Bose–Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon

Bose-Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering are studied in the HERMES experiment using nuclear targets of $^1$H, $^2$H, $^3$H, $^4$H, N, Ne, Kr, and Xe. A Gaussian approach is used to parametrize a two-particle correlation function determined from events with at least two charged hadrons of the same sign charge. This correlation function is compared to two different empirical distributions that do not include the Bose-Einstein correlations. Clear signals of Bose-Einstein correlations for all target nuclei without a significant variation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of the photon-nucleon system is found when the results are compared to those of previous experiments

Transverse and Longitudinal Lambda Polarization in Lepton Scattering by Unpolarized Nucleons at HERMES

Transverse and longitudinal polarization of $\Lambda$ hyperons has been studied. The transfer of polarization from high-energy positron to $\Lambda$ hyperon has been measured. The longitudinal spin transverse coefficient is found to be $D_{LL′}^{\Lambda} = 0.11\pm 0.10(stat) \pm 0.03(sys)$. The transverse polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons has been measured in inclusive quasireal photoproduction process for various target nuclei. The polarization observed is positive for light target nuclei and compatible with zero for heavy target nuclei

Charged hadron lepto-production off unpolarized protons and deuterons at HERMES

The HERMES collaboration has measured charge-separated pion and kaon multiplicities in semi-inclusive deep-inelastic scattering using a 27.6 GeV electron or positron beam scattering off a hydrogen or deuterium target. The results are presented as functions of the Bjorken variable xB, the negative squared four-momentum transfer Q2, a hadron fractional energy z and the hadron's transverse momentum. These data will be very useful to understand the quark-fragmentation process in deep-inelastic hadron electro-production and will serve as crucial input in the understanding of charge and flavour separated fragmentation functions. Furthermore, it provides important information on the transverse-momentum dependence of hadron production

Recent HERMES results on transverse-momentum dependent phenomena from scattering off unpolarised targets

HERMES experiment at DESY in Hamburg collected a wealth of semi-inclusive deep-inelastic scattering data using the 27.6 GeV lepton beam and pure gaseous, unpolarised hydrogen and deuterium targets. These data can be used in studies of the transverse-momentum dependent effects and can provide a check of existing models for transverse-momentum dependent parton distribution and fragmentation functions

Recent HERMES results on spin asymmetries in semi-inclusive deep-inelastic scattering

After fifty years of investigations, the nucleon structure is still far from being understood and continues to represent a unique test bench for QCD. Despite the enormous progresses achieved in five decades of deep-inelastic scattering (DIS) experiments, a number of crucial open questions are still on the carpet and subject of intense theoretical and experimental studies. In the last two decades, semi-inclusive DIS was established as a unique tool for the study of the non-collinear structure of nucleons, involving the parton transverse momentum pT as an additional degree of freedom. Requiring the detection of at least one final state-hadron in coincidence with the scattered lepton, it opened the way not only to measure of the chiral-odd transversity distribution, the last missing leading-twist collinear parton distribution function, but also to a variety of new pT-dependent PDFs, known as TMDs. Describing correlations between the quark transverse momentum and the quark or the nucleon spin (spin-orbit correlations), TMDs account for a number of intriguing effects observed in polarized and unpolarized reactions, and allow for a 3-dimensional description of the nucleon in momentum space. Furthermore, they could provide insights into the yet unmeasured quark orbital angular momentum. At leading-twist, eight TMDs enter the SIDIS cross section in conjunction with a fragmentation function. In addition, going to the twist-3 level allows us to probe novel quark-gluon correlations.The HERMES experiment collected a wealth of data using the 27.6 GeV polarized HERA lepton beam and various polarized and unpolarized gaseous targets. This allows for a series of unique measurements of observables sensitive to this multidimensional (spin) structure of the nucleon, probed through specific azimuthal modulations in the distribution of hadrons produced in semi-inclusive DIS. Amplitudes of some of these modulations sensitive to the beam and/or target polarization, recently extracted for the first time also in a three-dimensional kinematic space, will be presented in more detail

Bose-Einstein correlations in deep-inelastic scattering from nuclei

Bose-Einstein correlations of like-sign charged hadrons produced in deep-inelastic electron and positron scattering arestudied in the HERMES experiment using nuclear targets of $^1$H, $^2$H, $^3$He, $^4$He, N, Ne, Kr, and Xe. A Gaussian approach is usedto parametrize a two-particle correlation function determined from events with at least two charged hadrons of the samesign charge. This correlation function is compared to two different empirical distributions that do not include theBose-Einstein correlations. Clear signals of Bose-Einstein correlations for all target nuclei without a significantvariation with the nuclear target mass are found. Also, no evidence for a dependence on the invariant mass W of thephoton-nucleon system is found when the results are compared to those of previous experiments

Charged Hadron Lepto-Production off Unpolarized Protons and Deuterons at HERMES

The HERMES collaboration has measured charge-separated pion and kaon multiplicities in semi-inclusive deep-inelastic scattering using a 27.6GeV electron or positron beam scattering off a hydrogen or deuterium target. The results are presented as functions of the Bjorken variable x_B, the negative squared four-momentum transfer Q^2, a hadron fractional energy z and the hadron's transverse momentum. These data will be very useful to understand the quark-fragmentation process in deep-inelastic hadron electro-production and will serve as crucial input in the understanding of charge and flavour separated fragmentation functions. Furthermore, it provides important information on the transverse-momentum dependence of hadron production