Observation of a narrow feature at 1545 MeV in the system of two K S mesons

Preliminary results of examining the system of two K _S mesons in the region of comparatively high transferred momenta are reported. The events were observed in the π^? p interactions at an energy of 40 GeV on the ITEP 6-m magnetic spectrometer with a neutral trigger. At transferred momenta |t|>0.5 GeV², a maximum with width Γ?10 MeV was observed in the K _S K _S system at a mass of 1545 MeV with statistical significance of no less than 6 standard deviations. This phenomenon can be interpreted as the manifestation of a resonance with the indicated parameters.     

Resonance behavior of a K S K S system near the mass 1775 MeV

The preliminary results of an investigation of a system of two K _S mesons in the mass interval 1600–1950 MeV are reported. The events were obtained on a 6-m magnetic spark spectrometer at ITEP in π ⁻ p interactions at 40 GeV, using a neutral trigger which suppressed both charged particles and γ rays. A peak of width ≃30 MeV with statistical significance not lower than six standard deviations is observed with momentum transfer selection |tu|0.23 GeV² near the mass 1775 MeV of the K _S K _S system. The observed phenomena can be interpreted as the existence of one resonance with the indicated parameters, or two narrower resonances. In the latter case, their masses are 1768±1.5 and 1787±1.5 MeV. The widths of these states are comparable to the mass resolution of the spectrometer (∼5 MeV). Estimates of the product σ ⋅BR(K _S K _S ) give ∼1.5 and 2.5 nb, respectively, for the first and second states. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 10, 727–731 (25 November 1998)     

Discovery of a narrow resonance at 1070 MeV in the system of two K S mesons

Results are presented that were obtained by studying the previously unknown narrow resonance of mass about 1070 MeV. This state was discovered in the system of two K _S mesons. The experimental data subjected to the analysis here come from the 6-m spectrometer created at the Institute of Experimental and Theoretical Physics (ITEP, Moscow) and irradiated with a 40-GeV beam of negatively charged pions from the U-70 accelerator at the Institute for High Energy Physics (IHEP, Protvino) with the aim of studying π ^? p and π ^?C interactions. At the respective maximum, there are 69 events, the statistical significance being not less than six standard deviations. The mass and width of the observed meson are M = 1072.4 ± 0.8 MeV and Γ = 3.5 _+1.5 ^?1.0 MeV, respectively, the product of the cross section for its formation and the relevant branching ratio being not less than 20 nb. The preferable J ^PC assignment for this resonance is 0⁺⁺. Its extraordinary small width has no satisfactory theoretical explanation.     

Discovery of a narrow resonance state of the system K S K S at mass 1520 MeV

Data are presented which indicate the existence of a previously unknown narrow resonance near mass 1520 MeV, discovered while analyzing the system K _S K _S . The data were obtained at ITEP using the 6-m magnetic spectrometer in a beam of 40-GeV negative particles. The resonance is observed in π⁻ p and K ⁻ p interactions with a total statistical confidence of not less than 5 standard deviations. The width of this state is comparable to the mass resolution of the spectrometer (∼5 MeV). The mass is 1521.5±2.5 MeV. Estimates of the product σ·BR (K _S K _S ) give ∼5.0 nb in π⁻ p interactions and ∼250 nb in K ⁻ p interactions. From the fact that the production cross section of this resonance in the K ⁻ beam is approximately 50 times greater than the production cross section in the π⁻ beam, it can be concluded that this new state belongs to a system of mesons with hidden strangeness. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 4, 242–246 (25 August 1999)     

Discovery of a 1731-MeV narrow resonance

Results obtained by studying a previously unknown narrow meson of mass about 1731 MeV are presented. This state was found in a system of two K _S mesons. The experimental-data set subjected to the present analysis was obtained with a 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The statistical sample of event of double K _S -meson production was accumulated in π^? p interactions by using a beam of 40-GeV pions from the U-70 accelerator of the Institute of High Energy Physics (IHEP, Protvino). There are 58 events at the respective maximum, its statistical significance being close to six standard deviations. The parameters of the observed meson are the following; the mass is M = 1731 ± 2.5 MeV, the width is σ = 3.2 ± 2 MeV, and the product of the production cross section and the respective branching ratio is not less than 20 nb. The fact that the observed meson is extremely narrow does not have a satisfactory theoretical explanation.     

