Neutrino Induced Coherent Pion Production off Nuclei and PCAC

We review the Rein--Sehgal model and criticize its use for low energy neutrino induced coherent pion production. We have studied the validity of the main approximations implicit in that model, trying to compare with physical observables when that is possible and with microscopical calculations. Next, we have tried to elaborate a new improved model by removing the more problematic approximations, while keeping the model still reasonably simple. Last, we have discussed the limitations intrinsic to any approach based on the partial conservation of the axial current hypothesis. In particular, we have shown the inability of such models to determine the angular distribution of the outgoing pion with respect to the direction of the incoming neutrino, except for the $q^2= 0$ kinematical point.Comment: 19 latex pages, 7 figures, 1 table. Version accepted for publication in Physical Review

Theoretical study of neutrino-induced coherent pion production off nuclei at T2K and MiniBooNE energies

We have developed a model for neutrino-induced coherent pion production off nuclei in the energy regime of interest for present and forthcoming neutrino oscillation experiments. It is based on a microscopic model for pion production off the nucleon that, besides the dominant Delta pole contribution, takes into account the effect of background terms required by chiral symmetry. Moreover, the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads to coherent pion production cross sections around a factor two smaller than most of the previous theoretical estimates. In the coherent production, the main nuclear effects, namely medium corrections on the Delta propagator and the final pion distortion, are included. We have improved on previous similar models by taking into account the nucleon motion and employing a more sophisticated optical potential. As found in previous calculations the modification of the Delta self-energy inside the nuclear medium strongly reduces the cross section, while the final pion distortion mainly shifts the peak position to lower pion energies. The angular distribution profiles are not much affected by nuclear effects. Nucleon motion increases the cross section by 15% at neutrino energies of 650 MeV, while Coulomb effects on charged pions are estimated to be small. Finally, we discuss at length the deficiencies of the Rein-Sehgal pion coherent production model for neutrino energies below 2 GeV, and in particular for the MiniBooNE and T2K experiments. We also predict flux averaged cross sections for these two latter experiments and K2K.Comment: 19 latex pages, 10 figures, 2 tables. Minor changes. Version accepted for publication in Physical Review

GEOCHRONOLOGY AND SR-ND ISOTOPE GEOCHEMISTRY OF LATE PALEOZOIC COLLISIONAL GRANITOIDS OF UNDINSKY COMPLEX (EASTERN TRANSBAIKAL REGION)

There are several geodynamic models of the Central Asian Orogenic Belt (CAOB) development [Şengör et al., 1993, Zorin, 1999; Parfenov et al., 1999, 2003; Willem et al., 2012; and others]. The Mongol-Okhotsk Orogenic Belt (MOB) represents important part of CAOB. All geodymanic models of Late Riphean to Paleozoic structures of CAOB emphasize significance of subduction processes along Northern Asian craton margin at that time. Collage of CAOB terrains formed as a result of accretion of island arc, accretionary wedge, turbidite, and continental margin terrains to the Siberian paleocontinent.There are several geodynamic models of the Central Asian Orogenic Belt (CAOB) development [Şengör et al., 1993, Zorin, 1999; Parfenov et al., 1999, 2003; Willem et al., 2012; and others]. The Mongol-Okhotsk Orogenic Belt (MOB) represents important part of CAOB. All geodymanic models of Late Riphean to Paleozoic structures of CAOB emphasize significance of subduction processes along Northern Asian craton margin at that time. Collage of CAOB terrains formed as a result of accretion of island arc, accretionary wedge, turbidite, and continental margin terrains to the Siberian paleocontinent

Cyclotron Resonance Assisted Photocurrents in Surface States of a 3D Topological Insulator Based on a Strained High Mobility HgTe Film

We report on the observation of cyclotron resonance induced photocurrents, excited by continuous wave terahertz radiation, in a 3D topological insulator (TI) based on an 80 nm strained HgTe film. The analysis of the photocurrent formation is supported by complimentary measurements of magneto-transport and radiation transmission. We demonstrate that the photocurrent is generated in the topologically protected surface states. Studying the resonance response in a gated sample we examined the behavior of the photocurrent, which enables us to extract the mobility and the cyclotron mass as a function of the Fermi energy. For high gate voltages we also detected cyclotron resonance (CR) of bulk carriers, with a mass about two times larger than that obtained for the surface states. The origin of the CR assisted photocurrent is discussed in terms of asymmetric scattering of TI surface carriers in the momentum space. Furthermore, we show that studying the photocurrent in gated samples provides a sensitive method to probe the effective masses and the mobility of 2D Dirac surface states, when the Fermi level lies in the bulk energy gap or even in the conduction band

Search for Charged Current Coherent Pion Production on Carbon in a Few-GeV Neutrino Beam

