Incident Pion Momenta Research Articles

Momentum dependence of pion-induced ϕ meson production on nuclei near threshold

We study the near-threshold pion-induced production of ϕ mesons off nuclei in the kinematical conditions of the HADES experiment, recently performed at GSI. The calculations have been performed within a collision model based on the nuclear spectral function. The model accounts for both the primary π− meson–proton π−p → ϕn and the secondary pion–nucleon πN → ϕN ϕ production processes as well as the effects of the nuclear ϕ and nucleon mean-field potentials. We find that the primary reaction channel π−p → ϕn dominates in the ϕ production off 12C and 184W target nuclei in the HADES acceptance window at incident pion momentum of 1.7 GeV/c. We calculate the momentum dependence of the absolute and relative (transparency ratio) ϕ meson yields from the above direct channel. The calculations have been performed for this initial pion momentum allowing for different options for the ϕN absorption cross section σϕN and different scenarios for the in-medium mass shifts of the ϕ meson and secondary neutron, produced together with ϕ in this channel. We demonstrate that the transparency ratio for the ϕ mesons has, contrary to the absolute cross sections, an insignificant sensitivity to the ϕ meson and secondary neutron in-medium mass shifts at ϕ momenta studied in the HADES experiment. On the other hand, we show that there are measurable changes in the transparency ratio due to the ϕN absorption cross section, which means that such a relative observable can be useful to help determine this cross section from the data taken in the HADES experiment.

Investigation of near-threshold eta-meson production in the reaction π − p→ ηn

Differential and total cross sections for eta-meson production in the reaction π−p → ηn were measured within the experimental program eta-meson physics implemented in the pion channel of the synchrocyclotron of the Petersburg Nuclear Physics Institute (PNPI, Gatchina). These measurements were performed at incident-pion momenta (700, 710, 720, and 730 MeV/c) in the vicinity of the threshold for the process under study by using the neutral-meson spectrometer designed and created at the Meson Physics Laboratory of PNPI. It is shown that, in the immediate vicinity of the threshold (685 MeV/c), the process of eta-meson production proceeds predominantly via S11(1535)-resonance formation followed by the decay S11(1535) → ηn (the respective branching fraction is Br ≈ 60%), but that, as the momentum of incident pions increases, the role of the D wave becomes ever more important. A detailed analysis of this effect indicates that it is due to the increasing contribution of the D13(1520) resonance. Although the branching fraction of the decay of this resonance through the ηn channel is assumed to be very small (BR ≈ 0.24%), the effect is enhanced owing to the interference between the D wave and the dominant resonance S11(1535).

Formula omitted] and the ηN scattering length

We show that for incident pion momentum plab=903MeV/c the cross section of π+d→ηpp with the η produced in the backward direction is very sensitive to the low-energy ηN amplitude. We conclude that the measurement of this reaction at these kinematic conditions will allow a better determination of the ηN scattering length, which is known with a large uncertainty and attracts intense experimental and theoretical interest. Our result strongly motivates performing this experiment in the K1.8BR beam line area at the J-PARC facility in Japan. The experiment will eventually provide new insight on the important quest for eta-mesic nucleus in hadronic physics.

Measurement of differential cross sections for charge-exchange π − p scattering in the region of small scattering angles

Differential cross sections for the reaction π−p → π0n were measured for nearly forward scattering angles. The experiment was performed at the pion channel of the synchrocyclotron installed at the Petersburg Nuclear Physics Institute (PNPI, Gatchina), the incident-pion momenta ranging between 417 and 710 MeV/c. The measurements, which involved recording both photons from the decay process π0 → 2γ, employed the neutral-pion spectrometer developed at the PNPI. A description of the experimental facility is given, and the results of the measurements are presented.

Observation of an anomaly in the angular distribution of cumulative hadrons near the backward direction

The angular distributions of secondary pions, protons, and deuterons originating from π−Pb interactions at an incident-pion momentum of 5 GeV/c was determined in a new run of measurements relying on track reconstruction. While showing a decrease over a large angular interval with increasing emission angle, the yield of cumulative particles of each species was found to be anomalously large near the backward direction.

Pion-deuteron elastic scattering at large angles from 0.90 to 2.025 GeV/ c

The differential cross section for the backward (120° ⩽ θ c.m.s. ⩽ 180°) pion-deuteron elastic scattering was measured at eight incident pion momenta from 0.90 to 2.025 GeV/ c. A distinctive change in the shape of the angular distribution is observed. At 0.9 GeV/ c the differential cross section decreases smoothly to 180° in accordance with predictions of multiple-scattering theory. At 1.31 GeV/ c, i.e. in the region of the hypothetical 1I 6 dibaryon with a mass of 2.9 GeV, the differential cross section is practically independent of angle. At higher energies a sharp backward peak is clearly seen. Connections of our results with dibaryons and Regge asymptotic behaviour are discussed.

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

We report on results of an experiment to study the reaction π− p → π− π+ 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 Δ and ϱ resonance production. It indicates aI=0,J P = 0+ π− π+ final-state interaction.

