Measurements of the cross sections for open charm and beauty production in γγ collisions at –202 GeV

Abstract

The production of c and b quarks γ γ collisions is studied with the L3 detector at LEP with 410 pb −1 of data, collected at centre-of-mass energies from 189 GeV to 202 GeV. Hadronic final states containing c and b quarks are identified by detecting electrons or muons from their semileptonic decays. The cross sections σ (e + e − → e + e − ccX) and σ (e + e − → e + e − bbX) are measured and compared to next-to-leading order perturbative QCD calculations. The cross section of b production is measured in γ γ collisions for the first time. It is in excess of the QCD prediction by a factor of three.

Deep inelastic beauty production at HERA in thekT-factorization approach

“…First measurements [1] of the b-quark cross sections at HERA were significantly higher than the QCD predictions calculated at nextto-leading order (NLO) approximation. Similar observations were made in hadron-hadron collisions at Tevatron [2] and also in photon-photon interactions at LEP2 [3]. In last case, the theoretical NLO QCD predictions are more than three standard deviations below the experimental data.…”

“…The beauty production at high energies is a subject of intensive study from both theoretical and experimental points of view [1][2][3][4][5][6][7][8][9]. First measurements [1] of the b-quark cross sections at HERA were significantly higher than the QCD predictions calculated at nextto-leading order (NLO) approximation.…”

Supersymmetry explanation for the puzzling bottom quark production cross section

“…However, the disagreement is surprising because the relatively large mass of the bottom quark sets a hard scattering scale at which fixed-order perturbative QCD computations of other processes are generally successful. The photoproduction cross section at DESY's HERA [4] and and the cross section in photon-photon reactions at CERN's LEP [5] also exceed NLO expectations. The data invite the possibility of a contribution from "new physics".…”

“…The SUSY approach increases the b production rate at HERA and in γγ collisions at LEP by a small amount, not enough perhaps if early experimental indications in these cases are confirmed [4,5]. Full NLO SUSY-QCD studies should be undertaken.…”

Measurement of the bb̄ Cross Section at HERA-B

“…While the behavior of differential cross sections as a function of kinematical variables is usually reproduced quite well, the absolute values are still in disagreement by a factor of 2 to 7 [1]. This has been observed by several experiments: in γγ reactions at LEP (OPAL [2] and L3 [3]), in pp interactions at CDF [4], and in ep scattering at HERA (H1 [5,6] and ZEUS [7]). Although new calculations for CDF of the theoretical cross section [8] reduced the discrepancy, the theoretical predictions contain still large uncertainties and the measured cross sections and QCD NLO expectations are not yet in good agreement [9].…”