Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Survey of charge symmetry breaking operators for dd -> alpha pi0  [PDF]
A. Gardestig,C. J. Horowitz,A. Nogga,A. C. Fonseca,C. Hanhart,G. A. Miller,J. A. Niskanen,U. van Kolck
Physics , 2004, DOI: 10.1103/PhysRevC.69.044606
Abstract: The charge-symmetry-breaking amplitudes for the recently observed d d -> alpha pi0 reaction are investigated. Chiral perturbation theory is used to classify and identify the leading-order terms. Specific forms of the related one- and two-body tree level diagrams are derived. As a first step toward a full calculation, a few tree-level two-body diagrams are evaluated at each considered order, using a simplified set of d and alpha wave functions and a plane-wave approximation for the initial dd state. The leading-order pion-exchange term is shown to be suppressed in this model because of poor overlap of the initial and final states. The higher-order one-body and short-range (heavy-meson-exchange) amplitudes provide better matching between the initial and final states and therefore contribute significantly and coherently to the cross section. The consequences this might have for a full calculation, with realistic wave functions and a more complete set of amplitudes, are discussed.
Charge symmetry breaking and the d d -> alpha pi0 reaction -- recent theoretical developments  [PDF]
Anders Gardestig
Physics , 2004,
Abstract: The status of the theoretical effort to calculate charge-symmetry-breaking pion production reactions will be presented. The main emphasis will be on the d d -> alpha pi0 reaction, especially in relation to the recent IUCF experiment. Suggestions for future theoretical and experimental work will be made.
Has charge symmetry breaking been observed in the d d -> alpha pi0 reaction?  [PDF]
D. Dobrokhotov,G. Faldt,A. Gardestig,C. Wilkin
Physics , 1999, DOI: 10.1103/PhysRevLett.83.5246
Abstract: Estimates are made of the d d -> alpha gamma gamma production cross sections in a model where each neutron-proton pair in the beam and target initiates an n p -> d gamma reaction. This approach, which successfully reproduces observables in two-pion production at intermediate energies, suggests that direct two-photon production could provide a very significant background to the measurement of the charge-symmetry-breaking (CSB) reaction d d -> alpha pi0. A non-vanishing CSB cross section has been reported which might be confused with such two-photon production under the given experimental conditions.
Isospin violation in low-energy pion-nucleon scattering revisited  [PDF]
Martin Hoferichter,Bastian Kubis,Ulf-G. Mei?ner
Physics , 2009, DOI: 10.1016/j.nuclphysa.2009.11.012
Abstract: We calculate isospin breaking in pion-nucleon scattering in the threshold region in the framework of covariant baryon chiral perturbation theory. All effects due to quark mass differences as well as real and virtual photons are consistently included. As an application, we discuss the energy dependence of the triangle relation that connects elastic scattering on the proton pi+- p --> pi+- p with the charge exchange reaction pi- p --> pi0 n.
Realistic Few-Body Physics in the $dd\to απ^0$ Reaction  [PDF]
A. Nogga,A. C. Fonseca,A. Gardestig,C. Hanhart,C. J. Horowitz,G. A. Miller,J. A. Niskanen,U. van Kolck
Physics , 2006, DOI: 10.1016/j.physletb.2006.04.058
Abstract: We use realistic two- and three-nucleon interactions in a hybrid chiral-perturbation-theory calculation of the charge-symmetry-breaking reaction $dd\to\alpha\pi^0$ to show that a cross section of the experimentally measured size can be obtained using LO and NNLO pion-production operators. This result supports the validity of our power counting scheme and demonstrates the necessity of using an accurate treatment of ISI and FSI.
Breaking of Charge Independence of Nucleon-Nucleon Interaction and Bulk Properties of Nuclear Matter  [PDF]
G. H. Bordbar
Physics , 2003, DOI: 10.1142/S0217751X03016082
Abstract: The effects of charge independence breaking of nucleon-nucleon interaction on the bulk properties of nuclear matter are investigated. Our results indicate that at high densities, the inclusion of charge dependence in the nucleon-nucleon potential affects the bulk properties of nuclear matter. However, at low densities, this effect is not considerable. It is seen that the change of our results for the nuclear matter calculations due to the breaking of the charge independence increases by increasing density. It is shown that the energy contribution of the $^1S_0$ channel is sensitive to considering the charge dependence in the nucleon-nucleon interaction. It is indicated that the effects of charge independence breaking on the calculated equation of state of nuclear matter are ignorable.
Flavor Symmetry Breaking and Strangeness in the Nucleon  [PDF]
H. Weigel
Physics , 2002, DOI: 10.1140/epja/i2002-10283-5
Abstract: We suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave--functions while the charge operators have no (or only small) explicit symmetry breaking components. We utilize the collective coordinate approach to chiral soliton models to support this picture. In particular we compute the $g_A/g_V$ ratios for hyperon beta--decay and the strangeness contribution to the nucleon axial current matrix elements and analyze their variation with increasing flavor symmetry breaking.
Observation of the Charge Symmetry Breaking d + d -> 4He + pi0 Reaction Near Threshold  [PDF]
E. J. Stephenson,A. D. Bacher,C. E. Allgower,A. Gardestig,C. Lavelle,G. A. Miller,H. Nann,J. Olmsted,P. V. Pancella,M. A. Pickar,J. Rapaport,T. Rinckel,A. Smith,H. M. Spinka,U. van Kolck
Physics , 2003, DOI: 10.1103/PhysRevLett.91.142302
Abstract: We report the first observation of the charge symmetry breaking d + d -> 4He + pi0 reaction near threshold at the Indiana University Cyclotron Facility. Kinematic reconstruction permitted the separation of 4He + pi0 events from double radiative capture 4He + gamma + gamma events. We measured total cross sections for neutron pion production of 12.7 +- 2.2 pb at 228.5 MeV and 15.1 +- 3.1 pb at 231.8 MeV. The uncertainty is dominated by statistical errors.
Charge independence breaking and charge symmetry breaking in the nucleon-nucleon interaction from effective field theory  [PDF]
E. Epelbaum,Ulf-G. Mei?ner
Physics , 1999, DOI: 10.1016/S0370-2693(99)00776-5
Abstract: We discuss charge symmetry and charge independence breaking in an effective field theory approach for few-nucleon systems. We systematically introduce strong isospin-violating and electromagnetic operators in the theory. The charge dependence observed in the nucleon-nucleon scattering lengths is due to one-pion exchange and one electromagnetic four-nucleon contact term. This gives a parameter free expression for the charge dependence of the corresponding effective ranges, which is in agreement with the rather small and uncertain empirical determinations. We also compare the low energy phase shifts of the $nn$ and the $np$ system.
Initial-State Coulomb Interaction in the dd -> alpha pi^0 Reaction  [PDF]
Timo A. L?hde,G. A. Miller
Physics , 2007, DOI: 10.1103/PhysRevC.75.055204
Abstract: The effects of initial-state Coulomb interactions in the charge-symmetry-breaking reaction dd -> alpha pi^0 are investigated within a previously published formalism. This is a leading order effect in which the Coulomb interaction between the two initial state protons leads to the breakup of the two deuterons into a continuum state that is well connected to the final alpha pi^0 state by the strong emission of a pion. As a first step, we use a simplified set of d and alpha wave functions and a plane-wave approximation for the initial dd state. This Coulomb mechanism, by itself, yields cross sections that are much larger than the experimental ones, and which are comparable in size to the contributions from other mechanisms. Inclusion of this mechanism is therefore necessary in a realistic calculation.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.