Dispersion theory of nucleon Compton scattering and polarizabilities (original) (raw)
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Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities
Physical Review Letters, 2003
Differential cross sections for Compton scattering from the deuteron were measured at MAXlab for incident photon energies of 55 MeV and 66 MeV at nominal laboratory angles of 45 • , 125 • , and 135 • . Tagged photons were scattered from liquid deuterium and detected in three NaI spectrometers. By comparing the data with theoretical calculations in the framework of a one-bosonexchange potential model, the sum and difference of the isospin-averaged nucleon polarizabilities, αN + βN = 17.4 ± 3.7 and αN − βN = 6.4 ± 2.4 (in units of 10 −4 fm 3 ), have been determined. By combining the latter with the global-averaged value for αp−βp and using the predictions of the Baldin sum rule for the sum of the nucleon polarizabilities, we have obtained values for the neutron electric and magnetic polarizabilities of αn = 8.8 ± 2.4(total) ± 3.0(model) and βn = 6.5 ∓ 2.4(total) ∓ 3.0(model), respectively. PACS numbers: 25.20.Dc, 13.40.Em, 13.60.Fz, 14.20.Dh
Physical Review Letters, 2014
The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world dataset. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using Chiral Effective Field Theory with dynamical ∆(1232) degrees of freedom shows the data are consistent with and within the world dataset. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn = [11.55 ± 1.25(stat) ± 0.2(BSR) ± 0.8(th)] × 10 −4 fm 3 and βn = [3.65 ∓ 1.25(stat) ± 0.2(BSR) ∓ 0.8(th)] × 10 −4 fm 3 , with χ 2 = 45.2 for 44 degrees of freedom.
Physics Letters B, 2005
An effective field theory is used to give a model-independent description of Compton scattering at energies comparable to the pion mass. The amplitudes for scattering on the proton and the deuteron, calculated to fourth order in small momenta in chiral perturbation theory, contain four undetermined parameters that are in one-to-one correspondence with the nucleon polarizabilities. These polarizabilities are extracted from fits to data on elastic photon scattering on hydrogen and deuterium. For the proton we find: α p = (12.1 ± 1.1 (stat.)) +0.5 −0.5 (theory) and β p = (3.4 ± 1.1 (stat.)) +0.1 −0.1 (theory), both in units of 10 −4 fm 3. For the isoscalar polarizabilities we obtain: α N = (13.0 ± 1.9 (stat.)) +3.9 −1.5 (theory) (in the same units) while β N is consistent with zero within sizable error bars. Electromagnetic polarizabilities are a fundamental property of any composite object. For example, atomic polarizabilities contain information about the charge and current distributions that result from the interactions of the protons, neutrons, and electrons inside the atom. Protons and neutrons are, in turn, complex objects composed of quarks and gluons, with interactions governed by QCD. It has long been hoped that neutron and proton polarizabilities will give important information about the strong-interaction dynamics of QCD. For example, in a simple quark-model picture these polarizabilities contain averaged information about the charge and current distribution produced by the quarks inside the
Low-energy Compton scattering and the polarizabilities of the proton
The European Physical Journal A, 2001
Differential cross-sections for Compton scattering from the proton have been measured at the MAMI tagged photon facility using the TAPS setup. The data cover an angular range of θ lab γ = 59 •-155 • and photon energies ranging from 55 MeV to 165 MeV. Our results are in good agreement with those from previous experiments, but yield higher precision. Using dispersion relations the proton polarizabilities have been determined to beᾱ = [11.9 ± 0.5stat. ∓ 1.3syst. ± 0.3 mod. ] • 10 −4 fm 3 andβ = [1.2 ± 0.7stat. ± 0.3syst. ± 0.4 mod.)] • 10 −4 fm 3. These results confirm the Baldin sum rule which was re-evaluated to bē α +β = [13.8 ± 0.4] • 10 −4 fm 3. We can also conclude that there is no significant additional asymptotic contribution to the backward spin polarizability γπ beyond the t-channel π 0-exchange.
Structure of the nucleon investigated by Compton scattering
Nuclear Physics A, 2001
Experimental differential cross sections for Compton scattering by the proton measured with the LARge Acceptance arrangement at the tagged-photon facility MAMI (Mainz) are interpreted in terms of the nonsubtracted dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. Using the new global average for the difference of electric and magnetic polarizabilities of the proton α β 10 5 ¦0 9 stat·syst ¦0 7 model µ ¢10 4 fm 3 a backward spin-polarizability of γ π ´ 37 1 ¦0 6 stat·syst ¦3 5 model µ ¢10 4 fm 4 and a E2/M1 ratio of EMR(340 MeV)=´ 1 7 ¦0 4 stat·syst ¦0 2 model µ % have been obtained.
