Rotational bands in Ho

The excited states of the deformed odd-proton nucleus ¹⁶¹Ho have been studied in the reactions ¹⁵⁹Tb(, 2n), ¹⁶¹Dy(d, 2n) and ¹⁶¹Dy(p, n). Gamma-ray spectra in single and coincidence modes as well as angular distributions and excitation functions of the transitions were measured. The proposed level scheme of ¹⁶¹Ho contains besides of the ground state band ⁻[523] the bands ⁺[404], ⁺[411], ⁺[411] and ⁻ [541] (band heads at 252.7, 298.7, 211.2 and 423.9 keV, respectively). An attempt was made to estimate the influence of Coriolis coupling between the bands ⁺ [411] and ⁺ [411], which are very close in energy. The ⁺ [404] band was found to de-excite by very fast E1 transitions to the ground state band ⁻[523]. Nilsson retardation factors of about 0.03 for these transitions were deduced using the E2/E1 branching ratios. An investigation has also been made of the independent feeding of the levels from high-lying states.     

Hadronic production by ee collisions at the energy 990 MeV with the Orsay storage ring

Data were taken at the energy 2E = 990 MeV to search for multibody events, with the same large solid angle detector which has been used for the measurement of the , ω andφ production by e⁺e⁻ annilations. Assuming a π⁺π⁻π⁰π⁰ production by the quasi two-body process e⁺e⁻ → → ωπ⁰ we give the correspondi ng cross section σ(e⁺e⁻ → π⁺π⁻π⁰π⁰) = (1.1 ± 0.5) 10⁻³² cm². Since no events with 3 and 4 charged pions have been observed σ(e⁺e⁻ → π⁺π⁻π⁰π⁻) 1.5 × 10⁻³³ cm².     

Single and double dissociation in πp collisions at 11 and 16 GeV/c

The reactions π⁻p → 2π⁻π⁺p, π⁻p → 2π⁻π⁺π^op and π⁻p → 2π⁻2π⁺n are analysed at 11 and 16 GeV/c using longitudinal phase space (LPS) plots. The weighted LPS distributions for π⁻p → 2π⁻π⁺p is dominated by two well separated structures corresponding to single diffraction dissociation of the pion, π⁻p → (2π⁻π⁺)p, and of the proton, π⁻p → π⁻(π⁻π⁺p). The former is more abundant than the latter, and both are approximately constant with energy. In contrast, processes of type π⁻p → (2π)(πp) decrease with increasing energy.

In the five-body reactions the weighted LPS distribution reveals especially at 16 GeV/c a maximum for single dissociation of the proton into 3πp, namely π⁻p → π⁻(π⁻π⁺π^op); this process is likely to be diffractive. The neutron channel has a corresponding maximum displaced toward a multiperipheral configuration π⁻p → π⁻(π⁻2π⁺)n. Another strong maximum corresponds to the pion dissociation π⁻p → (2π⁻π⁺π^o)p. This is interpreted to be an ω-exchange process because no analogous structure occurs in π⁻p → (2π⁻2π⁺)n. Finally, a broad structure reveals double dissociation of both incident particles; it occurs in the two channels π⁻p → (2π⁻π⁺)(π^op) and π⁻p → (2π⁻π⁺)(π⁺n), being stronger in the latter. Further analysis of this process in terms of isospin exchange suggests that it is partially diffractive. Factorization is also discussed.

An appendix gives general aspects of the LPS analysis for the asymptotic study of n-body collisions at very high energy.     

Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

Symmetry breaking and the decays ψ′ → J/ψπ(η) and J/ψ → η(η′) γ

The theoretical mechanisms for the decays ψ′ → ψπ⁰ and ψ′ → ψη, which violate SU₂ and SU₃, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π⁰ −η −η′ mixing. The π⁰ −η mechanism ψ′ → ψν → ψπ⁰ leads to Γ(ψ′ → ψπ⁰) = (3.3±1.0) × 10⁻³ Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π⁰−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed.     

