Measurement and tricubic interpolation of the magnetic field for the OLYMPUS experiment

Bernauer, J. C.; Diefenbach, J.; Elbakian, G.; Gavrilov, G.; Goerrissen, N.; Hasell, D.; Henderson, Brian S.; Holler, Y.; Karyan, G.; Ludwig, J.; Marukyan, H.; Naryshkin, Y.; O'Connor, Colton; Russell, Rebecca L.; Schmidt, Axel; Schneekloth, U.; Suvorov, K.; Veretennikov, D.

doi:10.1016/j.nima.2016.03.115

Cited by 14 publications

(17 citation statements)

References 11 publications

(11 reference statements)

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“…Alternating beams of electrons and positrons in the DORIS storage ring were passed through a windowless unpolarized hydrogen target that was internal to the ring vacuum [15]. The OLYMPUS spectrometer [13] consisted of two instrumented sectors of an 8-coil toroid magnet [16] surrounding the target, shown in Fig. 1 right.…”

Section: The Olympus Experimentsmentioning

confidence: 99%

Charge-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Schmidt¹

2022

Proceedings of Particles and Nuclei International Conference 2021 — PoS(PANIC2021)

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Measurements of the proton's form factor ratio made with polarization transfer show a striking discrepancy relative to the ratio extracted from unpolarized elastic electron-proton scattering cross sections. One hypothesis is that the discrepancy is caused by hard two-photon exchange (TPE), a typically neglected radiative correction that may bias the two approaches differently. This hypothesis has been challenging to confirm. Theoretical estimates of TPE are model-dependent, and recent experimental determinations of TPE lacked the kinematic reach to be conclusive. The possible impact of TPE remains a cloud over our knowledge of the proton's form factors. Recently, the OLYMPUS experiment published new elastic scattering cross sections that are insensitive to the effects of TPE: specifically the average of electron-proton and positron-proton cross sections. The OLYMPUS experiment, conducted at DESY, Hamburg, measured elastic − and + scattering by detecting the scattered lepton and recoiling proton in coincidence in a large-acceptance, toroidal magnetic spectrometer. OLYMPUS was designed to measure the + / − cross section ratio to isolate the effects of TPE. By exploiting the over determined kinematics of the reaction, the absolute efficiency of spectrometer could be verified, allowing cross sections to be extracted from the data. These results can help refine our knowledge of the proton's form factors, especially in the squared momentum-transfer region of 1-2 GeV 2 , where some previous measurements are in tension.

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Section: The Olympus Experimentsmentioning

confidence: 99%

Charge-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Schmidt¹

2022

Proceedings of Particles and Nuclei International Conference 2021 — PoS(PANIC2021)

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“…unpolarized hydrogen target that was internal to the ring vacuum [19]. The OLYMPUS spectrometer [17] consisted of two instrumented sectors of an 8-coil toroid magnet [20] surrounding the target, shown in Fig. 2 left.…”

Section: The Olympus Experimentsmentioning

confidence: 99%

Charged-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Schmidt¹

2021

Preprint

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Measurements of the proton's form factor ratio made with polarization transfer show a striking discrepancy relative to the ratio extracted from unpolarized elastic electron-proton scattering cross sections. One hypothesis is that the discrepancy is caused by hard two-photon exchange (TPE), a typically neglected radiative correction that may bias the two approaches differently. This hypothesis has been challenging to confirm. Theoretical estimates of TPE are model-dependent, and recent experimental determinations of TPE lacked the kinematic reach to be conclusive. The possible impact of TPE remains a cloud over our knowledge of the proton's form factors. Recently, the OLYMPUS experiment published new elastic scattering cross sections that are insensitive to the effects of TPE: specifically the average of electron-proton and positron-proton cross sections. The OLYMPUS experiment, conducted at DESY, Hamburg, measured elastic 𝑒 − 𝑝 and 𝑒 + 𝑝 scattering by detecting the scattered lepton and recoiling proton in coincidence in a large-acceptance, toroidal magnetic spectrometer. OLYMPUS was designed to measure the 𝑒 + 𝑝/𝑒 − 𝑝 cross section raio to isolate the effects of TPE. By exploiting the over determined kinematics of the reaction, the absolute efficiency of spectrometer could be verified, allowing cross sections to be extracted from the data. These results can help refine our knowledge of the proton's form factors, especially in the squared momentum-transfer region of 1-2 GeV 2 , where some previous measurements are in tension.

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“…Walls of time-of-flight scintillator paddles provided a trigger signal for the tracking detectors and rough particle identification information, while large-acceptance drift chambers permitted exclusive reconstruction of leptons and protons trajectories from elastic scattering events. The lepton beam species was alternated daily to control long-period systematic effects on the measurement of the e + p and e − p cross sections, and the detector positions and magnetic field were surveyed in detail to properly account for the acceptance differences for e + p and e − p events [29]. Using the precise survey of the detector system and magnetic field in conjunction with a newly written generator for radiative e ± p events [26,30], a detailed Geant4 [31] simulation was developed to account for the effects of non-hard TPE lepton charge odd effects as well as the detector acceptance and efficiency.…”

Section: The Olympus Experimentsmentioning

confidence: 99%

Results from the OLYMPUS Experiment on the Contribution of Hard Two-Photon Exchange to Elastic Electron-Proton Scattering

Henderson¹

2018

Proceedings of XVII International Conference on Hadron Spectroscopy and Structure — PoS(Hadron2017)

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Measurements of the ratio of the elastic form factors of the proton (µ p G E /G M ) exhibit a strong discrepancy. Experiments using unpolarized beams and Rosenbluth separation to determine the form factors have found values of the ratio approximately consistent with unity over a wide range of Q 2 , while polarization transfer experiments suggest that the ratio decreases as a function of Q 2 . The most widely-accepted hypothesis to explain this discrepancy is that hard two-photon exchange (TPE) significantly contributes to the elastic ep cross section. Hard TPE has been neglected in previous analyses of electron-proton scattering scattering experiments, in part due to the fact that there exists no model independent way to calculate the contribution. The effect of hard TPE may be measured experimentally, however, via precise determination of the ratio of the electron-proton and positron-proton elastic cross sections. The OLYMPUS experiment collected more than 3 fb −1 of exclusive e − p and e + p elastic scattering data at DESY in 2012, and has determined the elastic σ e + p /σ e − p ratio to unprecedented precision up to Q 2 ≈ 2.2 (GeV/c) 2 , ε ≈ 0.4. This presentation will discuss the OLYMPUS experiment and analysis, and present the recently published results from OLYMPUS in the context of the results from the other two TPE experiments.

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Measurement and tricubic interpolation of the magnetic field for the OLYMPUS experiment

Cited by 14 publications

References 11 publications

Charge-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Charge-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Charged-averaged elastic lepton-proton scattering cross section results from OLYMPUS

Results from the OLYMPUS Experiment on the Contribution of Hard Two-Photon Exchange to Elastic Electron-Proton Scattering

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