An upper limit for the (α, π −) reaction on181Ta

In order to search for traces of the¹⁸¹Ta(α, π ^?)¹⁸⁵Os reaction a foil stack of very pure tantalum was bombarded with anα-beam of 173 MeV. A radiochemical separation method was applied to four parts of the stack. So two sources corresponding to energies above and below the (α, π ^?) threshold were obtained and searched for contents of¹⁸⁵Os. Using a well shielded Ge(Li) detector weak 646 keV transitions belonging to¹⁸⁵Os were observed for all samples. Since the origin of this activity is uncertain for the samples below threshold only an upper limit of 100 nb can be set for the (α, π ^?) reaction on¹⁸¹Ta above threshold.     

Quasi-free contributions in the6Li(d,tp)4He-reaction atE d =0.465 MeV

The⁶Li(d, tp)⁴He reaction was investigated at a bombarding energy ofE _d =0.465 MeV in a kinematically complete experiment. Evidence was found for a quasi-free reaction.     

Production rates for π+ K −, pK −, and pπ− atoms in inclusive processes

The yields of π⁺ K ^?, pK ^?, and pπ^? atoms in the reaction p + Al → atom + X at energies of 24, 70, 450 GeV and emission angles of θ_lab=1°–6° are calculated from inclusive-production cross sections for p, π⁺, π^?, and K ^?. Estimates of these hadronic-atom yields for a Ta target are also given. The inclusive-production cross sections for p, π⁺, π^?, and K ^? are obtained within the Lund model of string fragmentation. The accuracy of the calculations is estimated by comparing single particle yields calculated by the Lund model and experimental yields of particles in proton-nucleus interactions.     

Spectroscopy of 7Li in stopped pion absorption reactions

The structure of excited levels in the ⁷Li isotope is studied via inclusive and correlation measurements in the stopped π^? meson absorption reactions ¹⁰B(π^?, t)X and ¹²C(π^?, dt)X, respectively. The experiment is conducted using a low-energy pion beam at the LAMPF meson factory. Analysis of the missing mass spectra reveals ⁷Li states with the resonance parameters (E _x , Γ) (4.7, 0.1), (6.6, 0.9), (7.3, 0.1), (9.1, 2.8), and (9.6, 0.4) MeV. A highly excited state with E _x ≈ 11.2 MeV (i.e., an isobar analog of ⁷He) is observed in the ¹⁰B(π^?,t)X reaction. An excited state with E _x = 10.3 ± 0.1 MeV and γ = 1.8 ± 0.4 Mev is observed for the first time in the ¹²C(π^?,dt)X reaction.     

Theg factor of the lowest 7+ state in100Rh and 6− state in104Rh

Theg-factor of the 7⁺ state in¹⁰⁰Rh withT _1/2=140(5) ns and of the 6^? state in¹⁰⁴Rh withT _1/2=47(3)ns has been measured by the time-differential perturbedγ-ray angular distribution method (TDPAD). The obtained values are +0.67(2) and +0.33(1) respectively. The two nuclei were populated with reactions induced by⁷Li on^96,100Mo at a bombarding energy of 30 MeV. Shell model calculations using effective single particle moments show that the 7⁺ state in¹⁰⁰Rh has mostly a πg _9/2 ? vd _5/2 configuration, while the main component of the 6^? state in¹⁰⁴Rh is the πg _9/2 ? vh _11/2.     

The 6Li(α, 2α)2H reaction at 700 MeV and the α-d momentum distribution

The results of an experimental study of the reaction ⁶Li(α, 2α)²H at 700 MeV are given. A comparison with the data from seven other reactions pertaining to the α⁺d cluster structure of ⁶Li is presented. The amplitude for the virtual transition ⁶Li→α+d obtained three of these experiments and the present one are comparable. The internal momentum distributions extracted with the plane-wave impulse approximation in four of the experiments are compatible with a pole form, the width parameter being given by the α-separation energy in ⁶Li. The remarkable consistency among these results is seen as evidence for the validity of the simple models used for both the reaction mechanism (PWIA) and to describe the α d-vertex (pole approximation) in ⁶Li.     

