Transverse target spin asymmetry in inclusive DIS with two-photon exchange
- Department of Physics, Hampton University, Hampton, Virginia 23668 (United States)
- Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States)
- Theory Center, Jefferson Lab, Newport News, Virginia 23606 (United States)
We study the transverse target spin dependence of the cross section for inclusive electron-nucleon scattering with unpolarized beam. Such dependence is absent in the one-photon exchange approximation (Christ-Lee theorem) and arises only in higher orders of the QED expansion, from the interference of one-photon and absorptive two-photon exchange amplitudes as well as from real photon emission (bremsstrahlung). We demonstrate that the transverse spin-dependent two-photon exchange cross section is free of QED infrared and collinear divergences. We argue that in DIS kinematics the transverse spin dependence should be governed by a 'partonlike' mechanism in which the two-photon exchange couples mainly to a single quark. We calculate the normal spin asymmetry in an approximation where the dominant contribution arises from quark-helicity flip due to interactions with nonperturbative vacuum fields (constituent quark picture) and is proportional to the quark transversity distribution in the nucleon. Such helicity-flip processes are not significantly Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark subprocess is of the order of the chiral symmetry breaking scale, {mu}{sub chiral}{sup 2}>>{lambda}{sub QCD}{sup 2}. We estimate the asymmetry in the kinematics of the planned Jefferson Lab Hall A experiment to be of the order 10{sup -4}, with different sign for proton and neutron. We also comment on the spin dependence in the limit of soft high-energy scattering.
- OSTI ID:
- 21035711
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 77, Issue 1; Other Information: DOI: 10.1103/PhysRevD.77.014028; (c) 2008 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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