ar X iv : h ep - p h / 98 06 28 4 v 2 9 N ov 1 99 8 Energy Dependence of the Pomeron Spin - Flip
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چکیده
There is no theoretical reason to think that the spin-flip component of the Pomeron is zero. One can measure the spin-flip part using Coulomb-nuclear interference (CNI). Perturbative QCD calculations show that the spin-flip component is sensitive to the smallest quark separation in the proton, while the non-flip part probes the largest separation. According to HERA results on the proton structure function at very low x the energy dependence of the cross-section correlates with the size of the color dipole. Analysing the data from HERA we predict that the ratio of the spin-flip to non-flip amplitude grows with energy as r(s) ∝ (1/x) 0.1−0.2 , violating Regge factorization of the Pomeron. The Pomeron contribution to the elastic scattering amplitude of a spin 1/2 particle has a form 1,2 , f P (s, t) = f P 0 (s, t) 1 + i √ −t m N σ · n r(s, t) (1) The function r(s, t) characterises the Pomeron spin-flip to non-flip ratio. In the case of N N elastic scattering r can be expressed through the spin amplitude in standard notations 1,2 , r = 2m N √ −t Φ 5 Im(Φ 1 + Φ 3) (2) If the Pomeron is a Regge pole (factorization holds), the spin-flip and non-flip amplitudes have the same phase, i.e. r is pure imaginary. Either this is true, or Re r ≪ 1. Indeed, a real part of r would lead to a polarisation in the elastic amplitude due to " self-interference " of the two components of the Pomeron, A pp N (t) = √ −t m N 4Re r(t) 1 + |r| 2 |t| /m 2 N , (3) which is measured to be less that 1% at high energies. On the other hand, even if |r| is quite large, the polarisation may be small provided that factorization 1
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تاریخ انتشار 1998