Measurement of Exclusive $π^0$ Electroproduction Structure Functions and their Relationship to Transverse Generalized Parton Distributions
Exclusive $$\pi^0$$ electroproduction at a beam energy of 5.75 GeV has been measured with the Jefferson Lab CLAS spectrometer. Differential cross sections were measured at more than 1800 kinematic values in $Q^2$, $$x_B$$, $$t$$, and $$\phi_\pi$$, in the $Q^2$ range from 1.0 to 4.6 GeV$^2$$,\ $$-t$ up to 2 GeV$^2$, and $$x_B$$ from 0.1 to 0.58. Structure functions $$\sigma_T +\epsilon \sigma_L, \sigma_{TT}$$ and $$\sigma_{LT}$$ were extracted as functions of $$t$$ for each of 17 combinations of $Q^2$ and $$x_B$$. The data were compared directly with two handbag-based calculations including both longitudinal and transversity GPDs. Inclusion of only longitudinal GPDs very strongly underestimates $$\sigma_T +\epsilon \sigma_L$$ and fails to account for $$\sigma_{TT}$$ and $$\sigma_{LT}$$, while inclusion of transversity GPDs brings the calculations into substantially better agreement with the data. There is very strong sensitivity to the relative contributions of nucleon helicity flip and helicity non-flip processes. The results confirm that exclusive $$\pi^0$$ electroproduction offers direct experimental access to the transversity GPDs.
- 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:
- 1052994
- Report Number(s):
- JLAB-PHY-12-1595; DOE/OR/23177-2231; arXiv:1206.6355
- Journal Information:
- Phys. Rev. Lett., Vol. 109, Issue 11
- Country of Publication:
- United States
- Language:
- English
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