Measurement of azimuthal asymmetries in neutral current deep inelastic scattering at HERA

Abstract

The distribution of the azimuthal angle of charged and neutral hadrons relative to the lepton plane has been studied for neutral current deep inelastic ep scattering using an integrated luminosity of 45 pb −1 taken with the ZEUS detector at HERA. The measurements were made in the hadronic centre-of-mass system. The analysis exploits the energy-flow method, which allows the measurement to be made over a larger range of pseudorapidity compared to previous results. The dependence of the moments of the azimuthal distributions on the pseudorapidity and minimum transverse energy of the final-state hadrons are presented. Although the predictions from next-to-leading-order QCD describe the data better than do the Monte Carlo models incorporating leading-logarithm parton showers, they still fail to describe the magnitude of the asymmetries. This suggests that higher-order calculations may be necessary to describe these data.

cos2ϕasymmetries in unpolarized semi-inclusive DIS

“…First, we will calculate the cos 2φ asymmetries in SIDIS under the kinematics of ZEUS, and compare our prediction with their data [12]. ZEUS employs an unpolarized positron beam with energy 27.6 GeV to collide with a proton beam of 820 GeV.…”

“…Experimentally semi-inclusive deep inelastic scattering (SIDIS) provides a unique playground for these k T -dependent distributions, where the observables of most interest are the single-spin asymmetries (SSA) and other related asymmetries, which have been measured and are currently under direct experimental scrutiny [5,6,7,8,9,10,11,12,13].…”

Parton distributions and cos2ϕh asymmetry induced by anomalous photon-quark coupling

“…This leads to a reduction of about 1 order of magnitude of C q ðx; r ⊥ Þ compared to that at Q 2 0 . It should be mentioned here that the data of EMC [56] and ZEUS [57,58] are measured in very high Q 2 , so the contribution of both the Cahn effect and our new distribution to the cos 2ϕ h asymmetry are anticipated to be negligible.…”

“…The cos 2ϕ h asymmetries in SIDIS off the hydrogen, deuterium, and He targets have already been extensively explored by EMC [56], ZEUS [57,58], HERMES [59,60], COMPASS [61][62][63][64] Collaborations and at JLab [65][66][67]. Since both HERMES [59] and COMPASS [61] Collaborations have measured the SIDIS off the unpolarized proton for charged unidentified hadrons (h) among final particles but under slightly different Q 2 , here we try to compare our new asymmetry in Eqs.…”

Capture reactions into Borromean two-proton systems atrpwaiting points

“…We emphasize that these characteristics are not rigorous properties, although limiting cases would be observable [47], as they would leave distinct signatures in the energy distribution of the emerging fragments. Based on these limits the reaction mechanism can very convincingly be classified as sequential for the 2 + case, direct for the low-lying 1 − case, and either sequential or a mixture for the high-lying 1 − case.…”