Backward pion-deuteron elastic scattering from 1.75 to 3.1 GeV/ c

Measurements of the differential cross section for π −d elastic scattering in the backward angular region (−1 ⩽ cos θ cms ⩽ −0.98) are presented. These measurements were made at nine incident pion momenta P π ranging from 1.75 to 3.09 GeV/ c and at the largest values of q 2 [up to 7 (GeV/ c) 2] ever reached experimentally; here q 2 is the momentum transfer squared. The differential cross section was found to decrease rapidly with increasing momentum dσ dΩ cms (180°) ∼ P −15.7 π, dσ dt ∼ (q 2) −12.8 . The data are compared with predictions of Regge and quark bag models.

Decay distribution of high-transverse-momentum rho mesons.

The exclusive process π−p→ρ−p has been measured at 90° c.m. with an incident pion momentum of 9.9 GeV/c. We present data on the angular dependence of the decay ρ−→π−π0. We observe a strong azimuthal dependence in the decay in the c.m. helicity frame of the ρ. Such an azimuthal dependence is not compatible with SU(6) valence-quark perturbation calculations.

The (π, 2π) reaction and spin-isospin strength distribution in nuclei

We study pion production on nuclei within the distorted wave impulse approximation (DWIA) and using the local density approximation (LDA) for the treatment of possible nuclear spin-isospin mode enhancements. The scattering amplitude input is based on a one-nucleon mechanism since two-nucleon processes are here estimatedito be relatively unimportant. For discrete nuclear levels, we study differential and total (angle-integrated) cross sections for various pion-like levels ( J P = 0 −, 1 +, 2 −,…; T = 1); these are also compared with non-pion-like excitations. The cross sections for discrete excitations are quite small. The inclusive cross sections, achieved by summing over all nuclear states, are considerably larger, of the order of 0.1–10 mb. We use the Fermi gas model to test the importance of the quasi-free peak for various incident pion momenta k, and to study the closure approximation for summing over nuclear levels when calculating inclusive cross sections. It is found that for k of the order of about twice the Fermi momentum most of the quasi-free peak region contributes to the nuclear excitations, and the use of closure is justified and practical. All cases are studied as a function of g', the Migdal spin-isospin parameter, and it is found that the dependence upon this parameter may range from changes of an order of magnitude to a factor of two over the range 0.4 ⩽ g' ⩽ 0.7.

A three-body calculation of the πd → πnp reaction in the Δ-resonance region

The reaction d( π ±, p π ±)n at incident pion momentum 340 MeV/ c is analyzed based on a relativistic three-body formalism. The contributions of the various reaction mechanisms such as impulse processes, pion multiple scattering and nucleon-nucleon final-state interactions are investigated for several cases of typical kinematics. The impulse term is dominant when the recoil neutron momentum is small. On the other hand, the NN final-state interaction is found to be relatively important when the recoil neutron momentum is large. The effects of dibaryon resonances which have been suggested in πd elastic scattering are estimated using a phenomenological model. Comparisons with other work are also made.

Inelastic Interactions of 50 GeV/c Negative Pions with Nucleons

AbstractThe multiparticle production in π− ‐ N interactions at 50 GeV/c incident pion momentum is studied in the frame of the formation of resonance and the fireball production. The cross‐sections of production of the Δ(1236), N (1688), N (2220) and ϱ° resonances are measured.The fireballs are studied by the use of the Doller‐Walker plot and the target plot methods. The mass, emission angle and the velocity of each fireball are determined.

Reactionπd→pπnin theΔresonance region

Differential cross sections for the reaction $^{2}\mathrm{H}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},p{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})n$ at incident pion momentum 340 MeV/c in a kinematically complete experiment are reported for eleven angle pairs. At neutron momenta \ensuremath{\lesssim} 40 MeV/c the cross section peaks sharply and is described well by an impulse approximation corrected for entrance channel effects; the ratio of ${\ensuremath{\pi}}^{+}$ to ${\ensuremath{\pi}}^{\ensuremath{-}}$ cross section is approximately 9 to 1. For neutron momenta \ensuremath{\gtrsim} 40 MeV/c, the data are well fit by a combination of a ${J}^{\ensuremath{\pi}}={2}^{+} N\ensuremath{\Delta}$ dibaryon resonance amplitude and an impulse approximation background; in some cases the ratio of ${\ensuremath{\pi}}^{+}$ to ${\ensuremath{\pi}}^{\ensuremath{-}}$ cross section is 1 to 1.NUCLEAR REACTIONS $^{2}\mathrm{H}({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}},p{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}})n$, $p=340$ MeV/c; measured $\frac{{d}^{3}\ensuremath{\sigma}}{d{p}_{p}d{\ensuremath{\Omega}}_{p}d{\ensuremath{\Omega}}_{\ensuremath{\pi}}}$; model with DWIA, ${p}_{n}\ensuremath{\lesssim}40$ MeV/c; model with ${J}^{\ensuremath{\pi}}={2}^{+} T=1 N\ensuremath{\Delta}$ dibaryon resonance, ${p}_{n}\ensuremath{\gtrsim}40$ MeV/c.

