Narrow Results

The NuTeV collaboration has performed precision measurements of the ratio of neutral current to charged current cross-sections in high rate, high energy neutrino and anti-neutrino beams on a dense, primarily steel, target. The separate neutrino and anti-neutrino beams, high statistics, and improved control of other experimental systematics, allow the determination of electroweak parameters with significantly greater precision than past νN scattering experiments. Our null hypothesis test of the standard model prediction measures , a value which is 3.0σ above the prediction. We discuss possible explanations for and implications of this discrepancy.

We present a study of neutrino/antineutrino induced charged current (CC) and neutral current (NC) single pion production (SPP) off the nucleon. For this, we have considered $P_{33}(1232)$ resonance, nonresonant background (NRB) terms, other higher resonances like $P_{11}(1440)$, $S_{11}(1535)$, $D_{13}(1520)$, $S_{11}(1650)$ and $P_{13}(1720)$. For the NRB terms a microscopic approach based on $SU(2)$ nonlinear sigma model has been used. The vector form factors for the resonances are obtained by using the relationship between the electromagnetic resonance form factors and helicity amplitudes provided by MAID. Axial coupling $C_5^A(0)$ in the case of $P_{33}(1232)$ resonance is obtained by fitting the ANL and BNL $\nu$-deuteron reanalyzed scattering data. The results are presented with and without deuteron effect for the total scattering cross-sections for all possible channels, viz. ${\nu }_l({\bar{\nu }}_l)+N\to l^{-}(l^{+})+N^{\prime }+{\pi }^i$ and ${\nu }_l({\bar{\nu }}_l)+N\to {\nu }_l({\bar{\nu }}_l)+N^{\prime }+{\pi }^i$, where $N,N^{\prime }=p,n$, ${\pi }^i={\pi }^{\pm }$ or ${\pi }^0$ and $l=e,\mu$.

The existence of a new interaction involving the electron neutrino and the nucleons, which has received a convincing confirmation through a good agreement between the theoretical and experimental results concerning all observable processes with solar neutrinos, should also inevitably manifest itself in the deuteron disintegration by the neutral currents of reactor antineutrinos. The special attention is drawn to the problem of finding the neutron registration efficiency, discussed in the preparation of the experiment at the Sudbury Neutrino Observatory and in a number of special studies. Lessons are noted that can be learned from three long-standing experiments on the deuteron disintegration by reactor neutrinos.

Neutrinos make reactions with nuclei by means of neutral current (NC) as well as charged current (CC). The solar neutrinos (solar-v) have relatively low energy of up to ≈ 15 MeV. In this low-energy limit, the main component of the NC is the axial-IV current caused by the spin-isospin (στ) operator, while that of the CC is both the axial-IV current, and also the IV current caused by the isospin (τ) operator. The nuclear στ and τ responses can be well studied by using high energy-resolution (³He, t) reaction at the intermediate incident-energy of 140 MeV/nucleon. Since the reaction is caused by the strong interaction, we have a larger reaction rate. Therefore, NC and CC responses of nuclei to the solar-v can be studied efficiently. We first examine the properties of nuclear excitations that are induced by the CC for some of the nuclei that have been discussed as “good tools” for the study of solar-v. Also discussed are the properties of p-shell (mass number A = 5−16) and also sd-shell nuclei (A = 17−40) with the z-component of isospin T_z = (N−Z)/2 = ±1/2. We seek the possible use of these nuclei as good tools for the study of excitations by means of both NC and CC.

The NuTeV collaboration has performed precision measurements of the ratio of neutral current to charged current cross-sections in high rate, high energy neutrino and anti-neutrino beams on a dense, primarily steel, target. The separate neutrino and anti-neutrino beams, high statistics, and improved control of other experimental systematics, allow the determination of electroweak parameters with significantly greater precision than past νN scattering experiments. Our null hypothesis test of the standard model prediction measures , a value which is 3.0σ above the prodiction. We discuss possible explanations for and implications of this discrepancy.

The HERA experiments, H1 and ZEUS, have measured inclusive neutral current cross sections in e^±p deep inelastic interactions with longitudinally polarised lepton beams. These data are used for investigation of the interference of weak and electromagnetic interactions at high four-momentum transfer squared, Q². Measurements of the interference structure function , which is sensitive to the valence quark distributions, and of the polarised cross section asymmetries are presented. For the first time at HERA, the measurements of H1 and ZEUS are combined in order to improve the statistical precision at high Q². The combined data provide the most accurate measurement of at HERA and lead to the first observation of parity violation in neutral current e^±p scattering at distances down to 10^-18 m. The measurements are compared to predictions of the Standard Model which is able to provide a good description of the data.