arXiv 0903.47052009-03-26hep-ph

用方位角不对称性分析基本粒子的模型无关自旋

A model independent spin analysis of fundamental particles using azimuthal asymmetries

Fawzi Boudjema, Ritesh K. Singh

备注：: 42 pages, 7 figures, 4 tables
发表信息：: JHEP 0907:028,2009
DOI：: 10.1088/1126-6708/2009/07/028

摘要：

利用方位角依赖的密度矩阵，我们构建了直接测量重不稳定粒子的自旋的可观测量。该方法的新颖之处在于，在通常的螺旋度框架之外的框架中对方位角依赖性的分析提供了对自旋提取的独立交叉检查。此外，在某些情况下，当最高秩的横向极化张量为零时，由于意外或动力学原因，标准的方位角不对称性消失，并将导致具有错误自旋分配的测量。然而，在我们构造的框架中，正确的自旋赋值仍然是可能的。该方法给出了关于所考虑的粒子的自旋的直接信息，并且可以使用相同的事件样本来识别衰变链中每个粒子的自旋。该方法的一个缺点是，只有当测试粒子的动量可以重建时，它才是有用的。然而，我们希望它在只有部分重建的情况下仍然有用。我们还推导出的自旋的生产和衰变机制的条件，因此极化，在对撞机实验中测量。作为使用的方法的一个例子，我们考虑的同时重建，在部分子水平上，顶部和$W$在顶部对生产在$e^+ e^-$在半轻子通道的自旋。

英文摘要：

Exploiting the azimuthal angle dependence of the density matrices we construct observables that directly measure the spin of a heavy unstable particle. A novelty of the approach is that the analysis of the azimuthal angle dependence in a frame other than the usual helicity frame offers an independent cross-check on the extraction of the spin. Moreover, in some instances when the transverse polarisation tensor of highest rank is vanishing, for an accidental or dynamical reason, the standard azimuthal asymmetries vanish and would lead to a measurement with a wrong spin assignment. In a frame such as the one we construct, the correct spin assignment would however still be possible. The method gives direct information about the spin of the particle under consideration and the same event sample can be used to identify the spins of each particle in a decay chain. A drawback of the method is that it is instrumental only when the momenta of the test particle can be reconstructed. However we hope that it might still be of use in situations with only partial reconstruction. We also derive the conditions on the production and decay mechanisms for the spins, and hence the polarisations, to be measured at a collider experiment. As an example for the use of the method we consider the simultaneous reconstruction, at the partonic level, of the spin of both the top and the $W$ in top pair production in $e^+ e^-$ in the semi-leptonic channel.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

摘要：

英文摘要：

相关论文