Analysis of the3 He(K−,K +)n reaction by the potential quark model

We analyze the production of H dihyperson (J ^π=0⁺,S=?2) via the (K ^?, K⁺) reaction by means of the non-relativistic quark model. First, the H mass and mass spectrum of single baryons are calculated. When the single baryon spectrum is well reproduced, the H dihyperson has the binding energies about 20 MeV or 60 MeV corresponding to the choice of the strength of the confinement potential. Using this model and parameters, cross sections for H production are estimated. A new effect, contributions from color-octetQ ³?Q ³ components of H dihyperson, is taken into account. The cross sections for H production are enhanced about ten times by these contributions. TheK ⁺-neutron coincidence cross section for H production is found to be 99–115 nb/sr² at theK ⁺ forward direction forM _H=2212 MeV and theK ^? beam momentum 1.8 GeV/c.     

The K0 SK0 S final state in two-photon collisions and SU(3) tensor nonets

The K⁰ _SK⁰ _S final state in two-photon collisions is studied with the L3 experiment at LEP, using orbital angular momentum operators. The mass spectrum is dominated by the formation of tensor mesons, their two-photon partial width are determined. A signal at 1700-1800MeV is found to be a new tensor state f ₂(1750) with mass M = (1755±10)MeV and width Γ = (67±12)MeV. All observed tensor resonances obey SU(3) relations. The f ₂(1750) state forms a second tensor nonet together with f ₂(1560) and a ₂(1700). The SU(3) analysis allows us to determine with good accuracy mixing angles between nonstrange and strange components of the isoscalar members of tensor nonets.     

Evidence for formation of a narrow <Emphasis Type="Italic">K</Emphasis><Stack><Subscript>S</Subscript><Superscript>0</Superscript></Stack><Emphasis Type="Italic">p</Emphasis> resonance with mass near 1533 MeV in neutrino interactions

A narrow baryon resonance is observed in the invariant mass of the K _S ⁰ p system formed in neutrino and antineutrino collisions with nuclei. The mass of the resonance is estimated at 1533±5 MeV. The observed width is less than 20 MeV and is compatible with being entirely due to experimental resolution. The statistical significance of the signal is near 6.7 standard deviations. Since the position of the observed resonance does not match the mass of any known Σ*⁺ states, we believe that it arises from the neutrino production of the Θ⁺ pentaquark baryon. The analysis is based on the data obtained in past neutrino experiments with big bubble chambers: WA21, WA25, WA59, E180, and E632.     

Nuclear compression modulus and isotope shifts of Pb nuclei

Isotope shifts of Pb nuclei are studied by taking into account giant monopole and quadrupole resonance by a perturbative method. Giant monopole states are calculated by the HF + RPA response function method using three parameter sets of the Skyrme interactions SGI, SGII and SIII which give the compression moduli K_∞ = 269 MeV, 217 MeV and 356 MeV, respectively. Our calculations reproduce the kink of the observed isotope shifts at ²⁰⁸Pb, while the second-order effect due to the giant quadrupole resonances is not enough to explain the observed odd-even staggering. The Skyrme force SGII having K_∞ = 217 MeV shows the best quantitative agreement among three forces in comparison with the experimental data of the isotope shifts of Pb nuclei. The effect of the effective mass is also discussed.     

K1±(892) Production in π−N interactions at 200 GeV/c

K^1±(892) production is studied in the reaction π^?N → K_S⁰K_S⁰ + X where X includes up to five observed charged particles. An excess of K^1? over K¹⁺ is observed for Feynman-x > 0.1. The ratio of K¹⁺ to K^1? decreases with x as predicted by QCD counting rules. K_S⁰ and K¹ production are compared to recent D and D¹ data from other experiments.     

Study of the reaction KL0p → KS0p in the c.m. energy range 1490–1700 MeV

Experimental results on the K_L⁰p → K_S⁰p reaction at 11 laboratory momenta between 300 and 800 MeV/c are presented. The data are used to discriminate among the various sets of phase shifts for K⁺N scattering in the I = 0 state.     

Two-nucleon production of hyperons and the search for strange dibaryons

The double charge exchange reaction³He(K^?,π ⁺)Xn was studied at 870 MeV/c. In the X missing mass range below the sigma-nucleon production threshold (2130 MeV/c²), events were detected which can be attributed to the two-nucleon process pp(K^?,π ⁺)λn. This reaction and mass range also offers good prospects for finding theI=1/2,l=1 (¹ P₁) spin-singlet dibaryon D_s suggested as the lowest massS=?1 dibaryon in the MIT Bag Model. Although the existence of the D_s is not ruled out by the present data, there is no need to invoke such an object to account for the observed events below σ production threshold. We show that the cross section level for these events is compatible with a dominant two-nucleon mechanism K^?p→π ⁰λ,π ⁰p →π ⁺n. We also offer an interpretation of the recent (K^?,K⁺) data on nuclear targets from Iijimaet al., which display a broad peak centered around a K⁺ momentum of 600 MeV/c. We find that the two-nucleon mechanism K^?N →πY,πN→K⁺Y produces cross sections which are at least an order of magnitude smaller than those observed, and we suggest that the one nucleon process K^?p →Φλ, followed by the decayΦ → K⁺K^?, accounts for the data.     

