The final oscillation analysis of the complete set of data collected by CHORUS in the years 1994-1997 is presented. Reconstruction algorithms of data extracted by electronic detectors were improved and the data recorded in the emulsion target were analysed by new automated scanning systems, allowing the use of a new method for event reconstruction in emulsion. CHORUS has applied these new techniques to the sample of 1996-1997 events for which no muons were observed in the electronic detectors. Combining the new sample with the data analysed in previous papers, the overall sensitivity of the experiment to the nu(tau) appearance is thus improved. In a two-neutrino mixing scheme, a 90% C.L. upper limit of sin(2)2 theta(mu tau) < 4.4 x 10(-4) is set for large Delta m(2), improving by a factor 1.5 the previously published CHORUS result. (C) 2007 Elsevier B.V. All rights reserved.

We present a leading order QCD analysis of a sample of neutrino induced charged-current events with two muons in the final state originating in the lead-scintillating fibre calorimeter of the CHORUS detector. The results are based on a sample of 8910 neutrino and 430 antineutrino induced opposite-sign dimuon events collected during the exposure of the detector to the CERN Wide Band Neutrino Beam between 1995 and 1998. The analysis yields a value of the charm quark mass of m(c) = (1.26 +/- 0.16 +/- 0.09) GeV/c(2) and a value of the ratio of the strange to non-strange sea in the nucleon Of K = 0.33 +/- 0.05 +/- 0.05, improving the results obtained in similar analyses by previous experiments. (c) 2008 Elsevier B.V. All rights reserved.

In this paper a search for associated charm production both in neutral and charged current $\nu$-nucleus interactions is presented. The improvement of automatic scanning systems in the {CHORUS} experiment allows an efficient search to be performed in emulsion for short-lived particles. Hence a search for rare processes, like the associated charm production, becomes possible through the observation of the double charm-decay topology with a very low background. About 130,000 $\nu$ interactions located in the emulsion target have been analysed. Three events with two charm decays have been observed in the neutral-current sample with an estimated background of 0.18$\pm$0.05. The relative rate of the associated charm cross-section in deep inelastic $\nu$ interactions, $\sigma(c\bar{c}\nu)/\sigma_\mathrm{NC}^\mathrm{DIS}= (3.62^{+2.95}_{-2.42}({stat})\pm 0.54({syst}))\times 10^{-3}$ has been measured. One event with two charm decays has been observed in charged-current $\nu_\mu$ interactions with an estimated background of 0.18$\pm$0.06 and the upper limit on associated charm production in charged-current interactions at 90% C.L. has been found to be $\sigma (c\bar{c} \mu^-)/\sigma_\mathrm{CC} < 9.69 \times 10^{-4}$.

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.

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.

A systematic search for superfragments (charmed nuclei) has been performed in 22 200 neutrinoemulsion interactions obtained with the CHORUS experiment making use of automatic off-line image analysis. The absence of candidates provides an upper limit for the superfragment production rate of 1.9 x 10(-4) (90% C.L.) relative to neutrino charged-current interactions at an average neutrino energy of 27 GeV. In the same analysis 28 hyperfragment decays were found. For the first time, a production rate of hyperfragments in neutrino-emulsion interactions was obtained. The value of the hyperfragment production rate relative to the neutrino charged-current cross-section was found to be (2.0 +/- 0.4(stat) +/- 0.3 (syst)) x 10(-3). (c) 2005 Elsevier 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 of the CERN SPS of 27 GeV average neutrino energy. In total about 100 000 charged-current neutrino interactions were located in the nuclear emulsion target and fully reconstructed. From this sample of events which was based on the data acquired by new automatic scanning systems, 1048 charged-current interactions with a Do in the final state were selected by a pattern recognition program and confirmed as neutral-particle decays through visual inspection. The ratio of decay branching fractions of the Do into four charged particles to two charged particles was measured to be B(D-0 -> V4)/B(D-0 -> V2) = 0.207 +/- 0.016 +/- 0.004. The inclusive measurement of the observed production rate of the Do with a decay into four charged prongs in combination with external measurements of this topological branching ratio was used to determine the total Do production rate by neutrinos without additional assumption on the branching fractions. The value of this rate relative to the charged-current cross-section was found to be sigma (D-0) / sigma (CC) = 0.0269 +/- 0.0018 +/- 0.0013. In addition, the same normalization method was used to deduce the inclusive topological decay rate into final states with neutral particles only. A value of 0.218 +/- 0.049 +/- 0.036 was found for this branching fraction. From an observed number of three charged six-prong events the branching ratio into six charged particles was determined to be (1.2(-0.9)(+1.3) +/- 0.2) x 10(-3). A measurement of the energy dependence of the D-0 production by neutrinos relative to the total charged-current cross-section is also reported. This measurement was used to deduce for m(c), the effective charm-quark mass, a value of (1.42 +/- 0.08) GeV/c(2). (c) 2005 Elsevier B.V. All rights reserved.

