# SPIN 2018

9-14 September 2018
University of Ferrara
Europe/Rome timezone
23RD INTERNATIONAL SPIN SYMPOSIUM

## Measurements of polarization transfer to a bound proton in light nuclei by quasi-elastic scattering at MAMI

10 Sep 2018, 16:40
20m

### A8

Parallel Sessions Spin Physics in Nuclear Reactions and Nuclei

### Speaker

Prof. Israel Mardor (Tel Aviv University, Tel Aviv, Israel)

### Description

I will report on recent polarization transfer experiments carried out at the Mainz Microtron (MAMI), via the quasi-elastic A(e ⃗,e^' p ⃗ ) reaction, over a wide range of missing momentum and virtuality. We measured the ratio (Px/Pz)A of the transverse to longitudinal components of polarization transferred from an electron to a bound proton in 2H and 12C [1, 2] , and transverse (Px and Py) and longitudinal (Pz) components of the polarization transfer to a bound proton in 2H [3]. We observed consistent deviations from unity of the above ratio normalized to the free-proton ratio, (Px/Pz)A/(Px/Pz)1H, 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 2H and previous 4He data, suggesting a universal behavior, which seems to be independent of nuclear size, density and Q2. A precise determination of the electron beam polarization, along with a novel analysis method [4], enabled a detailed comparison of the measured polarization transfer components to a bound proton in 2H to a state-of-the-art calculation, which uses free-proton electromagnetic form factors. We observe very good agreement between the measured and the calculated (Px/Pz)2H ratios, but deviations of the individual components. Our results cannot be explained by medium modified electromagnetic form factors (FFs), unless the GE/GM ratio is kept intact. Excluding FF modifications, these deviations point to an incomplete description of the nuclear reaction mechanism in the calculation. References [1] I. Yaron, D. Izraeli, et al., Phys. Lett. B769 (2017) 21-24 [2] D. Izraeli, T. Brecelj, et al., Phys. Lett. B781 (2018) 95-98 [3] D. Izraeli, I. Yaron, B. S. Schlimme, et al., Phys. Lett. B781 (2018) 107-111 [4] D. Izraeli, I. Mardor, et al., arXiv:1803.06729 (2018)

### Primary author

Prof. Israel Mardor (Tel Aviv University, Tel Aviv, Israel)

 Slides