Document Type

Report

Publication Date

2017

Pages

1-48

Abstract

We propose to measure the transverse nucleon, single-spin asymmetries AUT (Φ, Φs) in the exclusive n→(e, e'π-)p reaction, during the transversely polarized ³He target SIDIS experiment (i.e. E12-10-006 [1]) with SoLID [2]. In principle, as many as six azimuthal modulations of the form Asin(μΦ+λΦS)/UT contribute (where μ and λ are integers) [3], but four of these modulations are small and the physics interest is concentrated in the largest two.

Our primarily goal is the measurment of A sin (Φ-Φs)/UT. This polarization observable has been noted as being sensitive to the spin-flip generalized parton distribution (GPD) E, and factorization studies have indicated that precocious scaling is likely to set in at moderate Q² ~ 2 - 4 GeV², as opposed to the absolute cross section, where scaling is not expected until Q² ~ 2 - 4 GeV², as opposed to the absolute cross section, where scaling is not expected until Q² > 10 GeV². Furthermore, this observable has been noted as being important for the reliable extraction of the charged pion form factor from pion electroproduction. Our secondary goal is the measurement of the Asin(Φs) asymmetry, which is sensitive to the higher twist transversity GPDs, and provides valuable information on transverse photon contributions at small -t. Both asymmetry datasets are projected to be of much higher quality than a pioneering measurement by HERMES [4]. The remaining four Asin(μΦ+λΦS)/UT modulations will also be measured, but are expected to be small.

The measurement is complementary to a proposal reviewed by PAC39 [5] for the SHMS+HMS in Hall C. The asymmetry that is most sensitive to E is the longitudinal photon, transverse nucleon, single-spin asymmetry AL (sin Φ - Φs)) in exclusive charged pion electroproduction. The SHMS+HMS allow the L-T separation needed to reliably measure this quantity. However, the limited detector acceptance and the error-magnification inherent in an L-T seperation necessitates the use of a next generation, externally polarized, continuous flow, high luminosity ³He target based on a large volume polarizer and compressor being developed at the University of New Hampshire.

A wide -t coverage is needed to obtain a good understanding of the asymmetries. Thus, it has always been intended to complement the SHMS+HMS AL (sin Φ-Φs)) measurement with an unseparated Asin/UT(Φ-Φs) measurement using a large solid angle detector. The high luminosity capabilities of SoLID make it well-suited for this measurement. Since an L-T separation is not possible with SoLID, the observed asymmetry is expected to be diluted by the ratio of the longitudinal cross section to the unseparated cross section. This was also true for the pioneering HERMES measurements, which provided a valuable constraint to models for the E GPD. In order to assure a clean measurement of exclusive π- production, it is required to detect the recoil proton from the n(e, e'π- - p triple coincidence events in SoLID for the case where the proton is emitted 8⁰ < 0 < 24⁰. This has no impact upon E12-01-006 whatsoever, and yields valuable unseparated asymmetry data.

Rights

© 2017 The Authors and Thomas Jefferson National Accelerator Facility. All rights reserved.

Included with the kind written permission of the author, in accordance with the policy of the copyright holders.

Comments

A run-group proposal submitted to PAC 45.

Original Publication Citation

Arrington, J., Hafidi, K., Hattawy, M., Reimer, P., Riordan, S., Ye, Z., Ahmed, Z., Ambrose, G. R., Basnet, S., Evans, R. S., Huber, G. M., Li, W., Paudyal, D., Papandreou, Z., Gao, H., Li, X., Liu, T., Peng, C., Xiong, W.,…Voutier, E. (2017). Measurement of deep exclusive π- production using a transversely polarized ³He target and the SoLID spectrometer (Report No. E12-10-006B). Thomas Jefferson National Accelerator Facility.

ORCID

0000-0003-2086-2807 (Hattawy), 0000-0001-7282-8120 (Hyde)

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