Polarisation circulaire du rayonnement gamma de Sb, Cs et Ag

The βγ circular polarization correlation of the 3⁻(β⁻ 621 keV)3⁻(γ 1692)2⁺ cascade in ¹²⁴Sb, the 4⁺(β⁻ 662)4⁺ (γ 796)2⁺ (γ 605)0⁺ in ^13Z4Cs and the 6⁺(β⁻529)6⁺ (γ 937)4⁺ (γ 885)2⁺ (γ 658)0⁺ in ^110mAg have been studied by using a Compton effect polarimeter. The measured asymmetry parameters are 0.172±0.004, −0.0702 ±0.0024 and 0.0549±0.0013 respectively.     

The decay ω(782)→5π in chiral theory.

The arguments are put forward that the many pion decays ω→2π⁺2π⁻π⁰ and π⁺π⁻3π⁰ provide an ideal test site for testing the predictions of chiral models of the vector meson decays into many pions. Using the approach based on the Weinberg Lagrangian or, in a new language, the Lagrangian of hidden local symmetry added with the term induced by the anomalous Lagrangian of Wess and Zumino, the partial widths of these decays are evaluated, and their excitation curves in e⁺e⁻ annihilation are obtained. The discussed are the perspectives of the experimental study of the decays ω→5π in e⁺e⁻ annihilation and photoproduction.     

Observation of two-photon emission in nuclear pion capture

The emission of two photons above 25 MeV energy was observed in the capture of stopped pions by beryllium and carbon with a rate of (1.0 ± 0.1) × 10⁻⁵, respectively (1.4 ± 0.2) × 10⁻⁵ per capture. These rates are about two to four times greater than various free-nucleon estimates based on the π⁻+π⁺→γγ annihilation mechanism alone.     

Identification of Hg and shape coexistence in odd-A Hg isotopes

In-beam γ-ray transitions in ¹⁸¹Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2⁻[521] ground state was observed up to 29/2⁻. A 5/2⁻[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i_13/2 orbitals and are proposed to decay to an i_13/2 isomeric state associated with an oblate state.     

High-spin study of Xe

High-spin states have been populated in ₅₄¹¹⁹Xe via the ⁹⁶Mo(²⁷Al,p3n) reaction at 133 MeV, using the γ-ray spectrometer to record triple γ-ray coincidences. The known level scheme has been significantly extended and several band crossings identified. In particular, the νh_11/2 yrast band has been extended to I^π = (83/2⁻) and shows features which are consistent with those of smooth band termination at high spin. Theoretical results for ¹¹⁹Xe at high spin are discussed within the framework of cranked Nilsson-Strutinsky calculations, together with results for ¹¹⁷Xe.     

Hadron-nucleus bound states

A new type of nuclear spectroscopy to study hadron-nucleus bound states is described. The first successful experiment was to search for deeply bound π⁻ states in heavy nuclei using the ²⁰⁸Pb(d,³He) reaction at GSI, in which a narrow peak arising from the 2p π⁻ orbital coupled with the neutron-hole states was observed at 135 MeV excitation energy. An improved experiment has just been carried out to separately identify the 1s and 2p π⁻ states. These experiments provide important information on the local potential strength, from which the effective mass of π⁻ is deduced to be 20 MeV. This method will be extended to search for η and ω bound states as well as for K⁻ bound states. The advantage of the bound-state spectroscopy versus invariant mass spectroscopy is emphasized.     

Radiative decay of ρ and φ mesons in a chiral unitary approach

We study the ρ⁰ and φ decays into π⁺π⁻γ, π⁰π⁰γ and φ into π⁰ηγ using a chiral unitary approach to deal with the final state interaction of the MM system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the ρ⁰→π⁺π⁻γ decay. In the case of φ decay the contribution to π⁺π⁻γ and π⁰π⁰γ decay proceeds via kaonic loops and gives a distribution of ππ invariant masses in which the f₀(980) resonance shows up with a very distinct peak. The spectrum found for φ→π⁰π⁰γ decay agrees with the recent experimental results obtained at Novosibirsk. The branching ratio for φ→π⁰ηγ, dominated by the a₀(980), is also in agreement with recent Novosibirsk results.     

Determination of the K(1800) spin parity

A spherical harmonic moment analysis of the reactions K⁻p → K⁻π⁺n and K⁺p → K⁺π⁻Δ⁺⁺ at 13 GeV/c demonstrates the existence of a broad K^* state with mass in the vicinity of 1800 MeV and spin parity 3⁻.     

