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1. The two-photon exchange experiment at DESY

   https://doi.org/10.1140/epja/s10050-024-01299-2  

   Alarcon, R. ; Beck, R. ; Bernauer, J. C. ; Broering, M. ; Christopher, A. ; Cline, E. W. ; Dhital, S. ; Dongwi, B. ; Fernando, I. ; Finger, M. ; et al ( April 2024 , The European Physical Journal A)

   We propose a new measurement of the ratio of positron-proton to electron-proton elastic scattering at DESY. The purpose is to determine the contributions beyond single-photon exchange, which are essential for the Quantum Electrodynamic (QED) description of the most fundamental process in hadronic physics. By utilizing a 20 cm long liquid hydrogen target in conjunction with the extracted beam from the DESY synchrotron, we can achieve an average luminosity of$$2.12\times 10^{35}$$$2.12\times {10}^{35}$ cm$$^{-2}\cdot $$${}^{-2}·$s$$^{-1}$$${}^{-1}$ ($$\approx 200$$$\approx 200$times the luminosity achieved by OLYMPUS). The proposed two-photon exchange experiment (TPEX) entails a commissioning run at a beam energy of 2 GeV, followed by measurements at 3 GeV, thereby providing new data up to$$Q^2=4.6$$$Q^2=4.6$ (GeV/c)$$^2$$${}^2$(twice the range of current measurements). We present and discuss the proposed experimental setup, run plan, and expectations.

    

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2. Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons

   https://doi.org/10.1007/JHEP12(2020)010  

   Airapetian, A. ; Akopov, N. ; Akopov, Z. ; Aschenauer, E. C. ; Augustyniak, W. ; Avakian, R. ; Bacchetta, A. ; Belostotski, S. ; Bryzgalov, V. ; Capitani, G. P. ; et al ( December 2020 , Journal of High Energy Physics)

   null (Ed.)

   A bstract A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos ( ϕ−ϕ S ) modulations provide evidence for a sizable worm-gear (II) distribution, $$ {g}_{1\mathrm{T}}^q\left(x,{\mathrm{p}}_T^2\right) $$ g 1 T q x p T 2 . Most of the other modulations are found to be consistent with zero with the notable exception of large sin ( ϕ S ) modulations for charged pions and K + . 

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3. Measurement of the beam-normal single-spin asymmetry for elastic electron scattering from 12C and 27Al

   Androic, D. ; Armstrong, D.S. ; Asaturyan, A ; Bartlett, K. ; Beaufait, J. ; Beminiwattha, R.S. ; Benesch, J. ; Benmokhtar, F. ; Birchall, J. ; Carlini, R.D. ; et al ( July 2021 , Physical review)

   null (Ed.)

   We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries Bn on 12C and 27Al, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of Bn on 12C and provide a first measurement on 27Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average laboratory scattering angle for both targets was 7.7∘, and the average Q2 for both targets was 0.024 37 GeV2 (Q=0.1561 GeV). The asymmetries are Bn=−10.68±0.90(stat)±0.57(syst) ppm for 12C and Bn=−12.16±0.58(stat)±0.62(syst) ppm for 27Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q dependence of all the far-forward angle (θ<10∘) data from 1H to 27Al can be described by the same slope out to Q≈0.35 GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep. 

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4. Proton form factor ratio \mu_p G_E^p/G_M^p from double spin asymmetry

   Liyanage, A. ; Armstrong, W. ; Kang, H. ; Maxwell, J. ; Mulholland, J. ; Ndukum, L. ; Ahmidouch, A. ; Albayrak, I. ; Asaturyan, A. ; Ates, O. ; et al ( March 2020 , Physical review)

   The ratio of the electric to magnetic form factors of the proton, μpGEp/GMp, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared Q2=5.66(GeV/c)2 using double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of μpGEp/GMp agrees with the Q2 dependence of previous recoil polarization data and reconfirms the discrepancy at high Q2 between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at Q2=2.06(GeV/c)2 has been measured as μpGEp/GMp=0.720±0.176stat±0.039sys, which is in agreement with an earlier measurement using the polarized target technique at similar kinematics. The form factor ratio at Q2=5.66(GeV/c)2 has been determined as μpGEp/GMp=0.244±0.353stat±0.013sys, which represents the highest Q2 measurement reached using double spin asymmetries with polarized target to date. 

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5. On-chip spin-orbit locking of quantum emitters in 2D materials for chiral emission

   https://doi.org/10.1364/OPTICA.463481  

   Ma, Yichen ; Zhao, Haoqi ; Liu, Na ; Gao, Zihe ; Mohajerani, Seyed Sepehr ; Xiao, Licheng ; Hone, James ; Feng, Liang ; Strauf, Stefan ( August 2022 , Optica)

   Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM), which can be used as potential degrees of freedom for quantum information processing. Quantum emitters are ideal candidates towards on-chip control and manipulation of the full SAM–OAM state space. Here, we show coupling of a spin-polarized quantum emitter in a monolayer${\mathrm{W}\mathrm{S}\mathrm{e}}_2$with the whispering gallery mode of a${\mathrm{S}\mathrm{i}}_3{\mathrm{N}}_4$ring resonator. The cavity mode carries a transverse SAM of$\mathrm{\sigma <\#comment/>}=\pm <\#comment/>1$in the evanescent regions, with the sign depending on the orbital power flow direction of the light. By tailoring the cavity–emitter interaction, we couple the intrinsic spin state of the quantum emitter to the SAM and propagation direction of the cavity mode, which leads to spin–orbit locking and subsequent chiral single-photon emission. Furthermore, by engineering how light is scattered from the WGM, we create a high-order Bessel beam which opens up the possibility to generate optical vortex carrying OAM states.

    

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