The focal plane proton-polarimeter for the 3-spectrometer setup at MAMI

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We report the first measurements of the transverse (P x and P y ) and longitudinal (P z ) components of the polarization transfer to a bound proton in the deuteron via the 2 H( e, e' p) reaction, over a wide range of missing momentum. A precise determination of the electron beam polarization reduces the systematic uncertainties on the individual components to a level that enables a detailed comparison to a state-of-the-art calculation of the deuteron using free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated P x /P z ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors. They point to an incomplete description of the nuclear reaction mechanism in the calculation.Measurements of the polarization transfer P = (P x , P y , P z ) from a polarized electron to a bound nucleon by the A( e, e' p) reaction and their comparison to those of a free proton were suggested as a powerful tool to observe modifications in the bound proton structure [1]. These require detailed calculations incorporating nuclear effects. However, it still might be conceptually difficult to separate such effects from internal nucleon structure changes.

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confidence: 99%

Components of polarization-transfer to a bound proton in a deuteron measured by quasi-elastic electron scattering

Izraeli¹,

Yaron²,

Schlimme³

et al. 2018

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“…This reduced the systematic uncertainty in the determined polarization transfer components at the reaction point. The proton spectrometer was equipped with a polarimeter placed behind its focal-plane (FPP) using a 7 cm thick carbon analyzer [8,9]. The spin-dependent scattering of the polarized proton by the carbon analyzer enables the determination of the proton transverse polarization components at the focal plane [9].…”

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confidence: 99%

“…The proton spectrometer was equipped with a polarimeter placed behind its focal-plane (FPP) using a 7 cm thick carbon analyzer [8,9]. The spin-dependent scattering of the polarized proton by the carbon analyzer enables the determination of the proton transverse polarization components at the focal plane [9]. The polarization-transfer components at the reaction point were obtained by correcting the measured components for the spin precession in the magnetic field of the spectrometer.…”

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confidence: 99%

Measurement of polarization-transfer to bound protons in carbon and its virtuality dependence

Izraeli¹,

Brecelj²,

Achenbach³

et al. 2018

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We measured the ratio P x /P z of the transverse to longitudinal components of polarization transferred from electrons to bound protons in 12 C by the 12 C( e, e p) process at the Mainz Microtron (MAMI). We observed consistent deviations from unity of this ratio normalized to the free-proton ratio, (P x /P z )12 C /(P x /P z )1 H , for both s-and p-shell knocked out protons, even though they are embedded in averaged local densities that differ by about a factor of two. The dependence of the double ratio on proton virtuality is similar to the one for knocked out protons from 2 H and 4 He, suggesting a universal behavior. It further implies no dependence on average local nuclear density.

“…It was measured periodically during the data taking by Moller and Mott polarimeters with an estimated accuracy of 2% (see the supplementary material). The carbon analyzing power in this kinematic region is known to about 1% [24][25][26]. However, the ratio P x /P z is independent of the analyzing power and beam polarization.…”

Section: Measured Polarization-transfermentioning

confidence: 95%

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

Paul¹,

Izraeli²,

Brecelj³

et al. 2019

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We present measurements of the polarization-transfer components in the 2 H( e, e p) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, p miss , up to 220 MeV/c, and Q 2 = 0.65 (GeV/c) 2 . These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components P x and P z and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio G E /G M at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for 2 H to those of a free (moving) proton. We find that the universal behavior of 2 H, 4 He and 12 C in the double ratio (Px/Pz) A (Px/Pz) 1 H is maintained in the positive missing-momentum region.