Multiplicity structure of proton and kaon diffractive dissociation in 10 and 16 GeV/c K-p interactions

A new method to calculate diffractive mass spectra has been developed. It is applied to K^-p interactions at 10 and 16 GeV/c. Cross sections and mass spectra are given for the difractive dissociation processes p→(N+iπ) and K^-p→(K+iπ) for i = 1 to 5 and also summed over all multiplicities. In addition to the diffractive peak at low mass coming from low multiplicities, a long tail extending to high masses and high multiplicities has been found. The multiplicity structure of diffraction dissociation can be understood in the context of the two-step dynamical picture of Pokorsky and Van Hove.     

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)     

Some consequences of exchange degeneracy and the triple-Regge-hypothesis

We extract the proton-Reggeised rho total cross-section from inclusive data for K⁺ + p → K⁰ + (anything) in the triple-Regge domain and find that it is of the same order as physical meson-proton cross-sections for a range of Reggeon mass. We also relate other processes such as pp→pX and K⁺p→K⁺X to K⁺p→K⁰X, and get good agreement with data. We suggest methods for calculating baryon exchange processes as well.     

Investigation of the diffractive reaction p + N → [∑+ K 0] + N at the proton energy of E p =70 GeV and observation of the decay process X(2000) → ∑+ K 0

The diffractive reaction p + N → [∑⁺ K ⁰] + N induced by 70-GeV protons is investigated at the SPHINX facility. The measured mass spectrum of the ∑⁺ K ⁰ system originating from this reaction shows a resonance structure with a mass of M=1995±18 MeV and a width of Γ=90±32 MeV. The cross section for the formation of this structure is found to be σ=182±38 nb per target nucleon. These data comply well with the results that we obtained previously in studying the reaction p + N → [∑⁰ K ⁺] + N, where we observed the formation of the X(2000) → ∑⁰ K ⁺ state, a candidate for an exotic baryon with hidden strangeness. The measured ratio R of the two branching fractions, R = Br[X(2000) → ∑⁺ K ⁰]/Br[X(2000) → ∑⁰ K ⁺] = 1.91 ± 0.38, is consistent with the value of R=2 expected for an isospin-1/2 baryon.     

Strangeness enhancement in sulphur—Nucleus collisions at 200 A GeV/c

The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35K _S ⁰ in S+S and S+Ag are consistent with the NA44 results forK ⁺ andK ^?. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of Λ to $\bar \Lambda $ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to σ^? is observed in S+Ag collisions compared to p+S reactions at the same energy. TheK _S ⁰ multiplicity in full phase space per negative hadron (h ^?) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for theK _S ⁰ multiplicity perh ^? in S+Pb is below the N+N value.     

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.     

Partial-wave analysis of backwardly produced three-pion systems in K−p interactions at 4.2 GeV/c

We report on the results of a partial-wave analysis of the 3π system produced by baryon exchange in the reaction K^?p→Σ^?π⁺π⁺π^? at 4.2 GeV/c. We confirm the existence of an enhancement in the 1⁺S(?π) wave as previously established from a Dalitz plot analysis of the same data. The phase variation of this wave is found to be consistent with that expected for a resonance and thus the enhancement is identified with A₁ production. No clear signal for this state is found in either the reaction K^?p→Σ⁺π⁺π⁺π^?π^? or K^?p→Λπ⁺π^?π⁰. We also find production via baryon exchange of the A₂ in all three reactions and the ω and $\text{ω}{}^1$ (1975) in the third reaction.     

Inclusive production cross sections of resonances in 32 GeV/c K+p interactions

The inclusive production of resonances is systematically studied in K⁺p interactions at 32 GeV/c. Total production cross sections are given for three baryon resonances, five vector and three 2⁺ tensor mesons. We also compare the central and fragmentation components of the total production cross sections with quark model predictions.     

Search for Θ+(1540) in exclusive proton-induced reaction p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N) at the energy of 70 GeV

A search for narrow Θ⁺(1540), a candidate for a pentaquark baryon with positive strangeness, has been performed in an exclusive proton-induced reaction $p + C(N) \to \Theta ^ + \bar \kappa ^0 + C(N)$ on carbon nuclei or quasifree nucleons at $E_{beam} = 70GeV(\sqrt s = 11.5GeV)$ studying nK ⁺, pK _S ⁰ , and pK _L ⁰ decay channels of Θ⁺(1540) in four different final states of the $\Theta ^ + \bar K^0 $ system. In order to assess the quality of the identification of the final states with neutron or K _L ⁰ , we reconstructed Λ(1520) → nK _S ⁰ and ? → K _L ⁰ K _S ⁰ decays in the calibration reactions p + C(N) → Λ (1520)K ⁺+C(N) and p+C(N) → p?+C(N). We found no evidence for a narrow pentaquark peak in any of the studied final states and decay channels. Assuming that the production characteristics of the $\Theta ^ + \bar K^0 $ system are not drastically different from those of the Λ(1520)K ⁺ and p? systems, we established upper limits on the cross-section ratios $\sigma (\Theta ^ + \bar K^0 )/\sigma (\Lambda (1520)K^ + ) < 0.02$ and $\sigma (\Theta ^ + \bar K^0 )/\sigma (p\phi ) < 0.15$ at 90% C.L. and a preliminary upper limit for the forward-hemisphere cross section $\sigma (\Theta ^ + \bar K^0 )$ nb/nucleon.     

