Threshold Two-Pion Photo- and Electroproduction: More neutrals than expected

We present an exploratory study of two pion photo-- and electroproduction off the nucleon in the threshold region. To calculate the pertinent amplitudes, we make use of heavy baryon chiral perturbation theory. We show that due to finite chiral loops the production cross section for final states with two neutral pions is considerably enhanced. The experimental implications are briefly discussed.Comment: 23pp, plain TeX, 11 figures available upon request, CRN 94/1

Threshold Photo/Electro Pion Production - Working Group Summary

We summarize the pertinent experimental and theoretical developments in the field of pion photo- and electroproduction in the threshold region. We discuss which experiments and which calculations should be done/performed in the future.Comment: plain TeX (macro included), 6pp, summary talk presented at the workshop on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199

Threshold Pion Electroproduction in Chiral Perturbation Theory

Electroproduction of pions on the nucleon near the threshold is analyzed within the framework of baryon chiral perturbation theory. We give a thorough discussion of the low--energy theorems related to charged and neutral electropionproduction. It is shown how the axial radius of the nucleon can be related to the S--wave multipoles $E_{0+}^{(-)}$ and $L_{0+}^{(-)}$. The chiral perturbation theory calculations of the $\gamma^\star p \to \pi^0 p$ reaction are found to be in good agreement with the recent near threshold data. We also discuss the influence of some isospin--breaking effects in this channel. For future experimental tests of the underlying chiral dynamics, extensive predictions of differential cross sections and multipole amplitudes are presented.Comment: 44pp, TeX, 15 figures available upon request, BUTP-93/23 and CRN 93-4

Improved description of threshold pion electroproduction in chiral perturbation theory

We investigate neutral pion electroproduction off protons in the framework of heavy baryon chiral perturbation theory. The chiral expansion of the S--wave multipoles $E_{0+}$ and $L_{0+}$ is carried out to three orders. There appear several undetermined low--energy constants. Three are taken from a recent study of the new TAPS threshold $\pi^0$ photoproduction data, one is fixed from the proton Dirac form factor and the novel S--wave constants appearing at orders $q^4$ and $q^5$ are determined from a best fit (constrained by resonance exchange) to the recent NIKHEF and MAMI data at photon momentum transfer squared $k^2 = -0.1 \, \, {\rm GeV}^2$. The inclusion of a particular set of dimension five operators is forced upon the fit by a soft--pion theorem which severely constrains the momentum dependence of the longitudinal S--wave multipole $L_{0+}$ at order $q^4$. We give predictions for lower photon virtualities for the various multipoles and differential cross sections. Further improvements are briefly touched upon.Comment: 25 pp, LaTeX, uses epsf and elsart12.sty, 8 figures in 10 PS file

Neutral Meson Photoproduction in SUf(3)SU_f(3) χ\chiPT

We present the results for the electric dipole amplitude for $\gamma N \to \pi^0 N$ at threshold at the $O(p^2)$ level in SU$_f$(3) chiral perturbation theory. We find that the SU$_f$(3) results differ only slightly from the SU$_f$(2) results. At the $O(p^3)$ level one encounters new, unknown counterterms to fix which one is likely to need the threshold photoproduction data themselves, thus losing predictive power. We suggest, instead, that the {\it difference} between the proton and neutron $\pi^0$ photoproduction amplitudes may provide a test of the convergence properties of the $\chi$PT in the present context. We urge that the neutron's electric dipole amplitude be measured.Comment: Revised version with corrected value of the Kaon loop contributio

Considerations on rescattering effects for threshold photo- and electro-production of π0\pi^0 on deuteron

We show that for the S-state $\pi^0$-production in processes $\gamma+d\to d+\pi^0$ and $e^-+d\to e^-+d+\pi^0$ the rescattering effects due to the transition: $\gamma+d\to p+p+\pi^-$ (or $n+n+\pi^+)\to d+\pi^0$ are cancelled out due to the Pauli principle. The large values for these effects predicted in the past may result from the fact that the spin structure of the corresponding matrix element and the necessary antisymmetrization induced by the presence of identical protons (or neutrons) in the intermediate state was not taken into account accurately. One of the important consequences of these considerations is that $\pi^0$ photo- and electro-production on deuteron near threshold can bring direct information about elementary neutron amplitudes.Comment: Add a new sectio

Threshold Pion Photo- and Electroproduction in Chiral Perturbation Theory

I present some recent results on neutral pion photo- and electroproduction in the threshold region and discuss the low energy theorem for $E_{0+}$ and some novel ones for the $P$-waves. I also study the two-pion production process $\gamma N \to \pi \pi N$ from which complementary information can be gained.Comment: 12 pages, 6 figures available upon request, talk given at the workshop on Chiral Dynamics: Theory and Experiments, MIT, USA, July 25-July 29, 1994, CRN-94/4

Coherent Line Removal: Filtering out harmonically related line interference from experimental data, with application to gravitational wave detectors

We describe a new technique for removing troublesome interference from external coherent signals present in the gravitational wave spectrum. The method works when the interference is present in many harmonics, as long as they remain coherent with one another. The method can remove interference even when the frequency changes. We apply the method to the data produced by the Glasgow laser interferometer in 1996 and the entire series of wide lines corresponding to the electricity supply frequency and its harmonics are removed, leaving the spectrum clean enough to detect possible signals previously masked by them. We also study the effects of the line removal on the statistics of the noise in the time domain. We find that this technique seems to reduce the level of non-Gaussian noise present in the interferometer and therefore, it can raise the sensitivity and duty cycle of the detectors.Comment: 14 pages, 8 figures, Revtex, psfig. To appear in Phys. Rev.

Removing non-stationary, non-harmonic external interference from gravitational wave interferometer data

We describe a procedure to identify and remove a class of non-stationary and non-harmonic interference lines from gravitational wave interferometer data. These lines appear to be associated with the external electricity main supply, but their amplitudes are non-stationary and they do not appear at harmonics of the fundamental supply frequency. We find an empirical model able to represent coherently all the non-harmonic lines we have found in the power spectrum, in terms of an assumed reference signal of the primary supply input signal. If this signal is not available then it can be reconstructed from the same data by making use of the coherent line removal algorithm that we have described elsewhere. All these lines are broadened by frequency changes of the supply signal, and they corrupt significant frequency ranges of the power spectrum. The physical process that generates this interference is so far unknown, but it is highly non-linear and non-stationary. Using our model, we cancel the interference in the time domain by an adaptive procedure that should work regardless of the source of the primary interference. We have applied the method to laser interferometer data from the Glasgow prototype detector, where all the features we describe in this paper were observed. The algorithm has been tuned in such a way that the entire series of wide lines corresponding to the electrical interference are removed, leaving the spectrum clean enough to detect signals previously masked by them. Single-line signals buried in the interference can be recovered with at least 75 % of their original signal amplitude.Comment: 14 pages, 5 figures, Revtex, psfi

The Adoption Challenge: An Analysis of Research Methods in JIBS

This study introduces the concepts of translational distance and complexity distance to explain challenges to adoption of research methods in JIBS. We examine three analytical techniques and data collection approaches: (1) Heckman models, (2) ethnographic studies, and (3) data collection equivalence procedures in survey-based research. We note that progress has been made to reduce translational and complexity distance for analytical techniques. However, concerns remain for data collection equivalence and ethnography as IB scholars are using increasingly advanced analytical techniques on less credible data