First Measurement of the 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>Q</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:math>
 Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon

Esser, A.; Thiel, M.; Achenbach, P.; Aulenbacher, K.; Baunack, S.; Beričič, J.; Bosnar, D.; Correa, L.; Dehn, M.; Distler, M. O.; Fonvieille, H.; Friščić, I.; Heidrich, Steffen; Herrmann, P.; Hoek, M.; Kegel, S.; Kohl, Y.; Kolar, T.; Kreidel, H. J.; Maas, F. E.; Merkel, H.; Mihovilovič, M.; Müller, J.; Müller, U.; Nillius, F.; Palatchi, C.; Paschke, K.; Pochodzalla, J.; Schlimme, B. S.; Schoth, M.; Schulz, Florian; Širca, S.; Spruck, Bjoern; Štajner, S.; Tioukine, V.; Tyukin, A.; Weber, A.; Sfienti, C.

doi:10.1103/physrevlett.121.022503

Cited by 19 publications

(28 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…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.…”

mentioning

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.

Self Cite

View full text Add to dashboard Cite

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...

show abstract

mentioning

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.

Self Cite

View full text Add to dashboard Cite

show abstract

“…However, these data do not indicate variations of the residual horizontal polarization components above the 1 % level. The correspond- ing uncertainties for the analysis of the A n experiment are sufficiently small compared to the achieved statistical precision [8].…”

Section: Stability During the Beamtimementioning

confidence: 93%

“…The sources of the disagreement are presently not understood and motivate more measurements for target nuclei in the intermediate mass range. In this context, A n of carbon has been recently measured at MAMI by using the spectrometer setup of the A1 collaboration [8].…”

Section: Introductionmentioning

confidence: 99%

Vertical Beam Polarization at MAMI

Schlimme

Achenbach

Aulenbacher

et al. 2017

Nuclear Instruments and Methods in Physics Research Section A:

Self Cite

View full text Add to dashboard Cite

For the first time a vertically polarized electron beam has been used for physics experiments at MAMI in the energy range between 180 and 855 MeV. The beam-normal single-spin asymmetry A n , which is a direct probe of higherorder photon exchange beyond the first Born approximation, has been measured in the reaction 12 C( e, e ) 12 C. Vertical polarization orientation was necessary to measure this asymmetry with the existing experimental setup. In this paper we describe the procedure to orient the electron polarization vector vertically, and the concept of determining both its magnitude and orientation with the available setup. A sophisticated method has been developed to overcome the lack of a polarimeter setup sensitive to the vertical polarization component.

show abstract

“…Scattered electrons were detected in the high-resolution spectrometer (HRS) and knocked-out neutrons were detected using the Hall A Neutron Detector (HAND) [14,15]. This experiment ran concurrently with multiple experiments that measured quasi-elastic structure on polarized 3 He [16,17,18,19]. The 3 He target was polarized through spin-exchange optical pumping (SEOP) [20,21,22,23,24].…”

Section: Scipost Physics Proceedings Submissionmentioning

confidence: 99%

Report on scipost_201910_00013v1

2019

View full text Add to dashboard Cite

Electron-induced proton, neutron and deuteron knock-out remains the most versatile probe of the electro-magnetic properties and spin structure of light nuclei. The advent of highly polarized beams and targets and improvements in recoil polarization methods, as well as analysis and simulation techniques, have enabled us to study the static and dynamical properties of few-body systems with unprecedented precision. Recent experiments at Jefferson Lab and MAMI are presented and put into perspective of state-of-the art Faddeev calculations, with focus on the 3 He nucleus. SciPost Physics ProceedingsSubmission Newport News, USA, or at the MAMI Accelerator Facility in Mainz, Germany. In this paper we present the results of a select list of the most relevant recent experiments: TJNAF E05-102, dedicated to the measurement of double-spin asymmetries in the 3 He( e, e d)p, 3 He( e, e p)d and 3 He( e, e p)pn processes in the quasi-elastic region; the TJNAF E05-015, whose main goal was the determination of target single-spin asymmetry in the quasi-elastic 3 He ↑ (e, e ) process; the TJNAF E08-005 in which we studied target single-spin asymmetries in quasi-elastic 3 He ↑ (e, e n) and double-spin asymmetries in quasi-elastic 3 He( e, e n); and the MAMI Project 'N' with the first-ever attempt to investigate the triple-polarized process 3 He( e, e p) in order to study the spin-dependent distribution of polarized pd clusters in 3 He. The 3 He nucleus is indeed the playground for tests of few-body nuclear dynamics [1, 2], but lately 2 H and 12 C have also received renewed attention due to their relevance for the study of medium modifications of elastic form-factors of nucleons; here we outline our efforts to determine the single-spin asymmetries in 12 C(e ↑ , e ) as well as recoil polarizations in 2 H( e, e p) and 12 C( e, e p) processes.

show abstract

First Measurement of the Q2 Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon

Cited by 19 publications

References 29 publications

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

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

Vertical Beam Polarization at MAMI

Report on scipost_201910_00013v1

Contact Info

Product

Resources

About