Search for the doubly charmed baryon ■

A search for the doubly charmed baryon Ξ_(cc)~+ is performed through its decay to the Λ_c~+K~-π~+ final state, using proton-proton collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 Te V. The data correspond to a total integrated luminosity of 9 fb~(-1). No significant signal is observed in the mass range from 3.4 to 3.8 Ge V/c~2. Upper limits are set at 95% credibility level on the ratio of the Ξ_(cc)~+ production cross-section times the branching fraction to that of Λ_c~+ and Ξ_(cc)~(++) baryons. The limits are determined as functions of the Ξ_(cc)~+ mass for different lifetime hypotheses, in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 4 to 15 GeV/c.     

Search forN ϕ (1960) baryon

In the experiments at the SPHINX facility in the 70 GeV proton beam of the IHEP accelerator the diffractive production reactionsp+N[(1385)⁰ K ⁺] +N andp+N[(1385)⁰ K ⁺]+N+ (neutral particles) were studied. In the effective mass spectra of the [(1385)⁰ K ⁺] system in these processes there were no signals from the anomalously narrow baryon stateN (1960) which had been observed earlier in the measurement at the BIS-2 setup.SPHINX Collaboration (IHEP-ITEP)     

Heavy baryon–light vector meson couplings in QCD

The strong coupling constants of heavy baryons with light vector mesons are calculated in the framework of the light cone QCD sum rules using the most general form of the interpolating currents for the heavy baryons. It is shown that the sextet–sextet, sextet–antitriplet and antitriplet–antitriplet transitions are described by one invariant function for each class of transitions. The values of the electric and magnetic coupling constants for these transitions are obtained.     

Weak annihilation in charm baryon decays — A re-evaluation

We discuss weak decays of charm baryons taking the mode Λ _c ⁺ →Δ⁺⁺ K ^? as the starting point of our analysis. This channel which can occur only due to weak annihilation has been seen at the ISR. Hence we conclude that weak annihilation is very significant for baryons. Further tests of this picture are listed, in particular concerning charm-strange baryons. We argue that τ(D°)~τ(Λ _c ⁺ )<τ(D ⁺) suggests that baryon and meson decays should be treated on an equal footing even when weak annihilation is included. We describe a framework based on evolution equations where this can be done.     

Study of the baryon resonances structure via η photoproduction

Within a quark model the process γp → ηp, for E_γ^lab < 1.2 GeV, is investigated. We find that the recent data from GRAAL on the polarized beam asymmetry require significant contributions from the resonances D₁₃(1520), F₁₅(1680), and to a lesser extent from P₁₃(1720) in addition to those from the dominant S₁₁(1535) resonance, implied by the Mainz differential cross-section data. The contributions from the resonances S₁₁(1650), D₁₃(1700) and D₁₅(1675) are found consistently small but sensitive to the polarized target asymmetry measured recently at ELSA. These results are shown to be consistent with the quark model predictions.     

S = −1 resonances in two meson-one baryon systems

We study the two meson-one baryon systems by solving Faddeev equations, using chiral dynamics. The calculations, carried out for the $\pi \overline{K} N$ system and its coupled channels for the case of strangeness = ?1, in the S-wave, lead to a dynamical generation of many strangeness = ?1 resonances in the 1500–1800?MeV region. While building the formalism, we found important cancellations between different sources of three-body forces.     

Observation of Cabibbo-suppressed and W-exchange Λ c + baryon decays

We present measurements of the Cabibbo-suppressed decays Λ _c ⁺→Λ ⁰ K ⁺ and Λ _c ⁺→Σ ⁰ K ⁺ (both first observations), Λ _c ⁺→Σ ⁺ K ⁺ π ⁻ (seen with large statistics for the first time), Λ _c ⁺→pK ⁺ K ⁻ and Λ _c ⁺→pφ (measured with improved accuracy). Improved branching ratio measurements for the decays Λ _c ⁺→Σ ⁺ K ⁺ K ⁻ and Λ _c ⁺→Σ ⁺ φ, which are attributed to W-exchange diagrams, are shown. We also present the first evidence for Λ _c ⁺→Ξ(1690)⁰ K ⁺ and set an upper limit on the non-resonant decay Λ _c ⁺→Σ ⁺ K ⁺ K ⁻. This analysis was performed using 32.6 fb⁻¹ of data collected by the Belle detector at the asymmetric e ⁺ e ⁻ collider KEKB.     

Observation of the Ξ(b)(0) baryon

The observation of the bottom, strange baryon Ξ(b)(0) through the decay chain Ξ(b)(0)→Ξ(c)(+)π-, where ΞΞ(c)(+)→Ξ- π+ π+, Ξ-→Λπ-, and Λ→pπ-, is reported by using data corresponding to an integrated luminosity of 4.2 fb(-1) from pp collisions at square root(s)=1.96 TeV recorded with the Collider Detector at Fermilab. A signal of 25.3(-5.4)(+5.6) candidates is observed whose probability of arising from a background fluctuation is 3.6×10(-12), corresponding to 6.8 gaussian standard deviations. The Ξ(b)(0) mass is measured to be 5787.8±5.0(stat)±1.3(syst) MeV/c2. In addition, the Ξ(b)- baryon is observed through the process Ξ(b)-→Ξ(c)(0)π-, where Ξ(c)(0)→Ξ- π+, Ξ-→Λπ-, and Λ→pπ-.     

