No abstract

No abstract

A precise measurement of the atomic-mass dependence of dimuon production induced by 800-GeV protons is reported. Over 450000 muon pairs with dimuon mass A/> 4 GeV were recorded from targets of 2 H, C, Ca, Fe, and W. The ratio of dimuon yield per nucleon for nuclei versus 2 H, R ~YA/YI H , is sensitive to modifications of the antiquark sea in nuclei. No nuclear dependence of this ratio is observed over the range of target-quark momentum fraction 0.1

Measurements of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360,000 Drell-Yan muon pairs remained after all cuts on the data. ¿From these data, the ratio of anti-down (d) to anti-up (ū) quark distributions in the proton sea is determined over a wide range in Bjorken-x. These results confirm previous measurements by E866 and extend them to lower x. From these data, (d −ū) and (d −ū)dx are evaluated for 0.015 < x < 0.35. These results are compared with parameterizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES. 13.85.Qk; 14.20.Dh; 24.85.+p; 14.65.Bt

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. A precise measurement of reactor electron antineutrino flux and spectrum evolution can be key inputs in improving the knowledge of neutrino mass and mixing as well as reactor nuclear physics and searching for physics beyond the standard model. In this work, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as their evolution with the 239 Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted IBD spectrum from 239 Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to 235 U fission is changed or the predicted 235 U, 238 U, 239 Pu, and 241 Pu spectra are changed in equal measure.