The interpretation of parity-violating electron-scattering experiments

Musolf, M. J.; Donnelly, T. W.

doi:10.1016/0375-9474(92)90545-u

Cited by 100 publications

(162 citation statements)

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“…The amplitudes for the γ-and Z-exchange processes are then given by [45] 38) where G µ is the Fermi constant for muon decay, g denote matrix elements of the electromagnetic and weak neutral currents, i.e. The parity-violating asymmetry A is given by the ratio of the difference over the sum of the inclusive cross sections dσ h /dΩdω for incident electrons with helicities h = ±1.…”

Section: A Longitudinal Asymmetry and Spin Rotation In Np Elastic Scmentioning

confidence: 99%

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Parity-violating interaction effects in thenpsystem

2004

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We investigate parity-violating observables in the np system, including the longitudinal asymmetry and neutron-spin rotation in np elastic scattering, the photon asymmetry in np radiative capture, and the asymmetries in deuteron photo-disintegration d( γ, n)p in the threshold region and electrodisintegration d( e, e ′ )np in quasi-elastic kinematics. To have an estimate of the model dependence for the various predictions, a number of different, latest-generation strong-interaction potentials-Argonne v 18 , Bonn 2000, and Nijmegen I-are used in combination with a weak-interaction potential consisting of π-, ρ-, and ω-meson exchanges-the model known as DDH. The complete bound and scattering problems in the presence of parity-conserving, including electromagnetic, and parity-violating potentials is solved in both configuration and momentum space. The issue of electromagnetic current conservation is examined carefully. We find large cancellations between the asymmetries induced by the parity-violating interactions and those arising from the associated pion-exchange currents. In the np capture, the model dependence is nevertheless quite small, because of constraints arising through the Siegert evaluation of the relevant E 1 matrix elements. In quasi-elastic electron scattering these processes are found to be insignificant compared to the asymmetry produced by γ-Z interference on individual nucleons. These two experiments, then, provide clean probes of different aspects of weakinteraction physics associated with parity violation in the np system. Finally, we find that the neutron spin rotation in np elastic scattering and asymmetry in deuteron disintegration by circularly-polarized photons exhibit significant sensitivity both to the values used for the weak vector-meson couplings in the DDH model and to the input strong-interaction potential adopted in the calculation. This reinforces the conclusion that these short-ranged meson couplings are not in themselves physical observables, rather the parity-violating 1 mixings are the physically relevant parameters. 21.30.+y, 25.40.Cm

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Section: A Longitudinal Asymmetry and Spin Rotation In Np Elastic Scmentioning

confidence: 99%

“…Standard manipulations then lead to the following expression for the asymmetry in the extreme relativistic limit for the electron [31,45] …”

Section: A Longitudinal Asymmetry and Spin Rotation In Np Elastic Scmentioning

confidence: 99%

Parity-violating interaction effects in thenpsystem

2004

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“…This last term G ewm A must be calculated in order to allow extraction of G s A from a measurement of G e A in elastic electron scattering. The difficulties in calculating this term have been noted already [9,12,13,14], and have played a role in recent experimental work. The SAMPLE experiment, which combined backward-angle electron-scattering data on proton and deuteron targets to extract G s M and G e A at Q 2 = 0.091 GeV 2 , originally reported [15] values of G s M = 0.14 ± 0.29 ± 0.31 and G e A = 0.22 ± 0.45 ± 0.39, which deviated from the calculated value [14] of G e A by 1.5σ and had the opposite sign.…”

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confidence: 99%

“…Another technique for avoiding the axial term is to observe the parity-violating asymmetry in scattering from a spinless, isoscalar target, like 4 He, as proposed by Musolf and Donnelly [13]. In this case, only the electric form factors contribute to the asymmetry.…”

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confidence: 99%

Determination of the Strange Form Factors of the Nucleon fromνp,ν¯p, and Parity-Violatinge→
Pate
¹

2004
Phys. Rev. Lett.
62
2
67
0
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Determination of the strange form factors of the nucleon from νp,νp, and parity-violating ep elastic scattering A new method of obtaining the strange form factors of the nucleon is presented, in which forwardangle parity-violating ep elastic scattering data is combined with νp andνp elastic scattering data. The axial form factor in electron-nucleon scattering is complicated by the presence of electro-weak radiative corrections that in principle need to be calculated or separately measured, but this axial form factor is suppressed at forward angles. The neutrino data has no such complication. Hence the use of forward-angle parity-violating ep data with νp andνp data allows the extraction of all three strange form factors: electric, magnetic and axial (G s E , G s M , and G s A ). In this letter, νp and νp data from the Brookhaven E734 experiment are combined with the Jefferson Lab HAPPEX ep data to obtain two distinct solutions for the strange form factors at Q 2 = 0.5 GeV 2 . More generally, combining the neutrino elastic scattering data from E734 with the existing and upcoming ep data will yield the strange form factors of the nucleon for Q 2 of 0.45-1.05 GeV 2 . Measurement of G s A is crucial to the determination of the strange quark contribution to the nucleon spin, ∆s.

