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Register a new userQCD analysis of Lambda hyperon production in DIS target-fragmentation region
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Federico Alberto Ceccopieri
Publication date
2012
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English
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We consider Lambda-hyperon production in the target-fragmentation region of semi-inclusive deep-inelastic scattering within the framework of fracture functions. We present a first attempt to determine the flavour and energy dependences of these non-perturbative distributions through a simultaneous QCD-based fit to available neutral- and charged-current semi-inclusive-DIS cross sections. Predictions based on the resulting nucleon-to-Lambda fracture functions are in good agreement with data and observables not included in the regression. The successful prediction of the $Q^2$ dependence of the Lambda multiplicity notably represents the first validation of the perturbative framework implied by fracture functions.
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By using a recently obtained set of Lambda fracture functions, we present predictions for Lambda production in the target fragmentation region of Semi-Inclusive Deep Inelastic Scattering in CLAS@12 GeV kinematics, supplemented with a conservative error estimates. We discuss a number of observables sensitive to the assumptions of the underlying theory and many of the assumptions of the proposed phenomenological model.
We consider forward neutron production in DIS within fracture functions formalism. By performing a QCD analysis of available data we extract proton-to-neutron fracture functions exploiting a method which is in close relation with the factorisation theorem for this class of processes.
In the target fragmentation region of Semi-Inclusive Deep Inelastic Scattering, the diffractively produced hadron has small transverse momentum. If it is at order of $Lambda_{QCD}$, it prevents to make predictions with the standard collinear factorization. However, in this case, differential cross-sections can be predicted by the factorization with fracture functions, diffractive parton distributions. If the transverse momentum is much larger than $Lambda_{QCD}$ but much smaller than $Q$ which is the virtuality of the virtual photon, both factorizations apply. In this case, fracture functions can be factorized with collinear parton distributions and fragmentation functions. We study the factorization up to twist-3 level and obtain gauge invariant results. They will be helpful for modeling fracture functions and useful for resummation of large logarithm of the transverse momentum appearing in collinear factorization.
We systematically study two-body nonleptonic decays of light lambda hyperon $Lambda to p pi^- (npi^0)$ with account for both short and long distance effects. The short distance effects are induced by five topologies of external and internal weak $W^pm$ exchange, while long distance effects are saturated by an inclusion of the so-called pole diagrams with an intermediate $frac12^+$ and $frac12^-$ baryon resonances. The contributions from $frac12^+$ resonances are calculated straightforwardly by account for nucleon and $Sigma$ baryons whereas the contributions from $frac12^+$ resonances are calculated by using the well-known soft-pion theorem in the current-algebra approach. It allows to express the parity-violating S-wave amplitude in terms of parity-conserving matrix elements. From our previous analysis of heavy baryons we know that short distance effects induced by internal topologies are not suppressed in comparison with external $W$-exchange diagram and must be included for description of data. Here, in the case of $Lambda$ decays we found that the contribution of external and internal $W$-exchange diagrams is sizably suppressed, e.g., by one order of magnitude in comparison with data, which are known with quite good accuracy. The major role to get consistency with experiment play pole diagrams.
We study the inclusive production of two hadrons in deep inelastic processes, l N ---> l h_1 h_2 X, with h_1 in the current fragmentation region (CFR) and h_2 in the target fragmentation region (TFR). Assuming a factorized scheme, the recently introduced polarized and transverse momentum dependent fracture functions couple to the transverse momentum dependent fragmentation functions. This allows the full exploration of the fracture functions for transversely polarized quarks. Some particular cases are considered.
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