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Physics Opportunities in Hall C at 12 GeV with a Neutral Particle Spectrometer (NPS)

Since August 2006, the Jefferson Laboratory (JLab) Program Advisory Committee (PACs 30-39) has approved experiments of high quality physics to be included in the top half of the priority list to run during the first years after the 12 GeV upgrade. This includes experiments aimed at probing the partonic picture, where hard and soft, non-perturbative physics have been shown to factorize. Studies of the transverse structure of the valence quarks in the nucleon are one of the key physics topics at the 12 GeV JLab, and one of the recommendations of the last DOE/NSAC Long Range Plan.

Over the last decade, hard exclusive processes have emerged as a class of reactions providing novel information on the quark and gluon distributions in hadrons. This information is more complete than what can be obtained from studies of inclusive and elastic scattering alone. QCD factorization theorems allow for expressing amplitudes of hard exclusive processes in terms of the Generalized Parton Distributions (GPDs). Measurements of reactions with neutral final states play an important role in this by, for instance, allowing one to probe universal features of GPDs and to verify the GPD formalism in thus far unexplored regimes. Hall C, with its two high-momentum, high-resolution spectrometers, has unique capabilities for studies of certain classes of deep exclusive and semi-inclusive measurements requiring L/T separations. The addition of a neutral particle detection facility in Hall C would significantly augment these scientific capabilities.

Here, we will present the scientific program one could carry out with a neutral-particle detection facility and conceptual design considerations based on the first workshop on this topic, which took place in Orsay, France, on 10 November 2012. The focus will initially be on 5-6 measurements with similar requirements on neutral particle detection, but the proposed facility includes flexible for future experiments.

Current Updates

For current updates see the Physics with a Neutral Particle Spectrometer Wiki

Experiments

• Unpolarized Deeply Virtual Compton Scattering: Energy Dependence to isolate twist-2 and twist-3 contributions
• Polarized Deeply Virtual Compton Scattering to separate GPDs on the x=ksi line
• Wide Angle Compton Scattering to validate GPD formalism at large t
• Exclusive pi0 production: relative sigL and sigT contributions
• Semi-inclusive pi0 production: relative sigL and sigT contributions
• Exclusive eta production

General design overview

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Workshops and Meetings

• Talks in Future Instrumentation section in Hall C Winter Users Meeting 2013
• Meeting at JLab, 12 December 2012
• Orsay, 10 November 2012