Isospin symmetry violating effects and scattering length extraction from kaon decays

The isospin symmetry breaking effects in the charged kaons decays to two or three pions are considered. In semileptonic decay K ^± → π ⁺ π ^?e^± ν (called K _e4) these effects turn out to be crucial for correct extraction of ππ scattering lengths. Taking in account electromagnetic interaction between the pions in the final state and isospin symmetry breaking due to different masses of charged and neutral pions allows to adjust the values of scattering lengths obtained from experimental data on K _e4 decay and predictions of Chiral Perturbation Theory (ChPT). Final state interactions of pions in the decay K ^± → π ^± π ⁰ π ⁰ leading to the anomaly (cusp) in the π ⁰ π ⁰ invariant mass distribution in the vicinity of charged pions’ threshold are discussed and recent results of accounting of the electromagnetic interaction among charged pions leading to π ⁺ π ^? bound states (pioniumatom) just under the charged pions’ threshold are presented.     

Inclusive yields and transverse spectra of non-strange mesons: Comparisons with the quark model,and an estimate of the fraction of “direct” pion production

Recent data on the production ofη, ?⁰, ω and other mesons in hadron-hadron collisions at intermediate energies are studied. Their transverse spectra dσ/dp_T² are all found to be approximately exponential, with similar slopes, ～3.4 (GeV/c)^?2, up to about p_T² = 2(GeV/c)². The inclusive yields of the mesons are broadly in agreement with quark model predictions. In the case of pions, a distimction is made between those directly produced and those produced indirectly via resonance decay. It is estimated that between 10% and 30% of pions are directly produced.     

Quasi-free scattering of pions on 3, 4He

Differential cross sections for ^{3, 4}He(π, π') are presented for angles of 60° and 120° at 200 MeV and 120° at 295 MeV. The momentum spectra for the scattered pions are dominated by a peak attributed to quasi-free scattering from individual nucleons. There are significant differences between the scattering on ³He and ⁴He as well as between the scattering of π⁺ and π^? on ³He. The data are compared to a simple model incorporating the free π+N scattering amplitudes. Modifications for the structure and dynamics of the target nucleus are discussed.     

Determination of the fire-ball dimensions from second-order interference between two pions

Positive correlations are observed for pion pairs of equal charge and similar momentum vectors, produced in the reactions πp→p+5π and πp→p + 7π at 4 to 25 GeV/c. The results are consistent with being due to the second-order interference effects expected for pairs of identical bosons and lead to the determination of the average dimension of the “fire-ball’ from which the pions are emitted (〈R〉 = 1.0 ± _?0.2^+0.4 fm). Attempts are made to study the fire-ball shape by selecting pions pair emitted in various polar and azimuthal directions.     

Kinematically complete measurement of the absorption of stopped pions in 3He

The reactions π^?3He → nnp and π^?3He → nd have been measured in a kinematically complete experiment with stopped pions. The results show strong preference for collinear events. About three quarters of all absorption processes occur as quasi-free absorption on np- or pp-pairs with a ratio of R = 10.1 ± 1.5. The remaining quarter shows energy sharing among all three nucleons and is located in the final-state interaction regions. Branching ratios for all observed final states are given.     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Properties of the inclusive pion spectrum from pp collisions: 28.5 GeV/c to about 10 GeV/c

The spectra of pions are studied in the inclusive reactions p + p → π^± + anything in bubble chamber data at 28.5 GeV/c. Comparisons are made with ISR π⁺ spectra to examine energy dependence.     

Elastic and charge exchange scattering of pions on3He in the (3,3)-resonance region

The elastic scattering of pions from³He and the single charge exchange reaction³He(π ^?,π ⁰)³H are calculated in the energy domain of the (3,3)-resonance within the framework of Glauber's theory, including spin and isospin degrees of freedom in all orders. It is pointed out that, from the first minimum on, the differential cross section strongly depends on the parametrization of theπN amplitude, especially on its continuation into the unphysical region of momentum transfer. Single and double spin flip contributions prove to be very important in the charge exchange reaction. Within a modified version of Glauber's formalism, directly usingπN phase shifts rather than amplitudes, the³He charge exchange scattering is reexamined. Whereas the shape of the angle-integrated cross section as a function of pion energy is confirmed, the magnitude is still uncertain within a factor of 2.     

