Abstract
Using 1.8 fb-1 of pp collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Upsilon(1S,2S,3S) mesons. Upsilon mesons are reconstructed using the di-muon decay mode. Total production cross sections for p_T<70 GeV and in the rapidity interval |Upsilon|<2.25 are measured to be 8.01+-0.02+-0.36+-0.31 nb, 2.05+-0.01+-0.12+-0.08 nb, 0.92+-0.01+-0.07+-0.04 nb respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times di-muon branching fractions for Upsilon(1S), Upsilon(2S), and Upsilon(3S) as a function of Upsilon transverse momentum p_T and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame the cross section may vary by approximately +-20%. If a non-trivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of two or more. We compare our results to several theoretical models of Upsilon meson production, finding that none provide an accurate description of our data over the full range of Upsilon transverse momenta accessible with this dataset.
Highlights
Since the discovery of the J=c and Ç mesons [1,2] the study of heavy quark-antiquark systems has provided valuable input for our understanding of quantum chromodynamics (QCD)
Measurements at the Large Hadron Collider (LHC) of differential production spectra of various charmonium and bottomonium states together with measurement of their spin alignments, prompt double-quarkonia production, and production of quarkonia in association with photons, vector bosons, or open heavy-flavor final states will allow discrimination between different theoretical approaches based on color-singlet corrections [14,15,16], color-octet terms [17], the kT-factorization approach [18], and other production models [19], and provide additional input toward an improved understanding of quarkonium hadroproduction
Studies of bottomonium production complement concurrent studies of charmonium systems due to the larger mass of the bottom quark compared to the charm quark, allowing more dependable theoretical calculations than in the charmonium family, which suffer from poor perturbative convergence [17]
Summary
Since the discovery of the J=c and Ç mesons [1,2] the study of heavy quark-antiquark systems has provided valuable input for our understanding of quantum chromodynamics (QCD). Ó 2013 CERN, for the ATLAS Collaboration to Ç production [15,16] such as from associated Ç þ bb" production may play a more important role, and the impact of the dependence of the production cross section on the spin alignment of the Ç is relatively small Both the fiducial cross section, measured in the kinematic region with muon transverse momentum p"T > 4 GeV and muon pseudorapidity j"j < 2:3, and the corrected cross section, which is defined in this paper as the cross section in the pT- phase space of the Ç corrected for the acceptance of the decay products to the full Ç production phase space, are reported. In the former case, the results have no dependence on assumptions about Ç spin alignment, while the latter measurements are more compared to model predictions and to the results of other experiments
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