H. K. Nguyen

Backward production in π−p→pfπ+π−π− on at 9 and 12 GeV/c

We have analyzed backward meson production in the reaction π−p → pfπ+π−π− at 9 GeV/c and 12 GeV/c incident π− momenta, from an experiment performed at the CERN Ω Spectrometer using a fast proton (pf) trigger device. We find strong production of quasi-two-body processes N∗ϱ and N∗f with a production mechanism consistent with u-channel nucleon exchange. At a lower level, we observe N∗π processes with a 3-body baryon decay through Δ(1232)π. In the (3π)− system, we find evidence for A1− and clear A2− backward production with similar cross sections (≈0.5 μb).

Further results on the narrow pp̄ resonances at 2020 and 2204 MeV

Abstract An unsuccessful search has been made for the reaction π − p → p F p n to find an M− state in pn corresponding to the M0 (2020) and M0 (2204) found earlier in the baryon exchange process π−p → Δ0 (or N0 (1520)) + M0. From this negative result, it is concluded that the previous reaction proceeds mainly by nucleon exchange and it is suggested that the NN coupling for the M0 is more important than the ΔN coupling. Some indications are also given for the NN mode as the main decay mode for these M0 states.

Backward enhancement in the A1 region and A2 production in the reaction π-p→pfπ+π-π- at 9 and 12 GeV/c

Abstract Results on backward (3 π ) - system produced in π - p→p f π + π - π - reaction at 9 and 12 GeV/ c are given. The ϱ 0 π - mass spectra show two clear signals at 1050 MeV (A 1 region) and 1303 MeV (A - 2 ). The width of the enhancement in the A 1 region (195±32 MeV) is narrower than found in diffractive experiments. Total backward cross sections for those signals are of the same order of magnitude (∼0.5 μb).

Is there structure in the f0 mass region

Evidence is presented for structure in the f0-mass region in the reaction π+n→pπ+π− at a pion momentum of 11.7 GeV/c. A detailed analysis indicates that it is most unlikely that the structure is a statistical effect.

Backward ω0 and η0 production in πp interactions at 9 and 12 GeV/c

We have studied the backward production of ω0 mesons in the u-channel Iu = 12 exchange reaction π−p → N0(1680)ω0 at 9 GeV/c and 12 GeV/c incident momenta. The data come from an experiment performed at the CERN Omega Spectrometer using a fast proton trigger device. The backward production of the η0 meson has also been observed and the coupling constant ratio gηNN/gπNN has been estimated.

Impact parameter analysis of the reaction π−p→pπ+π−π− at 9 and 12 GeV/c with very fast secondary proton

The results on the impact parameter for the reactions π−p→pπ+π−π−, pK+K−π−, with a fast secondary forward proton are given at 9 and 12 GeV/c. For the reaction π−p→pπ+π−π− our results corresponding to the small |u| region (|u| < 1 GeV2) are compared to the existing data for the small |t| region. We show that small |u| events are more central than small |t| events.

Backward K∗0 production in the reaction π−p→Λ0K+π− at 9 and 12 GeV/c

Abstract We have analysed about 85 000 fast Λ0 events, obtained in a fast proton triggered experiment performed at the CERN-Ω spectrometer at 9 and 12 GeV/c incident π− beam. Nearly 2500 Λ0K+π− events have been isolated. We find strong production of quasi-two-body processes Λ 0 K ∗0 and ∑ ∗− K + consistent with u-channel hyperon exchange. Results on Λ0 polarization, K∗0 decay parameters and differential cross sections are given for Λ 0 K ∗0 (892) and Λ 0 K ∗0 (1430) final states. A comparison is made with the associated backward Λ 0 (1520) K ∗0 production seen in the four-prong reaction π−p→pK−K+π− obtained in the same experiment.

Backward

CERN OMEGA SPECTROMETER. NUMERICAL VALUES OF DATA ON FIGURES 7 AND 8 SUPPLIED BY A. FERRER.