Quasi-elastic pion-helium scattering at 5 GeV/ c

We have measured the cross section for π − + 4 He→ π − + 3 H+p at 5 GeV/c incident pion momentum. The momentum transfer to the pion was in the region 0.005≦| t ππ |≦0.15 (GeV/ c) 2 and the triton recoil momentum in the region 0.24 ≦ p t ≦ 0.60 GeV/ c. A theoretical model including final-state interactions has also been developed. Strong final-state interactions prohibit a direct extraction of the relative proton-triton bound-state wave function. Nevertheless, we are able to conclude that the wave function remains positive for relative proton-triton momenta up to at least 0.6 GeV/ c. This result questions the relevance of wave functions derived from the helium electromagnetic form factor.

Pion Charge Exchange on Tritium

Measurements of the differential cross section for pion charge exchange on /sup 3/H have been carried out at incident pion momenta of 232 and 252 MeV/c. The results are compared with several theoretical predictions and also with charge-independence bounds determined from elastic-scattering cross sections obtained in the same experiment.

Reaction π−p → π0n in the 15–40 GeV/c momentum range

A high statistics measurement of the reaction π −p → π 0n has been performed at the Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/ c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. More than 3 million charge-exchange events have been recorded in total. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small | t|, as exponentials with the same slopes to within a few percent. Also the behaviour of the differential cross section for small and medium | t| agrees with the prediction of a geometrical s-channel model which describes binary reactions in terms of a complex pole b 0( s). The imaginary part of this universal pole, Im b 0( s), has been determined and found to be growing logarithmically with s.

Reaction π−p→ ηn in the 15 to 40 GeV/ c momentum range

A high-statistics measurement of the reaction π −p→ ηn; η→2 γ has been performed at the 70 GeV Serpukhov accelerator for 15, 20, 25, 30 and 40 GeV/ c incident pion momentum using the NICE set-up with its associated 648-channel hodoscope spectrometer for γ-ray detection. It is found that the spin-flip and non-spin-flip amplitudes can be parametrized, for small | t|, as exponentials with the same slopes to within a few percent. For | t| ≳ 1 (GeV/ c) 2 there is a break in the differential cross section. In addition, the A 2 effective trajectory deviates markedly for | t| ≳ 1 GeV/ c) 2 from the linear behaviour valid for smaller | t|.

Average charged-particle multiplicities inπ−pinclusive reactions at 147 GeV/c

The experimentally determined average charged-particle multiplicities, , of the systems, X, produced in the following reactions for 147 GeV/c incident pion momentum are presented as functions of the square of the invariant mass of X, M/sub x//sup 2/, and of *t*: ..pi../sup -/p ..-->.. ..pi../sup -//sub fast/X, ..pi../sup -/p ..-->.. pX, ..pi../sup -/p ..-->.. ..delta../sup + +/X, ..pi../sup -/p ..-->.. (..pi../sup -/..pi../sup +/)/sub rho//sup 0/X, and ..pi../sup -/p ..-->.. ..lambda../sup 0/X. Details of the analysis are discussed. These data can be fit by the expression = A + BlnM/sub X//sup 2/ + C*t* and the coefficients obtained for B are equal within their uncertainties. C is significantly different from zero only for ..pi../sup -/p ..-->.. ..pi../sup -//sub fast/X.

Generalized quark-line rule inSU 4 symmetry scheme

Recently, APEL et at. (1) have reported the observation of the cross-section for ~-p-+~on at 40 GeV/o incident pion momentum. CESTE~ e t a l . (2) have measured ~ ~ + D T * B o cross-section near the threshold 10.5GeV/c through carbon target. Pluto collaboration (s) has informed the observation of J/~ radiative decay into fo(I270)y. This is considered as an additional example of the two-body photonie decays of vector-tensor case, supplementing the known two-gamma cascade ~(3684)-~ -~ xT(a550)y-~ J / ~ V ('). 0KUBO (~) has discussed repeatedly the quark-line (known as 0kubo-Z~ceig-Iizuka) rule (QLR) (6) in a great detail by generalizing the original idea. The recent experimental works stated at the first paragraph and relevant problems will give a further insight to disclose the content of the QLR. The present author thinks that the study of hadron interactions under the assumption of strict QLR will give an important guido for constructing the future theory of hadron dynamics (D. The purpose of this paper is to generalize the quark-line in the form of 0kubo to SU, symmetry scheme and to analyse the consequences from that point of view.

Study of the reactionπ−p→K0Y*at 8.0, 10.7, and 15.7 GeV/c

We present differential and total cross sections for the reactions ..pi../sup -/p ..-->.. K/sup 0/(..sigma.. (1385)/..lambda.. (1405)) and ..pi../sup -/p ..-->.. K/sup 0/..lambda.. (1520) at incident pion momenta of 8.0, 10.7, and 15.7 GeV/c. Pions from the decay of the forward K/sup 0//sub S/'s were detected in the forward leg of the BNL double-vee spectrometer and the recoil Y*'s were identified by the missing-mass technique.