Search for the doubly heavy baryon ■ decaying to ■

A first search for the ■decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb^-1 recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local(global) significance of 4.3(2.8) and 4.1(2.4) standard deviations at masses of 6571 and 6694 MeV/c², respectively. Upper limits are set on the ■ baryon production cross-section times the branching fraction rela...     

Magnetic moment of the Δ++ baryon in QCD string approach

The magnetic moment of the Δ⁺⁺ baryon is computed within a new approach based on the QCD string Hamiltonian. The string tension σ is the only dimensionful quantity forming the magnetic moment of both the nucleon and the Δ⁺⁺ baryon; however, color Coulomb and spin-spin interactions cancel each other in the nucleon magnetic moment, while, in Δ⁺⁺, they add up coherently. The result π_Δ++ is in good agreement with experimental data.     

Doubly heavy baryon production at γγ collider

The inclusive production of doubly heavy baryons Ξ_cc${\Xi }_{cc}$ and Ξ_bb${\Xi }_{bb}$ at γγ collider is investigated. It is found that the contribution from the heavy quark pair QQ in color triplet and color sextet are important.     

A new search for the doubly charmed baryon ■ at the LHC

The standard quark model is capable of predicting the existence of doubly heavy baryons.Similar to doubly heavy mesons,doubly heavy baryons may allow the QCD-inspired potential model,the nonrelativistic QCD(NRQCD)factorization theory[1],etc.,to work on them well,while serving as a fruitful“laboratory”for testing these theories when a greatly enough collection of relevant data is available.Many attempts have been made to observe doubly heavy baryons,yet none of them succeeded due to the difficulties in producing such baryons either at the e^+e^- colliders or at the hadronic colliders.Noticeably,the running of the large hadronic collider(LHC)with a large centre-of-mass protonproton collision energy and a much higher luminosity provides a good opportunity for experimentalists to realize the aforementioned observation.     

First lattice QCD calculation of semileptonic decays of charmed-strange baryon Ξc

While the standard model is the most successful theory to describe all the interactions and constituents of elementary particle physics,it has been constantly s...     

Can the baryon number density and the cosmological constant be interrelated?

A toy model is proposed in which the cosmological constant and the baryon number density of the Universe are interrelated. The model combines the mechanism of Dimopoulos and Susskind [S. Dimopoulos, L. Susskind, Phys. Rev. D 18 (1978) 4500] in which the baryon number density of the Universe is generated by the time-dependence of the phase of a complex scalar field, i.e. its ‘angular momentum’ in the two-dimensional complex field space, with that of Yoshimura [M. Yoshimura, Phys. Lett. B 608 (2005) 183, hep-ph/0410183] in which the ‘centrifugal force’ due to the ‘angular momentum’ pushes the vacuum expectation value of the scalar field out of a negative potential minimum and provides a small but positive cosmological constant. Unfortunately, our model fails to relate the smallness of the two numbers directly, requiring a fine-tuning of the negative potential minimum.     

Experimental search for radiative decays of the pentaquark baryon Θ+(1540)

The data on the reactions K ⁺Xe → K ⁰ γX and K ⁺Xe → K ⁺ γX, obtained with the bubble chamber DIANA, have been analyzed for possible radiative decays of the Θ⁺(1540) baryon: Θ⁺ → K ⁰ pγ and Θ⁺ → K ⁺ nγ. No signals have been observed, and we derive the upper limits Γ(Θ⁺ → K ⁰ pγ)/Γ(Θ⁺ → K ⁰ p) < 0.032 and Γ(Θ⁺ → K ⁺ nγ)/Γ(Θ⁺ → K ⁺ nγ) < 0.041 which, using our previous measurement of Γ(Θ⁺ → KN) = 0.39 ± 0.10 MeV, translate to Γ(Θ⁺ → K ⁰ pγ) < 8 keV and Γ(Θ⁺ → K ⁺ nγ) < 11 keV at 90% confidence level. We have also measured the cross sections of K ⁺-induced reactions involving emission of a neutral pion: σ(K ⁺ n → K ⁰ pπ ⁰) = 68 ± 18 µb and σ(K ⁺ N → K ⁺ Nπ ⁰) = 30 ± 8 µb for incident K ⁺ momentum of 640 MeV.     

Neutron–antineutron oscillation and baryonic majoron: low scale spontaneous baryon violation

We discuss the possibility that baryon number B is spontaneously broken at low scales, of the order of MeV or even smaller, inducing the neutron–antineutron oscillation at the experimentally accessible level. An associated Goldstone particle–baryonic majoron can have observable effects in neutron to antineutron transitions in nuclei or dense nuclear matter. By extending baryon number to an anomaly-free \(B-L\) symmetry, the baryo-majoron can be identified with the ordinary majoron associated with the spontaneous breaking of lepton number, and it can have interesting implications for neutrinoless \(2\beta \) decay with the majoron emission. We also discuss the hypothesis that baryon number can be spontaneously broken by QCD itself via the six-quark condensates.