The Λ c (2940)+ as a D*N Molecule in a Constituent Quark Model and a Possible Λ b (6248)

The Λ _c (2940)⁺ is studied in a constituent quark model. The model describes the deuteron as an NN bound state and the X(3872) as a DD* molecule. We studied the meson baryon sector and found a D*N bound state consistent with the data available for the Λ _c (2940)⁺. The existence of this bound state in this picture implies the existence of a ${\bar B^* N}$ partner that we predict as a Λ _b (6248). Different decay channels for this state are also studied.     

Charmed Deuteron

Possible existence of bound states of a charmed baryon, Λ _c , Σ _c , Σ* _c with a nucleon, N, as well as two charmed baryons, Λ _c Λ _c , etc., are examined in the meson exchange potential approach. The heavy quark spin symmetry induces a strong tensor coupling between Λ _c N, Σ _c N and Σ* _c N states, which causes a bound state of Λ _c N (J = 0⁺ and 1⁺) states. Such a bound state is also seen in the spin-singlet Λ _c Λ _c channel, which resembles the H dibaryon in the strange sector.     

Λc5He and Λc9Be charmed nuclei versus Λ5He and Λ9Be hypernuclei

A comparative study is made for _Λc⁵He and _Λc⁹Be charmed nuclei versus _Λ⁵He and _Λ⁹Be hypernuclei. The Λ_c(Λ)+α and Λ_c(Λ)+α+α systems are treated in a microscopic way. Within certain range of the Λ_cN interaction strength, the energy properties of Λ_c+α and Λ_c+α+α are calculated and discussed. Similarity between the energy spectra of the noted charmed nuclei and hypernuclei is suggested.     

The cut-off dependence of the Higgs meson mass and the onset of new physics in the standard model

The scaleΛ ^cut before which the Weinberg-Salam model is expected to break down is predicted as the function of the Higgs meson massm _H by using two different approximate, but non-perturbative renormalization group procedures. The first scheme is the “local potential approximation”, the second is Wilson's recursion relation. For values of the functionΛ ^cut =Λ ^cut(m _H) of the order of the Higgs mass itself, we get an absolute upper bound onm _H . The conceptual background of these problems is discussed in detail.     

First observation of the production and decay of the Σc+

An event with the decay chain Σ_c⁺ → Λ_c⁺ + π⁰, Λ_c⁺ → K^? + p + π⁺, has been observed in an exposure of BEBC, equipped with a track sensitive target, to the wide band neutrino beam from the SPS at CERN. The event has a unique three constraint kinematic fit to the ΔS = ?ΔQ reaction v + p → μ^? + p + K^? + π⁺ + π⁺ + π⁰ with both gammas from the π⁰ decay detected. The proton and other final state particles are identified. The masses are M(Λ_c⁺) = 2290 ± 3 MeV/c², M(Σ_c⁺) = 2457 ± 4 MeV/c² and M(Σ_c⁺) ? M(Λ_c⁺) = 168 ± 3 MeV/c². Including other data one obtains M (Σ_c⁺⁺) ? M(Σ_c⁺) = 0 ± 4 MeV/c².     

Investigation of the electromagnetic structure of the η meson in the decay η → μ+μ−γ

600 events of the rare electromagnetic decay η → μ⁺μ^?γ have been detected. The branching ratio has been measured as BR(η → μ⁺μ^?γ) = (3.1 ± 0.4) × 10^?4. The electromagnetic form factor of the η meson, F(m_μμ²;0) = (1 ? m_μμ²/Λ²)^?1, has been determined. Λ = (0.72 ± 0.09) GeV/c² is in good agreement with the vector meson dominance model.     

Two body non-leptonic Λ b decays in the largeN c limit

The two body non-leptonic Λ _b decays are analysed in the HQET with factorization approximation and largeN _c limit. In this limit, Λ _b and Λ _c baryons can be treated as the bound states of chiral soliton and heavy meson, and consequently the Isgur-Wise function comes out in a straight forward manner. The results obtained remain well below their previously predicted upper limit.     

