Polarizability of the nucleon and Compton scattering

Schumacher, M.

doi:10.1016/j.ppnp.2005.01.033

Cited by 112 publications

(208 citation statements)

References 171 publications

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“…2 except for Mainz [18]. The solid curves are Op 3 HBChPT [4], the dashed curve is a low 2 , which is in near agreement with the HBChPT prediction [21] of 1:7 fm 2 . The experimental value is significantly larger than the proton mean square charge radius [22] of 0:757 :014 fm 2 , which is evidence for the dominance of mesonic effects in the electric polarizability.…”

supporting

confidence: 68%

“…By contrast, the electric polarizability of the nucleon is approximately 10 4 times smaller than the nucleon volume, demonstrating in a qualitative fashion the extreme stiffness of the nucleon relative to the atom. Although the electric and magnetic polarizabilities of the proton and are known with reasonable accuracy [2] from real Compton scattering (RCS), much less is known about the polarizability distributions inside the nucleon. To measure these distributions it is necessary to use the virtual-Compton-scattering (VCS) reaction [3], where the incident photon is virtual.…”

mentioning

confidence: 99%

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Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at LowQ2Using the Virtual-Compton-Scattering Reaction

Bourgeois¹,

Sato²,

Shaw³

et al. 2006

Phys. Rev. Lett.

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The mean square polarizability radii of the proton have been measured for the first time in a virtualCompton-scattering experiment performed at the MIT-Bates out-of-plane scattering facility. Response functions and polarizabilities obtained from a dispersion analysis of the data at Q 2 0:057 GeV 2 =c 2 are in agreement with Op 3 heavy baryon chiral perturbation theory. The data support the dominance of mesonic effects in the polarizabilities. DOI: 10.1103/PhysRevLett.97.212001 PACS numbers: 13.60.Fz, 13.40.Gp, 14.20.Dh The electromagnetic polarizabilities of the nucleon provide a vital testing ground for theories of low-energy QCD and nucleon structure, and are of compelling experimental and theoretical interest [1]. In the case of atomic polarizabilities the electric polarizability is approximately equal to the atomic volume. By contrast, the electric polarizability of the nucleon is approximately 10 4 times smaller than the nucleon volume, demonstrating in a qualitative fashion the extreme stiffness of the nucleon relative to the atom. Although the electric and magnetic polarizabilities of the proton and are known with reasonable accuracy [2] from real Compton scattering (RCS), much less is known about the polarizability distributions inside the nucleon. To measure these distributions it is necessary to use the virtual-Compton-scattering (VCS) reaction [3], where the incident photon is virtual. At low Q 2 it is expected [4] that Q 2 should decrease with increasing Q 2 with a characteristic length scale given by the pion range. The first VCS experiments at Mainz [5] at Q 2 0:33 GeV 2 =c 2 and later at Jefferson Lab (JLab) [6] at Q 2 0:92 and 1:76 GeV 2 =c 2 established that Q 2 is falling off, but with a form inconsistent with a simple dipole shape [6]. By contrast, because of the destructive interference between paramagnetism and diamagnetism which is necessary to generate a small , Q 2 is predicted [4] to be relatively flat as a function of Q 2 with a 20% peaking near Q 2 0:1 GeV 2 =c 2 caused by a paramagnetic pion-loop contribution that increases with Q 2 . This Letter reports on a VCS experiment on the proton performed at the out-ofplane scattering facility at the MIT-Bates linear accelerator at Q 2 0:057 GeV 2 =c 2 . Data taken at this low Q 2 can provide a test of chiral perturbation theory (ChPT), and are sensitive to the mean square electric and magnetic polarizability radii. At this low value of Q 2 ChPT also predicts increased sensitivity to the polarizabilities Q 2 and Q 2 relative to the Mainz kinematics [4]. The relationship between VCS cross sections and the polarizabilities is most easily seen in the low-energy expansion (LEX) of the unpolarized VCS cross section [3],where q (q 0 ) is the incident (final) photon three-momenta in the photon-nucleon c.m. frame, " is the photon polarization, () is the c.m. polar (azimuthal) angle for the outgoing photon, and is a phase space factor. d 5 BHBorn is the cross section for the Bethe-Heitler Born amplitudes only, i.e., no nucleon structure, and is e...

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supporting

confidence: 68%

mentioning

confidence: 99%

Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at LowQ2Using the Virtual-Compton-Scattering Reaction

Bourgeois¹,

Sato²,

Shaw³

et al. 2006

Phys. Rev. Lett.

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“…Whereas the scalar polarizabilities have been measured quite accurately by comparing the RCS data directly to the LEX [1,2], the quest to determine the vector polarizabilities is still going on. The difficulty to measure the vector polarizabilities is caused by their suppression at low energies, which makes it impossible to extract them at energies E γ < 100 MeV.…”

Section: Introductionmentioning

confidence: 99%

Higher order forward spin polarizability

2010

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As a guideline for future experiments to extract the four (leading) spin polarizabilities of the nucleon, we have constructed the forward amplitude for polarized Compton scattering by dispersion integrals. These integrals have been saturated by recently measured helicity-dependent photoabsorption cross sections as well as predictions for pion photoproduction multipoles from several phenomenological descriptions and chiral perturbation theory. The comparison of these results corroborates the strategy to extract the spin polarizabilities by fitting them to polarizedCompton data and fixing all higher order spin effects by dispersion relations based on pion photoproduction multipoles.

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“…The CB and TAPS detectors cover 96% of the 4π steradians around the target, upon which a bremsstrahlung photon beam, produced by the electron beam impinging on a thin radiator, is incident. Compton scattering from 3 He is a novel technique in this experimental pursuit that is expected to produce better results than the previous, largely unsuccessful technique of Compton scattering from deuterium [2].…”

Section: Methodsmentioning

confidence: 99%

Active helium target: Neutron scalar polarizability extraction via Compton scattering

Morris

Annand

Hornidge

et al. 2015

AIP Conference Proceedings

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Abstract. Precise measurement of the neutron scalar polarizabilities has been a lasting challenge because of the lack of a free-neutron target. Led by the University of Glasgow and the Mount Allison University groups of the A2 collaboration in Mainz, Germany, preparations have begun to test a recent theoretical model with an active helium target with the hope of determining these elusive quantities with small statistical, systematic, and model-dependent errors. Apparatus testing and background-event simulations have been carried out, with the full experiment projected to run in 2015. Once determined, these values can be applied to help understand quantum chromodynamics in the nonperturbative region.

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Polarizability of the nucleon and Compton scattering

Cited by 112 publications

References 171 publications

Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at LowQ2Using the Virtual-Compton-Scattering Reaction

Measurements of the Generalized Electric and Magnetic Polarizabilities of the Proton at LowQ2Using the Virtual-Compton-Scattering Reaction

Higher order forward spin polarizability

Active helium target: Neutron scalar polarizability extraction via Compton scattering

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