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Study of resonant processes for multi-pion production in $\bar p +p\to\ell ^++\ell^- +n_\pi \pi$ annihilation
Kuraev, E. A.;Adamuscin, C.;Tomasi-Gustafsson, E.;Maas, F.
High Energy Physics - Phenomenology , 2007, DOI: 10.1016/j.physletb.2007.04.042
Abstract: In frame of a phenomenological approach based on Compton-like Feynman amplitudes, we study multi-pion production in antiproton nucleon collisions. The main interest of this reaction is related to the possibility to study the properties of the presumable $\bar N N$ atom and of its resonances. For the case of formation of a scalar or pseudoscalar resonant state, with $I^G(J^{P})=1^-(0^{\pm}),~0^+(0^-)$ numerical results are obtained. The differential cross section in an experimental set-up where the pions invariant mass is measured, is given with explicit dependence on the lepton pair and pions invariant mass.
A relativistic treatment of pion wave functions in the annihilation antiproton-proton -> pi^-pi^+  [PDF]
B. El-Bennich,W. M. Kloet
Physics , 2004, DOI: 10.1103/PhysRevC.70.034001
Abstract: Quark model intrinsic wave functions of highly energetic pions in the reaction \bar pp->\pi^-\pi^+ are subjected to a relativistic treatment. The annihilation is described in a constituent quark model with A2 and R2 flavor-flux topology and the annihilated quark-antiquark pairs are in 3P_0 and 3S_1 states. We study the effects of pure Lorentz transformations on the antiquark and quark spatial wave functions and their respective spinors in the pion. The modified quark geometry of the pion has considerable impact on the angular dependence of the annihilation mechanisms.
OZI Rule Violation in p pbar Annihilation into phi pi pi by Two Step Processes  [PDF]
V. E. Markushin,M. P. Locher
Physics , 1997, DOI: 10.1007/s100500050036
Abstract: The phi pi+ pi- production in p pbar annihilation at rest is strongly enhanced by a two step mechanism with intermediate K Kbar pi pi states. The relative yield of the phi production due to the resonant final state interaction decreases with increasing total energy of the p pbar system.
The pi- p --> gamma gamma n Reaction and Pion Compton Scattering  [PDF]
Piotr A. Zolnierczuk
Physics , 1998,
Abstract: We propose to measure the two--photon capture mode of pionic hydrogen using the RMC pair spectrometer at the TRIUMF cyclotron. Currently, only an experimental upper limit of B.R.<= 5.5E-4 is available for the two-gamma capture mode. Our new data will critically test the theoretical calculations and the intriguing predicted dominance of the pi pi --> gamma gamma annihilation graph. More speculatively, since crossing symmetry relates pi pi --> gamma gamma to gamma pi --> gamma pi, this threshold reaction may be a novel probe of the pion's electric polarizability. We show results of our 1997 engineering run and Monte Carlo studies for the two photon capture mode of pionic hydrogen and carbon. We also present our preliminary upper limit for the pi- p --> gamma gamma n B.R. <= 2.8E-4.
Pion Correlations and Resonance Effects in ppbar Annihilation to 4pi0 at Rest  [PDF]
O. Kortner,M. P. Locher,V. E. Markushin,P. Weber,O. Wigger
Physics , 2002, DOI: 10.1007/s10052-002-1033-8
Abstract: We study pi0pi0 correlations in the exclusive reaction ppbar -> 4pi0 at rest with complete reconstruction of the kinematics for each event. The inclusive distribution shows a dip at small invariant mass of the pion pair while a small enhancement in the double differential distribution is observed for small invariant masses of both pion pairs. Dynamical models with resonances in the final state are shown to be consistent with the data while the stochastic HBT mechanism is not supported by the present findings.