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“…1(c) and 1(d) and other diagrams. The radiative corrections to A P V have been discussed in [9,10]. However, theoretical uncertainties remain.…”

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Erratum: Two-Photon-Exchange andγZ-Exchange Corrections to Parity-Violating Elastic Electron-Proton Scattering [Phys. Rev. Lett.99, 262001 (2007)]

Zhou¹,

Kao²,

Yang³

2008

Phys. Rev. Lett.

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Leading electroweak corrections play an important role in precision measurements of the strange form factors. We calculate the two-photon-exchange (TPE) and γZ-exchange corrections to the parity-violating asymmetry of the elastic electron-proton scattering in a simple hadronic model including the finite size of the proton. We find both can reach a few percent and are comparable in size with the current experimental measurements of strange-quark effects in the proton neutral weak current. The effect of γZ-exchange is in general larger than that of TPE, especially at low momentum transfer Q 2 ≤ 1GeV 2 . Their combined effects on the values of G s E + βG s M extracted in recent experiments can be as large as −40% in certain kinematics.PACS numbers: 13.40. Ks, 13.60.Fz, 13.88.+e, 14.20.Dh Strangeness content in the proton remains one of the most intriguing questions in hadron structure. Early indications on the contribution of strange quarks to the nucleon properties came from neutrino and electron deep inelastic scatterings and pion-nucleon sigma term, which suggested that strange quarks might give non-negligible contributions to the spin and mass of the proton [1]. Many other observables were later suggested, including excess φ production in pp annihilation [2], double polarizations in photo-and electroproduction of φ meson [3], and asymmetry in scattering of longitudinally polarized electrons from polarized targets, to probe the strangeness in the nucleon.Parity-violating asymmetryin polarized electron elastic scattering arises from the interference of weak and electromagnetic amplitudes. Weak neutral current elastic scattering is mediated by the Z-exchange and measures form factors which are sensitive to a different linear combination of the three light quark distributions. When combined with proton and neutron electromagnetic form factors and with the use of charge symmetry, the strange electric and magnetic form factors, G s E and G s M , can then be determined [4]. Since this is a rather clean technique to access the charge and magnetization distributions of the strange quark within nucleons, four experimental programs SAMPLE [5], HAPPEX [6], A4 [7], and G0 [8] have been designed to measure this important quantity, which is small and ranges from 0.1 to 100 ppm. This calls for greater efforts to reduce theoretical uncertainty in order to arrive at a more reliable interpretation of experiments.At tree level, parity violation in electron scattering e(p 1 ) + p(p 2 ) → e(p 3 ) + p(p 4 ) comes from the interference of diagrams with one-photon-exchange (OPE) and Z-boson exchange shown, respectively, in Figs. 1(a) and 1(b). Leading order radiative corrections include the box e(p 1 ) diagrams shown in Figs. 1(c) and 1(d) and other diagrams. The radiative corrections to A P V have been discussed in [9,10]. However, theoretical uncertainties remain. Recently, the contribution of the interference of the two-photon-exchange (TPE) process of Fig. 1(c) with diagram of Figs. 1(a) and 1(b) to A P V , has been evaluated in...

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The interpretation of parity-violating electron-scattering experiments

Cited by 100 publications

References 47 publications

Parity-violating interaction effects in thenpsystem

Parity-violating interaction effects in thenpsystem

Determination of the Strange Form Factors of the Nucleon fromνp,ν¯p, and Parity-Violatinge→
Pate
¹

2004
Phys. Rev. Lett.
62
2
67
0
View full text Add to dashboard Cite

Erratum: Two-Photon-Exchange andγZ-Exchange Corrections to Parity-Violating Elastic Electron-Proton Scattering [Phys. Rev. Lett.99, 262001 (2007)]

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The interpretation of parity-violating electron-scattering experiments

Cited by 100 publications

References 47 publications

Parity-violating interaction effects in thenpsystem

Parity-violating interaction effects in thenpsystem

Determination of the Strange Form Factors of the Nucleon fromνp,ν¯p, and Parity-Violatinge→Pate1 2004Phys. Rev. Lett.622670View full textAdd to dashboardCite

Erratum: Two-Photon-Exchange andγZ-Exchange Corrections to Parity-Violating Elastic Electron-Proton Scattering [Phys. Rev. Lett.99, 262001 (2007)]

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Determination of the Strange Form Factors of the Nucleon fromνp,ν¯p, and Parity-Violatinge→
Pate
¹

2004
Phys. Rev. Lett.
62
2
67
0
View full text Add to dashboard Cite