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.     

Production of charmed particles at the CERN intersecting storage rings in events triggered by an electron

Production of charmed particles has been investigated at √s = 63 GeV usi ng the Lampshade Magnet detector triggered by electrons and positrons emitted at 30% from the ISR beam axis. The results of a search for Λ_c and $\text{Λ}$_c signals in the K^?pπ⁺ and K⁺$\text{p}$π^? channels are presented. Cross sections for the reactions pp → $\text{D}$Λ_cX and pp → Λ_c$\text{Λ}$_cX, and upper limits. for pp → D$\text{D}$X, are evaluated under various models and compared with other values obtained at the ISR.     

On some effective mechanism for charmed particle production in neutrino and antineutrino beams

The paper describes an effective mechanism for charmed particle production in neutrino and antineutrino reactions, which consists in production of charmed virtual vector F1-meson in a weak vertex νF1μ (without suppression by the Cabibbo angle) with further strong rescattering of F1-meson on nucleon. This “quasidiffractive” mechanism should make the basic contribution to the production of charmed particles in neutrino experiments basic energies up to some hundreds of GeV. The charmed particles are mainly produced at limited momentum transfers $\text{|q}{}^2\text{| ≈ M}{}^2{}_{\mathrm{<mtext>F</mtext>}}\text{1}$ and with equal cross sections in the neutrino and antineutrino beams.     

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.     

Quantum chromodynamics and charm photoproduction

It is shown that charm photoproduction can be consistently described within an asymptotically free field theory. Quantum chromodynamics is used to derive sum rules for the total cross section σ_c^γ which includes both production of mesons with hidden charm (J/ψ, ψ′ and so on) and of charmed particles (pairs $\text{D}\text{D}$, $\text{F}\text{F}$ and so on). An estimate of σ_c^γ as a function of energy is given and fast growth is discovered up to energies ～ 1000 GeV. In this energy range σ_c^γ turns out to be equal to several μb. It is argued that measurements of charm photoproduction would give the most direct information on the gluon distribution within a nucleon. All the results are generalized to production of heavier particles containing new quarks. In particular, a simple rescaling law is derived connecting the cross sections for charm and beauty.     

Semi-leptonic decays of charmed baryons

We present estimates of semi-leptonic decays of the charmed $\text{1+}\text{2}$ baryons, members of the SU(3) 3¹ and 6 multiplets, into ordinary $\text{1+}\text{2}\text{and}\text{3+}\text{2}$ baryons. We give general expressions for decay rates and the mass M(B⁺?) spectra. We relate the relevant form factors for the $\text{1+}\text{2}\text{→}\text{1+}\text{2}$ transitions to the electromagnetic ones by means of CVC and SU(4). The form factors for $\text{1+}\text{2}\text{→}\text{3+}\text{2}$ transitions are related through SU(4) to those measured in Δ production. We discuss the dependence of the results on the masses of charmed baryons. The $\text{1+}\text{2}\text{→}\text{1+}\text{2}$ and $\text{1+}\text{2}\text{→}\text{3+}\text{2}$ transitions turn out to be dominant for the decays of the multiplets 3¹ and 6, respectively. The partial lifetimes are O(10^?10 ? 10^?14) sec as the masses of the decaying baryons are varied from 2 to 2.9 GeV. Possible ways of getting an idea about the masses of the charmed baryons are given.     

Decoupling of higher vector mesons and charmed meson production in e+e− annihilation

The striking feature that $\text{D}$¹D¹ production is greatly enhanced at energies just above threshold is explained. We argue that higher excited vector mesons successively decouple from lower spin final states which manifests itself in an explicit decoupling scheme. This can be verified on quite general grounds. A quantitative analysis of charmed meson production near threshold is given. Further evidence of the decoupling scheme coming from old data is discussed.     

The possibility of a (c,s) vector current and D→K1ℓν

The properties of the K¹ and charged lepton from the charmed particle decay $\text{D→K}{}_{\mathrm{1?\nu }}$ are used to give some model-independent tests for the presence of a purely vector (c, s) weak current. Present data on the electron energy spectrum may suggest that the (c, s) current is not purely vector. Models for the decay and general analysis techniques are also discussed.     

Five quarks,new particles and V + A currents

We propose an SU(5) model for the new heavy mesons, with a charge $\text{?1}\text{3}$ fancy quark in addition to a charge $\text{+2}\text{3}$ charmed quark. Besides interpreting the two narrow vector mesons J/Ψ and Ψ′ as c$\text{c}$ and f$\text{f}$ bound states and accounting for present data in a natural way, the model has (i) three new fancy vector mesons in addition to the charmed ones of the SU (4) model, (ii) at most two new $\text{C = P = +}\text{mesons}\text{(}\text{c}\text{c}\text{,}{}^3\text{P}{}_{\mathrm{J}}\text{, J = 0, 1)}$ between J/Ψ and Ψ ′, with suppressed radiative decays $\text{Ψ′ →}{}^3\text{P}{}_{\mathrm{J}}\text{+ γ}$, (iii) a state near 4.6 GeV in e⁺e^?, decaying mostly to fancy mesons if it is broad or perhaps charmed mesons if it is narrow, (iv) V + A weak currents and a large anomaly in $\text{ν}$N reactions, (v) a possible heavy lepton.     

