B.C. Maglić

Evidence for a two-peak structure in the A2 meson

Abstract The missing-mass spectrum of the A 2 meson [ M = 1297 ± 16 MeV, Γ = 95 ± 15 MeV] obtained in the reaction π − p → pX − in three independent runs at 6 and 7 GeV/ c shows a narrow dip of 6 standard deviations in the centre of the A 2 peak at 1297 MeV, thus suggesting a two-peak structure.

Structure within the R(1675) boson and possible structure within the A2(1290)

Abstract Three narrow peaks with masses 1632 ± 15, 1700 ± 15 and 1748 ± 15, reffered to as R1, R2 and R3, have been observed in missing-mass spectrometer runs at incident pion momenta of 7 and 12 GeV/c and a mass-resolution of ± 15 MeV. One-peak hypothesis gives a confidence level P(χ2)=0.8%; the three-peak one gives P(χ2)=60%. Statistical significance for R1, R2 and R3 is, respectively, 3.8, 6.6 and 6.1 standard deviations from the highest background line. R1 and R2 decay into one and three, while the R3 decays mainly into three charged particles. Their physical widths are compatible with zero, with upper limits of the order of Γ ⩽30 MeV. An apparent two-peak structure is observed within the A2(1286) peak, with the mass-values 1260 and 1312 MeV, at incident pion momenta of 6 and 7 GeV/c. The one-peak and two-peak hypotheses give the same confidence level P(χ2) = 5%.

Experimental confirmation of R-meson structure

Abstract Experimental confirmation of the structure in the region of the R(1700) meson, in the reaction π − + p → p + R − reported earlier at incident pion momenta of 7 and 12 GeV/ c , has been obtained at 11.5 GeV/ c with the missing-mass spectrometer. The peaks R 1 (1630), R 2 (1700) and R 3 (1748) have been observed; in addition a peak at 1830 ± 15 MeV, reported by the CERN-Liverpool bubble chamber group, is indicated. Speculative comparison of our peaks and bubble chamber data with the L -excitation quark-antiquark model predictions gives a suggestive agreement in both mass separations and G -parities; however, we cannot exclude this as being coincidence.

Observation of charged ρ-meson and its properties using a missing-mass spectrometer

SummaryPresented is the mass spectrum of charged bosons in the mass region (650÷850) MeV, obtained with a missing-mass spectrometer (MMS) operating on the principle of « Jacobian peaks in angular distribution » (1). The unstable bosons, x−, are produced in reaction π−+p → p+x− at incident momentap1=(3.0±0.1), (3.5±0.1), (4.5±0.045) and (5.05±0.05) GeV/c.RiassuntoSi presenta lo spettro delle masse dei bosoni carichi nella regione di masse (650 ÷ 850) MeV, ottenuto con uno spettrometro a difetto di massa (MMS) funzionante sul principio dei « picchi Jacobiani nelle distribuzioni angolari ». Si producono bosoni instabili, x−, nella reazione π−+p → p+x− ad impulsi incidentip1=(3.0±0.1), (3.5±0.1), (4.5±0.045) e (5.50±0.05) GeV/c.

Empirical one-to-one correspondence between the mass spectra of bosons and nucleon isobars

SummaryMasses of heavy bosons and «subtracted masses», of nucleon isobarsm*=MN*-Mnucleon, are clustered around the same values: for each of 13 established bosons there is anN* whose «subtracted mass» is within 3% equal to the boson mass andvice versa. There are no bosons in the middle region between two clusters, which are regularly (230±35) MeV apart. Combined spin parities of the bosons whose quantum numbers are certain (ν, θ, ω, Fo and A2) with that of the nucleon inl=1 state given the known spin parities of their nearestN*s. The observed «boson-isobar correspondence» suggests a physical picture of theN*s as either composite states (resonances or bound states) of nucleons and heavy bosons, or as heavy boson «threshold effects».RiassuntoLe masse dei bosoni pesanti e le «masse sottratte» dei nucleoni isobarici,m*=MN*-Mnucleone, sono raggruppate attorno agli stessi valori; per ognuno dei 13 bosoni accertati cè unN* la cui «massa sottratta», è, entro il 3%, uguale alla massa del bosone e viceversa. Non ci sono bosoni nella regione intermedia fra i due raggruppamenti, che sono regolarmente distanti (230±35) MeV. Le spin-parità dei bosoni i cui numeri quantici sono sicuri (η, ρ, ω, Fo e A2) combinate con quella del nucleone nello statol=1 danno le note spin-parità del più vicinoN*. La «corrispondenza bosone-isobaro» osservata suggerisce unimmagine fisica deiN* o come stati composti (risonanze o stati legati) dei nucleoni e dei bosoni pesanti, o come «effetti di soglia» dei bosoni pesanti.

Slope of differential cross section for inelastic processes at 12 GeV/c π−p interaction

The dependence on t of dσ/dt is studied for the processes π−p→ pMM− at 12 GeV/c and 0.26 < |t| < 0.37 (GeV/c)2.