been presented that suggest that available experimental data on the structure functions for the processes ep → eX and e ⁺ e ^? → p( $\bar p$ )X do not confirm the so-called reciprocity relation, which was obtained in the leading-logarithm approximation of perturbation theory. It has also been shown that the asymptotic relationship between the above processes that was obtained on the basis of more general considerations is compatible with existing data.     

Statistics and the average cross section

Average fluctuation cross sections were computed numerically from a unitary analytic K-matrix with normally distributed pole residue amplitudes and pole spacings having the Wigner distribution. Unexpected results included an elastic enhancement factor of 2.12 in the many channel limit, regardless of transmission factors. The enhancement factors were found to be very sensitive to variations in the statistical assumptions regarding both pole amplitudes and pole spacings. The results are discussed in the light of various theories of the fluctuation cross section.     

Low-energy cross section for 6Li(d,n)7Be

Cross sections were determined for the ⁶Li(d, n)⁷Be reaction between 100 and 180 keV deuteron energy using the activation method. Different methods of extrapolation were employed and compared down to the energy region of astrophysical interest.     

Low-energy behavior of the 3He(α, γ)7Be cross section

Cross sections for the ³He(α, γ)⁷Be reaction have been measured at several energies from E_c.m. = 165 to 1169 keV by counting prompt γ-rays from a windowless, differentially pumped, recirculating, ³He gas target. The cross-section factor S₃₄(E_c.m.) and branching ratio γ₁/γ₀ were determined at each energy. Cross sections were also measured at E_c.m. = 947 and 1255 keV by counting the γ-rays from the ⁷Be produced in a ³He gas cell with a Ni entrance foil. Combining the results of these two independent experiments yields a zero-energy intercept for the cross-section factor of S₃₄(0) = 0.53 ± 0.03 keV · b. The relationship between these measurements and several theoretical calculations, and the import of the extrapolated cross section for the solar-neutrino problem are discussed.     

Predicting the total charm cross section

We discuss the energy dependence of the total charm cross section and some of its theoretical uncertainties including the quark mass, scale choice and the parton densities.