Physics – High Energy Physics – High Energy Physics - Phenomenology
Scientific paper
1994-10-26
Nucl.Phys.Proc.Suppl. 39BC (1995) 101-105
Physics
High Energy Physics
High Energy Physics - Phenomenology
6 pages, SWAT 94-48
Scientific paper
10.1016/0920-5632(95)00051-A
Recent work by the author in collaboration with S. Narison and G. Veneziano on the EMC-SMC-SLAC `proton spin' effect is reviewed. This uses a novel approach to deep inelastic scattering in which the matrix elements arising from the OPE are factorised into composite operator propagators and proper vertices. For polarised $\mu p$ scattering, the composite operator propagator is equated to the square root of the first moment of the QCD topological susceptibility, $\sqrt{\chi^\prime(0)}$. We evaluate $\chi^\prime(0)$ using QCD spectral sum rules and find a significant suppression relative to its OZI expectation. This is identified as the source of the violation of the Ellis-Jaffe sum rule for the first moment of the polarised proton structure function $g_1^p$. Our predictions, $\int_0^1 dx g_1^p(x;Q^2=10GeV^2) = 0.143\pm 0.005$ and $\Delta\Sigma =0.353\pm 0.052$, are in excellent agreement with the new SMC data. This supports our earlier conjecture that the suppression in the flavour singlet component of the first moment of $g_1^p$ is a target-independent feature of QCD related to the $U(1)$ anomaly and is not a special property of the proton structure.
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