Observation of an exotic baryon with S=+1 in photoproduction from the proton

The reaction gamma p-->pi(+)K(-)K(+)n was studied at Jefferson Laboratory using a tagged photon beam with an energy range of 3-5.47 GeV. A narrow baryon state with strangeness S=+1 and mass M=1555+/-10 MeV/c(2) was observed in the nK(+) invariant mass spectrum. The peak's width is consistent with the CLAS resolution (FWHM=26 MeV/c(2)), and its statistical significance is (7.8+/-1.0)sigma. A baryon with positive strangeness has exotic structure and cannot be described in the framework of the naive constituent quark model. The mass of the observed state is consistent with the mass predicted by the chiral soliton model for the Theta(+) baryon. In addition, the pK(+) invariant mass distribution was analyzed in the reaction gamma p-->K(-)K(+)p with high statistics in search of doubly charged exotic baryon states. No resonance structures were found in this spectrum.     

Evidence for a narrow S = +1 baryon resonance in photoproduction from the neutron

The gamman-->K(+)K(-)n reaction on 12C has been studied by measuring both K+ and K- at forward angles. A sharp baryon resonance peak was observed at 1.54+/-0.01 GeV/c(2) with a width smaller than 25 MeV/c(2) and a Gaussian significance of 4.6sigma. The strangeness quantum number (S) of the baryon resonance is +1. It can be interpreted as a molecular meson-baryon resonance or alternatively as an exotic five-quark state (uuddsmacr;) that decays into a K+ and a neutron. The resonance is consistent with the lowest member of an antidecuplet of baryons predicted by the chiral soliton model.     

Evidence for an exotic S= -2, Q= -2 baryon resonance in proton-proton collisions at the CERN SPS

Results of resonance searches in the Xi(-)pi(-), Xi(-)pi(+), Xi;(+)pi(-), and Xi;(+)pi(+) invariant mass spectra in proton-proton collisions at sqrt[s]=17.2 GeV are presented. Evidence is shown for the existence of a narrow Xi(-)pi(-) baryon resonance with mass of 1.862+/-0.002 GeV/c(2) and width below the detector resolution of about 0.018 GeV/c(2). The significance is estimated to be above 4.2sigma. This state is a candidate for the hypothetical exotic Xi(--)(3/2) baryon with S=-2, I=3 / 2, and a quark content of (dsdsū). At the same mass, a peak is observed in the Xi(-)pi(+) spectrum which is a candidate for the Xi(0)(3/2) member of this isospin quartet with a quark content of (dsus[-]d). The corresponding antibaryon spectra also show enhancements at the same invariant mass.     

Observation of a baryon exchange dip and parton effects in backward photoproduction of ω

A measurement of backward photoproduction of omega mesons on protons is reported. Data are presented which show a dip in the differential cross section at u = ?0.15 (GeV/c)² and an s dependence which varies strongly with u. The s dependence suggests an incoherent sum of a Regge and a parton term and differential cross sections for the two components are presented.     

Search for narrow dibaryon resonances in neutral pion photoproduction from the deuteron

The reaction γd↦π⁰ X has been measured with TAPS at MAMI in the energy range E _γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c² were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution. Received: 25 October 2000 / Accepted: 24 November 2000     

Mass differences in baryon isomultiplets with Jp=1+ /2

The mass differences in baryon isomultiplets with J^p=1⁺ /2 were calculated with allowance for the contribution of weak interactions to the Okubo Reggeized tadpole models and violated isotopic Lipmanov symmetry.Translated from Izvestiya VUZ. Fizika, Vol. 11, No. 8, pp. 100–105, August, 1968.In conclusion the author expresses his deep appreciation to A. S. Shekhter and his colleagues at the Department of Theoretical Physics at Saratov State University for their discussion and to N. G. Fadeev (Joint Institute for Nuclear Research, Dubna) for his help in performing the numerical calculations.     

Final-state hyperon-nucleon interaction in the inclusive K photoproduction from the deuteron

We calculate d(γ, K⁺) inclusive cross sections with the full inclusion of the final ΛN - ΣN interaction. Modern hyperon-nucleon forces and a recently updated production operator for the γ + N → K⁺ + Y process are used. Significant effects of the hyperon-nucleon final-state interaction have been found especially around the K⁺ΣN threshold.     

Quasifree pion photoproduction on the deuteron in the Δ region

Photo production of pions on the deuteron is studied in the spectator nucleon model. The Born terms of the elementary production amplitude are determined in pseudovectorπN coupling and supplied with a form factor. TheΔ resonance is considered both in thes and theu channel. The parameters of theΔ resonance and the cutoff of the form factors are fixed on the leading photoproduction multipoles. Results for total and differential cross sections are compared with experimental data. Particular attention is paid to the role of Pauli correlations of the final state nucleons in the quasifree case. The results are compared with those for pion photoproduction on the nucleon.     

Quasifree pion photoproduction on the deuteron in the Δ region

Photo production of pions on the deuteron is studied in the spectator nucleon model. The Born terms of the elementary production amplitude are determined in pseu-dovector πN coupling and supplied with a form factor. The Δ resonance is considered both in the s and the u channel. The parameters of the Δ resonance and the cutoff of the form factors are fixed on the leading photoproduction multipoles. Results for total and differential cross sections are compared with experimental data. Particular attention is paid to the role of Pauli correlations of the final state nucleons in the quasifree case. The results are compared with those for pion photoproduction on the nucleon.     

双π系统与JPC=1-+的奇特混杂态

基本的守恒定律要求IG(JPC)=1-(1-+)的态和IG(JPC)=0+(1-+)的态都不能衰变到双π系统.文献[17,18]提出的关于可以在双π系统中寻找1-+混杂态的论点是不正确的.     

Zeeman levels with exotic field dependence in the high field phase of an S=1 Heisenberg antiferromagnetic chain

We have performed electron spin resonance measurements over a wide frequency and magnetic field range on a single crystal of the S=1 quasi-one-dimensional Heisenberg antiferromagnet Ni(C5H14N2)2N3(PF6). We observed gapped excitation branches above the critical field H(c) where the Haldane gap closes. These branches are analyzed by a phenomenological field theory using the complex-field phi(4) model. A satisfactory agreement between experiment and theory is obtained.     

The width of the $\Theta^{ + }$ exotic baryon in the chiral soliton model

In 1997 Diakonov, Petrov, and Polyakov, calculated the width of the exotic baryon that they called . The prediction, MeV, has received considerable attention, especially in light of the narrowness of the experimentally reported resonance. However, there is an arithmetic error in their work: when corrected, the width estimate quoted in that paper should have been MeV.Received: 29 January 2004, Published online: 5 May 2004