Sebouh J. Paul, Ryan Milton, Sebastián Morán, Barak Schmookler, Miguel Arratia
Key measurements at the future Electron-Ion Collider (EIC), including first-of-their-kind studies of kaon structure, require the detection of $Λ^0$ at forward angles. We present a feasibility study of $Λ^0 \to nπ^0$ measurements using a high-granularity Zero Degree Calorimeter to be located about 35 m from the interaction point. We introduce a method to address the unprecedented challenge of identifying $Λ^0$s with energy $O(100)$ GeV that produce displaced vertices of $O(10)$ m. In addition, we present a reconstruction approach using graph neural networks. We find that the energy and angle resolution for $Λ^0$ is similar to that for neutrons, both of which meet the requirements outlined in the EIC Yellow Report.Furthermore, we estimate performance for measuring the neutron's direction in the $Λ^0$ rest frame, which reflects the $Λ^0$ spin polarization. We estimate that the neutral-decay channel $Λ^0 \to nπ^0$ will greatly extend the measurable energy range for the charged-decay channel $Λ^0 \to pπ^-$, which is limited by the location of small-angle trackers and the accelerator magnets. This work paves the way for EIC studies of kaon structure and spin phenomena.
Tim Kolar, Sebouh J. Paul, Patrick Achenbach, Hartmuth Arenhövel, Adi Ashkenazi, Jure Beričič, Ralph Böhm, Damir Bosnar, Tilen Brecelj, Ethan Cline, Erez O. Cohen, Michael O. Distler, Anselm Esser, Ivica Friščić, Ronald Gilman, Carlotta Giusti, Matthias Heilig, Matthias Hoek, David Izraeli, Simon Kegel, Pascal Klag, Igor Korover, Jechiel Lichtenstadt, Israel Mardor, Harald Merkel, Duncan G. Middleton, Miha Mihovilovič, Julian Müller, Ulrich Müller, Mor Olivenboim, Eliezer Piasetzky, Josef Pochodzalla, Guy Ron, Björn S. Schlimme, Matthias Schoth, Florian Schulz, Concettina Sfienti, Simon Širca, Rouven Spreckels, Samo Štajner, Yvonne Stöttinger, Steffen Strauch, Michaela Thiel, Alexey Tyukin, Adrian Weber, Israel Yaron
We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from $^{2}$H and $^{12}$C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle $φ_{pq}$, with a polar angle $θ_{pq}$ coverage up to about 8 degrees. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual $^{11}$B system. We find that the helicity asymmetry for $p$-shell knockout from $^{12}$C depends on the final state of the residual system and is relatively large (up to $\approx 0.16$), especially at low missing momentum. It is considerably smaller (up to $\approx 0.01$) for $s$-shell knockout from both $^{12}$C and $^2$H. The data for $^2$H are in very good agreement with theoretical calculations, while the predictions for $^{12}$C exhibit differences with respect to the data.