K^{*0}

SummaryThe two coherent reactions π+d → dπ+π+π− and π+d → → dπ+π+π+π0 are studied in the 2 m DBC at the incoming momentum of 11.7 GeV/c. The production cross-sections are measured:σ=(0.37±±0.06) mb andσ=(0.24±0.05) mb respectively. The two reactions are analysed in the different LPS configurations. The dσ/dt′ distribution for the two reactions displays the same exp[−At′] shape withA⋍37 (GeV/c)−2 in both cases, thus indicating that the differential cross-sections are dominated by the deuteron form factor. The coherent inclastic interaction contains the channel π+d → θ0π+d with a cross-sectionσ==(20±5) µb and a signal for the B+-meson of about 12 µb. The four-pion masses display structures below 2 GeV/c.RiassuntoNella camera a bolle 2 m DBC del CERN esposta ad un fascio di π+ di 11.7 GeV/c si sono studiate le due interazioni coerenti π+d → π+π+π−d e π+d → π+π+π−π0d. Le sezioni d’urto di produzione sono rispettivamenteσ=(0.37±0.06) mb eσ=(0.24±0.05) mb. Si analizzano diversi aspetti dei due canali esclusivi tra cui le diverse configurazioni longitudinali più frequenti. La sezione d’urto differenziale dσ/dt′ presenta la stessa forma exp [−At′] con un valoreA⋍37 (GeV/c)−2 per entrambe le reazioni. Ciò implica la dominanza del fattore di forma del deutone su entrambi i processi in esame. La reazione coerente inelastica contiene un contributoσ=(20±5) µb del canale π+d → θ0π+d nel quale il segnale del mesone B+ è di circa 12 µb. Le masse effettive di quattro pioni mostrano strutture tipiche e significative perM∼2 GeV.РеэюмеИсследуются две когерентных реакции π+d → dπ+π−π+ и π+d → dπ+π−π+π0 в 2 м дейтериевой пуэырьковой камере при импульсе падающих частиц 11.7 ГзВ/с. Иэмеренные поперечные сечения рождения соответственно составляютσ=(0.37±±0.06))μб иσ=(0.24±0.05)μб. Исследуемые две реакции аналиэируются в раэли-чных LРS конфигурациях. Распределение dσ/dt′ для двух реакций обнаруживают ту же форму ехр [−At′] сA=37 (ГзВ/с)−2 в обоих случаях. Этот реэультат укаэы-вает, что дифференциальные поперечные сечения доминируют эа счет форм-фактора дейтрона. Когерентное неупругое вэаимодействие содержит канал π+d → ω0π+d с поперечным сечениемσ=(20±5)μб и сигнал для меэона В+ с величиной около 12μб. Эффективные массы четырех пионов обнаруживают типичную структуру дляM≼2ГзВ.

Production in

SummaryThe two coherent reactions π+d → dπ+π+π− and π+d → → dπ+π+π+π0 are studied in the 2 m DBC at the incoming momentum of 11.7 GeV/c. The production cross-sections are measured:σ=(0.37±±0.06) mb andσ=(0.24±0.05) mb respectively. The two reactions are analysed in the different LPS configurations. The dσ/dt′ distribution for the two reactions displays the same exp[−At′] shape withA⋍37 (GeV/c)−2 in both cases, thus indicating that the differential cross-sections are dominated by the deuteron form factor. The coherent inclastic interaction contains the channel π+d → θ0π+d with a cross-sectionσ==(20±5) µb and a signal for the B+-meson of about 12 µb. The four-pion masses display structures below 2 GeV/c.RiassuntoNella camera a bolle 2 m DBC del CERN esposta ad un fascio di π+ di 11.7 GeV/c si sono studiate le due interazioni coerenti π+d → π+π+π−d e π+d → π+π+π−π0d. Le sezioni d’urto di produzione sono rispettivamenteσ=(0.37±0.06) mb eσ=(0.24±0.05) mb. Si analizzano diversi aspetti dei due canali esclusivi tra cui le diverse configurazioni longitudinali più frequenti. La sezione d’urto differenziale dσ/dt′ presenta la stessa forma exp [−At′] con un valoreA⋍37 (GeV/c)−2 per entrambe le reazioni. Ciò implica la dominanza del fattore di forma del deutone su entrambi i processi in esame. La reazione coerente inelastica contiene un contributoσ=(20±5) µb del canale π+d → θ0π+d nel quale il segnale del mesone B+ è di circa 12 µb. Le masse effettive di quattro pioni mostrano strutture tipiche e significative perM∼2 GeV.РеэюмеИсследуются две когерентных реакции π+d → dπ+π−π+ и π+d → dπ+π−π+π0 в 2 м дейтериевой пуэырьковой камере при импульсе падающих частиц 11.7 ГзВ/с. Иэмеренные поперечные сечения рождения соответственно составляютσ=(0.37±±0.06))μб иσ=(0.24±0.05)μб. Исследуемые две реакции аналиэируются в раэли-чных LРS конфигурациях. Распределение dσ/dt′ для двух реакций обнаруживают ту же форму ехр [−At′] сA=37 (ГзВ/с)−2 в обоих случаях. Этот реэультат укаэы-вает, что дифференциальные поперечные сечения доминируют эа счет форм-фактора дейтрона. Когерентное неупругое вэаимодействие содержит канал π+d → ω0π+d с поперечным сечениемσ=(20±5)μб и сигнал для меэона В+ с величиной около 12μб. Эффективные массы четырех пионов обнаруживают типичную структуру дляM≼2ГзВ.