Production of thef 0 meson in the Double Pomeron Exchange reactionpp→ppπ+π−

Data are presented for the exclusive reaction pp → pp π⁺ π^? at \(\sqrt s = 62GeV\) with two leading protons at large Feynman-x and a centrally produced π^+;π^? system. In this kinematical configuration one expects a substantial contribution from Double Pomeron Exchange, which is a potential source of glueballs. The experiment was performed at the CERN ISR using the Split Field Magnet spectrometer. In the mass range between 1,000 and 1,700 MeV/c² the invariant mass distribution for the central π^+;π^? system exhibits a very significant signal for thef ⁰(1270) and no other obvious resonant states.     

Light hypernuclei in FINUDA

The FINUDA experiment produces Λ-hypernuclei stopping in thin targets the K ^?’s coming from the decay of the Φ particle inside the DAΦNE e ⁺-e ^? collider machine. The Λ-hypernucleus formation is detected by measuring the momentum of the outgoing π^? coming from the strangeness-exchange reaction (K ^?, π^?) inside the targets. Experimental results related to few-body issues, such as hypernuclear spectroscopy, hypernuclear decays, and neutron-rich hypernuclei will be presented.     

The reaction γ +d → π+ + π− +p + n between 570 and 850 MeV andΔ ++ Δ − production

The reaction γ+d → π⁺+π^? +p + n has been measured in a kinematically complete way at incident photon energies from 570 to 850 MeV in steps of 40 MeV. From detailed comparison of measured data with results of event simulations, it is concluded that three different mechanisms, the quasi-free, double-delta and phase space productions, contribute to the reaction. Each of the cross sections corresponding to these mechanisms is determined separately.     

The π N → e +e−N reaction close to the vector-meson production threshold

The π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections are calculated below and in the vicinity of the vector-meson (?⁰,ω) production threshold. These processes are largely responsible for the emission of e ⁺e^? pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector-meson-nucleon channels. The vector mesons materialize subsequently into e ⁺ e^? pairs. Using πN→?⁰ N and πN→ωN, amplitudes calculated in the center of mass energy interval 1.4 < √s<1.8 GeV, we compute the π^? p→e ⁺ e ^? n and π⁺ n→e ⁺ e ^? p reaction cross sections in these kinematics. Below the vector-meson production threshold, the π⁰?ω interference in the e ⁺ e^? channel appears largely destructive for the π^? p→e ⁺ e ^? n cross section and constructive for the π⁺ n→e ⁺ e ^? p cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector-meson-nucleon channels to low-lying baryon resonances.     

π+/π− Ratio and two particle production in Proton's fragmentation region by Monte Carlo simulation

Hadron jet at lowp _T is generated by Monte Carlo method using several models including our quark cascade model in which the recombination mechanism is taken into account. The predicted results from those models on π⁺/π^? ratio,K ⁺ /K ^? ratio, π^± meson spectra and π⁺/π^? ratio under π^± meson and Λ particle trigger, ratio between invariant two particle cross-section (p→π ⁺ /π ^? )/(p→π ^? /π ^? are compared with the experimental data. The effects of the asymmetric initialu- andd-quark distributions the scaling and its violation of particle spectra and particle ratios under the other particle trigger are discussed. Predictions from our recombination model fit to the experimental data fairly well.     

Latest Results From the HypHI Experiments at GSI: Hypernuclear Spectroscopy with Heavy Ion Induced Reactions

The HypHI Phase 0 experiment with ⁶Li projectiles at 2 AGeV on a carbon target has been performed at GSI in order to demonstrate the feasibility of hypernuclear spectroscopy with induced reaction of heavy ion beams. Current data analyses have shown peaks in invariant mass distributions of p + π ^? for Λ, ³He+ π ^? for ³ _Λ H and ⁴He + π ^? for ⁴ _Λ H. Lifetime values for the corresponding peaks have been also deduced, which are in good agreement with the former known values.     

Investigating highly excited states of the 8Li isotope

Highly excited states of the ⁸Li isotope are sought in absorption reactions of π^? mesons stopped by ^10,11B isotopes. The ground and three excited states of the ⁸Li isotope are observed in inclusive measurements of reactions ¹⁰B(π^?, d)X and ¹¹B(π^?, t)X. The states with excitation energies E _x ≈ 8.7 and 10.1 MeV are observed for the first time in correlation measurements of reactions ¹⁰B(π^?, dt)X and ¹¹B(π^?, tt)X.     

