After completion of the data taking for the v(mu) -> v(tau) oscillation search, the CHORUS lead-scintillator calorimeter was used in the 1998 run as an active target. High-statistics samples of charged-current interactions were collected in the CERN SPS west area neutrino beam. This beam contained predominantly muon (anti-)neutrinos from sign-selected pious and kaons. We measure the flux and energy spectrum of the incident neutrinos and compare them with beam simulations. The neutrino-nucleon and anti-neutrino-nucleon differential cross-sections are measured in the range 0.01 < x < 0.7, 0.05 < y < 0.95, 10 < E-v < 200 GeV. We extract the neutrino-nucleon structure functions F-2(x, Q(2)), xF(3) (x, Q(2)), and R(x, Q2) and compare these with results from other experiments. (c) 2005 Elsevier B.V. All rights reserved.

This Letter reports on a study of trimuon events induced by neutrino interactions in the CHORUS calorimeter exposed to the CERN SPS wide-band v(mu) beam. Among the multimuon events produced in the calorimeter, 42 mu(-) mu(-) mu(+) events were selected and their kinematical properties investigated. In the past, several groups collected a sample of about one hundred events of this type but their source was largely unknown. Taking advantage of experimental data presently available on the production and muonic branching ratios of light neutral mesons and resonances, we make absolute predictions for the expected rates in our experiment. Detailed Monte Carlo simulations described in this article show that more than half of the trimuon events can be attributed to this source. Muons from pi- and K- decays in charm dimuon events are responsible for an additional approximate to 25% contribution to the total mu(-)mu(-)mu(+) rate. The remaining 25% of events are likely to come from the internal bremsstrahlung of virtual photons into a muon pair. Associated-charm production with subsequent decays of both charmed particles into muons is a negligible source of trimuon events. (C) 2004 Elsevier B.V. All rights reserved.

A study of quasi-elastic production of charmed baryons in charged-current interactions of neutrinos with the nuclear emulsion target of CHORUS is presented. In a sample of about 46000 interactions located in the emulsion, candidates for decays of short-lived particles were identified by using new automatic scanning systems and later confirmed through visual inspection. Criteria based both on the topological and kinematical characteristics of quasi-elastic charm production allowed a clear separation between events of this type and those in which charm is produced in deep inelastic processes. A final sample containing 13 candidates consistent with quasi-elastic production of a charmed baryon with an estimated background of 1.7 events was obtained. At the average neutrino energy of 27 GeV the cross-section for the total quasi-elastic production of charmed baryons relative to the vN charged-current cross-section was measured to be sigma(QE)/sigma(CC) = (0.23(-0.06)(+0.12)(stat)(-0.03)(+0.02)(syst)) x 10(-2).

During the years 1994-1997, the emulsion target of the CHORUS detector was exposed to the CERN-SPS Wide Band Neutrino Beam. The improvements of the past few years in the automatic emulsion scanning systems allowed a sample of events located in emulsion to be used for studies of charm production. Based on a sample of 56 172nu(mu) charged-current interactions analysed so far, we find a value of B-mu = 0.093+/-0.009(stat.) +/-0.009(syst.) for the semi-leptonic branching fraction of charm hadrons. The result for events with visible energy larger than 30 GeV, B-mu = 0.102+/-0.016(stat.) +/-0.010(syst.), can be combined with the existing measurements of the dimuon rate to yield a value of 0.219+/-0.022 for the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element \V-cd\. (C) 2002 Elsevier Science B.V. All rights reserved.

White and grey kink events define a special class of soft hadron interactions in nuclear emulsion in which only one track (the scattered hadron) is leaving the interaction vertex. Due to their small and sometimes invisible activity at the scattering point, they represent a potential background source for all emulsion experiments hunting for decay topologies of short-lived particles like the lepton and charm mesons.For an extensive study of such hadronic kink signatures a dedicated experimental set-up has been built and exposed at the CERN PS hadron beam facility and it has collected about 300 000 pious with a fixed momentum ranging front 2 to 5 GeV/c. Each particle was tracked by silicon strip detectors to connect it to the proper track in the nuclear emulsion located in between. Threshold Cherenkov detectors for electron discrimination, a muon counter and an MWPC-based magnetic spectrometer completed the experimental configuration. A total of 222 white and 271 grey kinks could be successfully located in the emulsion target. Their angular and transverse momentum distributions were extensively studied. (C) 2001 Elsevier Science B.V. All rights reserved.

We report on a search for associated charm production in neutrino charged-current interactions in the CHORUS experiment, based on the visual observation of charmed-particle decays. The search differs from those carried out so far in which the production of c (c) over bar has been inferred from measurements of events with two or three nations in the final state, resulting from the decay of charmed hadrons. One event with a double charm-decay topology has been found and a corresponding background of 0.04 events has been evaluated. (C) 2002 Elsevier Science B.V. All rights reserved.

