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Title: Proton polarizabilities: Status, relevance, prospects

Abstract

This is a brief review of the status of understanding the proton polarizabilities in chiral perturbation theory and of their relevance to the 'proton charge radius puzzle'.

Authors:
 [1]
  1. Institut für Kernphysik, Johannes Gutenberg Universität Mainz (Germany)
Publication Date:
OSTI Identifier:
22280678
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1563; Journal Issue: 1; Conference: Workshop to explore physics opportunities with intense, polarized electron beams at 50-300 MeV, Cambridge, MA (United States), 14-16 Mar 2013; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CHIRALITY; PARTICLE RADII; PARTICLE STRUCTURE; PERTURBATION THEORY; POLARIZABILITY; PROTONS; REVIEWS

Citation Formats

Pascalutsa, Vladimir. Proton polarizabilities: Status, relevance, prospects. United States: N. p., 2013. Web. doi:10.1063/1.4829408.
Pascalutsa, Vladimir. Proton polarizabilities: Status, relevance, prospects. United States. doi:10.1063/1.4829408.
Pascalutsa, Vladimir. Thu . "Proton polarizabilities: Status, relevance, prospects". United States. doi:10.1063/1.4829408.
@article{osti_22280678,
title = {Proton polarizabilities: Status, relevance, prospects},
author = {Pascalutsa, Vladimir},
abstractNote = {This is a brief review of the status of understanding the proton polarizabilities in chiral perturbation theory and of their relevance to the 'proton charge radius puzzle'.},
doi = {10.1063/1.4829408},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1563,
place = {United States},
year = {Thu Nov 07 00:00:00 EST 2013},
month = {Thu Nov 07 00:00:00 EST 2013}
}
  • The STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) is carrying out a spin physics program colliding transversely or longitudinally polarized proton beams at {radical}(s) = 200-500 GeV to gain deeper insight into the spin structure and dynamics of the proton. These studies provide fundamental insight into Quantum Chromodynamics (QCD). One of the main objectives is the determination of the polarized gluon distribution function, {delta}g, through the measurement of the longitudinal double-spin asymmetry, A{sub LL}, for various processes. Inclusive hadron and jet production from polarized pp collision data collected so far at {radical}(s) =more » 200 GeV using the STAR detector at RHIC have placed important constraints on {delta}g. Di-jet production provides direct access to the initial parton kinematics at leading order (LO) QCD and thus provides sensitivity to the Bjorken-x dependence of {delta}g. The status of the mid-rapidity di-jet cross section analysis from the 2005 RHIC run and the longitudinal double-spin asymmetry at mid-rapidity for the 2006 data sample are discussed in these proceedings. Projections on future di-jet measurements at STAR are provided.« less
  • The sum rule ..cap alpha../sub p/--..beta../sub p/=3.4 x 10/sup -4/ F/sup 3/+1.4alpha-tilde/sub ..pi../ relating the pion polarizability alpha-tilde/sub ..pi../ to the electric and magnetic polarizabilities ..cap alpha../sub p/ and ..beta../sub p/ of the proton is obtained.
  • The Compton scattering cross section on the proton has been measured at laboratory angles of 90{degree} and 135{degree} using tagged photons in the energy range 70--100 MeV and simultaneously using untagged photons in the range 100--148 MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, {bar {alpha}} and {bar {beta}} respectively, of the proton. We find {bar {alpha}}+{bar {beta}}=(15.0 {plus_minus}2.9{plus_minus}1.1{plus_minus}0.4){times}10{sup {minus}4} fm{sup 3}, in agreement with a model-independent dispersion sum rule, and {bar {alpha}} {minus}{bar {beta}} =(10.8{plus_minus}1.1{plus_minus}1.4{plus_minus}1.0){times}10{sup {minus}4} fm{sup 3}, where the errors shown are statistical, systematic, and model-dependent, respectively.more » A comparison with previous experiments is given and global values for the polarizabilities are extracted.« less
  • Virtual Compton Scattering is studied at the Thomas Jefferson National Accelerator Facility at low Center-of-Mass energies, below pion threshold. Following the Low Energy Theorem for the ep {yields} ep{gamma} process, we obtain values for the two structure functions P{sub LL} - P{sub TT}/{var_epsilon} and P{sub LT} at four-momentum transfer squared Q{sup 2} = 0.92 and 1.76 GeV{sup 2}.
  • We report a Virtual Compton Scattering study of the proton at low CM energies. We have determined the structure functions P{sub LL} - P{sub TT}/{epsilon} and P{sub LT}, and the electric and magnetic Generalized Polarizabilities (GPs) {alpha}{sub E}(Q{sup 2}) and {beta}{sub M}(Q{sup 2}) at momentum transfer Q{sup 2} = 0.92 and 1.76 GeV{sup 2}. The electric GP shows a strong fall-off with Q{sup 2}, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a fall-off; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at lowmore » Q{sup 2}, compensated at higher Q{sup 2} by a paramagnetic contribution from {pi}N intermediate states.« less