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
We have measured the cosmic ray spectrum above 10 17.2 eV using the two air fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, photo-tube and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extra-galactic sources.
The Drell-Yan cross section ratios, (pϩd)/(pϩp), measured in Fermilab E866, have led to the first determination of d (x)/ū (x), d (x)Ϫū (x), and the integral of d (x)Ϫū (x) for the proton over the range 0.02 рxр0.345. The E866 results are compared with predictions based on parton distribution functions and various theoretical models. The relationship between the E866 results and the NMC measurement of the Gottfried integral is discussed. The agreement between the E866 results and models employing virtual mesons indicates that these non-perturbative processes play an important role in the origin of the d ,ū asymmetry in the nucleon sea. ͓S0556-2821͑98͒02821-5͔ PACS number͑s͒: 13.85. Qk, 11.55.Hx, 12.39.Ki, 24.85.ϩp Recent measurements ͓1-3͔ have revealed a marked asymmetry in the distributions of up and down quarks in the nucleon sea. While no known symmetry requires ū to equal d , a large d /ū asymmetry was not anticipated. The principal reason for expecting symmetry between up and down quarks in the sea is an assumption that the sea originates primarily from q-q pairs produced from gluons. As the masses of the up and down quarks are small compared to the confinement scale, nearly equal numbers of up and down pairs should result. Indeed, a theoretical investigation ͓4͔ of the lightquark asymmetry in the nucleon concluded that perturbative processes do not give rise to asymmetries in the up, down sea exceeding 1%. Thus a large d /ū asymmetry requires a non-perturbative origin for an appreciable fraction of these light antiquarks. This paper draws together several implications arising from this observed d /ū asymmetry-the effect of these measurements on existing parton distributions, an examination of the compatibility of the measurements of this asymmetry, and the origin of the effect.The issue of the equality of ū and d was first encountered in measurements of the Gottfried integral ͓5͔, defined as
Milagrito, a large, covered water-Cherenkov detector, was the world's first air-showerparticle detector sensitive to cosmic gamma rays below 1 TeV. It served as a prototype for the Milagro detector and operated from February 1997 to May 1998. This paper gives a description of Milagrito, a summary of the operating experience, and early results that demonstrate the capabilities of this technique. : 95.55.Ka, 29.40.Ka, 95.85.Pw
PACS
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