Coherent two pion photoproduction on 12C

We develop the formalism for coherent two pion photoproduction in nuclei and perform actual calculations of cross sections for π⁻π⁺ and π⁰π⁰ photoproduction on ¹²C. We find that due to the isospin symmetry the cross section for π⁰π⁰ production is very small and has a maximum when the pions propagate together. However, the kinematical region where the energies and polar angles of the two π⁰ mesons are equal and their relative azimuthal angle Ø = 180° is forbidden. Conversely in the π⁻π⁺ production the pions prefer to have a relative azimuthal angle 180° and the production of the pions propagating together is suppressed. The dominant one-body mechanism in both channels is related to the excitation of the Δ isobar. Hence the reaction can serve as a source of information about Δ's properties in nucleus. We have found that the reaction is sensitive to effects of the pion and Δ renormalization in the nuclear medium, similar to those found in the coherent (γ, π⁰) reaction, but magnified because of the presence of the two pions.     

On induced double-nucleon emission. III. 12C, (π−, NN) and short-range correlations

The reaction channel (π^?, NN) for the absorption of bound negative pions by nuclei is used as a means to study nuclear short range correlations. A three-body partial-wave analysis has been carried out for the final-state scattering which includes a Reid soft-core nucleon-nucleon interaction and an optical potential. This coupled-channel formalism rapidly converges as we eliminate the asymptotic single-nucleon and deuteron interactions. It is found that for ¹²C reasonable agreement with experiment cannot be obtained in this model without modification of the high relative-momentum components of bound shell model pair wave functions.     

Derp 3/2-Analogzustand in51V

In an investigation ofT=7/2 analogue states in⁵¹V the⁵⁰Ti(p, γ) excitation curve has been measured for proton bombarding energies 1280–1480 keV and 2340–2660 keV. From the (p, γ) resonances 29 new virtual levels in the region of 9316–9510 keV excitation energy in⁵¹V were determined. The strong resonance atE _p=1 371 keV has been identified as the isobaric analogue state of the⁵¹Ti ground state by determining spin and parity of this resonance to be 3/2^?. There is no evidence for a strong analogue resonance in⁵¹V corresponding to the 1.16 MeV _{p 1/2} state in⁵¹Ti. The γ-decay of the _{p 3/2} analogue state has been studied by measuring branching ratios and angular distributions of primary γ-transitions with a Ge(Li) detector.M1E2 mixing ratios have been determined for these transitions. The total width of the resonance for γ-decay is found to be Γ_γ=1.6±0.4 eV. New bound levels in⁵¹V have been introduced at 3576, 4651 and 4661 keV excitation energy. TheJ ^π values of the 3085, 4770, and 4863 keV states are determined to be 5/2^?, 5/2^?, 3/2^?, respectively. The analogue-antianalogueM1 transition strength is found to be considerably reduced compared to the situation ins-d shell nuclei.     

Pions in primary cosmic rays of ultrahigh energies

In the framework of the Coleman-Glashow hypothesis of an extremely weak violation of Lorentz invariance, neutral and charged pions can be stable for energies above 10¹⁹ eV and enter into the composition of primary cosmic rays of ultrahigh energies. The kinematic exclusion of reactions of pions with relic photons is particularly important, because it allows the Greisen-Zatsepin-Kuzmin paradox to be resolved. The parameters of extensive air showers induced by primary pions calculated within the model of quark-gluon strings with allowance for the Landau-Pomeranchuk-Migdal effect and interactions of neutral pions of ultrahigh energies are not contradictory to the available data of observations. It has been shown that observations of production heights of muons with energies above 10GeV will make it possible to distinguish between primary nuclei, protons, and pions; to verify Lorentz invariance for energies above 10²⁰ eV; and to obtain a new limit on the difference between the maximum possible velocities of muons and pions (c_µ?c_π)<4×10^?26.     

