M. Metcalf

A detector for neutral-current interactions of high-energy neutrinod

Abstract The construction and performance of a large detector, designed principally to investigate neutral-current interactions of high-energy neutrinos, are described. The detector consists of an ionization calorimeter as a target to determine the energy and the direction of the shower produced by the neutrino scattering, and of a magnetic muon spectrometer. The calorimeter has also been used as a muon polarimeter.

Experimental study of neutral-current and charged-current neutrino cross sections

Abstract Samples of 9200 muon-neutrino and 3800 muon-antineutrino interactions on nuclei were obtained with the fine-grain calorimeter of the CHARM Collaboration at the CERN 200 GeV narrow-band neutrino beam. The interactions were classified as either neutral-current or charged-current processes on an event-by-event basis. Neutral-current and charged-current cross sections in neutrino and antineutrino interactions are presented. From these results we deduce a statistically significant contribution of right-handed coupling to the neutral hadronic current, and a value of the electroweak mixing angle corresponding to sin 2 θ = 0.220 ± 0.014.

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.

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.

Experimental study of inverse muon decay

The reaction νμe−→μ−νe, the inverse of muon decay, has been studied using an electronic neutrino detector exposed to the CERN SPS horn-focused wide-band neutrino and antineutrino beams. A sample of 171±29 events has been found. The rate agrees with the prediction derived for V - A interaction and for left-handed two-component neutrinos; the ratio is 0.98±0.18. A search for the reaction νμe−→μ−νe, allowed by a multiplicative lepton number conservation, gave a limit of σ(νμe−→μ−νe)σ(νμe−→μ−νe)<0.09, with 90% confidence.

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.

Polarization of positive muons produced in high-energy antineutrino interactions

The polarization of positive muons produced in charged current interactions of high-energy antineutrinos in iron has been measured at an average momentum transfer of = 3.2 GeV2. The muon spin is found to be oriented forward with respect to the muon momentum vector with an average polarization of 1.09 ± 0.22, consistent with helicity +1. It is concluded that the weak leptonic charged current retains its dominant vector and axial vector structure at high energies.

Performance of a large system of proportional drift tubes for a fine-grain calorimeter

Abstract The features of proportional counters and of drift chambers have been combined in a single detector element. For a fine-grain calorimeter used in a neutrino experiment a system of 13 000 counters has been built. The performance and long-term stability of the proportional drift tubes and the electronics are discussed.