Resonances of any spin in pion photoproduction and nucleon Compton scattering

Describing the vertices by form factors and the propagators by their spectral representations, we calculate the contribution of the exchange diagramsγπ→M ^j→ ¯N N andγN→N ^j+1/2→γN to the invariant and helicity amplitudes, for meson (M _j) and baryon (N ^j+1/2) resonances of any spin (j integer ≧ 1) and both parities ((?)^j and (?)^j+1).     

Study of strange bosons decaying into baryon-antibaryon pairs

We have collected 6100 events in the reactions $\text{K}\text{>}{}^{\mathrm{+}}\text{p→(}\text{Λ}\text{p}\text{)}\text{p}$ and K^?p→(Λ$\text{p}$)p at an incident energy of 50 GeV, with the Geneva-Lausanne spectrometer at the SPS. We have investigated the productioon of strangeness S = ± 1 baryon-antibaryon pairs with mass up to 3 GeV, by performing a moment analysis of the decay angular distribution. An amplitude analysis of the moments shows evidence for two broad states with spin-parity 2^? and 4^?, at 2.3 GeV and 2.5 GeV, respectively, coupling to $\text{Λ}$p and Λ$\text{p}$.     

SuperB production,matter stability and gauge hierarchy in SUSY GUTs

We analyze the connections between the problems of the cosmological baryon asymmetry (CBA), matter stability and mass hierarchy in supersymmetric Grand Unified models. We show that the typical delay of the phase transition in supersymmetric theories as well as a natural solution to the triplet-doublet Higgs hierarchy problem imply baryon production after the Grand Unification phase transition which in a wide class of SUSY GUTs takes place atT～10⁹–10¹⁰ GeV. Light Higgs colour triplets as a means of producing the CBA are discussed in detail. An alternative mechanism involving a singlet superfield is proposed leading to striking consequences in proton decay with the appearance of (B+L) conserving modes with a muon and a kaon in the final state:n→μ^? K ⁺,p μ ^2212;π⁺ K ⁺ and a lifetime of 10³¹ years.     

Hypercharge annihilation

Aspects of the process K^?p → Λ + pions for K^? mesons of momentum 8.25 GeV/c are examined. It is shown that the hypercharge annihilation process can be effectively separated into off-shell baryon (B?B) and strangeness (K?K) annihilation. Both annihilation regions have many features in common and show strong similarities to on-shell annihilation processes; some differences are also noted.     

Diffractive production of the charmed baryon Λ+c at the CERN ISR

In a sample of diffractive events of high multiplicity a sharp five standard deviation signal is observed at M = 2255 MeV/c² in the K^?pπ⁺ mass distribution and, although with less statistical strength, at the same mass in the Λ⁰π⁺π⁺π^? channel. These signals are identified as being due to the decay of the charmed baryon Λ⁺_c which is produced with a cross section times branching ratio σ_cB in the range 0.7?1.8 μb for the K^?π⁺p decay and 0.3?0.7 μb for the Λ^-π⁺π⁺ π^? system.     

A study ofK + p elastic scattering and reactionK + p→K + pπ+π− at 70 GeV/c

Results are presented onK ⁺ p elastic scattering and on the reactionK ⁺ p→K ⁺ pπ⁺π^? at 70 GeV/c. For the elastic channel, we measured the total ((2.29±0.04)mb) and differentialdσ/dt cross sections. The reactionK ⁺ p→K ⁺ pπ⁺π^? has a total cross section of (470±23) μb and is shown to be dominated by diffractive dissociation processes. The contributions of the quasi-two-body channels $$K^ + p \to K*^0 (890)\Delta ^{ + + } (1,236)$$ and $$K^ + p \to K*^0 (1,430)\Delta ^{ + + } (1,236)$$ and of the Double-Pomeron Exchange (DPE) processes are estimated.     

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.     

Applications of Mueller theory of two-particle inclusive processes

Assuming factorization, and extracting inclusive Reggeon vertices from one-particle inclusive data, we predict Regge corrections to scaling for several two-particle inclusive processes. The data on p + P → π^? + π^? + X, K⁺ + p → π^? + π^? + X, K^? + p → π⁺ + π^? + X, and π⁺ + p → π^? + π^? + X agree with our predictions.     

The behaviour in terms of angular variables of the inclusive reactions Kp → KX and Kp → KπX at 5.0 and 8.2 GeV/c

The inclusive reactions K⁺p → K⁰ + X⁺⁺ at 5.0 and 8.2 GeV/c and K⁺p → K⁰ + π⁺ + X⁺ at 8.2 GeV/c are analysed in terms of angular variables θ and ø. The data are compared and found consistent with various theoretical bounds on the s-dependence of the inclusive reaction cross sections. Experimental evidence is presented that dσ/dcos θ = a exp (−b sinθ) with b ∼ √s and a increasing with energy. Correlations between the angular variables and between the variable ø and the K⁰ and π⁺ momenta in the c.m.s. are observed and discussed.     

Experimental tests of the factorisation of Regge trajectories in the proton fragmentation region

We present double differential cross sections for the reactions K^? + p → π^± + anything at 8.25 GeV/c. Using published data for reactions K⁺ + p→ π^? + anything and p + p → π⁺ anything we predict the differential cross sections for γ + p → π^? + anything, π^? + p → π^? + anything and π^? + p → π⁺ + anything in the target fragmentation region based on factorisation of the pomeron and Regge trajectories. Our predictions agree with the experimental data and support the hypothesis of factorisation of the Regge trajectories in the target fragmentation region.     

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.