Energy dependence of the reactions KLop→KSop,π+Λ, π+Σo from 1540 to 1610 MeV

The reactions K_L^op→K_S^op, π⁺Λ, π⁺Σ^o have been measured for center-of-mass energies from 1540 to 1610 MeV. Channel cross sections and coefficients of the Legendre polynomial expansion of the differential cross sections and hyperon polarizations are presented. We see no evidence in the πΛ channel for the suggested $\text{3}\text{2}{}^{\mathrm{?}}$ resonance at 1580 MeV. The cross section for the K_S^op channel shows an energy dependence which is not predicted by the existing phase shift solutions based on charged kaon data.     

Analysis of the K S K S system from the reaction π − p → K S K S n at 40 GeV

On the basis of experimental data from the 6-m spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow), an amplitude analysis of 40 553 events of the reaction π ^? p → K _S K _S n induced by a negatively charged pion of energy 40 GeV is performed over a broad momentumtransfer range by using a new procedure. The results for |t| > 0.1 GeV² are obtained for the first time. In particular, resonances of mass 1700 and 1900 MeV and width 120 MeV are discovered in the D ₊ wave (there were no such resonances for |t| < 0.1 GeV²). In the region of low momentum transfers, the S wave exhibits a structure that lies in the mass region around 1370 MeV and which requires three resonances for its explanation. Two of these (that of mass 1234 ± 6 MeV and width 47 ± 33 MeV and that of mass 1478 ± 6 MeV and width 119 ± 10 MeV) were found in the studies of A. Etkin et al. [Phys. Rev. D 25, 2446 (1982)] and O.N. Baloshin et al. {Yad. Fiz. 43, 1487 (1986) [Phys. At. Nucl. 43, 959 (1986)]}. The third has a mass of 1389 ± 9 MeV and a width of 30 ± 24 MeV. At high momentum transfers, the S wave is found to feature resonances that have the following parameters: M = 1328 ± 8 MeV and Γ = 237 ± 20 MeV, M = 1440 ± 6 MeV and Γ = 121 ± 15 MeV, and M = 1776 ± 15 MeV and Γ = 250 ± 30 MeV. For the D ₀ wave, it is found that, in addition to the well-known resonances f ₂, a ₂, and f′ ₂, there appear the following resonances in this wave: a resonance of mass 2005 ± 12 MeV and width 209 ± 32 MeV and a resonance of mass 2270 ± 12 MeV and width 90 ± 29 MeV at low |t| and a resonance of mass 1659 ± 6 and width 152 ± 18 and a resonance of mass 2200 ± 13 MeV and width 91 ± 62 MeV at high |t|.     

Search for the P11Σ(1660) resonance in the reactions K− + p → Σ± + π∓ in the momentum range 597 to 888 MeVc

The reaction cross sections, differential cross sections and Σ ⁺ polarization for the reactions K^? + p → Σ^± + π^? at 8 momenta in the range 688 to 833 MeV/c were obtained. A partial-wave analysis was performed over the momentum range 597 to 888 MeV/c using the present data together with data in the neighboring momentum regions. A satisfactory solution was obtained with the well-established S₀₁ Λ(1670), D₀₃ Λ(1690) and D₁₃ Σ(1670) resonances. The addition of a P₁₁ resonance with a mass, width, and branching ratio of 1665 MeV/c², 82 MeV/c² and ?0.13 improved the χ² per degree of freedom by an insignificant amount, indicating that the coupling of the p¹¹Σ(1660) to the Σ^±ν^? channels is at best marginal.     

Measurement of K production in the reaction Kp → Kp

The K^∗− spectrum in the reaction K⁻+p → K^∗−+p has been measured at beam momenta 10.9, 13.4 and 15.9 GeV/c using the missing mass technique. Production of the L(1770), and a Q-K^∗(1420) enhancement are observed. Differential cross sections in the range of momentum transfer 0.12 < | t_pp | < 0.40 (GeV/c)² are given. The L meson is observed with a width Γ = 100 ± 26 MeV. The mass spectrum between the L and 2.5 GeV does not show significant structure.     

