Helicity selection rules and tests of gluon spin in exclusive quantum-chromodynamic processes
Helicity selection rules and tests of gluon spin in exclusive quantum-chromodynamic processes
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DOI：
10.1103/physrevd.24.2848
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发表时间：
1981-12
影响因子：
5
通讯作者：
S. Brodsky;G. Lepage
中科院分区：
文献类型：
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作者：
S. Brodsky;G. Lepage
我们展示了如何利用大动量转移排他过程的螺旋度和角依赖性来测试胶子自旋和摄动量子色动力学（QCD）的其他基本元素。与包容反应不同，在所有相互作用夸克的螺旋度都受到控制的情况下，这些过程隔离了QCD硬散射子过程。这些预测可以用一般的自旋选择规则来概括，该规则指出，强子的总螺旋度是守恒的（Σ初始λ H= Σ最终λ H），直到动量转移中的修正作为逆功率下降。特别是e+ e−→γ*→h A+ h B中的强子在较大的Q 2下产生，其螺旋度λ A+ λ B= 0，且| λ i|≤12。这也意味着d σ d cos θ∝(1+ cos 2 θ)适用于所有重子对，d σ d cos θ∝sin 2 θ适用于所有介子对，在1 q中有领先的顺序，给出了许多过程的应用，包括电弱形状因子、双光子过程、强子-强子散射和重夸克衰变（例如，ψ→pp）。
We show how the helicity and angular dependence of large-momentum-transfer exclusive processes can be used to test the gluon spin and other basic elements of perturbative quantum chromodynamics (QCD). Unlike inclusive reactions, these processes isolate QCD hard-scattering subprocesses in situations where the helicities of all the interacting quarks are controlled. The predictions can be summarized in terms of a general spin selection rule which states that the total hadron helicity is conserved (Σ initial λ H= Σ final λ H) up to corrections falling as an inverse power in the momentum transfer. In particular, the hadrons in e+ e−→ γ*→ h A+ h B are produced at large Q 2 with opposite helicity λ A+ λ B= 0, and| λ i|≤ 1 2. This also implies d σ d cos θ∝(1+ cos 2 θ) for all baryon pairs and d σ d cos θ∝ sin 2 θ for all meson pairs, to leading order in 1 Q. Applications to many processes are given, including electroweak form factors, two-photon processes, hadron-hadron scattering, and heavy-quark decays (eg, ψ→ p p).