Electric Form Factor of the Neutron
Recent polarization-based precision measurements of the nucleons' elastic electric form factors have led to surprising results. The measurement of the ratio of the proton's electromagnetic form factors, $$\mu_p G_E^p/G_M^p$$, was found to drop nearly linearly with $Q^2$ out to at least $$5 \mathrm{GeV}^2$$, inconsistent with the older Rosenbluth-type experiments. A recent measurement of $$G_E^n$$, the neutron's electric form-factor saw $$G_E^n$$ does not fall off as quickly as commonly expected up to $$Q^2 \approx 1.5 \mathrm{GeV}^2$$. Extending this study, a precision measurement of $$G_E^n$$ up to $$Q^2=3.5 \mathrm{GeV}^2$$ was completed in Hall A at Jefferson Lab. The ratio $$G_E^n/G_M^n$$ was measured through the beam-target asymmetry $$A_\perp$$ of electrons quasi-elastically scattered off polarized neutrons in the reaction $${}^{3}\overrightarrow{He}(\overrightarrow{e},e' n)$$. The experiment took full advantage of the electron beam, recent target developments, as well as two detectors new to Jefferson Lab. The measurement used the accelerator's 100\% duty-cycle high-polarization (typically 84\%) electron beam and a new, hybrid optically-pumped polarized $${}^{3}\overrightarrow{He}$$ target which achieved in-beam polarizations in excess of 50\%. A medium acceptance (80msr) open-geometry magnetic spectrometer (BigBite) detected the scattered electron, while a geometrically matched neutron detector observed the struck neutron. Preliminary results from this measurement will be discussed and compared to modern calculations of $$G_E^n$$.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 918578
- Report Number(s):
- JLAB-PHY-07-730; DOE/OR/23177-0178; TRN: US0805425
- Resource Relation:
- Conference: DNP 2007, October 10-13, 2007, Newport News, VA
- Country of Publication:
- United States
- Language:
- English
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