Abstract Compton Scattering by the Nucleon ⋆
2004
The status of Compton scattering by the nucleon at energies of the first and second resonance is summarized. In addition to a general test of dispersion theories and a precise determination of polarizabilities, the validities of four fundamental sum rules are explored. Recommended averages of experimental values for the electromagnetic polarizabilities and spin-polarizabilities of the nucleon are determined: αp = 12.0 ± 0.6, βp = 1.9 ∓ 0.6, αn = 12.5 ± 1.7, βn = 2.7 ∓ 1.8 (unit 10 −4 fm 3), γ (p) π = −38.7 ± 1.8, γ (n) π = 58.6 ± 4.0 (unit 10 −4 fm 4).
Compton scattering on the proton, neutron, and deuteron in chiral perturbation theory to
Nuclear Physics A, 2005
We study Compton scattering in systems with A=1 and 2 using chiral perturbation theory up to fourth order. For the proton we fit the two undetermined parameters in the O(Q 4) γp amplitude of McGovern to experimental data in the region ω, |t| ≤ 180 MeV, obtaining a χ 2 /d.o.f. of 133/113. This yields a modelindependent extraction of proton polarizabilities based solely on low-energy data: α p = (12.1 ± 1.1 (stat.)) +0.5 −0.5 (theory) and β p = (3.4 ± 1.1 (stat.)) +0.1 −0.1 (theory), both in units of 10 −4 fm 3. We also compute Compton scattering on deuterium to O(Q 4). The γd amplitude is a sum of one-and two-nucleon mechanisms, and contains two undetermined parameters, which are related to the isoscalar nucleon polarizabilities. We fit data points from three recent γd scattering experiments with a χ 2 /d.o.f. = 26.6/20, and find α N = (13.0 ± 1.9 (stat.)) +3.9 −1.5 (theory) and a β N that is consistent with zero within sizeable error bars.
Compton scattering by the nucleon
Radiation Physics and Chemistry, 2006
The status of Compton scattering by the nucleon at energies of the first and second resonance is summarized. In addition to a general test of dispersion theories and a precise determination of polarizabilities, the validities of four fundamental sum rules are explored. Recommended averages of experimental values for the electromagnetic polarizabilities and spin-polarizabilities of the nucleon are determined: αp = 12.0 ± 0.6, βp = 1.9 ∓ 0.6, αn = 12.5 ± 1.7, βn = 2.7 ∓ 1.8 (unit 10 −4 fm 3), γ (p) π = −38.7 ± 1.8, γ (n) π = 58.6 ± 4.0 (unit 10 −4 fm 4).
The European Physical Journal A, 2007
The signs and values of the two-photon couplings FMγγ of mesons (M) and their couplings gMNN to the nucleon as entering into the t-channel parts of the difference of the electromagnetic polarizabilities (α − β) and the backward angle spin polarizabilities γπ are determined. The excellent agreement achieved with the experimental polarizabilities of the proton makes it possible to make reliable predictions for the neutron. The results obtained are αn = 13.4 ± 1.0, βn = 1.8 ∓ 1.0 (10 −4 fm 3), and γ (n) π = 57.6 ± 1.8 (10 −4 fm 4). New empirical information on the flavor wave functions of the f0(980)-and the a0(980)-meson is obtained.
Quasi-free Compton scattering and the polarizabilities of the neutron
The European Physical Journal A - Hadrons and Nuclei, 2003
Differential cross-sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz photon tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48 cm Ø × 64 cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at θ LAB γ = 136.2 • . Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction p(γ, π + n). The "free" proton Compton scattering cross sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross section for free scattering from quasi-free data. Differential cross-sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron has been determined to be αn − βn = 9.8 ± 3.6(stat) +2.1 −1.1 (syst) ± 2.2(model) in units of 10 −4 fm 3 . In combination with the polarizability sum αn + βn = 15.2 ± 0.5 deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, αn = 12.5 ± 1.8(stat) +1.1 −0.6 (syst) ± 1.1(model) and βn = 2.7 ∓ 1.8(stat) +0.6 −1.1 (syst) ∓ 1.1(model) are obtained. The backward spin polarizability of the neutron was determined to be γ (n) π = (58.6 ± 4.0) × 10 −4 fm 4 .