A search for charmed particles originating from the interactions of 300 GeV/c protons in emulsion nuclei

The associated production of charmed particles by the interactions of 300 GeV/c protons with complex nuclei has been sought using nuclear emulsions. The failure to observe any candidates for this process among some 60,000 interactions investigated implies, provided charmed particles lifetimes are in the range 10^?12 to 10^?14 s, a cross section for their associated production by the interactions of 300 GeV/c protons with nucleons of less than 1.5 microbarns at a 90% confidence level.     

Weak decays of charm and quark masses

We calculate the effects of finite quark masses for the semileptonic and nonleptonic decays of charmed particles. The total lifetimes of charmed particles are not sensitive to the masses of the quarks in the final state. However the semileptonic branching ratios changes considerably. Using conventional constituent quark masses, one expect e.g. B_e(D⁺)≈ 21%. The brancing ratios and lifetimes of the charmed particles are estimated, taking into account the annihilation hypothesis.     

Some comments on selection rules for nonleptonic decays of charmed particles

We show that even if only the decays of charmed mesons into two body final states are concerned, the Δn _t=0 rule is stillnot equivalent to sextet dominance. We also isolate the significant contribution of each quark diagram to non-leptonic decays of charmed particles. Thereby pointing out that the recent SLAC observation of Λ _c ⁺ →K ^?Δ⁺⁺ has already given evidence that theW-exchange diagram may be important in charmed baryon decays.     

Direct observation of a pair decay of neutral charmed particles produced in 400 GeVc proton interaction

The second evidence of a pair decay of charmed particles has been obtained in an emulsion chamber exposed to $\text{400}\text{GeV}\text{c}$ protons. The life time and production cross section of the charmed particles have been evaluated as several times 10^?13 s and several tens of microbarns.     

Neutrino production of charmed particles in a hybrid experiment E-564

Cryogenically sensitive nuclear emulsion was placed inside the 15-foot bubble chamber of FNAL and exposed to a wide-band energy (up to 200 GeV) neutrino beam. 194 charged-current neutrino interactions and 13 decays of charmed particles were registered. Using the nuclear emulsion as a vertex detector with the good spectrometric properties of the 15-foot bubble chamber has allowed the decays of charmed particles to be effectively analysed. Attentions is focussed on the new physical results. Λ _c ⁺ baryon andD _s ⁺ meson decay channels, production of charmed ∑ _c baryons and Λ _c ⁺ via ∑ _c . For the first time an event interpreted as production of the excited (c \(\overline s\) )-state with mass ～2790 MeV/c² has been registered.     

Observation of pairs of charmed particles produced by high-energy photons in nuclear emulsions coupled with a magnetic spectrometer

Preliminary results of an experiment using nuclear emulsions exposed to a tagged photon beam at the CERN SPS (experiment WA58) are presented. Six events showing pairs of charmed particles have been found. One of these has been interpreted as an associated production of Λ_c⁺ and $\text{D}$⁰. The mean lifetime of the neutral D meson based on three events is τ⁰ = (0.58_?0.2^+0.8 × 10^?13 s,, whereas a statistical analysis of eight charged charmed particles, assumed to be D mesons, leads to an estimate of the mean lifetime of τ^± ≈ 4.4 × 10^?13 s.     

Persistent threshold effects characterizing dimuon and hadron distributions due to charmed particle production by neutrinos

If massive charmed particles are being produced in current νN scattering experiments, their semi-leptonic decay leads to dimuon states. The production and decay of such particles in this process is examined in a parton model which has been modified to realistically incorporate the threshold due to the large mass of the charmed particle.The model then predicts threshold scaling violations which are unexpectedly large, and persist out to several hundred GeV in neutrino energy. These effects are particularly striking in the distributions of the charmed particle and its decay products, whose naive-scaling violations are so extreme as to be better described in terms of new anomalous scaling “laws”.The resultant dimuon and hadron distributions are qualitatively consistent with all trends observed in the recent dimuon experiments. Comparative tests between charm and other mechanisms for dimuon production are proposed. An important feature of these tests is their reliance on the persistent threshold effects predicted above. The present data on the muonic energy asymmetry β as a function of incoming neutrino energy is in agreement with the anomalous scaling predicted in the above model.     

