Search

In this report, recent results from the HERA-B experiment on heavy flavour production in proton?nucleus interactions using a 920 GeV proton beam are presented. The topics include the production of the charmonium states J/?, ?' and ?c, of the D-meson states D0, D?, D*, the open beauty production cross section ( production) and the production cross section. The nuclear dependence for the differential cross sections of charmonium production is discussed. The results are mainly preliminary. The report closes with a summary of the HERA-B search for pentaquark states with strangeness, which yielded quite stringent upper limits for the production of such states in hadronic environments.

HERA-B is a fixed target experiment at the 920 GeV HERA proton beam at DESY which uses a variety of nuclear targets. During the last data-taking period 200 million minimum bias triggered events were recorded along with a similar number of dilepton triggered events. From the minimum bias data clean samples of D0 → K−π+ + c.c., D+ → K−π+π+ + c.c. and D*+ → D0π+ → K−π+π+ + c.c. have been obtained. About 530k K*0 → K+π− + c.c. and 50k → K+K− decays have also been reconstructed. These samples allow measurements of D0 and D+ production cross sections and their ratio R(D+/D0). In addition, detailed studies of the production mechanisms of strange resonances production at mid-rapidity were measured.

A search for Theta^+(1540) and Xi^{--}_{3/2}(1862) pentaquark candidates has been performed in proton-induced reactions on C, Ti and W targets at sqrt(s) = 41.6 GeV studying the pK_s resp. Xi^-pi^- and Xi^-pi^+ (and charge conjugated) decay channels at mid-rapidity. With sensitivities of (Br)x(dsigma/dx_F) < 5 to 25 microbarn/nucleon, we find no evidence for narrow pentaquark peaks in any of the studied final states. Preliminary values for the upper limit of relative yield ratios at mid-rapidity are (Theta^+(1540)) / (Lambda(1520)) < 0.02, (Br)x(Xi^{--}_{3/2}(1862)) / (Xi(1530)^0) < 0.077, and (Br)x(Xi_bar^{++}_{3/2}(1862)) / (Xi_bar(1530)^0) < 0.058 at 95% CL.

Measurements of the dependence of the J/Psi production cross section on its kinematic variables as well as on the target atomic numbers for 920 GeV/c protons incident on different targets have been made with the Hera-B detector. The large collected di-lepton sample allows to study the production ratio of Psi(2S) to J/Psi and of Chic to J/Psi . We also report on measurements of the b-bbar and Upsilon production cross section., Comment: 9 pages, 11 figures