Coherent ρ 0 Meson Production at HERMES

Precise determination of the spin structure functiong1of the proton, deuteron, and neutron

“…In the case of B-H background events, the radiated photon has a significant probability of hitting the detector frames close to the beam line in the front region of the HERMES detector. As a consequence, an extensive electromagnetic shower is produced causing a very high hit multiplicity in the tracking detectors, making the track reconstruction impossible [74]. This detector inefficiency for B-H events was taken into account in order to not overcorrect for radiative processes that are not observed in the spectrometer.…”

Experimental results on TMDs

“…The observed x dependence of this amplitude (Fig. 5) is less pronounced in COMPASS [116] than in HERMES [117] due to difference in selection and kinematic coverage, but comes in agreement when the same analysis is applied.…”

“…The data from CLAS at 6 GeV indicate large azimuthal moments both for sin φ and sin 2φ [36]. The phenomenological studies of the sin 2φ asymmetry in the longitudinally polarised SIDIS process [36,117,210] have been performed in [21,212,217,218] and recently in [219], Fig. 24.…”

Measurement of Collins asymmetries in inclusive production of pion pairs in e+e- collisions at BABAR

“…It describes the relation between the transverse spin of the fragmenting quark and the azimuthal distribution of the final-state hadrons around the quark momentum. Experimental evidence for non-zero Collins functions was found by the HERMES [4,5] and COMPASS [6,7] collaborations, from the analysis of semi-inclusive deep inelastic scattering (SIDIS) of leptons off transversely polarized hydrogen and/or deuteron targets. The cross sections for these processes are proportional to the convolution of the Collins function and the chiral-odd transversity distribution function.…”