J. Pernegr

Evidence for resonance behaviour of A1 and A3 mesons coherently produced on nuclei

Abstract An analysis of about 60 000 events produced in the reaction π − A → ( π + π − π − )A on nine different nuclear targets A at 8.9, 12.9, and 15.1 GeV/ c has been performed using the Illinois PWA program. In the A 1 region our “coherent” sample of events (which contains about 11% of incoherently produced events) is described by only four partial waves: the 1 + S and 1 + P amplitudes, which both show a peak, and the O − S and O − P waves, which are rather constant. We observed variations of both 1 + S and 1 + P phases relative to the O − P phase by about 90° across the A 1 peak. This observation suggests the presence of resonant 1 + waves in the A 1 mass region (∼1.1 GeV). In the A 3 region we observe that the 2 − state shows resonance behaviour and that fπ and ϱπ are two decays modes with amplitudes of opposite signs.

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.

Evidence that absorption in the π+ π− π− system in nuclear matter is stronger in the JP = 0− than in the JP = 1+ state☆

Abstract In the reaction π− + A → π+ π− π− + A at 15.1 GeV/c the coherently produced 3π mass spectrum has a broad peak around 1.1 GeV which consists mainly of a JP = 1+ state and of a smaller fraction of 0-. Comparing the observed dependence of the production of these diffractive states on the atomic weight A of the target nuclei with the optical model, we have studied the absorption of the produced states in nuclear matter. We have found the following values of the absorption cross-sections: σ2(0-) = 49−7+9 mb and σ2(1+) = 15.8−1.3+1.5 mb.

A Partial Wave Analysis of the (

Abstract A partial wave analysis of the non-diffractively produced ( K 0 π + π - system has been performed. The system was produced in the reaction K - p→ K 0 π + π - n at 10 GeV/c, measured in the CERN Omega spectrometer. Besides the well-known K∗(1420) resonance, we find good evidence for the production of Q2(1400) and some indication for Q1(1290) production in JP=1+. In addition we clearly observe a bump in the 1800 MeV region, the properties of which are discussed.

\bar{K}0 \pi^+ \pi^-

Abstract A partial wave analysis of the non-diffractively produced ( K 0 π + π - system has been performed. The system was produced in the reaction K - p→ K 0 π + π - n at 10 GeV/c, measured in the CERN Omega spectrometer. Besides the well-known K∗(1420) resonance, we find good evidence for the production of Q2(1400) and some indication for Q1(1290) production in JP=1+. In addition we clearly observe a bump in the 1800 MeV region, the properties of which are discussed.

) System Produced in

Abstract A partial wave analysis of the non-diffractively produced ( K 0 π + π - system has been performed. The system was produced in the reaction K - p→ K 0 π + π - n at 10 GeV/c, measured in the CERN Omega spectrometer. Besides the well-known K∗(1420) resonance, we find good evidence for the production of Q2(1400) and some indication for Q1(1290) production in JP=1+. In addition we clearly observe a bump in the 1800 MeV region, the properties of which are discussed.