After completion of the data taking for the νμ→ντ 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 pions 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<Eν<200 GeV. We extract the neutrino–nucleon structure functions F2(x,Q2), xF3(x,Q2), and R(x,Q2) and compare these with results from other experiments.
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
κ
=
0.33
±
0.05
±
0.05
, improving the results obtained in similar analyses by previous experiments.
A measurement of Λc+ production in neutrino nucleon charged-current interactions is presented. In a subsample of about 50000 interactions located in the emulsion target of the CHORUS detector, ...exposed to the wide band neutrino beam of the CERN SPS, candidates for decays of short-lived particles were identified using new automatic scanning systems and later confirmed through visual inspection. Criteria based on the flight length allowed a statistical separation among the different charm species thus enabling a sample particularly rich in Λc+ to be defined. At an average neutrino energy of 27 GeV, the product σ(Λc+)/σ(CC)×BR(Λc+→3p) was measured to be (0.37±0.10(stat)±0.02(syst))×10−2, while the values of (1.54±0.35(stat)±0.18(syst))×10−2 and of 0.24±0.07(stat)±0.04(syst) were obtained for σ(Λc+)/σ(CC) and BR(Λc+→3p), respectively.
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 νN charged-current cross-section was measured to be σ(QE)/σ(CC)=(0.23+0.12−0.06(stat)+0.02−0.03(syst))×10−2. Through an analysis of the topology at the production and decay vertices the relative cross-sections were measured separately for singly (Λc+,Σc+,Σc+∗) and doubly (Σc++,Σc++∗) charged baryons.
During the years 1994–1997, the emulsion target of the CHORUS detector was exposed to the wide-band neutrino beam of the CERN SPS collecting about 106 neutrino interactions. A measurement of ...ν¯μ-induced charm production is performed by using the presence of a 5% ν¯μ component in the νμ beam. The measurement takes advantage of the capability to observe the decay topology in the emulsion. The analysis is based on a sample of charged-current interactions with at least one identified muon. About 100 000 were located in the emulsion target and fully reconstructed. By requiring a positive muon charge as determined by the CHORUS muon spectrometer, 32ν¯μ-induced charm events were observed with an estimated background of 3.2 events. At an average antineutrino energy in the neutrino beam of 18 GeV, the charm production rate induced by antineutrinos is measured to be σ(ν¯μN→μ+c¯X)/σ(ν¯μN→μ+X)=(5.0−0.9+1.4(stat)±0.7(syst))%. The ratio between neutral and charged charm production rates in this process is (2.6−1.0+1.7(stat)±0.8(syst)). The charm production rate as a function of the antineutrino energy is found to be in good agreement with previous results derived from di-lepton data.
This Letter reports on a study of trimuon events induced by neutrino interactions in the CHORUS calorimeter exposed to the CERN SPS wide-band νμ beam. Among the multimuon events produced in the ...calorimeter, 42 μ−μ−μ+ 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 π− and K− decays in charm dimuon events are responsible for an additional ≈25% contribution to the total μ−μ−μ+ 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.
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
̄
has been inferred from measurements of events with two or three muons 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.
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 56172νμ charged-current interactions analysed so far, we find a value of Bμ=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, Bμ=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 |Vcd|.
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