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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.

 

The differential cross section for the quasi-free photoproduction reaction$$\gamma n\rightarrow K^0\Sigma ^0$$$\gamma n\to K^0{\Sigma }^0$was measured at BGOOD at ELSA from threshold to a centre-of-mass energy of$$2400\,\hbox {MeV}$$$2400\text{MeV}$. Close to threshold the results are consistent with existing data and are in agreement with partial wave analysis solutions over the full measured energy range, with a large coupling to the$$\Delta (1900)1/2^-$$$\Delta \left(1900\right)1/2^{-}$evident. This is the first dataset covering the$$K^*$$$K^{\ast }$threshold region, where there are model predictions of dynamically generated vector meson-baryon resonance contributions.

 

The late-time integrated Sachs-Wolfe (ISW) imprint of $R\gtrsim 100~h^{-1}\, \mathrm{Mpc}$ superstructures is sourced by evolving large-scale potentials due to a dominant dark energy component in the ΛCDM model. The aspect that makes the ISW effect distinctly interesting is the repeated observation of stronger-than-expected imprints from supervoids at z ≲ 0.9. Here we analyse the un-probed key redshift range 0.8 < z < 2.2 where the ISW signal is expected to fade in ΛCDM, due to a weakening dark energy component, and eventually become consistent with zero in the matter dominated epoch. On the contrary, alternative cosmological models, proposed to explain the excess low-z ISW signals, predicted a sign-change in the ISW effect at z ≈ 1.5 due to the possible growth of large-scale potentials that is absent in the standard model. To discriminate, we estimated the high-z ΛCDM ISW signal using the Millennium XXL mock catalogue, and compared it to our measurements from about 800 supervoids identified in the eBOSS DR16 quasar catalogue. At 0.8 < z < 1.2, we found an excess ISW signal with AISW ≈ 3.6 ± 2.1 amplitude. The signal is then consistent with the ΛCDM expectation (AISW = 1) at 1.2 < z < 1.5 where the standard and alternative models predict similar amplitudes. Most interestingly, we also observed an opposite-sign ISW signal at 1.5 < z < 2.2 that is in 2.7σ tension with the ΛCDM prediction. Taken at face value, these recurring hints for ISW anomalies suggest an alternative growth rate of structure in low-density environments at $\sim 100~h^{-1}\, \mathrm{Mpc}$ scales.

 

The development of color centers in diamond as the basis for emerging quantum technologies has been limited by the need for ion implantation to create the appropriate defects. We present a versatile method to dope diamond without ion implantation by synthesis of a doped amorphous carbon precursor and transformation at high temperatures and high pressures. To explore this bottom-up method for color center generation, we rationally create silicon vacancy defects in nanodiamond and investigate them for optical pressure metrology. In addition, we show that this process can generate noble gas defects within diamond from the typically inactive argon pressure medium, which may explain the hysteresis effects observed in other high-pressure experiments and the presence of noble gases in some meteoritic nanodiamonds. Our results illustrate a general method to produce color centers in diamond and may enable the controlled generation of designer defects.