New limits on D0 (1.865) production in proton-nucleus collisions at 400 GeV/c

We present final results of a sensitive search for new particles in π^±K^? effective mass spectra observed in proton-nucleus collisions at 400 GeV/c. We establish a limit for D⁰ (1.865) production B_π⁺π^? dσ/dy < 360 nb/nucleon at y_cm^≈ ?0.4. For D?⁰ → π^?K⁺ the limit is 290 nb/nucleon.     

Angular distribution of recoil 8Li in the reaction 9Be (π-, πN) 8Li at 1.0 GeV/c

The angular distribution of recoil ⁸Li in the reaction ⁹Be(π^-, πN) ⁸Li at 1.0 GeV/c was measured with a solid state track detector. The experimental results seem consistent with the assumption that the heavy-fragment knockout process is dominant, but other mechanisms are also required.     

Observation of the (π−, π−n) and (π+, π+p) reactions at 165 MeV

The (π^?, π^?n) and the (π⁺, π⁺p) reactions were studied on C, Fe, and Bi at 165 MeV by coincidence measurement o outgoing particles. The nucleon-knockout reaction is the dominant inelastic process at backward pion-scattering angles at this energy. The quasifree (π^?, π^?n) and (π⁺, π⁺p) cross sections were determined from the π-N an correlations. Their σ_qf(π^?, π^?n)/σ_qf(π⁺, π⁺p) ratio is consistent with unity for C and is larger than the N/Z ratio for the heavier nuclei.     

Study of process e + e − → π+π−π0π0 at energies √s < 1 GeV with the spherical neutral detector

The cross section for the process e ⁺ e ^? → π⁺π^?π⁰π⁰ has been measured in an experiment with a spherical neutral detector, with the cross section at energies √s < 920 MeV having been measured for the first time. The model of vector dominance describes well the data obtained if the ρ, ρ′, and ρ″ resonances are taken into account. The probability of the decay ρ → π⁺π^?π⁰π⁰ is B(ρ → π⁺π^?π⁰π⁰) = (1.60 ± 0.74 ± 0.18) × 10^?5. The upper limit for the decay ω → π⁺π^?π⁰π⁰ has been improved by two orders of magnitude compared to previous measurements and is B(ω → π⁺π^?π⁰π⁰) < 2 × 10^?4 at a 90% confidence level.     

Three-particle correlations from208Pb+6Li

Three-particle correlations in the reaction²⁰⁸Pb+⁶Li were studied near the Coulomb threshold between \(E_{6_{Li} } = 24\) and 30 MeV. Three reaction mechanisms contribute predominantly to the observed coincidences of the charged particles: 1. Coulomb excitation of the 2.184 MeV,J=3⁺ state of⁶Li, followed by the decay intoα+d, 2. Deuteron pick-up of the⁶Li to the ground state of⁸Be and sequential decay into twoα-particles and 3. Neutron-transfer to the ground state and the first excited states of²⁰⁹Pb:²⁰⁸Pb(⁶Li,αp). The last two reaction mechanisms explain the previously measured large contributions to theα-channel relative to thed-channel.     

Dynamics of pion double-charge-exchange reactions

The (π⁺, π^?) reactions leading to the double isobaric analog state are studied at pion energies 50 to 300 MeV, with¹⁴C as an example. Effects of nuclear structure, nuclear recoil, the reaction pathway and off-shell πN interactions are examined in detail. Our study reveals a very strong dependence of calculated cross sections on off-shell πN dynamics. Consequently, use of a self-consistent off-shell πN theory is essential to studying short-range nucleon-nucleon correlations from double-charge-exchange data. The present study further shows that reaction dynamics other than two successive pion single charge exchanges is needed to account for the experimental data.     

A new experimental limit for the decay K+ → π+γγ

A search for K⁺ → π⁺γ, π⁺γγ, π⁺γγγ was made detecting pions from stopped kaons in the kinetic energy region between 117 MeV and 127 MeV. New Limits of 1.4 ×10^?6, 8.4 × 10^?6 and 1.0 × 10^?4 for the branching ratio were obtained assuming a phase-space spectrum on the pion energy. The first limit also aplies to another process K⁺ → π⁺ + a, where a is a light meson with mass smaller than 100 MeV/c² and decays into nγ's with lifetime less than 10^?9 s.