Study of quasi two-body final states in K−n reactions at 8.25 GeV/c

Cross sections for various channels in 3 prong + V₀ final states of K^?n interactions are obtained at 8.25 GeV/c. An energy dependence study of the quasi two-body reactions Σ^?(1385) + vector meson and ΛB^? seem to imply the presence of cuts in the Regge exchange formalism, whereas the reaction Δ(1236) $\text{K}$¹ (890) does not require such cuts. Upper limits of 1 and 2 μb are found for the reactions K^?n → ΛA₁ and K^?n → ΛA₂.     

Observation of a doubly charged charmed baryon in the reaction υp→μ−Σ++c

Evidence for the quasi-elastic production of the doubly charged charmed barron Σ⁺⁺_c has been observed in a vp interaction in BEBC. The mass of the Σ⁺⁺_c and of its decay product, the Λ⁺_c, are 2454±5 MeV and 2288±5 MeV, respectively. The mass difference M(Σ⁺⁺_c)? M(Λ⁺_c) is 166±1 MeV. Combining the Λ⁺_c mass value obtained here with the values obtained in the two Λ⁺_c events previously observed in this experiment, thevalue M(Λ⁺_c)=2283±3 MeV is deduced.     

Ultra heavy fermion bound states via Higgs exchange

We study the characteristic features of the ultra heavy fermion bound state via Higgs exchange. The constraint under which such a bound state occurs is presented. For a typical example of Higgs and fermion mass, M_H≅ 100 GeV / c² and M_F≅ 700 GeV/c², the wave function at the origin of the bound states via Higgs exchange becomes about 100 times larger than that via gluon exchange.     

B → F + X decay and pseudoscalar decay constants of explicitly flavored heavy mesons

If the current theoretical pictures of explicitly flavored heavy mesons are quantitatively correct, we expect that the branching ratio of B → $\text{F}$ + X (anything) may be 6 percent even in a conservative estimate. Accurate measurement of this branching ratio will determine the value of the pseudoscalar decay constant f_F, of the wave function at origin of the s wave $\text{c}$ s bound state in the potential picture, and help to clarify dynamical properties of heavy meson binding.     

Evidence for two strangeonium resonances with JPC=1++ and 1+− in K−p interactions at 11 GeV/c

The results of a partial wave analysis of the low mass KK̄π system produced in the reactions K⁻p→K⁰_sK^±π^±Λ at 11 GeV/c using the LASS spectrometer are presented. Evidence is given for two ss̄ axial-vector meson states: one with quantum numbers J^PC = 1⁺⁺, mass ∼ 1530 MeV/c², and width ∼ 100 MeV/c², and the other with quantum numbers J^PC=1⁺⁻, mass ∼ 1380 MeV/c², and width ∼ 80 MeV/c². These states are good candidates to be the mostly strangeonium members of the ground state 1⁺⁺ and 1⁺⁻ nonets predicted by the quark model.     

Coherent production of theK −π+π− system inK −d interactions at 4.5 GeV/c

After summarizing the properties of the socalled Dalitz Array (DA), which is a genuine characteristics of a resonance, we determine those of the well known ε, γ, andA ₂ resonances produced in theK ^? p→π⁺π^?π⁰ Λ final state at 4.2 Ge V/c. A tentative measurement of the DA of theA ₁ meson produced backwards in the reactionK ^? p→π⁺π⁺π^?Σ^? is also presented. The data for this analysis come from the high statistics (130 events/μb) experiment performed by the ACNO Collaboration.     

The study of prompt and delayed muon induced fission

The mean life times of negative muons bound to actinide nuclei have been measured by detecting the time difference between a stopped muon and the arrival of fragments from delayed fission after muon capture. The deduced capture ratesΛ _c are 1.392(4)·10⁷/s for²³⁷Np, 1.290(7)·10⁷/s for²⁴²Pu and 1.240(7)·10⁷/s for²⁴⁴Pu. The results are compared with published data for the fission and the neutron decay channels and for the electron decay of the bound muon. Including a former measurement ofΛ _c for²³⁹Pu, an isotopic dependence of the muon capture rates in the Pu isotopes is clearly observed.     

