P. Legros

Study of D+ and D− Feynman's x distributions in π−-nucleus interactions at the SPS

Abstract Experiment WA82 studied charm production by a π− beam of 340 GeV/c at the CERN Ω′ spectrometer, using a silicon microstrip vertex detector and an impact parameter trigger. Results on the xF distributions of D+ and D− mesons are presented and discussed. A clear excess of D− over D+, increasing at high xF, is observed.

A study of the semileptonic decay

Abstract The decay D+→K−π+e+νe has been studied by the hadroproduction experiment WA82. The decay is dominated by the K ∗0 (892) resonance. The ratio of branching ratios, B( D + → K ∗0 e + ν e )/B( D + → K − π + π + ) , is found to be 0.62±0.15±0.09. The K ∗0 mesons have a ratio of longitudinal to transverse polarization of 0.6±0.3+0.3−0.1.

Nuclear dependence of charm production by a 340 GeV π- beam

Abstract Charmed mesons, produced on silicon, copper and tungsten by 340 GeV π - , have been identified as peaks in invariant mass distributions. The comparison of the yields of charmed particles originating from interactions in Si, Cu and W allows the mass number dependence of the charm hadroproduction cross section to be measured. Assuming the usual parametrization σ c = σ 0 A α , we find α =0.92±0.06 for charmed mesons with 〈 x F 〉=0.24. We do not find any decrease of α with increasing x F in contrast to the case of the production of particles containing only light quarks.

Measurement of relative branching fractions for D+→K−K+K+ and Ds+→π−π+π+ decays

Abstract The decay modes D s + → π − π + π + and D + → K − K + K + have been studied in the hadroproduction experiment WA82. The following ratios of branching fractions have been measured: , , .

Results on heavy quark selection through an impact parameter trigger

The implementation of a trigger aimed at selecting those nuclear interactions which contain a charm particle is described. The trigger uses a fast emulator of the PDP-11 which calculates the impact parameter of the decaying charged tracks originating from the charm decay. An enrichment factor of 15 is thereby obtained. The results obtained show that, in its present implementation, this trigger, while giving a good enrichment factor, performs a correct rejection, since it does not eliminate many good events that would have been retained by the more sophisticated selection of the offline programs. >

Measurement of relative branching fractions of D° Cabibbo-suppressed decays

The decay modes D0→K−π+, K−K+, π−π+, K−π−π+π+ and π−π−π+π+ have been studied by the hadroproduction experiment WA82. The following ratios of branching fractions have been measured: B(D0→K−K+)B(D0→π−π+)=2.23±0.81±0.46, B(D0→K−K+)B(D0→K−π+)=0.107±0.029±0.015, B(D0→π−π+)B(D0→K−π+)=0.048±0.013±0.008, B(D0→π−π−π+π+)B(D0→K−π−π−π+π+)=0.115±0.023±0.016.

Results on a 10 micron pitch detector with individual strip readout

Abstract A 10 μm pitch silicon microstrip detector with individual strip readout via hybrid electronics has been produced and operated. Connections to digital and analog electronics is realized through an insensitive fan-out structure on the detector itself. The detector has been used in the WA82 experiment at the CERN Ω′ spectrometer.

A microstrip vertex detector for studying charm hadroproduction

Abstract The WA82 experiment has collected data at the Ω facility at CERN for the study of charmed particles produced in hadronic interactions. In order to select charmed particles in the much larger background of ordinary hadronic interactions precise reconstruction of tracks in high-multiplicity events is necessary. The required accuracy, 10 μm in the transverse plane, has been obtained with a telescope made of 23 silicon microstrip detectors, with pitch ranging from 10 to 50 μm. This telescope has been operated in a 1.3 T magnetic field and has been specially designed to select on-line events with secondary vertices. The trigger, based on the measurement of the impact parameter of a track relative to the primary vertex, enriched the charm sample by a factor 15.

Results on charm physics from WA82

Abstract Experiment WA82 studies the hadroproduction of charmed mesons with a 340 GeV/c pion beam and a 370 GeV/c proton beam. The high and clean statistics of collected charms has been used to measure the differential cross section and its dependence on target nucleon number. The analysis of semileptonic decay D→K ∗ eν is presented.

Results on charm hadroproduction from CERN experiment WA82

Experiment WA82 has collected data from 1987 to 1989 with the Ω’ spectrometer at the CERN SPS. The aim of WA82 was a high statistics study of charm hadroproduction, using a silicon microstrip vertex detector and an impact parameter trigger. Latest results on the nuclear dependence of charm production and on the xF distributions of D+ and D− mesons are presented and discussed.