Resonance production in the reaction π±p→Ks0K±p at 30 and 50 GeV/c

The mass and momentum transfer spectra of the charged $\text{K}\text{K}$ system produced in the reaction π^±p→K_s⁰K^±p are analyzed. The data have been collected at the CERN SPS with the Geneva-Lausanne two-arm, non-magnetic spectrometer at 30 and 50 GeV/c incident momenta. The general features of the reactions at these energies and the results of partial-wave analyses of the two kaon system are presented.The channel is dominated by the diffractive production of even spin resonances. The spin 4 recurrence of the A₂(1320) is clearly observed at 2040 MeV (Γ=380 MeV. A new resonance is observed with a mass M=2450MeV and a width Γ=400 MeV; the quantum numbers of this state are found to be I^G(J^PC)=1^?(6++). The analysis also shows the decay of the decay of the meson ?′(1600) through the $\text{K}\text{K}$ channel at both energies.The production amplitudes are determined both as a function of the $\text{K}\text{K}$ effective mass and of the momentum transfer. Isoscalar natural parity exchange is dominant. The energy dependence between 10 and 50 GeV/c is shown to be well described by a Regge pole model based on the f-dominated pomeron hypothesis. We compare the production mechanisms of the 2⁺ resonances A₂(1320) and K¹(1430). Finally, we estimate the $\text{K}\text{K}$ branching ratios of the spin 4 A₂(2040) and spin 6 A₂(2450) resonances.     

Features of carbon-carbon interactions at a momentum of 4.2 GeV/c per nucleon that are accompanied by the production of Λ hyperons and K S 0 mesons versus the degree of nuclei collision centrality

Experiemntal data obtained by using the 2-m propane bubble chamber of the Joint Institute for Nuclear Research (JINR, Dubna) are used to study the effect collision centrality on the spectra of Λ hyperons and K _S ⁰ mesons produced in carbon-carbon interactions at 4.2 A GeV/c. The multiplicity of participant protons having momenta in excess of 300 MeV/c is taken to be a measure of collision centrality. The features of pions and protons accompanying strange-particle production are also presented. The experimental data in question are compared with the prediction of a modified version of the FRITIOF model. It is shown that strange particles are predominantly produced in central and semicentral collisions. The average kinematical features of K _S ⁰ mesons are found to be indepedent of collision centrality. At the same time, the average transverse momentum of Λ hyperons and the average value of their emission angle increase slowly with increasing degree of collision centrality. The anisotropy of the angular distributions of both Λ hypersons and K _S/0 mesons in the c.m. frame of nucleon-nucleon collisions decreases with increasing collision centrality. The average transverse momentum of K _S ⁰ mesons is approximately 1.6 times higher than the average transverse momentum of π ^? mesons.     

Comparing the p̅p → K − K + and p̅p → π−π+ reactions

A partial wave amplitude analysis of LEAR data on differential cross sections and analyzing powers of p?p → K ^? K ⁺ has been performed in the range p _lab = 360 ? 1000 MeV/c, and compared to the results from the same observables for p?p → π^?π⁺. Contrary to other analyses we see no compelling evidence of resonance behavior in our amplitudes. However, as we discuss, the resulting amplitudes are not unique since a third observable remains to be measured for both reactions. Another remarkable result is that for p?p → K ^? K ⁺ all our solutions in the momentum interval below 900 MeV/c, only partial wave amplitudes including J _max = 2 are necessary. This upper limit on the angular momentum is smaller than J _max = 3 which is required for the data of the reaction p?p → π^?π⁺ in the same momentum interval. This finding is consistent with a model analysis for data above 1 GeV/c. Annihilation models with short range baryon exchange give too small J ≥ 2 amplitudes and final state ππ and K?K interactions are presumably very important.     

Measurements of the reaction K−n → π−Λ in the C.M.S. energy range 2050 MeV to 2175 MeV and partial-wave analysis of this reaction between 1875 MeV and 2175 MeV

New bubble chamber data on the reaction K^?n → π^?Λ in the c.m.s. energy range 2050 MeV to 2175 MeV are presented. These new data have been combined with published data on this reaction and on the reaction K^?p → π⁰Λ and a partial-wave analysis has been carried out between 1875 MeV and 2175 MeV. Parameters of the established resonances in this c.m.s. energy region have been determined and further evidence is presented for the existence of a Σ resonance with mass around 2100 MeV/c² in the P₃ partial wave.