Letter of Intent for Alpha Knockout from Nuclei in Hard Exclusive Processes with ALERT
Abstract
We propose to measure hard exclusive α-knockout reactions from the light α-conjugate nuclei 12C, 16O, and 20Ne using electron scattering. Three reaction channels will be measured for the first time on the same target set: (i) the quasi-elastic knockout $(e, e' α)$ knockout, which establishes a baseline against α-clustering model calculations and tests final-state-interaction (FSI) models; (ii) coherent deeply virtual Compton scattering (DVCS) on a bound α, which provides a quark-level probe of the bound system through the beam-spin asymmetry; and (iii) coherent vector-meson production (ϕ and J/{ψ}) on a bound α, which probes the gluon distribution of the bound cluster through two-gluon exchange. The central observables are ratios of cross sections and beam-spin asymmetries between the bound α in 12C, 16O, and 20 Ne and the free 4He ground state. Together these measurements directly address the question of the role of QCD in the structure of light nuclei : do the quark and gluon distributions of an α embedded in a heavier nucleus differ from those of a free 4He, and do those modifications track the increasing α-clustering strength along the α-conjugate chain? The measurement will use the 12 GeV CEBAF accelerator in Hall B with the CLAS12 spectrometer instrumented with the ALERT low-energy recoil detector and high-pressure gas straw targets. ALERT, which replaced the CLAS12 silicon vertex tracker, was successfully commissioned and operated during Run Group L (RG-L) from April through August 2025. It uniquely provides identification of low-momentum recoiling light ions (p, d, t, 3He, and 4He) close to the beamline at the high luminosities required by these exclusive channels.
Related
- Nucleon Correlations in Unstable Nuclei via Knockout Reactions
- Low-x parton densities accounting for absorptive effects and exclusive J/ψ and Υ data from the LHC
- Paired charmonium and bottomonium production in rare exclusive decays of Z boson
- Twist decomposition of exclusive heavy meson production cross sections
- Exclusive production of doubly charmed baryon pair at B Factories
BibTeX
@misc{armstrong2026letter,
title = {{Letter of Intent for Alpha Knockout from Nuclei in Hard Exclusive Processes with ALERT}},
author = {Whitney R. Armstrong and Ian Cloët and Fernando A. Flor and Sylvester Joosten and Bobae Kim and Minho Kim and Henry T. Klest and Zein-Eddine Meziani and Chao Peng and Valerii Klimenko and Noémie Pilleux and Maria Żurek and Jacob C. Dulya and Zhiwan Xu and Lamiaa El Fassi and Penn Smith and Nazmus S. Ifat and Sangbaek Lee and Suman Shrestha and Nikos Sparveris and Fatiha Benmokhtar and Christine Ploen and Raphaël Dupré and Jennifer Rittenhouse West and Stanley J. Brodsky},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.16218},
eprint = {2610.16218},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.16218},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Letter of Intent for Alpha Knockout from Nuclei in Hard Exclusive Processes with ALERT
AU - Whitney R. Armstrong
AU - Ian Cloët
AU - Fernando A. Flor
AU - Sylvester Joosten
AU - Bobae Kim
AU - Minho Kim
AU - Henry T. Klest
AU - Zein-Eddine Meziani
AU - Chao Peng
AU - Valerii Klimenko
AU - Noémie Pilleux
AU - Maria Żurek
AU - Jacob C. Dulya
AU - Zhiwan Xu
AU - Lamiaa El Fassi
AU - Penn Smith
AU - Nazmus S. Ifat
AU - Sangbaek Lee
AU - Suman Shrestha
AU - Nikos Sparveris
AU - Fatiha Benmokhtar
AU - Christine Ploen
AU - Raphaël Dupré
AU - Jennifer Rittenhouse West
AU - Stanley J. Brodsky
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.16218
UR - https://arxiv.org/abs/2610.16218
AB - We propose to measure hard exclusive α-knockout reactions from the light α-conjugate nuclei ^12C, ^16O, and ^20Ne using electron scattering. Three reaction channels will be measured for the first time on the same target set: (i) the quasi-elastic knockout $(e, e' α)$ knockout, which establishes a baseline against α-clustering model calculations and tests final-state-interaction (FSI) models; (ii) coherent deeply virtual Compton scattering (DVCS) on a bound α, which provides a quark-level probe of the bound system through the beam-spin asymmetry; and (iii) coherent vector-meson production (ϕ and J/{ψ}) on a bound α, which probes the gluon distribution of the bound cluster through two-gluon exchange. The central observables are ratios of cross sections and beam-spin asymmetries between the bound α in ^12C, ^16O, and ^20 Ne and the free ^4He ground state. Together these measurements directly address the question of the role of QCD in the structure of light nuclei : do the quark and gluon distributions of an α embedded in a heavier nucleus differ from those of a free 4He, and do those modifications track the increasing α-clustering strength along the α-conjugate chain? The measurement will use the 12 GeV CEBAF accelerator in Hall B with the CLAS12 spectrometer instrumented with the ALERT low-energy recoil detector and high-pressure gas straw targets. ALERT, which replaced the CLAS12 silicon vertex tracker, was successfully commissioned and operated during Run Group L (RG-L) from April through August 2025. It uniquely provides identification of low-momentum recoiling light ions (p, d, t, ^3He, and ^4He) close to the beamline at the high luminosities required by these exclusive channels.
ER -