ausblenden:
Schlagwörter:
mesons; Cross section; Proton–nucleus collisions
Zusammenfassung:
The cross section ratio RJ/ψ=Br(Υ→l+l−)dσ(Υ)/dy|y=0/σ(J/ψ) has been measured with the HERA-B spectrometer in fixed-target proton–nucleus collisions at 920 GeV proton beam energy corresponding to a proton–nucleon c.m.s. energy of √s=41.6 GeV. The combined results for the decay channels Υ→e+e− and Υ→μ+μ− yield a ratio RJ/ψ=(9.0±2.1)×10−6. The corresponding Υ production cross section per nucleon at mid-rapidity (y=0) has been determined to be Br(Υ→l+l−)dσ(Υ)/dy|y=0=4.5±1.1 pb/nucleon.