Study of theK + K − π+ π− system centrally produced in the reactions π+ p→π+(K + K − π+ π−)p andpp→p(K + K − π+ π−)p at 85 GeV/c

The reactions π⁺ p→π⁺(K ⁺ K ^? π⁺ π^? p andpp→p(K ⁺ K ^? π⁺ π^?)p where the (K ⁺ K ^? π⁺ π^?) system is centrally produced have been studied at 85 GeV/c. 48% of the final state proceeds through single or double vector meson resonant production i.e.,K ^*0(890) (37%), ? (4%),ρ ⁰ (7%). Evidence is found for associatedK ^*0 (890) \(\bar K\) ^*o (890) production (6.4±1.1%) with a cross section ten times higher than that found for associated ? ? production in the same experiment.     

Experimental study of π− π+ system at low invariant-masses

We report on results of an experiment to study the reaction ^– p ^{– +} in the incident pion momentum region between 295 and 450 MeV/c. A departure from phase space was observed in invariant-mass spectra and angular distributions which cannot be explained with and resonance production. It indicates aI=0,J ^P = 0^{+ – +} final-state interaction.Deceased     

Annihilation of + \bar p + p → e + + e ? + π0 and + \bar p + p → γ + π0 through an ω-Meson intermediate state

The s-channel annihilation of a proton and an antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such a mechanism is expected to play a role at moderate values of the total energy $ \sqrt s $ , when the pion is emitted in the angular region around 90° in the center-of-mass system. A fair comparison with the existing data is obtained taking scattering and annihilation channels into account. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.     

Production of Λ hypernuclei in π+ A interactions

The production of Λ hyperons in π⁺ A interactions is studied on the basis of the intranuclear-cascade model, and the excitation-energy, momentum, angular-momentum, charge, and mass distributions of the ensemble of product hypernuclei are determined. The decay of excited hypernuclei via particle emission and fission is considered. It is shown that, for the production of heavy Λ hypernuclei, the optimal momentum of the incident π⁺ meson is about 1 GeV/c. The cross section of the channel in which heavy-nucleus decay induced by a π⁺ meson is accompanied by the emission of a K ⁺ meson is estimated, and it is proposed to use the reaction (π⁺, K ⁺ f) in measurements of the fission barrier in hypernuclei and of their level density.     

The p + p → π+ + d reaction close to threshold at COSY

Differential and total cross sections of the p + p → π⁺ + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π⁰ + d and the π⁺ + d → 2p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.     

The π+-emission puzzle in Λ4He decay

We re-examine the puzzling π⁺ emission from the weak decay of _Λ⁴He and propose an explanation in terms of a three-body decay of the virtual Σ⁺. Such a resolution of the π⁺ decay puzzle is consistent with the calculated Σ⁺ probability in light Λ hypernuclei as well as the experimentally observed π⁺ energy spectrum and s-wave angular distribution.     

Measurements of π+p,K+p and pp elastic scattering)

The paper presents the results on differential cross sections for elastic scattering of 7⁺-, K⁺-mesons and protons on protons in the 4-momentum transfer squared range 0·08 ¦t¦ 1·0 (GeV/c)² and incident particle momentum of 29 and 43 GeV/c for pions and kaons and 29, 43, 50 and 65 GeV/c for protons. The measurements were taken with the spectrometer Sigma, installed in the positive beam of the IHEP accelerator.Presented by F. A. Yotch at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.The authors would like to express their gratitude to A. A.Logunov, Yu. D.Prokoshkin, L. D.Soloviev and V. A.Yarba for their support of this experiment. We are indebted to CERN Administration for giving us a permission to use a part of equipment of the CIBS spectrometer and to W.Kienzle for useful discussions.     