Distribution of charmed constituent quarks in hadrons

By using a statistical approach within noncovariant perturbation theory, the distributions of light and charmed quarks in hadrons are derived with allowance for the charmed-quark mass. The parameters of the model are extracted from a comparison with NA3 data on the hadroproduction of J/ψ particles. A reanalysis of EMC data on charm production in muon-nucleon scattering is performed. In relation to the conventional source of charmed quarks from photon-gluon fusion, the EMC data are found to suggest the presence of an additional contribution from deep-inelastic scattering on charmed quarks at large x. The resulting admixture of Fock states that contain charmed quarks in the decomposition of the proton wave function is about 1%. The approach presented for the excitation of Fock states involving charmed quarks can also be applied to states featuring beauty quarks, as well as to the hadronic component of the virtual photon (resolved photon component).     

Gluon bremsstrahlung production of heavy particles in neutrino and antineutrino scattering

Weak charged current production of charmed quark pairs is studied in the framework of the QCD inspired parton model. The magnitude of the cross section strongly depends on the charmed quark pair production threshold, above which the gluons are assumed to decay into either charmed particle pairs of hidden charmonium states. The normalized distributions are rather insensitive to the choice of this threshold value and the angular distribution of J/gy particles will show significant azimuthal asymmetry about the current-target axis. The sign of the asymmetry cannot be mimicked by the parton primordial transverse momentum effects and thus the process can serve a clean test of the gluon bremsstrahlung mechanism.     

Investigation of the decay of charmed particles produced in neutrino interactions

The decay of charmed particles produced by high-energy neutrinos has been studied by an experiment using simultaneously emulsion, bubble chamber and counter techniques. Eight charmed particle candidates, 5 positively charged and 3 neutral, have been found in the emulsion, where their production and decay have been directly observed. One of these events is identified as a Λ_c⁺ baryon of mass 2.26±0.02 GeV/c² which undergoes the decay Λ_c⁺→pK^?π⁺ after a proper time of (7.3±0.1) · 10^?13 s.A statistical analysis of the other observed decays leads to the mean-life values τ⁺=(2.5_?1.1^+2.2) · 10^?13 s, τ⁰=(0.53_?0.25^+0.57) · 10^?13 s, for the sample of charged particles enriched by a similar event found in a previous experiment, and for the sample of 3 neutral particles, respectively. The former value is only slightly affected by including in the sample the Λ_c⁺ event or excluding that of the previous experiment.     

Production of lepton pairs,J/Ψ and charm with hadron beams

Data for J/Ψ production with nucleon and pion beams are used, together with electro-production data, to extract information about distributions of quarks within hadrons. These distributions are used to make further predictions about J/Ψ production with beams of hadrons of various types, and about the production of lepton pairs. It is argued that, even at SPG or FNAL energies, J/Ψ production does not usually involve the conjont production to charmed particles. The production of charmed particles without the J/Ψ is also considered; the cross section is estimated to be smaller than has been previously predicted.     

Opposite-side angular correlation of high-pT particles as a probe of gluons

Opposite-side angular distributions of high-p_T particles in the jet trigger experiments are studied in the lowest-order QCD. Gluon jets play a crucial role in understanding correlations between two high-p_T jets. The angular distribution of the positive-to-negative particle ratio and that of charmed particles can be good probes of the gluon density inside a nucleon.     

Present status of the opera experiment for the direct observation of neutrino oscillations in the νμ → ν τ channel

The OPERA experiment (Oscillation Project with an Emulsion-Tracking Apparatus) for the direct observation of neutrino oscillations in the ν_μ → ν _τ channel has been underway at the underground laboratory in Gran Sasso since 2007. In the course of data collection, more than 3000 ν_μ interactions have been registered in emulsion detectors. Twenty charmed neutrino interaction candidates have been found. Multidimensional criteria have been developed in order to select ν _τ interactions against νμ interactions accompanied by charmed hadron production. The first results from automated PAVIKOM emulsion scanning have been obtained. We discuss the measurements of the muon charge ratio of μ⁺ to μ^?.     

