A.G. Cocco

Measurement of charm production in neutrino charged-current interactions

The nuclear emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS of 27 GeV average neutrino energy from 1994 to 1997. In total, about 100 000 charged-current (CC) neutrino interactions with at least one identified muon were located in the emulsion target and fully reconstructed, using newly developed automated scanning systems. Charmed particles were searched for by a program recognizing particle decays. The observation of the decay in nuclear emulsion makes it possible to select a sample with very low background and minimal kinematical bias. In all, 2013 CC interactions with a charmed hadron candidate in the final state were selected and confirmed through visual inspection. The charm production rate induced by neutrinos relative to the CC cross-section is measured to be σ(νμN→μ−CX)/σ(CC)=(5.75 ± 0.32(stat)±0.30(syst))%. The charm production cross-section as a function of neutrino energy is also obtained. The results are in good agreement with previous measurements. The charm-quark hadronization produces the following charmed hadrons with relative fractions (in %): fD0=43.7±4.5, fΛc+=19.2±4.2, fD+=25.3±4.2 and fDs+=11.8±4.7.

Construction and test of calorimeter modules for the CHORUS experiment

Abstract The construction of modules and the assembly of the calorimeter for CHORUS, an experiment that searches for ν μ ↔ ν τ oscillation, have been completed. Within the experiment, the calorimeter is required to measure the energy of hadronic showers produced in neutrino interactions with a resolution of /∼30%/√ E (GeV). To achieve this performance, the technique, developed in recent years, of embedding scintillating fibers of 1 mm diameter into a lead matrix has been adopted for the most upstream part of the calorimeter. A more conventional system, of alternating layers of lead and scintillator strips, was used for the rest. Details of module construction as well as results obtained when modules were exposed to electron and muon beams are presented.

Search for νμ → ντ oscillation

Abstract The fine granularity of the CHARM-II detector has been exploited to search, in the CERN-SPS wide band neutrino beam, for quasi-elastic ντ interactions followed by the decay τ → πντ. Since the sampling thickness of the target calorimeter corresponds to ∼ 1 9 of an interaction length, these events appear in the detector as a single track followed by a hadronic shower. The study of the “single pion” events is used to set limits on the νμ → ντ oscillation parameters. The maximum sensitivity to the mixing angle θ is reached for Δm2 = 50 eV2 allowing to exclude values of sin22θ greater than 6.4 × 10−3 at 90% CL.

Response to electrons and pions of the calorimeter for the CHORUS experiment

We built and tested on charged particle beams the high energy-resolution calorimeter for the CHORUS experiment, which searches for νμ-ντ oscillations in the CERN Wide Band Neutrino Beam. This calorimeter is longitudinally divided into three sectors: one electromagnetic and two hadronic. The first two upstream sectors are made of lead and plastic scintillating fibers in the volume ratio of 41, and they represent the first large scale application of this technique for combined electromagnetic and hadronic calorimetry. The third sector is made of a sandwich of lead plates and scintillator strips and complements the measurement of the hadronic energy flow. In this paper, we briefly describe the calorimeter design and we show results on its response to electrons and pions, obtained from tests performed at the CERN SPS and PS. An energy resolution of σ(E)/E=(32.3±2.4)%/E(GeV) + (1.4±0.7)% was achieved for pions, and σ(E)/E=(13.8±0.9)%/E(GeV) + (−0.2±0.4)% for electrons.

Coherent single charged pion production by neutrinos

Abstract We report on a measurement of coherent single charged pion production in neutrino-nucleus scattering. The analysis is based on data taken with the CHARM II detector in beams of muon-neutrinos and -antineutrinos. The event numbers amount to N ( μ − π ) = 748 and N ( μ + π ) = 631. Cross sections and their dependence on the neutrino energy are determined. The results are in agreement with the predictions of models based on the PCAC hypothesis.

Experimental study of electromagnetic properties of the muon-neutrino in neutrino - electron scattering

Abstract We report new bounds on electromagnetic properties of the muon neutrino obtained from a study of neutrino-electron scattering. The results are based on the analysis of differential cross section data collected with the CHARM II detector. The 90% C.L. limit on the magnetic moment of the muon-neutrino μ ν μ −9 μ B confirms limits obtained at much lower energies. The limit on the anomalous charge radius of the muon neutrino |〈 r 2 〉 anom | −33 cm 2 im earlier results by nearly a factor three.

A Precise measurement of the cross-section of the inverse muon decay muon-neutrino + e- --> mu- + electron-neutrino

We report our final results from the analysis of the full high statistics sample of events of the reaction up + e- --+ /*- + v, collected with the CHARM II detector in the CERN wide-band neutrino beam during the years 1988 to 1991. From a signal of 15 758 f 324 inverse muon decay events we derived, in the Born approximation, a value of ( 16.51 f 0.93) x lO-42 cm*GeV-’ for the asymptotic cross section slope a/E,, in good agreement with the Standard Model prediction of 17.23 x IO-” cm* GeV- ‘. The result constrains the scalar coupling of the electron and the muon to [&l’ < 0.475 at 90% CL.

Flavour universality of neutrino couplings with the Z

Abstract We are reporting the first experimental result of the coupling of the muon neutrino with the Z. This result is in good agreement with the average value of the coupling of the three neutrino families as derived from the invisible decay width of the Z. We also determined g ν τ assuming N ν =3.

Charged-particle multiplicities in charged-current neutrino– and anti-neutrino–nucleus interactions

The CHORUS experiment, designed to search for νμ→ντ oscillations, consists of a nuclear emulsion target and electronic detectors. In this paper, results on the production of charged particles in a small sample of charged-current neutrino– and anti-neutrino–nucleus interactions at high energy are presented. For each event, the emission angle and the ionization features of the charged particles produced in the interaction are recorded, while the standard kinematic variables are reconstructed using the electronic detectors. The average multiplicities for charged tracks, the pseudo-rapidity distributions, the dispersion in the multiplicity of charged particles and the KNO scaling are studied in different kinematical regions. A study of quasi-elastic topologies performed for the first time in nuclear emulsions is also reported. The results are presented in a form suitable for use in the validation of Monte Carlo generators of neutrino–nucleus interactions.

Search for muon to electron neutrino oscillations

AbstractA search for νμ → νe and