The π+ d → pp reaction at intermediate energies

Conclusion The joint efforts of the laboratories with intermediate energies accelerators at ANL, KEK, LANL, LNPI, Saclay, SIN and TRIUMF produced a rather definite picture of the ⁺pp reaction in the isobar region. However the problem of anomalies for the square-root branch point due to the production of isobar in the intermediate state have not been resolved so far. The poles obtained in different phenomenological analyses could be just the effective parametrization of these cuts (see e.g. [13]). Anyway, some singularities are definitely necessary to describe the data.The experimental data in regions s < 2·05 GeV and s < 2·25 GeV are clearly insufficient. Further accumulation of the data in these regions is necessary. Polarized deuteron data are badly needed in the whole kinematical range [13]. Besides as it was mentioned before it is necessary to measure accurately cross sections of other inelastic reactions which are important for the investigation (observation?) of dibaryonsNN N, NN andd N, NN [21]. It would be of interest also to measure cross sections of non quasi two-particle channels likeNN N, 2N andd N, 2N [22]. (In the case ofNN scattering quasi two-particle channels are known to dominate in a wide energy range.)Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.I am grateful to L. A. Kondratyuk, M. G. Ryskin and M. I. Strikman for valuable discussions of the considered problems.     

Search for lepton number violating decays B+ → π- μ+ μ+ and B+ → K- μ+ μ+

A search is performed for the lepton number violating decay B+ → h- μ+ μ+, where h- represents a K- or a π-, using an integrated luminosity of 36 pb(-1) of data collected with the LHCb detector. The decay is forbidden in the standard model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of B(B+ → K- μ+ μ+) < 5.4×10(-8) and B(B+ → π- μ+ μ+) < 5.8×10(-8) are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.     

Search for the ϕ → π+π−γγ and ϕ → π+π−η decays with the CMD-2 detector

The ? → π⁺π^?γγ and ? → π⁺π^?η decays are sought in the experimental data obtained with the CMD-2 detector in the region of the ?-meson resonance. Upper limits ?(? → ππγγ)< 1.2 × 10^?4 and ?(? → ππη) < 6.1 × 10^?5 (both at a C.L. of 90%) are determined for the branching ratios of these decays.     

P-Odd effects in the γ+He4 → He4 + π0 reaction

P-Odd effects with the elastic photoinformation of neutral pions in He⁴ nuclei are due to the interference of the P-odd amplitude of weak interaction with the P-even amplitude of strong interaction, and originate only for polarized photons. It is shown that close to the reaction threshold P-odd effects should be small. The interference amplitude of the mechanisms corresponding to exchange with a Regge or-pole and a neutral Z-boson at high energies is studied. P-Odd effects in this case increase with increase of energy of the interacting particles and with the square of the imparted momentum. P-Odd effects due to interference of the s ingle-photon and Z-boson mechanisms are also investigated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 71–76, September, 1978.     

Searching for physics beyond the Standard Model in the decay B+ → K+K+ π−

The observation potential of the decay B⁺ K⁺K^+– with the ATLAS detector at LHC is described in this paper. In the Standard Model this decay mode is highly suppressed, while in models beyond the Standard Model it could be significantly enhanced. To improve the selection of the K⁺K^+– final state, a charged hadron identification using Time-over-Threshold measurements in the ATLAS Transition Radiation Tracker was developed and used.     

Numerical analysis of the π+π− atom lifetime in ChPT

We apply Chiral perturbation theory at one loop to analyze the general formula for the π⁺π⁻ atom lifetime derived recently in the framework of QCD [A. Gall et al., Phys. Lett. B 462 (1999) 335]. The corresponding analytic expression is investigated numerically, and compared with recent work in the literature.     

