P. L. Frabetti

The (3π)-nucleon collision in coherent production on nuclei at 40 GeV/c

Abstract Coherent 3 π production on nine different nuclear targets has been studied using a 40 GeV/ c π − beam at the Serpukhov accelerator (CERN-Serpukhov experiment no. 5). The absorption in nuclear matter of the produced system has been measured, analysing the data on the different nuclear targets. Identica results are obtained from the differential cross sections and from the coherent nuclear cross sections. The 1 + waves show a very weak absorption, definitely smaller than 0 − and 2 − waves. No influence on the absorption comes from the spin-flip amplitudes, which have been found to be negligible in the coherent region.

Nuclear targets as a powerful tool in selecting resonant states

SummaryThe 0-S and 1+S waves have been analysed studying the coherent production ofπ−π−π+ states at 25 and 40 GeV/c with nine different nuclear targets. The absorption in nuclear matter of the meson systems, produced within the nucleus, helps in disentangling the resonant states from the nonresonant background. It was so possible to analyse the A1 resonance with a reduced Deck background and to obtain evidence of two new 0-S resonant states, which can be interpreted as the first and the second radial excitations of the pion.RiassuntoIl comportamento delle onde 0-S e 1+S è stato analizzato, studiando la produzione coerente su nucleo di sistemiπ−π−π+. L’esperienza ha avuto luogo all’acceleratore di Serpukov, a 25 e 40 GeV di energia incidente, utilizzando nove diversi bersagli nucleari. L’assorbimento nella materia nucleare dei sistemi mesonici prodotti nel nucleo favorisce i contributi risonanti rispetto al fondo non risonante. In tal modo è stato possibile analizzare la risonanza A1 con un fondo risonante molto ridotto e ottenere evidenza di due nuovi stati risonanti 0-S, che possono essere interpretati come la prima e la seconda eccitazione radiale del pione.РезюмеПроводится анализ 0−S и 1+S волн, исследуя когерентное рождениеπ−π−π+ состояний при 25 и 40 ГэВ/с на девяти различных ядерных мишенях. Поглощение в ядерном веществе мезонных систем, образованных внутри ядер, отдает предпочтение резонансным вкладам по сравнению с нерезонансным фоном. Такой подход позволяет провести анализ A1 резонанса и получить подтверждение двух новых 0−S резонансных состояний, которые могут быть интерпретированы, как первое и второе радиальные возбуждения пиона.

Multiplicity of charged particles π− interactions on nuclei at 40 GeV/c

Multiparticle production in π−-nucleus interactions at 40 GeV/c (Fifth Joint CERN-Serpukhov Experiment) has been studied using a spark-chamber technique at the Serpukhov accelerator. The mean multiplicities, the pseudorapidity distributions and the dispersion of the multiplicity distributions of charged particles produced on C, Al, Cu and Pb targets are presented. The data have been analysed, both subtracting and including secondary protons with p 3.4 the average multiplicity is nearly independent of the size (ν) of the target nucleus, while it increases for η 4) the mean multiplicity on nuclei is smaller than the mean multiplicity on hydrogen. The dependence upon ν in the target fragmentation region is stronger when the emitted protons are included in the pseudorapidity distributions of the secondary particles. The dispersion of the multiplicity distributions for the different nuclear targets versus the mean multiplicity shows the same slope as found by the world statistics on hydrogen and by other experiments on nuclei at different energies. The results are compared with the predictions of the coherent tube model and with the soft hadron-nucleus collision model.

Semicoherent elastic pion-carbon scattering at 25 and 40 GeV/c

Abstract In the frame of a systematic study of hadron-nucleus interactions performed at the Serpukhov accelerator (CERN-IHEP 5th experiment), semicoherent elastic scattering on carbon π −12 C a π −12 C ∗ (4.44 MeV ) was investigated with 25 and 40 GeV/c incident pions. The experimental data were obtained with a counter technique, looking at the coincidence between the scattered pion and the 4.44 MeV photon from the JP = 2+ carbon excited state detected by a NaI counter. The value obtained for the integrated cross section at 40 GeV/c in the 0.0032 ⩽ |t| ⩽ 0.27 (GeV/c)2 four-momentum transfer range is σ = 1.16 ± 0.11 mb. According to the theoretical models, this t-range at 40 GeV/c covers more than 99% of the angular distribution, so the above value almost corresponds to the total semicoherent elastic cross section.

Coherent production of 3π states at 25 GeV/c

SummaryThe coherent production of π−π−π+ states has been studied at 25.7 GeV incident energy with an Al target. The partial-wave analysis of the data confirms the evidence of aIGJPL=1−0−S resonant state in the mass region near to 1.2 GeV, already found by our collaboration at 40 GeV incident energy.

Identification of decay positrons in a high-intensity high-energy muon beam

Abstract Positrons from muon decay in the M2 beam line at the CERN SPS have been identified using a 34 r.l. lead-glass detector operated in coincidence with a synchrotron radiation tag.

Study of backward-produced protons in π−-nucleus interactions at 40 GeV/c

SummaryThe backward production of protons in the reaction π−A → p↓X is studied at 40 GeV incident energy with the different nuclear targets : C, Cu, Pb. The structure function shows a slope independent of the target atomic weightA and slightly dependent on the proton production angle. The invariant cross-section, normalized to the nucleon, increases withA up to a plateau which varies with the incident energy. Finally the ratiosR = (FA/A)/(FC/AC) andn = ln(FA/FC)/ln(A/AC), whereF = (E/p2)(d2σ/(dp dΩ)), show a flat dependence on the momentum of the proton backward produced. These results are in favour of few-nucleon correlation models.

Study of the structure of hadronic and electromagnetic showers with a segmented iron-scintillator calorimeter

Abstract The lateral development of hadronic and electromagnetic showers has been measured in an iron-scintillator calorimeter equipped with 2 cm wide hodoscopes at 20, 40 and 86 GeV c −1 .

Measurement of the π- absorption length in iron between 15 and 140 GeV/c

The interaction length of a particle can be measured directly by studying the attenuat ion of a particle beam in a material. The number of particles which have not interacted after a depth z of absorber is given by .N(z) = .N0 exp [-z/k], .N o being the incoming flux. In an unseparated negative high-energy beam, pions predominate, and the number of particles which have not suffered an interaction is given by

The total cross section of (5π)-nucleon collision

Coherent 5π production on nine nuclear targets has been studied at 40 GeV incident energy at the Serpukhov accelerator (CERN-Serpukhov experiment No. 5). The collision cross section of the 5π system on the nucleon has been determined in the frame of the Kolbig-Margolis-Glauber model; its value, <10 mb, is definitely lower than the (3π)-nucleon cross section at the same energy.