First direct observation of the decay of neutral charmed particles produced by neutrinos in emulsion

Three examples of the production in emulsion by neutrinos and subsequent decay of neutral short-lived particles are reported. The flight times are ≈ 10^?13s, similar in order of magnitude to those previously determined for charged charmed particles in the same experiment.     

On the lifetime of charged charmed particles first direct observation of a charmed baryon decay

Two new examples of production by neutrinos and subsequent decay of charged charmed hadrons are reported. Together with two similar events reported previously they show that the lifetime of charged charmed particles is in the neighbourhood of 5 × 10^?13 s, as expected from current theoretical models. One of the new events is identified as a baryon λ_c⁺ of mass 2.295 ± 0.015 GeV/c² which undergoes the decay process λ_c⁺ → pπ⁺K^? with a proper decay time (7.3 ± 0.1) × 10^?13 s.     

Production characteristics of charmed particles in neutrino interactions

Using a hybrid emulsion spectrometer installed in the Fermilab wide-band neutrino beam, we located a total of 3855 neutrino interactions in the fiducial volume of our target. For 122 charmed-particle decays found in these interactions, we present distributions of x,y, charm-muon angular projection, Feynman-X, and the fragmentation Z. We find that the number of strange quarks in the nucleon sea is 4.2±2.1±2.6% of the number of down quarks.     

Evidence for the production of a new particle in neutrino interactions

We present here evidence, based on 5 events recorded in cosmic ray experiments deep underground, for the production of new, massive (? 2 GeV) and long lived (τ ～^?9 sec) particles in neutrino with rock nuclei.     

Observation of charmed baryon production in νp interactions in BEBC

Two examples of charmed baryon production by neutrinos have been observed in BEBC filled with hydrogen. Both events fit uniquely the reaction νp → μ^?pK^?π⁺π⁺ and thus apparently violate the ΔS = ΔQ rule. None of the appropriate mass combinations is consistent with the mass values of the D⁰ and D⁺ mesons. However, for the mass combinations of the pK^?π⁺ systems, values of (2.285 ± 0.005) GeV and (2.280 ± 0.003) GeV are found for event 1 and 2, respectively. These values agree with the mass of (2.285 ± 0.006) GeV for the Λ_c⁺ charmed baryon determined recently in e⁺e^? collisions at SLAC.     

Transverse momentum of hadrons produced in ν and ν interactions on an isoscalar target in BEBC

The average transverse momentum squared, 〈p_⊥²〉, of hadrons is studied as a function of W² and of Q² for ν and $\text{ν}$ interactions on an isoscalar target. An increase of 〈p_⊥²〉 with W² is observed for the hadrons emitted forward in the hadronic c.m.s. The p_⊥ dependence of the fragmentation function is found to factorise from the structure function at fixed W, but does not factorise at fixed Q². Unlike the case of forward-going particles, the 〈p_⊥²〉 of hadrons going backward in the c.m.s. shows no strong dependence on W².     

A test of ν stability using a 200 GeV narrow-band neutrino beam at BEBC

ν_e induced events obtained in a 200 GeV narrow-band beam have been studied and compared to the number expected from K_e3⁺ decay. Agreement is found between the expected and observed numbers allowing limits to be set on ν_e → ν_x mixing.     

Transverse momentum of charmed quarks produced in deep inelastic neutrino scattering

QCD predictions on the transverse momentum of charmed quarks produced in neutrino production are presented and contrasted to similar predictions of the transverse momentum of jets in electroproduction. The effects of including charmed quark mass are also considered and turn out to be significant.     

A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment

Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (, Λ, ) have been measured. Decays of resonances and heavy hyperons with an identified or Λ in the final state have been analyzed. Clear signals corresponding to and Σ(1385)^± have been observed. First results on the measurements of the Λ polarization in neutral current interactions have been obtained.     

