ARC Centre of Excellence for Particle Physics at the Tera-scale, and CSSM, Department of Physics, The University of Adelaide, Adelaide, 5005 South Australia, Australia.
Yerevan Physics Institute, 2 Alikhanyan Brothers Street, 375036 Yerevan, Armenia.
Phys Rev Lett. 2018 Jun 22;120(25):252001. doi: 10.1103/PhysRevLett.120.252001.
We present a new proposal to study the helicity-dependent dihadron fragmentation functions (DiFF), which describe the correlations of the longitudinal polarization of a fragmenting quark with the transverse momenta of the produced hadron pair. Recent experimental searches for this DiFF via azimuthal asymmetries in back-to-back hadron pair production in e^{+}e^{-} annihilation by the BELLE Collaboration did not yield a signal. Here we propose a new way to access this DiFF in e^{+}e^{-} annihilation, motivated by the recently recalculated cross section of this reaction, which explains why there was in fact no signal for the BELLE Collaboration to see. In this new approach the azimuthal asymmetry is weighted by the virtual photon's transverse momentum square multiplying sine and cosine functions of difference of azimuthal angles of relative and total momentum for each pair. The integration over the virtual photon's transverse momentum has the effect of separating the convolution between the helicity-dependent DiFFs in the quark and antiquark jets and results in a nonzero collinear expression containing Fourier moments of helicity-dependent DiFFs. A second new measurement is also proposed for two-hadron production in semi-inclusive deep inelastic scattering, where the asymmetry is weighted in a similar way for a single pair. This results in a collinear factorized form of the asymmetry, which includes the quark helicity parton distribution function and the same helicity-dependent DiFF, as in e^{+}e^{-} production and will allow us to check the universality of this DiFF.
我们提出了一种新的方法来研究螺旋度依赖的双强子碎裂函数（DiFF），它描述了碎裂夸克的纵向极化与产生的强子对的横向动量之间的相关性。最近，BELLE 合作通过在正负电子对撞湮灭中背对背强子对产生的各向异性实验搜索，并未发现这种 DiFF 的信号。在这里，我们提出了一种在正负电子对撞湮灭中研究这种 DiFF 的新方法，这种方法受到了最近重新计算的这个反应截面的启发，这解释了为什么 BELLE 合作实际上没有看到信号的原因。在这种新方法中，各向异性通过虚拟光子的横向动量平方乘以相对和总动量的方位角差的正弦和余弦函数进行加权。对虚拟光子的横向动量的积分具有分离在夸克和反夸克喷流中螺旋度依赖的 DiFF 的卷积的效果，并导致含有螺旋度依赖的 DiFF 的傅里叶矩的非零共线表达式。还提出了另一种新的半单举深度非弹性散射中两强子产生的测量方法，其中对单个强子对以类似的方式加权不对称性。这导致了不对称性的共线因子化形式，它包括夸克螺旋度部分分布函数和相同的螺旋度依赖的 DiFF，就像在正负电子对撞产生中一样，并将允许我们检查这个 DiFF 的普遍性。
