Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSingle-spin asymmetries at two loops
297
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We find a novel mechanism for generating transverse single-spin asymmetry (SSA) in semi-inclusive deep inelastic scattering, distinct from the known ones which involve the Sivers and Collins functions, or their collinear twist-three counterparts. It is demonstrated that a phase needed for SSA can be produced purely within a parton-level cross section starting at two loops. We identify the complete set of two-loop diagrams for SSA, and discuss their gauge invariance and collinear factorization which features the $g_T$ distribution function. In the $k_T$ factorization framework, many more sources for SSA exist, and contributions from all possible two-parton transverse-momentum-dependent parton distribution functions are presented up to two loops and twist three.
rate research
Read More
In order to measure spin-dependent parton distributions in production of weak bosons using the non-hermetic detectors of the Relativistic Heavy Ion Collider, an accurate model for distributions of charged leptons from the W boson decay is needed. We discuss the predictions for production and decay of the W bosons based on a calculation for resummation of large logarithmic contributions originating from multiple soft gluon radiation. We compare the predictions for the spin-dependent resummed cross sections with the corresponding next-to-leading order results. We show that the lepton-level asymmetries can be reliably predicted by the resummation calculation and directly compared to the experimental data. A program for the numerical analysis of such cross sections in $gamma ^{*}, W^{pm},$ and $Z^{0}$ boson production is also presented.
We consider possible mechanisms for single spin asymmetries in inclusive Deep Inelastic Scattering (DIS) processes with unpolarized leptons and transversely polarized nucleons. Tests for the effects of non-zero $bfk_perp$, for the properties of spin dependent quark fragmentations and for quark helicity conservation are suggested.
The study of the Sivers effect, describing correlations between the transverse polarization of the nucleon and its constituent (unpolarized) partons transverse momentum, has been the topic of a great deal of experimental, phenomenological and theoretical effort in recent years. Semi-inclusive deep inelastic scattering measurements of the corresponding single spin asymmetries (SSA) at the upcoming CLAS12 experiment at JLab and the proposed Electron-Ion Collider will help to pinpoint the flavor structure and the momentum dependence of the Sivers parton distribution function describing this effect. Here we describe a modified version of the $tt{PYTHIA}$ Monte Carlo event generator that includes the Sivers effect. Then we use it to estimate the size of these SSAs, in the kinematics of these experiments, for both one and two hadron final states of pions and kaons. For this purpose we utilize the existing Sivers parton distribution function (PDF) parametrization extracted from HERMES and COMPASS experiments. Using this modified version of $tt{PYTHIA}$, we also show that the the leading order approximation commonly used in such extractions may provide significantly underestimated values of Sivers PDFs, as in our Monte Carlo simulations the omitted parton showers and non-DIS processes play an important role in these SSAs, for example in the COMPASS kinematics.
We present singlet-Majoron couplings to Standard Model particles through two loops at leading order in the seesaw expansion, including couplings to gauge bosons as well as flavor-changing quark interactions. We discuss and compare the relevant phenomenological constraints on Majoron production as well as decaying Majoron dark matter. A comparison with standard seesaw observables in low-scale settings highlights the importance of searches for lepton-flavor-violating two-body decays $ell to ell +$Majoron in both the muon and tau sectors.
A consistent phenomenological approach to the computation of transverse single spin asymmetries in inclusive hadron production is presented, based on the assumed generalization of the QCD factorization theorem to the case in which quark intrinsic motion is taken into account. New k_T and spin dependent quark distribution and fragmentation functions are considered: some of them are fixed by fitting data on p(transv. polarized) + p -> pion + X and predictions are given for single spin asymmetries in l + p(transv. polarized) -> pion + X and gamma^* + p(transv. polarized) -> pion + X processes.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