Nonleptonic Cabibbo favouredB-decays andCP-asymmetries for charmed final hadron states in Isgur and Wise theory

The Cabibbo allowed non-leptonicB-decays in two hadrons are studied, within the factorization hypothesis, in the framework of Isgur and Wise theory for the matrix elements of the ΔB=?ΔC=±1 weak currents. TheSU(2) _HF symmetry relates |ΔB|=1 to |ΔC|=1 currents, which have been measured in the semileptonic strange decays of charmed particles. By assuming colour screening and allowing forSU(3) invariant contributions from the annihilation terms with charmed final states one is able to comply with the present experimental knowledge. TheCP violating asymmetries in neutralB decays are given charmed final states in terms of theK-M angles. With the central values found for the annihilation parameters there is a destructive (constructive) interference between the direct and annihilation terms in the Cabibbo allowed (doubly forbidden) amplitudes for the decays intoD ⁰(D ^*0)π⁰ and {D ⁰ρ⁰ so that they may be of the same order. This would imply large asymmetries, for which however our present knowledge on the amplitudes does not allow to predict even their sign. We have better confidence in our predictions for the charged final states than the neutral ones and can draw the conclusion that the detection of the corresponding asymmetries requires, at least, 10⁶ tagged neutralB-particles.     

Hadroproduction of heavy quark flavors in QCD

Within the framework of perturbative QCD, we investigate the hadroproduction of charmed particles via two-gluon as well as quark-pair annihilation. The total production cross section is found to be sensitive to the choice of the scale parameter Q² and in general not free from non-perturbative effects. Charmed-particle production in the high-p_T region is also studied.     

On the free parton model for weak semileptonic decays of charmed particles

It is argued that the fitted charmed quark mass and Fermi momentum in the free parton model for semileptonic decays of charmed particles, are unreasonably large. Furthermore, the charmed quark mass needed to explain the estimated semileptonic width of charmed particles is also too large (～2 GeV). It is reasoned that the failure of the free parton picture is due to strong initial and final state binding effects.     

Can charm account for prompt lepton production?

The production and subsequent semi-leptonic decay of charmed particles is investigated in order to determine whether it could account for the prompt lepton data. Most of the central region data is easily accommodated but there are difficulties at large x. Large cross-sections for charmed particle production are implied. Correlations in $\text{pp}\text{→}\text{D}\text{(→}\text{e}\text{) +}\text{D}\text{?}\text{(→ μ) + …}$ events are discussed.     

On the fragmentation functions of heavy quarks into hadrons

An explicit form for the charmed quark fragmentation function D^C_c(z) into hadrons has been obtained with the help of the “reciprocity relation” and the c-quark distribution function in charmed mesons (the function calculated in terms of the Kuti-Weisskopf model). D^C_c(z) turns out to peak mainly at z close to 1. The analysis of new data on muon pair production in neutrino reactions points to such a behaviour of the D^C_c(z) function. The obtained fragmentation function, contrary to those, used earlier, leads to a charmed particle (average) multiplicity in e⁺e^?-annihilation independent of energy.     

Cross sections for exclusive channels in\bar pp reactions at 12 GeV/c

The data obtained in an exposure of BEBC to an r.f. separated beam of antiprotons at 12 GeV/c are used to derive exclusive cross sections for reactions having one or more neutral strange particles in the final state. Particular attention is given to the estimation of the background. An upper limit of the cross section for the inclusive production of the charmed mesonD ^* is also given.     

Production ofψ particles in N-N collisions and largeP T phenomenon

We calculate the yield ofψ (3105) particles in N-N collisions in a model which associates the production of heavy particles with largeP _T phenomenon. Our results show thatψ (3105) has a fairly strong coupling to other hadrons. We propose a criterion in the search for charmed particles and a parametrization for the expected yields of such particles.