New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei

Abrahamyan, Sergey; Acha, A.; Afanasev, A.; Ahmed, Z.; Al-Bataineh, H.; Aniol, K.; Armstrong, David; Armstrong, W.; Arrington, J.; Averett, T.; Babineau, B.; Bailey, S. L.; Barber, Jim; Barbieri, A.; Beck, A.; Bellini, V.; Beminiwattha, R.; Benaoum, H.; Benesch, J.; Benmokhtar, F.; Bertin, P.Y.; Bielarski, T.; Boeglin, W.; Bosted, P.; Butaru, F.; Burtin, E.; Cahoon, J.L.; Camsonne, A.; Canan, M.; Carter, P.; Cc, Chang; Cates, G. D.; Chao, Yu‐Chiu; Chen, C.; Chen, J. P.; Choi, S.; Chudakov, E.; Cisbani, E.; Craver, B.; Cusanno, F.; Dalton, M. M.; Лео, Р. Де; Jager, Kees de; Deconinck, W.; Decowski, P.; Deepa, D.; Deng, X.; Deur, A.; Dutta, D.; Étilé, A.; Ferdi, C.; Feuerbach, R. J.; Finn, J. M.; Flay, D.; Franklin, G.; Friend, M.; Frullani, S.; Fuchey, E.; Fuchs, Sabine; Fuoti, K.; Garibaldi, F.; Gasser, E.; Gilman, R.; Giusa, A.; Glamazdin, A.; Glesener, Lindsay; Gómez, J.; Gorchtein, Mikhail; Grames, Joseph; Grimm, K.; Gu, C.; Hansén, O.; Hansknecht, J.; Hen, O.; Higinbotham, D. W.; Holmes, R.; Holmstrom, T.; Horowitz, C. J.; Hoskins, J. R.; Huang, J.; Humensky, T. B.; Hyde‐Wright, C. E.; Ibrahim, H.; Itard, F.; Jen, C. M.; Jensen, Eric R.; Jiang, X.; Gao, Jin; Johnston, S.; Katich, Joseph M.; Kaufman, L. J.; Kelleher, A.; Kliakhandler, K.; P, King; Kolarkar, A.; Kowalski, S.; Kuchina, E.; Kumar, Krishna; Lagamba, L.; Lambert, D.; LaViolette, Paul A.; Leacock, J.; Leckey, J.; Lee, Jeong Han; LeRose, J.; Lhuillier, D.; Lindgren, R.; Liyanage, N.; Lubinsky, N.; Mammei, J.; Mammoliti, F.; Margaziotis, D. J.; Markowitz, P.; Mazouz, M.; McCormick, K.; McCreary, Amber; McNulty, D.; Meekins, D.; Mercado, L.; Meziani, Z. E.; Michaels, R.; Mihovilovič, M.; Moffit, B.; Monaghan, Peter; Muangma, N.; Muñoz-Camacho, C.; Nanda, S.; Nelyubin, V.; Neyret, D.; Nuruzzaman, Md.; Oh, Yongseok; Otis, K.; Palmer, Adam James; Parno, D. S.; Paschke, K.; Phillips, S. K.; Poelker, M.; Pomatsalyuk, R.; Posik, M.; Potokar, M.; Prok, K.; Puckett, A. J. R.; Qian, X.; Qiang, Y.; Quinn, B.; Rakhman, A.; Reimer, P. E.; Reitz, B.; Riordan, S.; Roche, J.; Rogan, P.; Ron, G.; Russo, G.; Saenboonruang, Kiadtisak; Saha, A.; Sawatzky, B.; Shahinyan, A.; Silwal, R.; Singh, J.; Širca, S.; Slifer, K.; Snyder, R.; Solvignon, P.; Souder, P. A.; Sperduto, M. L.; Subedi, R.; Stutzman, Marcy; Suleiman, R.; Sulkosky, V.; Sutera, C.; Tobias, W. A.; Troth, W.; Urciuoli, G. M.; Ulmer, P. E.; Vacheret, A.; Voutier, E.; Waidyawansa, B.; Wang, D.; Wang, K.; Wexler, J.; Whitbeck, A.; Wilson, Richard; Wojtsekhowski, B.; Yan, X.; Huang, Yao; Ye, Y.; Ye, Z.; Yim, V.; Zana, L.; Zhan, X.; Zhang, J.; Zhang, Y.; Zheng, X.; Ziskin, V.; Zhu, P.

doi:10.1103/physrevlett.109.192501

Cited by 51 publications

(66 citation statements)

References 33 publications

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“…The exchange of two virtual photons implies the excitation of nucleon intermediate states offering the possibility of testing models of hadronic structure [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In contrast to previous measurements at forward [23,24] and close to right angles [25], the A4 measurements presented in this work have been performed at large backward angles. The A4 measurements explore a new important parameter region of the virtualities of the exchanged virtual photons, involved in the theoretical calculation of the nucleon intermediate states, see Fig.…”

