18 research outputs found
Chiral Perturbation Theory and Nucleon Polarizabilities
Compton scattering offers in principle an intriguing new window on nucleon
structure. Existing experiments and future programs are discussed and the state
of theoretical understanding of such measurements is explored.Comment: 15 page standard Latex file---invited talk at Chiral Dynamics
Workshop, Mainz, Germany---typos correcte
A Brief Introduction to Chiral Perturbation Theory
A brief introduction to the subject of chiral perturbation theory (pt)
is presented, including a discussion of effective field theory and applications
of pt in the arena of purely mesonic interactions as well as in the sector.Comment: 15 pages, talk given at TAPS detector workshop, Rez, Czech Republic,
Sept. 1999, to be published in Czech. J. Phy
Exclusive 16O(γ,π-p) reaction in the Δ resonance region
We report the first exclusive (γ,π-p) measurements on a complex nucleus. The 16O(γ,π-p) reaction was measured at pion laboratory angles of 64° and 120°. Coincident protons were detected over the quasifree angular correlation range using a vertical array of seven plastic scintillator detectors spanning ±33° about the scattering plane. The cross sections are compared to factorized distorted-wave impulse approximation calculations; these provide a good description of the backward angle data, but are in serious disagreement with the forward angle data
Higher Order Polarizabilities of the Proton
Compton scattering results are used to probe proton structure via measurement
of higher order polarizabilities. Values for
determined via
dispersion relations are compared to predictions based upon chiral symmetry and
from the constituent quark model. Extensions to spin-polarizabilities are also
discussed.Comment: 18 pages, revised version with one reference adde
Compton Scattering and the Spin Structure of the Nucleon at Low Energies
We analyze polarized Compton scattering which provides information on the
spin-structure of the nucleon. For scattering processes with photon energies up
to 100 MeV the spin-structure dependence can be encoded into four independent
parameters-the so-called spin-polarizabilities of the
nucleon, which we calculate within the framework of the "small scale expansion"
in SU(2) baryon chiral perturbation theory. Specific application is made to
"forward" and "backward" spin- polarizabilities.Comment: 8 pages revtex file, separation between pion-pole and regular
contributions detailed + minor wording changes, results and conclusions
unchange
Real and Virtual Compton Scattering: the nucleon polarisabilities
We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma
p) with a real or virtual incoming photon. These processes allow the
investigation of one of the fundamental properties of the nucleon, i.e. how its
internal structure deforms under an applied static electromagnetic field. Our
knowledge of nucleon polarisabilities and their generalization to non-zero
four-momentum transfer will be reviewed, including the presently ongoing
experiments and future perspectives.Comment: 20 pages, 12 figures. Minireview/Proceedings of "Many-Body Structure
of Strongly Interacting Systems", Mainz, Germany, Feb. 23-25 2011 . V2: typos
corrected. version to appear in EPJ Special Topic
Generalized Polarizabilities of the Nucleon in Chiral Effective Theories
Using the techniques of chiral effective field theories we evaluate the so
called generalized polarizabilities of the nucleon, which characterize the
structure dependent components in virtual Compton scattering (VCS) as probed in
the electron scattering reaction e N \to e' N gamma. Results are given for both
spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy
Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale
Expansion. Finally we compare our calculations with results from the pioneering
VCS experiment on the proton from Mainz.Comment: 39 pages, 12 figures, revte
Predictive powers of chiral perturbation theory in Compton scattering off protons
We study low-energy nucleon Compton scattering in the framework of baryon
chiral perturbation theory (BPT) with pion, nucleon, and (1232)
degrees of freedom, up to and including the next-to-next-to-leading order
(NNLO). We include the effects of order , and , with
MeV the -resonance excitation energy. These are
all "predictive" powers in the sense that no unknown low-energy constants enter
until at least one order higher (i.e, ). Estimating the theoretical
uncertainty on the basis of natural size for effects, we find that
uncertainty of such a NNLO result is comparable to the uncertainty of the
present experimental data for low-energy Compton scattering. We find an
excellent agreement with the experimental cross section data up to at least the
pion-production threshold. Nevertheless, for the proton's magnetic
polarizability we obtain a value of fm, in
significant disagreement with the current PDG value. Unlike the previous
PT studies of Compton scattering, we perform the calculations in a
manifestly Lorentz-covariant fashion, refraining from the heavy-baryon (HB)
expansion. The difference between the lowest order HBPT and BPT
results for polarizabilities is found to be appreciable. We discuss the chiral
behavior of proton polarizabilities in both HBPT and BPT with the
hope to confront it with lattice QCD calculations in a near future. In studying
some of the polarized observables, we identify the regime where their naive
low-energy expansion begins to break down, thus addressing the forthcoming
precision measurements at the HIGS facility.Comment: 24 pages, 9 figures, RevTeX4, revised version published in EPJ
Recommended from our members
Results of the LSND search for {ovr {nu}}{sub {mu}} {yields} {ovr {nu}}{sub e} oscillations
A search for {ovr {nu}}{sub {mu}}{yields}{ovr {nu}}{sub e} oscillations has been conducted at the Los Alamos Meson Physics Facility by using {ovr {nu}}{sub {mu}} from {mu}{sup +} decay at rest. The {ovr {nu}}{sub e} are detected via the reaction {ovr {nu}}{sub e}p {yields} e{sup +} n , correlated with a {gamma} from np {yields} d{gamma} (2.2 MeV). The use of tight cuts to identify e{sup +} events with correlated {gamma} rays yields 22 events with e{sup +} energy between 36 and 60 MeV and only 4.6 {plus_minus} 0.6 background events. The probability that this observation can be explained by statistical fluctuation is less than 10{sup -7}. Assuming these events are due to oscillations, a likelihood fit to all the e{sup +} events between 20 and 60 MeV has been performed to extract the oscillation parameters sin{sup 2} 2{theta} and {Delta}m{sup 2}. The favored region resulting from this fit is shown
Recommended from our members
Evidence for nu bar sub mu to nu bar sub e oscillations
A search for {bar {nu}}{sub e}`s in excess of the number expected from conventional sources has been made using the Liquid Scintillator Neutrino Detector, located 30 m behind the LAMPF beam stop. The {bar {nu}}{sub e} are detected via {bar {nu}}{sub e}p{r_arrow}e{sup +}n with e{sup +} energy between 36 and 60 MeV, followed by a {gamma} from np{r_arrow}d{gamma} (2.2 MeV). Using strict cuts to identify {gamma}`s correlated with an e{sup +} yields 9 events with only 2.1{+-}0.3 background expected. A likelihood fit to the entire e{sup +} sample results in a total excess of 16.4{sup +9.7}{sub -8.9}{+-}3.3 events. If attributed to {bar {nu}}{sub {mu}}{r_arrow}{bar {nu}}{sub e} oscillations, this corresponds to an oscillation probability of (0.34{sup +0.200}{sub -0.18}{+-}0.07)%