The improved two-scale model is used to perform the fit to the semi-inclusive deep-inelastic scattering (SIDIS) data of HERMES experiment at DESY on nuclear targets. The ratio of hadron multiplicity ...on nuclear target to the deuterium one is chosen as observable, as usually. The two-parameter’s fit gives satisfactory agreement with the data in term of
χ
2
criterium. Best values of parameters are then used to calculate the nuclear multiplicity ratio for the hadrons not included in the fit procedure.
The two-scale model and its improved version were used to perform a fit to the HERMES data for the \(\nu\) (the virtual photon energy) and z (the fraction of \(\nu\) carried by hadron) dependences of ...the nuclear multiplicity ratios for \(\pi^ + \) and \(\pi^-\) mesons electro-produced on two nuclear targets (14N and 84Kr). The quantitative criterion \(\chi^2\) was used for the first time to analyze the results of the model fit to the nuclear multiplicity ratios data. The two-parameter's fit gave satisfactory agreement with the HERMES data. Best values of the parameters were then used to calculate the \(\nu\) and z dependences of the nuclear attenuation for \(\pi^0\), K + , K-, and \(\bar{p}\) produced on the 84Kr target, and also make predictions for \(\nu\), z, and the Q2 (the photon virtuality) dependences of the nuclear attenuation data for those identified hadrons and nuclei that will be published by HERMES.
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.
Nuclear attenuation of the two-hadron system is considered in the string model. The two-scale model and its improved version, with two different choices of constituent formation time and sets of ...parameters obtained earlier for the single hadron attenuation, are used to describe the available experimental data for the z-dependence of the subleading hadron, whereas satisfactory agreement with the experimental data has been observed. A model prediction for the ν-dependence of the nuclear attenuation of the two-hadron system is also presented.
A
bstract
A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized ...protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos (
ϕ−ϕ
S
) modulations provide evidence for a sizable worm-gear (II) distribution,
g
1
T
q
x
p
T
2
. Most of the other modulations are found to be consistent with zero with the notable exception of large sin (
ϕ
S
) modulations for charged pions and
K
+
.
The verification scheme in the package “Professor2” for setting parameters of the most used physics generator PYTHIA8.2 for simulating the processes in high energy physics is described. The goal is ...to tune the PYTHIA8.2 parameter list for the fragmentation process below
the production threshold. As an initial parameter list, we use the Belle (predecessor of the Belle II experiment) default parameter settings for fragmentation. For the MC pseudo-data, we use the Belle II software package i.e. basf2, and generator script developed by the main author of this paper. To validate the whole procedure, we use momentum distribution of charged pions and kaons to tune two free parameters of the fragmentation model in PYTHIA8 i.e. LUND fragmentation model. We demonstrate that the Professor2 package is a handful to perform multi-parameter tunes simultaneously.
Exclusive Formula omitted-meson electroproduction is studied by the HERMES experiment, using the 27.6 GeV longitudinally polarized electron/positron beam of HERA and a transversely polarized hydrogen ...target, in the kinematic region 1.0 GeV Formula omitted 7.0 GeV Formula omitted, 3.0 GeV Formula omitted 6.3 GeV, and Formula omitted 0.4 GeV Formula omitted. Using an unbinned maximum-likelihood method, 25 parameters are extracted. These determine the real and imaginary parts of the ratios of several helicity amplitudes describing Formula omitted-meson production by a virtual photon. The denominator of those ratios is the dominant amplitude, the nucleon-helicity-non-flip amplitude Formula omitted, which describes the production of a longitudinal Formula omitted-meson by a longitudinal virtual photon. The ratios of nucleon-helicity-non-flip amplitudes are found to be in good agreement with those from the previous HERMES analysis. The transverse target polarization allows for the first time the extraction of ratios of a number of nucleon-helicity-flip amplitudes to Formula omitted. Results obtained in a handbag approach based on generalized parton distributions taking into account the contribution from pion exchange are found to be in good agreement with these ratios. Within the model, the data favor a positive sign for the Formula omitted transition form factor. By also exploiting the longitudinal beam polarization, a total of 71 Formula omitted spin-density matrix elements is determined from the extracted 25 parameters, in contrast to only 53 elements as directly determined in earlier analyses.
A
bstract
Beam-helicity and beam-charge asymmetries in the hard exclusive leptoproduction of real photons from an unpolarised hydrogen target by a 27.6 GeV lepton beam are extracted from the H
ermes
...data set of 2006-2007 using a missing-mass event selection technique. The asymmetry amplitudes extracted from this data set are more precise than those extracted from the earlier data set of 1996-2005 previously analysed in the same manner by H
ermes
. The results from the two data sets are compatible with each other. Results from these combined data sets are extracted and constitute the most precise asymmetry amplitude measurements made in the H
ermes
kinematic region using a missing-mass event selection technique.
Double-spin asymmetries in exclusive electroproduction of real photons from a transversely polarized hydrogen target are measured with respect to the product of target polarization with beam helicity ...and beam charge, and with respect to the product of target polarization with beam helicity alone. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe–Heitler process. They are related to the real part of the same combination of Compton form factors as that determining the previously published transverse target single-spin asymmetries through the imaginary part. The results for the double-spin asymmetries are found to be compatible with zero within the uncertainties of the measurement, and are not incompatible with the predictions of the only available GPD-based calculation.
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