Medium-indused modification of kaons spectra measured in SIDIS at HERMES

The predicted high sensitivity of the nuclear modification factor for K– in SIDIS due to the QCD based effect of medium-induced flavour conversion in the fragmentation function is studied at HERMES experiment. Unlike π+, π– and K+ nuclear modification factor for K– is assumed to increase at high value of Bjorken variable xB and a hadron fraction energy z. The experimental signature of this phenomenon is an enhanced K– nuclear modification factor compared with those of K+ for high xB and z range. The z spectra of nuclear attenuation ratios for charged kaons in different slices of xB extracted on Ne, Kr and Xe targets will be presented and discussed.

Measurement of multiplicities of charged hadrons, pions and kaons in DIS at COMPASS

Precise measurements of multiplicities of charged hadrons, pions and kaons in deep inelastic scattering were performed. The data were obtained by the COMPASS Collaboration by scattering 160 GeV muons off an isoscalar 6LiD target. The results were obtained in three-dimensional bins of the Bjorken scaling variable x, the relative virtual-photon energy y, and the fraction z of the virtual-photon energy carried by the produced hadron. A leading-order pQCD analysis was performed using the pion multiplicity results to extract quark fragmentation functions into pions. The results for the sum of the z-integrated multiplicities for pions and for kaons, differ from earlier results from the HERMES experiment. The results from the sum of the z-integrated K+ and K- multiplicities at high x point to a value of the non-strange quark fragmentation function larger than obtained by the earlier DSS fit.

DVCS at HERMES

Deeply virtual Compton scattering process was studied widely at the HERMES experiment through measurements of various cross-section asymmetries. These measurements exploited the rich data collected at HERMES on scattering a longitudinally polarized lepton (electron/positron) beam off unpolarized, longitudinally and transversely polarized hydrogen targets, unpolarized and longitudinally polarized deuterium targets, as well as unpolarized nuclear targets. The operation of a recoil detector during the last two years of HERMES running enabled for the full kinematic reconstruction of the events of exclusively produced real photons and a clean (with a background well below the 1[Formula: see text]) measurement of the beam-helicity asymmetry. Also, first measurement of the beam-helicity asymmetry related to the associated deeply virtual Compton scattering process, where the proton is excited to a [Formula: see text]-resonance state, was possible using the recoil detector information.