From 1994 to 1997, the emulsion target of the CHORUS detector was exposed to the wideband neutrino beam of the CERN SPS. In total about 100 000 charged-current neutrino interactions were located in the nuclear emulsion target and fully reconstructed. From this sample of events based on the data acquired by new automatic scanning systems; 2013 charm-decay events were selected by a pattern recognition program. They were confirmed as decays through visual inspection. Based on these events, the effective branching ratio of charmed particles into muons was determined to be (B) over bar (mu) = [7.3 +/- 0.8(stat) +/- 0.2(syst)] x 10(-2). In addition, the muonic branching ratios are presented for dominating charm-decay topologies. Normalization of the muonic decays to charged-current interactions provides sigma(mu)-(mu)+/sigma(cc) = [3.16 +/- 0.34(stat) 0.09(syst)] x 10(-3). Selecting only events with visible energy greater than 30 GeV gives a value of (B) over bar (mu) that is less affected by the charm production threshold and quasi-elastic Delta(+)(c) production. Combining this value with the current average of B 12 of vertical bar V-cd vertical bar(LO) = 0. 236 +/- 0.016. (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.

Results are given on tests of large particle trackers for the detection of neutrino interactions in long-baseline experiments. Module prototypes have been assembled using TiO2-doped polycarbonate panels. These were subdivided into cells of ∼1cm2 cross-section and 6m length, filled with liquid scintillator. A wavelength-shifting fibre inserted into each cell captured a part of the scintillation light emitted when a cell was traversed by an ionizing particle. Two different fibre-readout systems have been tested: an optoelectronic chain comprising an image intensifier and an electron-bombarded CCD (EBCCD); and a hybrid photodiode (HPD). New, low-cost liquid scintillators have been investigated for applications in large underground detectors. Testbeam studies have been performed using a commercially available liquid scintillator. The number of detected photoelectrons for minimum-ionizing particles crossing a module at different distances from the fibre readout end was 6–12 with the EBCCD chain and a mirror at the non-readout end; 4–10 with the HPD and no mirror. The light-attenuation lengths in the fibres were ∼9.4m with the EBCCD and ∼6.4m with the HPD. The detector response to electron showers has also been measured. After ten radiation lengths of lead, the transverse position of the incoming electron was determined with a precision of a few millimetres for electrons of 4GeV, and with a precision of 1.5–2.0cm for electrons of 1GeV.

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.

Results are given on tests of a high-resolution tracking hodoscope based on layers of 26-μm-bore glass capillaries filled with organic liquid scintillator (1-methylnaphthalene doped with R39). The detector prototype consisted of three 2-mm-thick parallel layers, with surface areas of 2.1×21cm2. The layers had a centre-to-centre spacing of 6mm, and were read by an optoelectronic chain comprising two electrostatically focused image intensifiers and an Electron-Bombarded Charge-Coupled Device (EBCCD). Tracks of cosmic-ray particles were recorded and analysed. The observed hit density was 6.6hits/mm for particles crossing the layers perpendicularly, at a distance of 1cm from the capillaries’ readout end, and 4.2hits/mm for particles at a distance of 20cm. A track segment reconstructed in a single layer had an rms residual of ∼20μm, and allowed determination of the track position in a neighbouring layer with a precision of ∼170μm. This latter value corresponded to an rms angular resolution per layer of about 30mrad. A comparison is made between capillary layers and silicon microstrip planes.