Is J~(PC)=3~(-+) molecule possible?

The confirmation of charged charmonium-like states indicates that heavy quark molecules should exist.Here we discuss the possibility of a molecule state with J P C= 3-+. In a one-boson-exchange model investigation for the S wave C = + D* ˉD*2states, one finds that the strongest attraction is in the case J = 3 and I = 0 for bothπ and σ exchanges. Numerical analysis indicates that this hadronic bound state might exist if a phenomenological cutoff parameter around 2.3 Ge V(1.5 Ge V) is reasonable with a dipole(monopole) type form factor in the one-pionexchange model. The cutoff for binding solutions may be reduced to a smaller value once the σ exchange contribution is included. If a state around the D* ˉD*2threshold(≈4472 Me V) in the channel J/ψω(P wave) is observed, the heavy quark spin symmetry implies that it is not a cˉc meson and the J P C are likely to be 3-+.     

Spin effects in two-body hadronic decays of the B c mesons

Spin effects in the weak two-body hadronic decays of the B _c and B _c ^* mesons into J/ψ and ρ(π) mesons are considered within the model of hard one-gluon exchange between quarks at high momentum transfers. It is shown that the polarization of the J/ψ meson in the decays of the B _c ^* meson differs substantially from that in the decays of the B _c ^* meson. The decay widths of the B _c ^* meson differ significantly from the widths of the B _c ^* meson.     

Bound states of heavy quarks on the light plane

We investigate in detail the light plane formulation of bound state equations and of the interactions of bound states. This formalism is particularly well suited to discuss bound states of heavy quarks since these states can be well approximated as two particle states but yet there are significant relativistic corrections to the conventional nonrelativistic approach. Applications are made to electromagnetic decays of charmonium (ψ→e ⁺ e ^?, η _c →γγ, ψ′→η _c γ, etc.).     

On some three-meson vertex sum rules in quantum chromodynamics

We discuss some applications of the Laplace transform sum rules to the three-point function of currents and current divergences. Evaluating the QCD part of the vertex function in the symmetrical subtraction configuration, where all external masses are equal and much larger thanΛ _QCD, we obtain relations between the meson couplingsg _ωρπ,g _δKK ,g _ρππ and quark masses and vacuum condensates.     

QCD sum rules for heavy quark systems

In this paper we present in a detailed and coherent fashion our work on QCD sum rules for equal mass heavy quark meson states. We discuss the technical procedures used to calculate the perturbative and non-perturbative contributions to the vacuum polarization, which have been calculated for all currents up to and including spin 2⁺⁺. Using dispersion relations, sum rules are derived. Extensive applications are made to the lowest lying states of the charmonium and upsilon systems. The masses of the S- and P-wave charmonium levels are reproduced to a high degree of accuracy, and the mass of the ¹P₁ level is predicted at 3.51 GeV. For the upsilon system it only appears to be possible to predict the γ-η_b splitting which gives 60 MeV. Very accurate values are given for the current quark masses at p² = ?m_q²: m_c = 1.28 GeV and m_b = 4.25 GeV.     

Charm production in 400 GeV/c proton-emulsion interactions: Bombay-Chandigarh-Delhi-Jammu Collaboration

5032 proton-emulsion interactions at 400 GeV/c momentum have been carefully scrutinized for production and decay of charged charm particles. In order to detect these decays, shower tracks from 3056 stars have been followed to a maximum length of 1 mm and those from 1976 stars up to 2 mm. A total of 23 three-prong charm-like candidates have been recorded in the forward cone. The background due to γ-overlap on a shower track, trident/pseudo-trident production and secondary interactions is estimated to be 15. Attributing the signal of 8 events to Λ_c⁺ and assuming the branching ratio of Λ_c⁺ → 3 prong to be 0.6 and τ_Λc to be 10^?13 sec we obtain the production cross section to be 106±39μb/nucleon. Out of these 8 events one example of semileptonic decay of Λ_c⁺ is seen.