Abstract
In the fragmentation of a transversely polarized quark several left–right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as the Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows quantitative relationships to be established among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.
Highlights
The description of the partonic structure of the nucleon at leading twist in the collinear case requires the knowledge of three parton distribution functions (PDFs), the number, helicity and transversity functions
We have shown that in semi-inclusive DIS (SIDIS) hadron-pair production the x-dependent Collins-like single hadron asymmetries of the positive and negative hadrons are well compatible with the standard Collins asymmetries and are mirror symmetric
For the first time it has been shown that the amplitude of the di-hadron asymmetry as a function of ∆φ has a very simple relation to that of the single hadron asymmetries in the 2h sample, namely it can be written as a a 2(1 − cos ∆φ), where the constant a is the same as that which appears in the expressions for the Collins-like asymmetries
Summary
The description of the partonic structure of the nucleon at leading twist in the collinear case requires the knowledge of three parton distribution functions (PDFs), the number, helicity and transversity functions. As suggested more than 20 years ago [1, 2], it can be accessed in semi-inclusive DIS (SIDIS) off transversely polarized nucleons from a left-right asymmetry of the hadrons produced in the struck quark fragmentation with respect to the plane defined by the quark momentum and spin directions Both the HERMES and the COMPASS experiments have provided unambiguous evidence that transversity is different from zero by measuring SIDIS off transversely polarized protons [3]. The integrated values of the three asymmetries have been compared
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