R. Biancastelli

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.

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.

Evidence for a resonant structure of the hadron production from e+e− annihilations in the 1700–1950 cm energy region

Abstract We present experimental evidence for a resonant behaviour of the hadron production from e + e − annihilations at the e + e − storage ring ADONE. A Breit-Wigner fit to the enhancement present between 1800 and 1850 MeV gives the following parameters M = 1812 −13 +7 MeV, Γ = 34 −15 +21 MeV.

Total cross section for hadron production by electron-positron annihilation at adone

Abstract The total cross section for electron-positron annihilation into three or more hadrons has been measured for centre of mass energies between 1.4 and 2.0 GeV. The data were obtained at ADONE by the BB experiment.

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 limits on the production of fractionally charged particles in proton-nucleus and neutrino-nucleus collisions

A search for fractionally chargedQ=1/3 (2/3) particles of different properties of interaction produced in (anti)neutrino-nucleus and in protonnucleus collisions was performed using the scintillator system of the CHARM neutrino detector at the CERN SPS. No events of the cases considered were found. In (anti)neutrino beams production was found to be less than a few times 10−5 per interaction of a beam particle. In a proton beam an upper limit on the production cross section of ∼10−40 cm2 was obtained.

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

Results are reported from a proton beam‐dump experiment performed at the 400 GeV CERN SPS using the Charm neutrino detector. Prompt electron‐neutrinos and prompt muon‐neutrinos, produced by decays of short‐lived parents, have been observed. The ratio of the fluxes of (?e+νe) and of (?μ+νμ), measured by the rates of charged‐current interactions with Evis≳20 GeV, is 0.48±0.12 (statistical) ±0.10 (systematic). The ratio of ?μ and νμ fluxes is 1.3+0.6−0.5. At low shower energies, 2 <Evis<20 GeV, we observe 54±19 (statistical) ±9 (systematic) prompt muonless events in excess of electron‐ and muon‐neutrino interactions expected from standard DD production and decay.