Search for narrow NNπ resonances in exclusive pp→ppππ measurements

Narrow structures in the range of a few MeV have been searched for in ppπ⁺ and ppπ⁻ invariant mass spectra (M_ppπ⁺ and M_ppπ⁻) obtained from exclusive measurements of the pp→ppπ⁺π⁻ reaction at T_p=725,750 and 775 MeV using the PROMICE/WASA detector at CELSIUS. The selected reaction is particularly well suited for the search for dibaryon resonances decoupled from NN and/or NΔ. In the mass range 2020 MeV/c²<m_dibaryon<2085 MeV/c² no narrow structures could be identified on the 3σ level of statistical significance neither in M_ppπ⁻ nor in M_ppπ⁺ giving an upper limit (95% C.L.) for dibaryon production in this reaction of σ<20 nb.     

Interpretation of the Θ as an isotensor pentaquark with weakly decaying partners

The Θ⁺(1540), recently observed at LEPS, DIANA and CLAS, is hypothesized to be an isotensor resonance. This implies the existence of a multiplet where the Θ⁺⁺, Θ⁺ and Θ⁰ have isospin-violating strong decays, and the Θ⁺⁺⁺ and Θ⁻ have weak decays and so are long-lived. Production mechanisms for the weakly-decaying states are discussed. The J^P assignment of the Θ is most likely 1/2⁻ or 3/2⁻.     

A new measurement of the weak magnetism term in the betaspectra of B and N

The betaspectra of ¹²B and ¹²N have been measured with a NaI crystal as spectrometer. Assuming a shape correction factor 1 + aW + bW² and b₋ = 1.106 × 10⁻⁴ MeV⁻², b₊ = −1.397 × 10⁻⁴ MeV⁻², the spectra yield a₋ = (+0.91 ± 0.11) × 10⁻² MeV⁻¹ and a₊ = (−0.07 ± 0.09) × 10⁻² MeV⁻. the a₋ − a₊ = (+0.98 ± 0.09) × 10⁻² MeV⁻¹ is in agreement with the weak magnetism prediction.     

Double charge exchange and one-pion production in π He collisions at 1.7 GeV/c

We present the results of a study of the exclusive reactions π^{+ 4}He → π⁻ 4p (double charge exchange, DCE) and π^{+ 4}He → π⁺ π⁻ 3pn (one-pion production). The experiment was performed with the Oxford/RHEL helium bubble chamber irradiated with a 1.7 GeV/c π⁺ beam. A general review of DCE models is presented and experimental results at other energies are discussed in the light of these models. None of the existing theoretical models is compatible with out data at 1.7 GeV/c. We propose a new mechanism for DCE, involving three nucleons, which reproduces the integrated as well as the differential cross sections. Some consequences for other models are also discussed.     

Measurement of the cascade time of ∑ in liquid helium

In a study of ∑⁻π⁺ production by stopped K⁻ in liquid helium, (19 ± 6)% of stopped ∑⁻ were observed to decay. This corresponds to a “cascade time” of 28 ± 8 psec.     

Nombres D''ondes Absolus De La Bande ν3 De OCS Par Spectroscopie De Fourier

Absolute wavenumbers of 140 lines belonging to ν₃ band of ¹⁶O¹²C³²S, around 2060 cm⁻¹, are measured under vacuum with a high resolution Fourier Spectrometer, within ±0.11 × 10⁻³ cm⁻¹ (3.1 MHz) . They achieve a 20-fold improvement in accuracy over previous measurements and are consequently proposed as secondary infrared standards. Molecular constants are reported.     

Duree de vie et depolarisation par collisions avec l''helium des niveaux 5P3/2 Et 5P1/2 de l''ion Cd

The lifetimes of the Cd⁺ 5²P_3/2 and 5²P_1/2 states have been measured by the Hanle effect. The Cd⁺ ions are produced in a d.c. discharge in cadmium vapor, with helium as buffer gas. The results are: τ(5²P_3/2) = (2.60±0.20) ×10⁻⁹sec, and τ(5²P_1/2) = (3.05 ± 0.13) × 10⁻⁹sec.

We measured also the cross sections for the destruction of the orientation in the 5²P_1/2Cd⁺ state (<5Ų), of the orientation (18±10Ų) and of the alignment (46±10Ų) in the 5²P_3/2 state due to collisions with the helium atoms.