More Like this

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)

   Abstract 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. 

   more » « less
2. Sub-1 V/cm E-FISH-based picosecond electric field measurements in atmospheric pressure air

   https://doi.org/10.1088/1361-6595/adae32  

   LaCombe, Grayson; Wang, Jianan; Frederickson, Kraig; Simeni_Simeni, Marien (February 2025, Plasma Sources Science and Technology)

   Abstract We report on the development of a highly sensitive electric field induced second harmonic generation diagnostic setup capable of measuring electric field strengths as low as 1 $\mathrm{V}{\mathrm{cm}}^{-1}$at the picosecond time scale under atmospheric pressure conditions. This unprecedented sensitivity is achieved through passive homodyne detection, which utilizes stray signals generated by an optical component in the beam path. Our detection limit of 0.3–0.5 $\mathrm{V}{\mathrm{cm}}^{-1}$represents an improvement of over 2–3 orders of magnitude compared to previous reports (100–1000 $\mathrm{V}{\mathrm{cm}}^{-1}$) in the literature. Additionally, we demonstrate sensitivity to the polarity of the electric field. Experimental results are corroborated by simulations of the 400 ps time-resolved homodyne process, offering deeper insights into the enhanced detection capabilities and the system’s ability to resolve the field sign. 

   more » « less
3. Ground-state phase diagram of the t-t ′ -J model

   https://doi.org/10.1073/pnas.2109978118  

   Jiang, Shengtao; Scalapino, Douglas J.; White, Steven R. (October 2021, Proceedings of the National Academy of Sciences)

   We report results of large-scale ground-state density matrix renormalization group (DMRG) calculations on t- $t^{\prime }$-J cylinders with circumferences 6 and 8. We determine a rough phase diagram that appears to approximate the two-dimensional (2D) system. While for many properties, positive and negative $t^{\prime }$values ( $t^{\prime }/t=\pm 0.2$) appear to correspond to electron- and hole-doped cuprate systems, respectively, the behavior of superconductivity itself shows an inconsistency between the model and the materials. The $t^{\prime }<0$(hole-doped) region shows antiferromagnetism limited to very low doping, stripes more generally, and the familiar Fermi surface of the hole-doped cuprates. However, we find $t^{\prime }<0$strongly suppresses superconductivity. The $t^{\prime }>0$(electron-doped) region shows the expected circular Fermi pocket of holes around the $\left(\pi ,\pi \right)$point and a broad low-doped region of coexisting antiferromagnetism and d-wave pairing with a triplet p component at wavevector $\left(\pi ,\pi \right)$induced by the antiferromagnetism and d-wave pairing. The pairing for the electron low-doped system with $t^{\prime }>0$is strong and unambiguous in the DMRG simulations. At larger doping another broad region with stripes in addition to weaker d-wave pairing and striped p-wave pairing appears. In a small doping region near $x=0.08$for $t^{\prime }\sim -0.2$, we find an unconventional type of stripe involving unpaired holes located predominantly on chains spaced three lattice spacings apart. The undoped two-leg ladder regions in between mimic the short-ranged spin correlations seen in two-leg Heisenberg ladders. 

   more » « less
4. Positron pair interactions in a nearly free-electron metal

   https://doi.org/10.1140/epjd/s10053-022-00406-6  

   Mills, Jr., Allen Paine; Fuentes-Garcia, Melina (June 2022, The European Physical Journal D)

   AbstractThe electric field surrounding a single positron in a metal is screened by an increase in the local electron density which, in the case of nearly free-electron metals (like Al, Na, etc.), has a radial distribution similar to that of the electron in positronium (Ps). In such metals, a singlet pair of positrons would experience an attractive interaction and at low enough electron densities could possibly form a bound state that is held together by exchange and correlation energies, thus forming structures analogous to that of the positronium molecule (Ps$$_2$$ ${}_2$), with binding energies of a few tenths of an eV. Such di-positrons could be prevalent at positron densities of around 10$$^{18}$$ ${}^{18}$cm$$^{-3}$$ ${}^{-3}$and, if so, would be evident from an apparent broadening of the sharp step at the Fermi surface in measurements of the electron momentum distribution by the angular correlation of the 2$$\gamma $$ $\gamma$annihilation radiation. Even if di-positrons are not directly formed in a metal, optical spectroscopy of Ps$$_2$$ ${}_2$formed in vacuum via pairs of positrons simultaneously being emitted from the surface could be applied to the direct measurement of the momentum distribution of Cooper pairs. If they exist, di-positrons in metals would yield interesting information about electron and positron interactions and at very high densities might allow the study of a di-positron Bose–Einstein condensate immersed in an electron gas. Graphic Abstract 

   more » « less
5. Determination of size and complex index of refraction of single particles with elastic light scattering

   https://doi.org/10.1364/AO.413675  

   Waez, Mir_Seliman; Eckels, Steven_J; Sorensen, Christopher_M (January 2021, Applied Optics)

   We show that for spherical particles greater than ca. 5 µm, the differential scattering cross section is only weakly dependent on the real and imaginary parts of the refractive index ( $m=n+i\mathrm{\kappa <\#comment/>}$) when integrated over angle ranges near $37\pm <\#comment/>5^{\circ <\#comment/>}$and $115\pm <\#comment/>5^{\circ <\#comment/>}$, respectively. With this knowledge, we set up an arrangement that collects scattered light in the ranges $37\pm <\#comment/>5^{\circ <\#comment/>}$, $115\pm <\#comment/>5^{\circ <\#comment/>}$, and $80\pm <\#comment/>5^{\circ <\#comment/>}$. The weak functionality on refractive index for the first two angle ranges simplifies the inversion of scattering to the particle properties of diameter and the real and imaginary refractive indices. Our setup also uses a diamond-shaped incident beam profile that allows us to determine when a particle went through the exact center of the beam. Application of our setup to droplets of an absorbing liquid successfully determined the diameter and complex refractive index to accuracies ranging from a few to ten percent. Comparisons to simulated data derived from the Mie equations yielded similar results. 

   more » « less