Pionic and radiative decay widths of charmed hadrons in a badly broken SU(4) symmetry

The width of ψ(4.414) is surprisingly small for a c$\text{c}$ state far above the charm threshold, Γ_exp ≈ 33 MeV. This fact can be qualitatively understood if one makes the conservative assignment 4 ³S₁. The nodes of the wave function reflect as zero's of the decay amplitude in the momentum of the decay products, and are responsible for the suppression of the couplings to the ground state charmed mesons, Γ(ψ(4.414)→D$\text{D}$+ D$\text{D}$¹ + $\text{D}$D¹ + D¹$\text{D}$¹ + F$\text{F}$ + F$\text{F}$¹ + $\text{F}$F¹ + F¹$\text{F}$¹) ≈ 15 MeV. All the modes are suppressed by factors of the order of 10³ with respect to the k³ spin counting prediction. The dominant modes are predicted to be D¹$\text{D}$¹, F$\text{F}$¹ + $\text{F}$F¹ and D$\text{D}$. Moreover, we show that the contributions from P-wave charmed mesons are reasonably expected to be suppressed either by phase space or by the nodes if their masses lie within certain range. We emphasize however that the smallness of the photon coupling remains to be understood.     

Quarks with charm and colour: A new model of their strong and weak interactions

We discuss the motivation and the consequences of taking the charmed quark to be a $\text{6}$ under colour SU(3). Among the many features of this new quark scheme is that charmed mesons are heavier than charmed baryons.     

Weak decays of the charmed baryon C0+ and the inclusive yield of Λ and p

We calculate the decay rates of the charmed baryon state C₀⁺(2.26) into 25 two body and quasi two body states involving baryons and mesons with $\text{J}{}^{\mathrm{P}}\text{=}\text{1}\text{2}{}^{\mathrm{+}}\text{,}\text{3}\text{2}{}^{\mathrm{+}}\text{, 0}{}^{\mathrm{?}}\text{and}\text{1}{}^{\mathrm{?}}$. These modes yield a width of Γ = 16.3 × 10¹²s^?1and an inclusive yield of $\text{Λ/}\text{p}\text{? 40\%}$.     

The properties of charmed baryon (Λc+) and the proton revisited

A statistical model for baryons was suggested leading to an analytical expression for the square modulus ∥ψ(r)∥² of baryon wavefunctions, which is not only free of constituent quark masses but also devoid of the interaction parameters of the effective linear potential in which a quark moves. Using ∥ψ(r)∥² as an input the lifetimes of the newly established charmed baryon ($\text{Λ}{}_{\mathrm{c}}{}^{\mathrm{+}}$) and the proton were studied and compared with other existing theoretical estimates.     

The invariance of CP effects under particle phase choices

Recent data give unexpectedly large cross-sections for charmed particle production at high x_F in hadron collisions. This may imply that the proton has a non-negligible uudc$\text{c}$ Fock component. The interesting consequences of such a hypothesis are explored.     

The reaction 55Mn(d, t)54Mn

Neutron pick-up cross sections and vector analyzing powers have been measured for the reaction ⁵⁵Mn($\text{d}$, t)⁵⁴Mn at 17 MeV. The mixture of $\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ to $\text{p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ transfer to the low-lying l_n = 1 states has been found. Evidence of the $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ hole nature of several strong l_n = 3 states above 1 MeV has been obtained.     

Effects of multiplicity on charm semileptonic decay distributions

We consider the effects of multiplicity in semileptonic decays of charmed D(1.87) mesons, produced near threshold in e⁺e^? collisions. We calculate the decay distributions from uncorrelated D → (nπ)Kev and resonance dominated $\text{D}\text{→}\text{K}{}^1\text{e}\text{v}$ modes. Recent data from DORIS suggest that modes with two or more final hadrons dominate strongly.     

Excitation of the deeply bound g92 neutron hole state in 117Sn by a neutron pickup reaction with 81.7 MeV 3He particles

Neutron hole states have been investigated by neutron pickup reactions on ⁹²Mo, ¹¹⁸Sn, ¹⁴⁰Ce and ²⁰⁸Pb with 81.7 MeV ³He particles. A strong effect of angular momentum mismatch has been observed to reduce the cross section for low-spin orbits. It causes the deeply bound $\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbit to appear in the spectrum of the α-particles from the ${}^{118}\text{Sn(τ, α)}{}^{117}$Sn reaction as a strong broad peak. It may provide a nice tool for investigating the coupling mechanism between the deeply bound holes and the core.     

Elastic scattering of α particles on light nuclei at Pα=7 GeV/c

Elastic scattering differential cross sections of α particles have been measured at P_α=7.0 GeV/c ($\text{T}\text{N}\text{=1.05}\text{GeV}$) on ¹H, ²H, ³He and ⁴He target up to a momentum transfer of ～4 (GeV/c)². A preliminary interpretation of the data is given in the framework of the Glauber theory.     

Polarizations of spin 32 particles and 7Li58Ni interactions

New representations of polarizations of spin $\text{3}\text{2}$ particles are proposed for elastic scattering. They are useful in investigating spin-dependent interactions. The application to ⁷Li⁵⁸Ni scattering gives weak spin-orbit interactions and rather strong tensor ones of ⁷Li.     

Predictions of duality for the charmed meson masses

The constraints of duality via FESR's are applied to the processes P+P→P+V, using particles with a new quantum number (charm) as both external and internal (resonance saturation) states. The results are independent of any detailed dynamics or symmetry schemes, as well as independent of coupling strengths. We use the masses of the recently-discovered D and D¹ to set the scale. We predict , m_F = 1938 ± 33 MeV, . Thus slopes of Regge trajectories for charmed mesons are predicted to be substantially smaller than those for ordinary mesons.