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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} \cdot

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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