Production of charmed hadrons in neutrino proton and antineutrino proton charged current interactions

Usind data from avp and \(\bar v\) p experiment with BEBC at CERN, the rates for inclusive production ofD ^*+,Λ _c ⁺ andD ⁰ invp scattering and ofD ^*? in \(\bar v\) p scattering are measured. Some examples of the exclusive production ofD ^*+,Λ _c ⁺ and∑ _c ⁺⁺ are given. The cross section for the reactionvp→μ ^? _c ⁺⁺ is estimated.     

Correlations associated with particles produced at small angles in pp collisions at the CERN ISR

Data on correlations between momentum analysed protons, pions or K mesons, and charged particles produced in pp collisions at the CERN ISR are presented. The charged particles were detected in a ～4π scintillation counter hodoscope. The pseudo-rapidity distributions are well described by production within the limits of cylindrical phase space, with negative kaons and antiprotons yielding narrower distributions than protons, pions and positive kaons. The azimuthal distributions show symmetry around the t-channel axis in the rest frame of the recoiling mass M_x in pp → aX (a = detected proton, pion, positive kaon).     

Leading particles and charged particle multiplicity in annihilation and non-annihilation interactions

Using data from our K^?p experiment at 8.25 GeV/c we have investigated the charged particle multiplicity, and the variation of charged pion multiplicity as a function of the effective mass squared of all pions, for various samples of data, and compared our results with $\text{p}$p annihilation data and pp data. Evidence is presented which suggests that the difference in behaviour between the annihilation and non-annihilation data is not due to some specific mechanism such as baryon exchange, but is related to the absence of leading particles in the former case.     

Total cross sections for ve and ve interactions and search for neutrino oscillations and decay

About 200 and 60 candidates for electron neutrino and antineutrino interactions, respectively, have been analyzed in the heavy liquid bubble chamber Gargamelle exposed to the CERN PS neutrino beam. Evidence for scaling has been found for these interactions, with slopes of the cross sections in good agreement with those obtained for muon neutrino and antineutrino events in the same chamber. No evidence appears for oscillations of neutrinos or antineutrinos, which would induce in the present experiment an excess of electron or positron events. The corresponding limits are given as functions of the mixing parameter, for the finite mass Majorana neutrinos. The possibility of a multiplicative law for the lepton number has also been investigated. A search for isolated electron-positron pairs revealed no excess in the forward direction, in contradiction to the expectation for muonic neutrino and antineutrino decays. The corresponding limits on the c.m. half lifetimes are given.     

Spatially dependent quantum interference effects in the detection probability of charged leptons produced in neutrino interactions or weak decay processes

Feynmans path amplitude formulation of quantum mechanics is used to analyse the production of charged leptons from charged current weak interaction processes. For neutrino induced reactions the interference effects predicted are usually called neutrino oscillations. Similar effects in the detection of muons from pion decay are here termed muon oscillations. Processes considered include pion decay (at rest and in flight), and muon decay and nuclear -decay at rest. In all cases studied, a neutrino oscillation phase different from the conventionally used one is found.Received: 3 February 2004, Revised: 20 July 2004, Published online: 14 September 2004     

Correlations associated with small angle protons produced in proton-proton collisions at 31 GeV total energy

High energy inelastic protons with $\text{x = 2 p}{}_{\mathrm{<mtext>L</mtext>}}\text{/s}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{> 0.99}$ observed in 15.3/15.3 GeV proton-proton collisions at the CERN ISR are accompanied by particles whose angular distribution is confined to a narrow cone in the opposite direction. In constrast, lower energy protons (0.72 < x < 0.84) are accompanied in addition, by particles emitted at larger angles. The ratio of the associated charged multiplicities is approximately 0.4.     

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/cπ⁺p and K^?p interactions (2 × 10⁶ and 10⁶ pion pair combinations, respectively) and in a smaller sample of $\text{p}\text{p}$ annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.     

On the slope of the scalar Kℓ3 decay form factor

We discuss a mechanism, based on exact threshold theorems in the limit of SU(2) × SU(2) symmetry, which can be used to estimate a certain suppression of the scalar K_?3 decay form factor at low momentum transfers, while maintaining the validity of the Callan-Treiman relation.