Structural and spectroscopic studies on concentration dependent Er3+ doped boro-tellurite glasses

Er³⁺ doped boro-tellurite glasses have been prepared by the conventional melt quenching technique with the chemical composition (39?x) B₂O₃+30TeO₂+15MgO+15K₂O+xEr₂O₃ (where x=0.01, 0.1, 1, 2 and 3 wt%). The structural analysis of the glasses were made through XRD, FTIR spectral measurements and the optical absorption, luminescence measurements were made to analyze the optical behavior of the prepared glasses. The bonding parameters were determined from the optical absorption spectra and were found to be ionic in nature. The experimental oscillator strengths were determined from the absorption spectra have been used to determine the Judd–Ofelt parameters. The Judd?Ofelt parameters were used to explore the important radiative parameters such as transition probability (A), stimulated emission cross-section (σ_P^E) and branching ratios (β_R) of the emission transitions ²H_9/2→⁴I_15/2 and ²H_11/2 and ⁴S_3/2→⁴I_15/2 of the trivalent erbium ions. The optical band gap energy (E_opt) values corresponding to the direct and indirect allowed transitions and the Urbach energy values of the prepared Er³⁺ doped boro-tellurite glasses have been calculated and discussed with similar studies. The spectroscopic behavior of the Er³⁺ boro-tellurite glasses have been studied by varying the trivalent erbium ion content and the results were discussed and compared with similar studies.     

Formation of six-nucleon systems and nuclei in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

The results obtained by studying the production of six-nucleon systems and nuclei that is accompanied by the yield of charged pions in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. It is shown that the correlation of the yield of mirror ³H (³He) nuclei with the production of π ⁺ (π ^?) mesons is due to the charge-exchange process involving an oxygen-nucleus proton (neutron) knocked out predominantly from an alpha-particle cluster.     

Interference of secondary pions and time-space characteristics of their emission volume in π− p interactions at 40 GeV/c

The interference of positive and negative pions produced in π^? p interactions at 40 GeV/c is studied. It is shown that negative pions are emitted from larger distance than positive ones. The influence of resonance production on the size of pion emission volume is observed.     

Observation of a narrow hyperon state of mass 3.17 GeV

We present evidence for a narrow Y¹ with a mass of 3.17 GeV and a width ? 20 MeV decaying to ΣKK? + pions, ΛKK? + pions and ΞK + pions. The data come from two high statistics K^?p bubble chamber experiments with a sensitivity of ≈100 eV/μbat 8.25 GeV/c and ≈ 45 eV/μbat 6.5 GeV/c.     

Probing nuclear expansion dynamics with π−/π+-spectra

We study the dynamics of charged pions in the nuclear medium via the ratio of differential π^? - and π⁺-spectra in a coupled-channel BUU (CBUU) approach. The relative energy shift of the charged pions is found to correlate with the pion freeze-out time in nucleus-nucleus collisions as well as with the impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb force provides valuable information on the expansion dynamics of the hot nuclear system. Detailed comparisons with experimental data for Au + Au at 1 AGeV and Ni + Ni at 2.0 AGeV are presented.     

Searching for exotic cluster structure in the absorption of pions by the 11B nucleus

Correlation measurements of the reaction of stopped pion absorption ¹¹B(π^?, tt)X are made with a semiconductor double-arm charged particle spectrometer on a low-energy pion beam at the LAMPF meson factory. Analysis of a two-dimensional Dalitz plot and the momentum distribution of the residual nucleus allows us to identify the absorption of pions in a 6Li intranuclear cluster and demonstrate the configuration ⁶Li + ⁵He_g.s is present in the ¹¹B nucleus.