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confidence: 40%

“…The measurement of A ⊥ is so far the only measured observable to access the imaginary part ofF 4 andF 5 . Moreover, it allows for a test of models of the excitation of the intermediate state in the double virtual Compton scattering on the nucleon.The first measurement of the SAMPLE experiment of A ⊥ in the elastic electron-proton scattering is at backward angles at [25], the measurements of Happex at GeV energies, which include besides the hydrogen target heavier nuclei [24], and the preliminary measurements of the Q weak experiment in the elastic electron-proton scattering and in the inelastic scattering on hydrogen, aluminum, and carbon [41]. There is a very recent measurement of the A1 experiment at MAMI of A ⊥ in the reaction 12 Cð ⃗e; e 0 Þ 12 C [42,43].…”

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confidence: 99%

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New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets

Ríos¹,

Aulenbacher²,

Baunack³

et al. 2017

Phys. Rev. Lett.

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New measurements of the beam normal single spin asymmetry in the electron elastic and quasielastic scattering on the proton and deuteron, respectively, at large backward angles and at hQ 2 i ¼ 0.22 ðGeV=cÞ The exchange of two hard virtual photons in the elastic electron-nucleon scattering beyond the one-photon exchange Born approximation has been the subject of recent investigation [1,2]. Two complementary methods, a determination from a measurement of a differential cross section using unpolarized electrons (Rosenbluth separation) and the measurement of the polarization transfer to the proton final state, gave significantly different results forThe two-photon exchange has been addressed as the explanation for such a discrepancy. Other observables in which the two-photon exchange physics plays a role are: neutron form factors, resonance electroproduction, the pion form factor and the elastic electron-nucleus cross section, in particular deuteron and 3 He [1]. The exchange of two virtual photons implies the excitation of nucleon intermediate states offering the possibility of testing models of hadronic structure [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. In contrast to previous measurements at forward [23,24] and close to right angles [25], the A4 measurements presented in this work have been performed at large backward angles. The A4 measurements explore a new important parameter region of the virtualities of the exchanged virtual photons, involved in the theoretical calculation of the nucleon intermediate states, see Fig. 2 from Ref. [11]. Moreover, in contrast to the SAMPLE measurement [26], at similar backward scattering angle, the A4 measurements have improved the precision by a factor ∼4. The A4 measurements have been performed at larger beam energies, probing the πN and Δ resonance inelastic intermediate states.The two-photon exchange physics affects the parity violating asymmetry through the normalization to the electromagnetic amplitude [27] and it is of special relevance in precision measurements of the weak charge of the proton at low Q 2 like Q weak [28] and P2 [29]. It is also useful in the theoretical determination of the γZ box diagrams which also takes part in the proton weak charge radiative corrections [30][31][32][33].Two-photon exchange effects can be observed in radiative corrections to the cross section, the ratio in e − p and e þ p elastic scattering cross sections, the depolarization tensor, and the target and beam normal single spin asymmetries [34][35][36][37]. Six generalized form factors depending on two kinematic variables parametrize the elastic electron-proton scatteringG M ðs; Q 2 Þ,G E ðs; Q 2 Þ, [10]. There are also partonic calculations which resort to generalized parton distributions of the nucleon and are able to resolve the discrepancy at large Q 2 [12,16]. The T-odd observables target and beam normal spin asymmetries arise from the interference of the one-photon and two-photon exchange amplitudes, see Fig. 1 in Ref. [39]. The target normal spi...

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confidence: 40%

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confidence: 99%

New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets

Ríos¹,

Aulenbacher²,

Baunack³

et al. 2017

Phys. Rev. Lett.

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“…At the time when the interest on the two-photon exchange was revived by the polarization-Rosenbluth discrepancy, the techniques as well as expertise for measuring asymmetries of part per million (ppm) had been developed at several facilities like MIT-Bates, JLab and MAMI, aiming at measuring parity-violating asymmetries in electron scattering [56]. With these facilities, investigations of transverse beam spin asymmetries in various kinematic regions have been performed with transversely polarized electrons scattering off different targets [57][58][59][60][61][62], including A4 measurements [63,64] with both hydrogen and deuterium targets at the A4 experiment. In this letter, we report new results of the beam transverse spin asymmetry A ep ⊥ in ep elastic scattering at forward angles over a wide energy range, measured with a full azimuthal-angle detector at the A4 experiment.…”

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confidence: 99%

Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range

Gou¹,

Arvieux²,

Aulenbacher³

et al. 2020

Phys. Rev. Lett.

