P. Gorbunov

Experimental study of opposite-sign and same-sign dimuon events produced in wide-band neutrino and antineutrino beams

Abstract We report on a study of 495 ± 32 ν μ -induced and 285 ± 29 ν μ - induced prompt opposite-sign dimuon events, obtained in the CERN Super Proton Synchrotron (SPS) horn-focused beam, using the CHARM neutrino detector. Prompt events are selected using the observed distribution of the distance between the two muons at the vertex. The observed increase of the ratio of prompt dimuon to single muon events with E vis is compatible with the expected behaviour for charm quark production and decay. Assuming the GIM mechanism, we fond a strange-sea contribution of 0.050 ± 0.015, in agreement with our previous result not involving the charm-changing currents. In the same sample we observed 74 ± 17 ν μ -induced and 52 ± 13 ν μ - induced prompt same-sign dimuon events. On the basis of their kinematics, these events can be well described as being of hadronic origin. The ratios μ − μ − /μ − μ + and μ + μ + /μ + μ − are found to be 0.14 ± 0.04 (stat.) ± 0.03 (syst.) and 0.18 ± 0.06 (stat.) ± 0.03 (syst.), respectively. The observed ratio σ(μ + μ + ) σ(μ − μ − ) = 0.50 ± 0.20 is compatible with the ratio of the single-muon charged-current cross sections, σ( ν μ N → μ + X ) σ(ν μ N → μ − X ) = 0.498 ± 0.019 .

Experimental study of differential cross sections in charged-current neutrino and antineutrino interactions

Abstract We present differential cross sections d σ /d y corrected for resolution and acceptance, for events induced by both the neutral- and charged-current interactions of neutrinos and antineutrinos. They are based on 8553 neutrino and 3578 antineutrino events obtained using the CHARM fine-grain calorimeter in the CERN 200 GeV narrow-band beam. From these differential cross sections we demonstrate that the coupling strength of the weak neutral current to the strange quark is compatible with being equal to that of the down quark. Assuming this equality we then describe the weak neutral current in terms of one parameter, sin 2 θ , which we find to be 0.222 ± 0.016. The charged-current differential cross sections yield values of the fractional momentum-weighted content of the nucleon for non-strange (0.12 ± 0.04) and strange (0.06 ± 0.04) sea quarks. Furthermore, from the strength of the allowed y 2 term in the neutral-current differential cross sections we put a limit of 3% on the presence of scalar or pseudoscalar contributions to the weak neutral current. This can alternatively be expressed in terms of the Callan-Gross violation parameter R , where we find R = 0 .10 ± 0.10.

Experimental study of prompt neutrino production in 400 GeV proton-nucleus collisions

Abstract A proton beam-dump experiment using the CHARM neutrino detector has been performed at the CERN SPS. We report the observation of events induced by prompt ν¯ μ neutrinos and confirm previous evidence for prompt electron neutrinos. The ratio of prompt (ν¯ e + ν e ) and (ν¯ μ +ν μ ) fluxes is found to be 0.48±0.12 (st atistical) ± 0.10 (systematic), whereas a flux ratio of 1 is expected for charmed meson production and subsequent semileptonic decay. The ν¯ μ to ν μ flux ratio obtained is 1.3 −0.6 +6 . We also observe 54 ± 19 (statistical) ± 9 (systematic) promp t muonless events, with shower energy in the range from 2 to 20 GeV, in excess of electron and muon neutrino interactions expected from D and D¯ meson decay.

Bounds on supersymmetric particles from a proton beam-dump experiment

Abstract We estimate the magnitude of effects induced by gluino hadroproduction and subsequent gluino decay into a photino and hadrons in a proton beam-dump experiment. By comparing our estimates with results obtained by us in an experiment performed at the CERN SPS we set a lower bound on the gluino mass which is a function of the scalar quark mass. The results do not favour the existence of low mass gluinos (

The response and resolution of a fine-grain marble calorimeter for hadronic and electromagnetic showers

The response of the fine-grained CHARM target calorimeter built to detect ν interactions has been studied in π− and e− beams of 15–140 GeV. The development of hadronic and electromagnetic showers was studied and the precision of energy measurements determined. Methods used to measure the direction of particle showers and to distinguish electromagnetic from hadronic showers have been developed and the results are given.

Measurement of the ratio of the cross sections of muon neutrino and antineutrino scattering on electrons

Abstract The ratio R of muon neutrino-electron and antineutrino-electron cross sections has been determined based on a sample of 46 ± 12 neutrino events and 77 ± 19 antineutrino events obtained in the CHARM fine-grain calorimeter using the CERN Super Proton Synchroton horn-focused wide-band beams. The experimental result is R=1.37−0.44+0.65, corresponding to a value of sin2θW=0.215±0.040. The systematic error of sin2θW is estimated to be ±0.015.

Measurement of the cross section of antineutrino scattering on electrons

A sample of 1 450 000 interactions with shower energy larger than 2 GeV has been observed in a fine-grain calorimeter exposed to the CERN SPS wide-band antineutrino beam. Among these, 72±16 events can be attributed to the neutrino-electron interaction and lead to a value of sin2θ=0.29±0.05 (stat.) corresponding to a cross section for the reaction νμe →νμe of (1.70±0.33)×10−42 Eν (cm2/GeV). The systematic error, due to the uncertainties in the knowledge of the antineutrino spectrum, of the electron detection efficiency and of the antineutrino-nucleon total cross section, is estimated to be ±25%.

Experimental study of x-distributions in semileptonic neutral-current neutrino reactions

Abstract Neutral-current differential cross sections as a function of the scaling variable x for deep inelastic neutrino-nucleon and antineutrino-nucleon scattering on an isoscalar target were measured in the CERN SPS 200 GeV/ c Narrow-Band Beam with the CHARM fine-grained calorimeter. The data have been corrected for the experimental resolutions using a novel unfolding procedure. Its validity is tested on charged-current reactions. The x -distributions determined in neutral-current reactions are found to be compatible with the results obtained in charged-current reactions, as expected by the quark model of the nucleon and by the standard model of the weak interactions.

Pattern recognition for hadronic showers in the CHARM calorimeter

Abstract The pattern-recognition procedure for hadronic showers in the fine-grained CHARM calorimeter is presented. The vertex and angular resolutions achieved after the upgrading of the detector are given.

The Neutrino Calorimeter of the CHARM Collaboration

The fine-grain and low-density neutrino calorimeter of the CHARM Collaboration has been designed to measure the energy and the direction of particle showers. Data are presented on the trigger efficiency and results of a new energy calibration of the upgraded detector using electrons and pions from 5 to 140 GeV/c, and on the angular and spatial resolution.