Asymmetry In Collisions Research Articles

Analysis of the double-spin asymmetryALTin inelastic nucleon-nucleon collisions

Within the collinear twist-3 framework, we analyze the double-spin asymmetry in collisions between longitudinally polarized nucleons and transversely polarized nucleons with focus on hadron and jet production. As was the case in direct photon production, the double-spin dependent cross section for hadron and jet production has the advantage of involving a complete set of collinear twist-3 functions. In addition, we outline further benefits of this observable for a potential future measurement at RHIC, which includes insight on the gluon helicity distribution as well as information on the Efremov-Teryaev-Qiu-Sterman function T_F(x,x) that plays a crucial role in single-spin asymmetries.

Neutrino helicity asymmetries in leptogenesis

It is pointed out that the heavy singlet neutrinos characteristic of leptogenesis develop asymmetries in the abundances of the two helicity states as a result of the same mechanism that generates asymmetries in the standard lepton sector. Neutrinos and standard leptons interchange asymmetries in collisions with each other. It is shown that an appropriate quantum number, $B\ensuremath{-}{L}^{\ensuremath{'}}$, combining baryon, lepton and neutrino asymmetries, is not violated as fast as the standard $B\ensuremath{-}L$. This suppresses the washout effects relevant for the derivation of the final baryon asymmetry. One presents detailed calculations for the period of neutrino thermal production in the framework of the singlet seesaw mechanism.

Asymmetries in collisions between electrons and oriented chiral molecules

General expressions for asymmetries in collisions between polarized electrons and oriented chiral molecules are derived. Numerical results for elastic scattering from H2S2 and CHBrClF molecules are presented for energies 5 eV and 10 eV. We have found large values for one of the asymmetry parameters up to 80%. The physical reason for these large asymmetries is analysed and discussed. A general symmetry rule is derived which relates the results for the two optical isomers to each other.

Perturbative QCD and weak asymmetries in lepton pair production

The interference of electromagnetic and weak production mechanisms for lepton pair production may give rise to several effects which violate parity and charge symmetry. These effects are generally of the order of 1% for dilepton masses of 10 GeV. The theoretical calculations presented here show that experimental studies of these asymmetries may be useful. In particular, measurements of these asymmetries in collisions of pions with polarized protons may lead to a greatly enhanced understanding of the polarization distribution of quarks in a polarized proton. The polarization structure of the d quark is shown to be of special interest. Measurement of the parity-violating asymmetries in proton-polarized proton collisions may prove to be a sensitive probe of the flavor symmetry of the proton antiquark sea. Analysis of the parity conserving charge asymmetry (which is predicted to occur in collisions of unpolarized hadrons) allows a unique further test of the Drell-Yan model for lepton pair production, as well as of our understanding of weak interactions. The above asymmetries mentioned are computed within the framework of the parton model. The focus of this work is on the asymmetries calculated with the inclusion of first-order perturbative QCD effects. The asymmetries are calculated in a differential form for values of the dilepton transverse momentum large compared with the typical (∼1 GeV) scale of nonperturbative effects, and also in a form in which this transverse momentum has been integrated over. Corrections to the parton model results, which can be large, show rather different structure for the various asymmetries. A parity-violating asymmetry which may occur in collisions of unpolarized hadrons is also discussed. This asymmetry is very sensitive to the nonperturbative structure of hadrons, and is estimated to be approximately 0.01% for dilepton masses of 10 GeV.