During the years 1994-1997, the emulsion target of the CHORUS detector was exposed to the Wide Band Neutrino Beam from the CERN-SPS. About 170 000 neutrino interactions were successfully located in the emulsion. Improvements in the automatic emulsion scanning systems and application of different criteria allowed the sample of located events to be used for studies of charm production. We present a measurement of the production rate of Do mesons based on a sample of 25 693 located nu(mu) charged-current (CC) interactions analysed so far. After reconstruction of the event topology in the vertex region, 283 D-0 decays were observed with an estimated background of 9.2 K-0 and Lambda decays. The ratio of cross-section of D-0 production and nu(mu) CC interactions is found to be (1.99 +/- 0.13(stat.) +/- 0.17(syst.)) x 10(-2) at 27 GeV average nu(mu) energy. (C) 2002 Elsevier Science B.V. All rights reserved.

In the years 1994–1998 the CHORUS Collaboration has recorded data in the CERN WA95 experiment. Here we describe the data acquisition system that has been used, featuring concurrent hierarchical state machines, a remote operating system, a buffer manager, a dispatcher, a control panel and a supervisor.

A first analysis of the complete set of data collected by CHORUS in the years 1994-1997 is presented. The search for nu (tau) charged current events has been performed for both leptonic and hadronic decays of the tau lepton. No tau candidate has been found, A nu (tau) --> nu (tau) mixing is excluded down to sin(2)2 theta (mu tau) = 6.8 x 10(-4) for large Deltam(2) (90% C.L.). (C) 2001 Elsevier Science B.V. All rights reserved.

Observation of J/psi production by neutrinos in the calorimeter of the CHORUS detector exposed to the CERN SPS wide-band nu (mu) beam is reported. A spectrum-averaged cross section sigma (J/psi) = (6.3 +/- 3.0) x 10(-41) cm(2) is obtained for 20 GeV less than or equal to E-nu less than or equal to 200 GeV. The data are compared with the theoretical model based on the QCD Z-gluon fusion mechanism. (C) 2001 Published by Elsevier Science B.V.

Part of the neutrino events collected in 1994-1995 by the CHORUS experiment has been analysed. A search was performed for n charged current interactions followed by the t lepton decay into a single charged negative hadron, a t possible indication for n TMn oscillation. A sample of 6844 events without an identified muon has been located in the m t emulsion target. Within the selection criteria, no t candidate has been found. Combining this result with the one from the Ž . search for n interactions using the muonic decay mode 36 182 events with an identified muon , a 90% C.L. limit on the t 2 y3 Ž 2. mixing angle sin 2u -1.8P10 at large Dm has been derived. q 1998 Published by Elsevier Science B.V. All rights mt

Part of the neutrino events collected in 1994-1995 by the CHORUS experiment has been analysed. A search was performed for nu(tau) charged current interactions followed by the tau lepton decay into a single charged negative hadron, a possible indication for nu(mu) --> nu(tau) oscillation. A sample of 6844 events without an identified muon has been located in the emulsion target. Within the selection criteria, no tau(-) candidate has been found. Combining this result with the one from the search fur nu(tau) interactions using the muonic decay mode (36182 events with an identified muon), a 90% C.L. limit on the mixing angle sin(2)2 theta(mu tau) < 1.8.10(-3) (at large Delta m(2)) has been derived. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

Part of the neutrino events collected in 1994-1995 by the CHORUS experiment has been analysed. A search was performed for ντ charged current interactions followed by the τ lepton decay into a single charged negative hadron, a possible indication for νμ→ντ oscillation. A sample of 6844 events without an identified muon has been located in the emulsion target. Within the selection criteria, no τ− candidate has been found. Combining this result with the one from the search for ντ interactions using the muonic decay mode (36 182 events with an identified muon), a 90% C.L. limit on the mixing angle sin22θμτ<1.8·10−3 (at large Δm2) has been derived.

CHORUS is an experiment searching for nu(mu) --> nu(tau) oscillation in the CERN wide band neutrino beam with a hybrid setup consisting of a nuclear emulsion target followed by electronic detectors. The experiment has been taking data from 1994 through 1997. A subset of the neutrino interactions collected in 1994 and 1995 have been analyzed, looking for nu(tau) charged current interactions where the tau lepton decays to mu<(nu)over bar>(mu)nu(tau). In a sample of 31,423 nu(mu) charged current interactions, no nu(tau) candidates were found. For large Delta m(mu tau)(2) values, a limit on the mixing angle of sin(2)2 theta(mu tau) < 3.5 x 10(-3) at 90% C.L. can be set, thus improving the previous best result. (C) 1998 Elsevier Science B.V.

We report on the first direct observation of a neutrino induced charged-current interaction with two subsequent decays of short-lived particles close to the interaction vertex. This rare double-kink signature in the CHORUS emulsion target is interpreted as a D-s*(+) production followed by the decay chain D-s*(+) --> D-s(+) gamma, D-s(+) --> tau(+) v(tau),tau(+) --> mu(+) v(mu)v(tau). The event is characterised by small Q(2) and small four-momentum transfer squared t to the target nucleon, which indicates a diffractive production mechanism. A complete analysis of the event is presented. (C) 1998 Elsevier Science B.V. All rights reserved.