CP-violation in B → π+π- and the unitarity triangle

We analyze the extraction of weak phases from CP-violation in B → π⁺π^- decays. We propose to determine the unitarity triangle by combining the information on mixing-induced CP-violation in B → π⁺π^-, S, with the precision observable sin2β obtained from the CP-asymmetry in B → ψK_S. It is then possible to write down exact analytical expressions for and as simple functions of the observables S and sin2β and of the penguin parameters r and ϕ. As an application clean lower bounds on and can be derived as functions of S and sin2β, essentially without hadronic uncertainty. Computing r and ϕ within QCD factorization yields precise determinations of and since the dependence on r and ϕ is rather weak. It is emphasized that the sensitivity to the phase ϕ enters only at second order and is extremely small for moderate values of this phase, predicted in the heavy-quark limit. Transparent analytical formulas are further given and discussed for the parameter C of direct CP-violation in B → π⁺π^-. Predictions and uncertainties for r and ϕ in QCD factorization are examined in detail. It is pointed out that a simultaneous expansion in 1/m_b and 1/N leads to interesting simplifications. At first order infrared divergences are absent, while the most important effects are retained. Independent experimental tests of the factorization framework are briefly discussed. Received: 16 April 2005, Revised: 6 August 2005, Published online: 21 November 2005 PACS: 11.30.Er, 12.15.Hh, 13.25.Hw     

Θ+-Pentaquark parity from associative baryon production in πd collisions, π ± + d → Θ+ + Σ±

We derive, in model-independent way, the spin structure of the matrix element for the reaction of associative Θ⁺-pentaquark production, π ^± + d → Θ⁺ + Σ^±, in the threshold region and in collinear kinematics. The expressions for the polarization observables in this reaction are found assuming spin 1/2 and different parities for Θ⁺. We have proved that such a reaction can be used for a model-independent determination of the P parity of Θ⁺ only by measuring the Θ⁺ polarization. Other polarization observables, such as the dependence of the Σ^± polarization on the vector and tensor deuteron polarizations, are insensitive to the Θ⁺ parity under the considered kinematical conditions. The linear and quadratic relations between polarization observables in (Θ⁺ is unpolarized) do not depend on the parity of the Θ⁺ pentaquark. The analysis performed for this reaction is also applicable without any modification to the reaction K ⁺ + d → Θ⁺ + p. Using the pole model for the reaction mechanism, we estimated the value of the cross section for the reaction K ⁺ + d → Θ⁺ + p near the threshold. The text was submitted by the authors in English.     

T invariance and polarization effects in the reactions p+3He → π++4He and π++4He → p+3He

On the basis of T invariance, it is established that the dependence of the effective cross section for a binary reaction of the a+b → c+d type on the polarization vectors of primary particles a and b determines completely the polarization vectors and spin correlations for the same particles in the inverse reaction c+d → a+b induced by collisions between unpolarized primary particles c and d. By using the formalism of helicity amplitudes, polarization effects are studied in the process p+³He → π⁺+⁴He and in the inverse process π⁺+⁴He → p+³He. It is shown that, in the reaction π⁺+⁴He → p+³He, the spins of the final-state particles (proton and ³He nucleus) are strongly correlated. An expression for the correlation tensor is obtained for arbitrary values of the (p, ³He) emission angle.     

ηπ+ π- resonant structure around 1.8 GeV/c(2) and η(1405) in J/ψ → ωηπ+ π-

We present results of a study of the decay J/ψ → ωηπ+ π- using a sample of (225.2 ± 2.8) × 10(6) J/ψ events collected by the BESIII detector, and report the observation of a new process J/ψ → ωX(1870) with a statistical significance of 7.2σ, in which X(1870) decays to a(0)(±)(980)π±. Fitting to ηπ+ π- mass spectrum yields a mass M = 1877.3 ± 6.3(stat)(-7.4)(+3.4)(syst) MeV/c(2), a width Γ = 57 ± 12(stat)(-4)(+19)(syst) MeV/c(2), and a product branching fraction B(J/ψ → ωX) × B(X→a(0)(±)(980)π±) × B(a(0) (±)(980) → ηπ±) = [1.50 ± 0.26(stat)(-0.36)(+0.72) (syst)] × 10(-4). Signals for J/ψ → ωf(1)(1285) and J/ψ → ω η(1405) are also clearly observed and measured.