Large logarithms in the beam normal spin asymmetry of elastic electron-proton scattering

Afanasev, A.; Merenkov, N. P.

doi:10.1103/physrevd.70.073002

Cited by 43 publications

(83 citation statements)

References 29 publications

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“…The predictions of Eqs. (47,49) are confronted with the experimental data of Ref. [47] at high energies and for Q 2 that ranged from zero to several GeV 2 in Fig.…”

Section: Uncertainty In Isospin Rotating the Backgroundmentioning

confidence: 99%

“…However, real experiments are carried out at finite momentum transfer t, in particular |t| = 0.03 GeV 2 for the kinematics of the QWEAK experiment. To extrapolate the forward sum rule to non-zero momentum transfer, we employ the phenomenological model that was successfully used for the beam normal spin (Mott) asymmetry in elastic ep-scattering [49][50][51]. This model is inspired by i) experimental data on the Compton differential cross section at small t and high energy, and ii) the assumption of the predominantly imaginary phase of the Compton amplitude at high energies (as for the pomeron).…”

Section: Additional T-dependence Of Dispersion Correctionsmentioning

confidence: 99%

“…Based on this ansatz, Ref. [49] proposed parameterizing the t-dependence of the slightly off-forward total cross section as…”

Section: Additional T-dependence Of Dispersion Correctionsmentioning

confidence: 99%

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Model dependence of theγZdispersion correction to the parity-violating asymmetry in elasticepscattering

2011

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We analyze the dispersion correction to elastic parity violating electron-proton scattering due to γZ exchange. In particular, we explore the theoretical uncertainties associated with modeling contributions of hadronic intermediate states. Taking into account constraints from low-and high-energy, parity-conserving electroproduction measurements, choosing different models for contributions from the non-resonant processes, and performing the corresponding flavor rotations to obtain the electroweak amplitude, we arrive at an estimate of the uncertainty in the total contribution to the parity-violating asymmetry. At the kinematics of the Q-Weak experiment, we obtain a correction to the asymmetry equivalent to a shift in the proton weak charge of (0.0054 ± 0.0020). This should be compared to the value of the proton's weak charge of Q p W = 0.0713 ± 0.0008 that includes Standard Model contributions at tree level and one-loop radiative corrections. Therefore, we obtain a new Standard Model prediction for the parity-violating asymmetry in the kinematics of the Q-Weak experiment of (0.0767 ± 0.0008 ± 0.0020γZ ). The latter error leads to a relative uncertainty of 2.8% in the determination of the proton's weak charge, and is dominated by the uncertainty in the isospin structure of the inclusive cross section. We argue that future parity-violating inelastic ep asymmetry measurements at low-to-moderate Q 2 and W 2 could be exploited to reduce the uncertainty associated with the dispersion correction. Because the corresponding shift and error bar decrease monotonically with decreasing beam energy, a determination of the proton's weak charge with a lower-energy experiment or measurements of "isotope ratios" in atomic parity-violation could provide a useful cross check on any implications for physics beyond the Standard Model derived from the Q-Weak measurement.

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“…The predictions of Eqs. (47,49) are confronted with the experimental data of Ref. [47] at high energies and for Q 2 that ranged from zero to several GeV 2 in Fig.…”

Section: Uncertainty In Isospin Rotating the Backgroundmentioning

confidence: 99%

Section: Additional T-dependence Of Dispersion Correctionsmentioning

confidence: 99%

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Model dependence of theγZdispersion correction to the parity-violating asymmetry in elasticepscattering

2011

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“…Recent calculations have shown that in the forward kinematics, a logarithmic enhancement takes place [13], but the contribution of the ln 2 (−t/m 2 ) term comes with photon helicity flip amplitude of RCS and its contribution is negligibly small [14,15]. Vanishing of the RCS contribution at the exact quasi-RCS point requires that we take into account the full k 1 and Q 2 1,2 dependence of the hadronic tensor.…”

Section: Calculation Of B N In the Forward Kinematicsmentioning

confidence: 99%

Doubly virtual Compton scattering and the beam normal spin asymmetry

Gorchtein

2006

Phys. Rev. C

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We construct an invariant basis for Compton scattering with two virtual photons (VVCS). The basis tensors are chosen to be gauge invariant and orthogonal to each other. The properties of the corresponding 18 invariant amplitudes are studied in detail. We consider the special case of elastic VVCS with the virtualities of the initial and final photons equal. The invariant basis for VVCS in this orthogonal form does not exist in the literature. We furthermore use this VVCS tensor for a calculation of the beam normal spin asymmetry in the forward kinematics. For this, we relate the invariant amplitudes to the helicity amplitudes of the VVCS reaction. The imaginary parts of the latter are related to the inclusive cross section by means of the optical theorem. We use the phenomenological value of the transverse cross section σ T ∼ 0.1 mb and the Callan-Gross relation which relates the longitudinal cross section σ L to the transverse one. The result of the calculation agrees with an existing calculation, and predicts negative values of the asymmetry B n of order of 5 ppm in the energy range from 3 to 45 GeV and for very forward angles.

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“…In Refs. [8,9,10,11] (double) logarithms of the type log(Q 2 /m 2 l ) were advocated in connection with the transverse beam SSA in elastic lepton-nucleon scattering. Such logarithmic terms might also increase the beam SSA in DIS considered here.…”

Section: Two-photon Exchange In Inclusive Dismentioning

confidence: 99%

Two-Photon Exchange in (Semi-)Inclusive DIS

Schlegel¹,

Metz²,

Crabb³

et al. 2009

AIP Conference Proceedings

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Abstract. In this note 1 we consider effects of a Two-Photon Exchange (TPE) in inclusive DIS and semi-inclusive DIS (SIDIS). In particular, transverse single spin asymmetries are generated in inclusive DIS if more than one photon is exchanged between the lepton and the hadron. We briefly summarize the TPE in DIS in the parton model and extend our approach to SIDIS, where a new leading twist sin(2φ ) contribution to the longitudinal beam spin asymmetry shows up. Possible TPE effects for the Sivers and the Collins asymmetries in SIDIS are power-suppressed.

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Large logarithms in the beam normal spin asymmetry of elastic electron-proton scattering

Cited by 43 publications

References 29 publications

Model dependence of theγZdispersion correction to the parity-violating asymmetry in elasticepscattering

Model dependence of theγZdispersion correction to the parity-violating asymmetry in elasticepscattering

Doubly virtual Compton scattering and the beam normal spin asymmetry

Two-Photon Exchange in (Semi-)Inclusive DIS

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