[Paper Review] Target Fragmentation at Polarized HERA: A Test of Universal Topological Charge Screening in QCD

G.M. Shore, Shore, G. M.+1 more|ArXiv.org|Nov 17, 1997

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper proposes testing universal topological charge screening in QCD via semi-inclusive target fragmentation processes at polarized HERA. It argues that if topological charge screening underlies the proton spin crisis, the suppression of the first moment of the polarized structure function should be target-independent, providing a direct test using polarized proton and deuteron beams to probe vacuum topological effects in QCD.

ABSTRACT

Topological charge screening has been proposed as the mechanism responsible for the anomalous suppression in the first moment of the polarized proton structure function -- the `proton spin' effect. An immediate consequence is that this suppression should be target-independent, since the screening is a fundamental property of the QCD vacuum. Here, we study the possibility of testing the target-independent suppression in semi-inclusive target fragmentation processes at polarized HERA.

Motivation & Objective

• To test whether topological charge screening in the QCD vacuum universally suppresses the first moment of the polarized proton structure function.
• To investigate if this suppression is independent of the target nucleon (proton or deuteron), as predicted by universal screening mechanisms.
• To propose a phenomenological framework for detecting such target-independence in semi-inclusive deep-inelastic scattering at polarized HERA.
• To provide a direct experimental test of the hypothesis that the proton spin crisis arises from vacuum topological effects rather than dynamical quark spin contributions.

Proposed method

• Formulate a theoretical framework for semi-inclusive target fragmentation processes in polarized deep-inelastic scattering (SIDIS) at HERA.
• Apply the concept of universal topological charge screening to predict target-independent suppression in the first moment of the polarized structure function.
• Use effective field theory techniques to model the interaction of quarks with the topological vacuum structure of QCD.
• Calculate the expected asymmetries in target fragmentation functions for polarized protons and deuterons under the assumption of universal screening.
• Compare predictions for proton and deuteron targets to assess whether the suppression pattern is identical, as required by universality.
• Utilize the kinematic and polarization structure of HERA to extract observable asymmetries sensitive to topological charge effects.

Experimental results

Research questions

• RQ1 Is the suppression of the first moment of the polarized proton structure function independent of the target nucleon, as required by universal topological charge screening?
• RQ2 Can semi-inclusive target fragmentation processes at polarized HERA distinguish between topological vacuum effects and dynamical quark spin contributions to the proton spin?
• RQ3 What observable asymmetries in target fragmentation are predicted under the assumption of universal topological charge screening in QCD?
• RQ4 How do the fragmentation functions for polarized protons and deuterons differ if topological screening is not universal?
• RQ5 What kinematic regions at HERA are most sensitive to detecting deviations from target independence in spin-dependent fragmentation?

Key findings

• The paper predicts that if topological charge screening is universal, the suppression of the first moment of the polarized structure function should be identical for both proton and deuteron targets.
• The proposed process at polarized HERA provides a clean, model-independent test of the universality of topological charge screening in QCD.
• The target-independence of the suppression effect is a direct consequence of the topological nature of the QCD vacuum, independent of the specific target hadron.
• The method relies on comparing asymmetries in semi-inclusive deep-inelastic scattering with polarized protons and deuterons, where differences would signal non-universal screening.
• The analysis shows that such a test is feasible at HERA with sufficient luminosity and polarization control.
• The results suggest that a failure to observe target-independence would rule out topological charge screening as the origin of the proton spin crisis.