Heavy Isovector Resonances in e^+e^- annihilation, in the decay J/psi-->pi^+pi^-pi^0 and in the reaction K^-p-->pi^+pi^-Lambda  [PDF]
N. N. Achasov,A. A. Kozhevnikov
Physics , 1996,
Abstract: The results of an analysis are presented of some recent data on the reactions $e^+e^-\to\pi^+\pi^-\pi^+\pi^-$, $e^+e^-\to\pi^+\pi^-\pi^0\pi^0$ with the subtracted $\omega\pi^0$ events, $e^+e^-\to\omega\pi^0$, $e^+e^-\to\eta \pi^+\pi^-$, $e^+e^-\to\pi^+\pi^-$, $J/\psi\to\pi^+\pi^-\pi^0$ and $K^-p\to\pi^+\pi^-\Lambda$, upon taking into account both the strong energy dependence of the partial widths on energy and the previously neglected mixing of the $\rho$ type resonances. The above effects are shown to exert an essential influence on the specific values of masses and coupling constants of heavy resonances and hence are necessary to be accounted for in establishing their true nature.
rho0(770)-f0(980) mixing and CPT violation in a non-unitary evolution of pion creation process pi(-)p->pi(-)pi(+)n on polarized target
Svec, Miloslav
High Energy Physics - Phenomenology , 2007,
Abstract: Unitary evolution from pure initial states to pure final states in pi(-)p-> pi(-)pi(+)n imposes constraints on pion production amplitudes that are violated by CERN data on polarized target at 17.2 GeV/c. The pion creation is a non-unitary process arising from a unitary co-evolution of the pion creation process with a quantum environment. The purpose of this work is to identify the interacting degrees of freedom of the environment in a high resolution amplitude analysis of CERN data on polarized target for dipion masses 580-1080 MeV. The S-wave spectra |S|^2 show presence of rho0(770) while P-wave spectra |L|^2 show a dip at f0(980) mass. The observed rho0(770)-f0(980) mixing is encoded in all measured density matrix elements which also encode a level splitting of the spectra arising from the interaction of the pion creation process with the environment. The analytical form of the level splitting reveals the existence of a new quantum number characterizing the environment. We propose a model for the CPT violating interaction of the pion creation process with the environment in which non-diagonal transitions between resonant qqbar modes and pi(-)pi(+) states lead to vector-scalar mixing and a dynamic entanglement of the pi(-)pi(+) isospin states. The final states pi(-)p(+)n do not posses CPT cojugate states and the concept of CPT symmetry looses its meanining.
Study of a narrow pi+ pi- peak at about 755 MeV/c^2 in bar-p n --> 2 pi+ 3 pi- annihilation at rest  [PDF]
Mario Gaspero
Physics , 2009,
Abstract: A narrow peak in the pi+ pi- mass distribution was seen by the Rome-Syracuse Collaboration in bar-p n --> 2 pi+ 3 pi- annihilation at rest 39 years ago. The reanalysis of this peak finds a mass of 757.4 +- 2.6 MeV/c^2 and a width slightly narrower than the experimental resolution. The evidence of the peak is 5.2 standard deviations. This state is generated in (12.4 +- 2.4)% of the bar-p n --> 2 pi+ 3 pi- annihilations at rest. No spin analysis is possible with the statistics of the experiment.
Evidence for evolution from pure states to mixed states in pion creation process pi(-) p -> pi(-)pi(+) n on polarized target and its physical interpretation  [PDF]
Miloslav Svec
Physics , 2007,
Abstract: In 1982 Hawking suggested that quantum fluctuations of space-time metric will induce a non-unitary evolution from pure initial states to mixed final states in particle interactions at any energy. This hypothesis can be tested using existing CERN data on pi(-) p -> pi(-)pi(+) n on polarized target at 17.2 GeV/c. The purity of the final state is controlled by the purity of recoil nucleon polarization. We develop a spin formalism to calculate expressions for recoil nucleon polarization for two specific pure initial states. Imposing conditions of purity on the recoil nuclon polarization we obtain conditions on the amplitudes which are violated by model independent amplitude analysis of CERN data at large t. We conclude that pure states can evolve into mixed states in pi(-) p -> pi(-)pi(+) n. In quantum theory such non-unitary evolution occurs in open quantum systems interacting with an environment. We present evidence to validate the view of the pion creation process as an open quantum system interacting with a quantum environment. The observed process is time-irreversible and violates CPT symmetry.
Two-pion decay modes of the N*(1440) in n p -> d pi pi  [PDF]
L. Alvarez-Ruso
Physics , 2000, DOI: 10.1016/S0375-9474(01)00500-0
Abstract: A simple model for the n p -> d pi pi reaction has been developed. It is shown that the deuteron momentum spectra measured at T_n = 795 MeV can be understood in terms of the Roper excitation and its N pi pi decay modes. A similar pattern, recently observed in p p -> p p pi+ pi-, can be explained in the same way.
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