The SciBooNE Collaboration has performed a search for charged current coherent pion production from muon neutrinos scattering on carbon, \nu_\mu ^{12}C \to \mu^- ^{12}C \pi^+, with two distinct data samples. No evidence for coherent pion production is observed. We set 90% confidence level upper limits on the cross section ratio of charged current coherent pion production to the total charged current cross section at 0.67\times 10^{-2} at mean neutrino energy 1.1 GeV and 1.36\times 10^{-2} at mean neutrino energy 2.2 GeV.Comment: 18 pages, 16 figures, Minor revisions to match version accepted for publication in Physical Review

Index-free Heat Kernel Coefficients

Using index-free notation, we present the diagonal values of the first five heat kernel coefficients associated with a general Laplace-type operator on a compact Riemannian space without boundary. The fifth coefficient appears here for the first time. For a flat space with a gauge connection, the sixth coefficient is given too. Also provided are the leading terms for any coefficient, both in ascending and descending powers of the Yang-Mills and Riemann curvatures, to the same order as required for the fourth coefficient. These results are obtained by directly solving the relevant recursion relations, working in Fock-Schwinger gauge and Riemann normal coordinates. Our procedure is thus noncovariant, but we show that for any coefficient the `gauged' respectively `curved' version is found from the corresponding `non-gauged' respectively `flat' coefficient by making some simple covariant substitutions. These substitutions being understood, the coefficients retain their `flat' form and size. In this sense the fifth and sixth coefficient have only 26 and 75 terms respectively, allowing us to write them down. Using index-free notation also clarifies the general structure of the heat kernel coefficients. In particular, in flat space we find that from the fifth coefficient onward, certain scalars are absent. This may be relevant for the anomalies of quantum field theories in ten or more dimensions.Comment: 38 pages, LaTe

Relativistic Effects in the Scalar Meson Dynamics

A separable potential formalism is used to describe the $\pi\pi$ and $K\overline{K}$ interactions in the scalar-isoscalar states in the energy range from the $\pi\pi$ threshold up to 1.4 GeV. Introduction of relativistic propagators into a system of Lippmann-Schwinger equations leads to a very good description of the data ($\chi^{2}=0.93$ per one degree of freedom). Three poles are found in this energy region: fo(500) ($M=506\pm 10$ MeV, $\Gamma=494\pm 5$ MeV), fo(975) ($M=973\pm 2$ MeV, $\Gamma=29\pm 2$ MeV) and fo(1400) ($M=1430\pm 5$ MeV, $\Gamma=145\pm 25$ MeV). The fo(975) state can be interpreted as a $K\overline{K}$ bound state. The fo(500) state may be associated with the often postulated very broad scalar resonance under the $K\overline{K}$ threshold (sometimes called $\sigma$ or $\epsilon$ meson). The scattering lengths in the $\pi\pi$ and $K\overline{K}$ channels have also been obtained. The relativistic approach provides qualitatively new results (e.g. the appearance of the fo(500)) in comparison with previously used nonrelativistic approach.Comment: 30 pages in LaTeX + 5 figures available on request. Preprint Orsay No IPNO/TH 93-3

Aging Studies for the Large Honeycomb Drift Tube System of the Outer Tracker of HERA-B

The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects (like Malter currents, gain loss due to anode aging and etching of the anode gold surface) have been observed and cures by tuning of operation parameters have been developed.Comment: 14 pages, 6 figures, to be published in the Proceedings of the International Workshop On Aging Phenomena In Gaseous Detectors, 2-5 Oct 2001, Hamburg, German

Open and Hidden Charm Production in 920 GeV Proton-Nucleus Collisions

The HERA-B collaboration has studied the production of charmonium and open charm states in collisions of 920 GeV protons with wire targets of different materials. The acceptance of the HERA-B spectrometer covers negative values of xF up to xF=-0.3 and a broad range in transverse momentum from 0.0 to 4.8 GeV/c. The studies presented in this paper include J/psi differential distributions and the suppression of J/psi production in nuclear media. Furthermore, production cross sections and cross section ratios for open charm mesons are discussed.Comment: 5 pages, 9 figures, to be published in the proceedings of the 6th International Conference on Hyperons, Charm & Beauty Hadrons (BEACH04), Chicago, IL, June 27 - July 3, 200

Analyticity, Crossing Symmetry and the Limits of Chiral Perturbation Theory

The chiral Lagrangian for Goldstone boson scattering is a power series expansion in numbers of derivatives. Each successive term is suppressed by powers of a scale, $\Lambda_\chi$, which must be less than of order $4\pi f/\sqrt{N}$ where $f$ is the Goldstone boson decay constant and $N$ is the number of flavors. The chiral expansion therefore breaks down at or below $4 \pi f/\sqrt{N}$. We argue that the breakdown of the chiral expansion is associated with the appearance of physical states other than Goldstone bosons. Because of crossing symmetry, some ``isospin'' channels will deviate from their low energy behavior well before they approach the scale at which their low energy amplitudes would violate unitarity. We argue that the estimates of ``oblique'' corrections from technicolor obtained by scaling from QCD are untrustworthy.Comment: harvmac, 18 pages (3 figures), HUTP-92/A025, BUHEP-92-18, new version fixes a TeX problem in little mod