348 research outputs found
Simple parameterization of nuclear attenuation data
Based on the nuclear attenuation data obtained by the HERMES experiment on
nitrogen and krypton nuclei, it is shown that the nuclear attenuation
can be parametrised in a form of a linear polynomial + , where is the formation time, which depends on the energy of the
virtual photon and fraction of that energy carried by the final
hadron. Three widely known parameterizations for were used for the
performed fit. The fit parameters and do not depend on
and
Possible influence of the two string events on the hadron formation in a nuclear environment
One of the basic assumptions of the string model is that as a result of a DIS
in nucleus a single string arises, which then breaks into hadrons. However the
pomeron exchange considered in this work, leads to the production of two
strings in the one event. The hadrons produced in these events have smaller
formation lengths, than those with the same energy produced in the single
string events. As a consequence, they undergo more substantial absorption in
the nuclear matter
Q(2) dependence of nuclear transparency for exclusive rho(0) production
Exclusive coherent and incoherent electroproduction of the rho(0) meson from H-1 and N-14 targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q(2)). The ratio of N-14 to H-1 cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q(2) is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency
Application of the Two-Scale Model to the HERMES Data on Nuclear Attenuation
The Two-Scale Model and its improved version were used to perform the fit to
the HERMES data for (the virtual photon energy) and z (the fraction of
carried by hadron) dependencies of nuclear multiplicity ratios for
and mesons electro-produced on two nuclear targets (N
and Kr). The quantitative criterium was used for the first
time to analyse the results of the model fit to the nuclear multiplicity ratios
data. The two-parameter's fit gives satisfactory agreement with the HERMES
data. Best values of the parameters were then used to calculate the - and
- dependencies of nuclear attenuation for , K, K and
produced on Kr target, and also make a predictions for ,
z and the Q (the photon virtuality) - dependencies of nuclear attenuation
data for those identified hadrons and nuclea, that will be published by HERMES
Evidence for quark-hadron duality in the proton spin asymmetry A(1)
Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A(1). Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q(2) between 1.2 and 12 GeV2 and values of W-2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A(1) in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q(2) above 1.6 GeV2
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