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We report on a new measurement of the beam transverse single spin asymmetry in electron-proton elastic scattering, A ep ⊥ , at five beam energies from 315.1 MeV to 1508.4 MeV and at a scattering angle of 30 • < θ < 40 • . The covered Q 2 values are 0.032, 0.057, 0.082, 0.218, 0.613 (GeV/c) 2 . The measurement clearly indicates significant inelastic contributions to the two-photon-exchange (TPE) amplitude in the low-Q 2 kinematic region. No theoretical calculation is able to reproduce our result. Comparison with a calculation based on unitarity, which only takes into account elastic and πN inelastic intermediate states, suggests that there are other inelastic intermediate states such as ππN, KΛ and ηN. Covering a wide energy range, our new high-precision data provide a benchmark to study those intermediate states.PACS numbers: 13.60. Fz, 11.30.Er, 13.40.Gp As a probe of hadron structure, electron scattering has two advantages: the structurelessness of the electron and the smallness of the electromagnetic coupling (α ≈ 1/137). The small coupling allows to expand the scattering amplitude in powers of α and to interpret experiments within the one-photon-exchange (Born) approximation. This leading order approximation enables a straightforward extraction of the electromagnetic form factors with the Rosenbluth separation technique [1]. For a precise extraction of the form factors it is necessary to include higher order quantum corrections [2,3]. Importantly, most of those corrections do not alter the Rosenbluth formula in that they contribute an overall factor to the cross section.The contribution that is expected to break this pattern [4,5] is the two-photon-exchange (TPE) diagram depicted in Fig. 1. For a long time the TPE effects have eluded direct experimental searches [6][7][8]. The situation changed when a striking discrepancy between the Rosenbluth separation [9, 10] and the polarization transfer [11?-13] data on the proton form factor ratio µ p G E /G M was observed. To evaluate the TPE corrections one needs to model the doubly-virtual Compton scattering (VVCS) in the most general kinematics. This involves calculating the two-current correlator with inclusive hadronic intermediate states. The full account of the inclusive intermediate states contribution can be made in the limited nearforward kinematics [15]. Beyond the forward kinematics, it is only possible to account for the elastic [16][17][18][19] or the pion-nucleon (πN) [20] intermediate state contributions.The theoretical framework for calculating the TPE contributions plays an important role in evaluating the two-boson-exchange corrections to precision low-energy tests of the Standard Model (SM) in the electroweak sector. The proton polarizability contribution to the fine structure of light muonic atoms stems from the TPE diagram and is a substantial ingredient [21] in the proton radius puzzle, the 7σ discrepancy in the value of the proton charge radius extracted from hydrogen spectroscopy [22] and electron-proton (ep) scattering [23] on one hand, an...

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“…, where σ ↑(↓) is the elastic cross sections for the case that the beam spin polarisation is parallel (antiparallel) to a vector − → k which is defined, using the momentum vectors of incident and outgoing electrons (k in and k out ), by: [4]. The physical cause of the beam normal spin asymmetry is an interference term amongst oneand multi-photon exchange.…”

Section: Beam Normal Spin Asymmetrymentioning

confidence: 99%

“…At the Jefferson-Lab the PREX-Collaboration together with HAPPEX performed a measurement of A n for several nuclei ( 1 H, 4 He, 12 C, 208 Pb) in the Q 2 range between 0.01 and 0.1 GeV 2 /c 2 . While they found an agreement between their measurement and the theoretical calculations from [5] for light nuclei, for lead the theory predicted a value of A (th) n ≈ −8 ppm, but the measurement resulted in a value of A (ex) n = 0.28 ± 0.25 ppm.…”

Section: Beam Normal Spin Asymmetrymentioning

confidence: 99%

Measurement of the Beam Normal Single-Spin Asymmetry of $^{12}$C

Esser¹,

Merkel²,

Thiel³

et al. 2016

Proceedings of 54th International Winter Meeting on Nuclear Physics — PoS(BORMIO2016)

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Beam normal single-spin asymmetry in the elastic scattering of electrons is a direct probe for the two photon exchange. At the Mainz Mictrotron, this asymmetry has been measured for 12 C in the Q 2 range between 0.02 and 0.05 GeV 2 /c 2 . A 570 MeV continuous wave electrons beam was scattered on a carbon target and detected by two magnetic spectrometers. Quartz glass Cherenkov detectors located at the elastic line in the spectrometer's focal plane were used to measure the amount of scattered electrons. The PMTs of which were read out with integrating current ADCs allowing for particle rates too high for counting. The resulting asymmetry shows a surprising deviation from the theoretical predictions.

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New Measurements of the Transverse Beam Asymmetry for Elastic Electron Scattering from Selected Nuclei

Cited by 51 publications

References 33 publications

New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets

New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets

Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range

Measurement of the Beam Normal Single-Spin Asymmetry of $^{12}$C

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