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Study of narrow mesons near their thresholds

Binnie, D.M. ; Camilleri, L. ; Debenham, N.C. ; et al.
Phys.Rev.D 8 (1973) 2789-2813, 1973.
Inspire Record 93328 DOI 10.17182/hepdata.47579

A novel form of mass spectrometer has been used to measure the masses, widths, and cross sections of the η, ω, X0(958), and φ mesons near their respective thresholds in the reaction π−+p→missingmass+n. The incident momentum is varied in small steps through the threshold while neutrons of a given momentum are detected near zero degrees. The lower limit of the c.m. momentum P* at which measurements have been made ranges from about 50 MeV/c at the φ to about 30 MeV/c at the η. A somewhat low value for the ω mass, 782.3 ± 0.6 MeV, is found. The width of the X0 is < 1.9 MeV (95% confidence level). All four mesons show evidence of S-wave production, with values of σP* of 21.2 ± 1.8, 0.35 ± 0.03, and 0.29 ± 0.06 μb/(MeV/c) for the η, X0, and φ, respectively. A rapid rise in the ω cross section appears to be modified by a final-state interaction. The effect of this rise can probably be seen in some S11 pion-nucleon phase-shift solutions. Evidence is also presented of a sudden drop in the π+π− mass spectrum just above the threshold for the production of a K+K− pair. The paper includes a comprehensive discussion of the method and of the details of the spectrometer.

1 data table
Table 1

CROSS SECTIONS NEAR THRESHOLD.


Further evidence for the decay mode phi ---> eta gamma and measurement of the branching ratio gamma(phi ---> eta gamma)/gamma(phi ---> total)

Basile, M. ; Dalpiaz, P. ; Frabetti, P.L. ; et al.
Nucl.Phys.B 44 (1972) 605-617, 1972.
Inspire Record 75023 DOI 10.17182/hepdata.32854

The reaction π − p → ηφ has been studied at 1.8 GeV/ c incident pion momentum using the Bologna-CERN NBC set-up, in order to investigate the electromagnetic decay mode φ → ηγ . We observed (27 ± 6) events, yielding a branching ratio Γ(φ → ηγ) Γ(φ → total ) = (7.3 ± 1.9)% . The theoretical implications of this result are discussed.

1 data table
Table 1

ASSUMING THE TOTAL PHI CROSS SECTION IS 35 +- 5 MUB, THIS YIELDS THE BRANCHING RATIO OF (7.3 +- 1.9) PCT FOR PHI --> ETA GAMMA.


Phi Production in pi- p Collisions Near Threshold

Courant, H. ; Makdisi, Y.I. ; Marshak, M.L. ; et al.
Phys.Rev.D 16 (1977) 1-6, 1977.
Inspire Record 125080 DOI 10.17182/hepdata.24607

Using a secondary pion beam from the Argonne Zero Gradient Synchrotron we have studied the process π−p→φn in the region of the cross-section enhancement near kinematic threshold. For incident momenta between 1.6 and 2 GeV/c, we have determined production and decay angular distributions and extrapolated total cross sections from a sample of about 160 φ's above background. The production and decay distributions are consistent with isotropy over this entire incident-momentum range. The extrapolated total cross section varies between 19 and 25 μb.

2 data tables
Table 1

Axis error includes +- 16/16 contribution (RES-DEF(RES=PHI,BACK=CORRECTED)).

Table 2

Axis error includes +- 16/16 contribution (RES-DEF(RES=PHI,BACK=CORRECTED)).


Phi-Meson Production in the Reactions pi+- n --> K- K+ n at 6-GeV/c

Cohen, Daniel H. ; Ayres, D.S. ; Diebold, R. ; et al.
Phys.Rev.Lett. 38 (1977) 269, 1977.
Inspire Record 110508 DOI 10.17182/hepdata.21019

A sample of 1200 ϕ mesons produced in the Zweig-rule-forbidden reactions π±N→ϕN shows a flat t distribution (slope=1.7 ± 0.2 GeV−2) and a cross section suppressed by 0.0032±0.0004 relative to π−p→ωn. Natural-parity-exchange ω and ϕ production have similar t dependences, while ω and ϕ production by unnatural-parity exchange differ markedly. Interference between the ϕ and the underlying K¯K S wave indicates substantial nucleon-spin incoherence between the amplitudes for ϕ and S-wave production.

3 data tables
Table 1

Axis error includes +- 10/10 contribution (RES-DEF(RES=PHI,BACK=CORRECTED)).

Table 2

Axis error includes +- 10/10 contribution (RES-DEF(RES=PHI,BACK=CORRECTED)).

Table 3

STATISTICAL ERRORS ONLY.