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Register a new userTagging emc effects and hadronization mechanisms by semi-inclusive deep inelastic scattering off nuclei
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The semi-inclusive deep inelastic scattering of electrons off a nucleus A with detection of a slow nucleus (A-1) in the ground or low excitation states, i.e. the process A(e,e(A-1))X, can provide useful information on the origin of the EMC effect and the mechanisms of hadronization. The theoretical description of the process is reviewed and the results of several calculations on few-body systems and complex nuclei are presented.
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The semi-inclusive deep inelastic scattering of electrons off the deuteron ($^2H equiv D$) and $^3He$ with detection of slow protons and deuterons, respectively, i.e. the processes $D(e,ep)X$ and $^3He(e,eD)X$, are calculated within the spectator mechanism, taking into account the final state interaction of the hadronizing quark with the detected protons and deuterons, respectively. It is shown that by a proper choice of the kinematics the origin of the EMC effect and the details of the interaction between the hadronizing quark and the nuclear medium can be investigated at a level which cannot be reached by inclusive deep inelastic scattering. A comparison of our calculations with recently available experimental data on the process $D(e,ep)X$ shows a good agreement in the backward hemisphere of the emitted nucleons. Theoretical predictions at the energies thyat will be available at the upgraded Thomas Jefferson National Accelerator Facilty are presented, and the possibility to investigate the proposed semi-inclusive processes at electron-ion colliders is briefly discussed.
The effects of the final state interaction in slow proton production in semi inclusive deep inelastic scattering processes off nuclei, A(e,ep)X, are investigated in details within the spectator and target fragmentation mechanisms; in the former mechanism, the hard interaction on a nucleon of a correlated pair leads, by recoil, to the emission of the partner nucleon, whereas in the latter mechanism proton is produced when the diquark, which is formed right after the visrtual photon-quark interaction, captures a quark from the vacuum. Unlike previous papers on the subject, particular attention is paid on the effects of the final state interaction of the hadronizing quark with the nuclear medium within an approach based upon an effective time-dependent cross section which combines the soft and hard parts of hadronization dynamics in terms of the string model and perturbative QCD, respectively. It is shown that the final state interaction of the hadronizing quark with the medium plays a relevant role both in deuteron and complex nuclei; nonetheless, kinematical regions where final state interaction effects are minimized can experimentally be selected, which would allow one to investigate the structure functions of nucleons embedded in the nuclear medium; likewise, regions where the interaction of the struck hadronizing quark with the nuclear medium is maximized can be found, which would make it possible to study non perturbative hadronization mechanisms.
We determine nuclear structure functions and quark distributions for $^7$Li, $^{11}$B, $^{15}$N and $^{27}$Al. For the nucleon bound state we solve the covariant quark-diquark equations in a confining Nambu--Jona-Lasinio model, which yields excellent results for the free nucleon structure functions. The nucleus is described using a relativistic shell model, including mean scalar and vector fields that couple to the quarks in the nucleon. The nuclear structure functions are then obtained as a convolution of the structure function of the bound nucleon with the light-cone nucleon distributions. We find that we are readily able to reproduce the EMC effect in finite nuclei and confirm earlier nuclear matter studies that found a large polarized EMC effect.
It is shown that in semi-inclusive deep inelastic scattering (DIS) of electrons off a complex nucleus A, the detection, in coincidence with the scattered electron, of a nucleus (A-1) in the ground state, as well as of a nucleon and a nucleus (A-2), also in the ground state, may provide unique information on several long standing problems, such as : i) the nature and the relevance of the final state interaction in DIS; ii) validity of the spectator mechanism in DIS; iii) the medium induced modifications of the nucleon structure function; iv) the origin of the EMC effect.
The CLAS experiment E02-104, part of the EG2 run at Jefferson Lab, was performed to study the hadronization process using semi inclusive deep inelastic scattering off nuclei. Electron beam energy of 5 GeV and the CLAS large acceptance detector were used to study charged pion production. The high luminosity available at Jefferson Lab and the CLAS large acceptance are key factors for such measurements allowing high statistics and therefore multidimensional analyses of the data. Both the multiplicity ratio and the transverse momentum broadening for carbon, iron and lead relative to deuterium are measured. Preliminary results for positive pions are discussed.
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