Search

We present results from a high momentum resolution measurement of the π − p elastic differential cross section near the η production threshold. By analysing the cusp discontinuity in the elastic cross section we deduce the non-spin-flip elastic amplitude and compare it with solutions from phase-shift analyses.

We have measured inclusive cross sections for the reaction $\mathrm{pd}\ensuremath{\rightarrow}\mathrm{pX}$ in the region $0.15l|t|l0.39$ Ge${\mathrm{V}}^{2}$, $100lsl750$ Ge${\mathrm{V}}^{2}$ and $0.80lxl0.92$ using the acceleration ramp and deuterium-gas jet target at Fermilab. These measurements are combined with our earlier measurements of $\mathrm{pp}\ensuremath{\rightarrow}\mathrm{pX}$ to obtain inclusive cross sections for $\mathrm{pn}\ensuremath{\rightarrow}\mathrm{pX}$.

We have investigated ..omega.. production in the reaction ..pi../sup -/p ..-->.. ..omega..n very close to threshold. The dependence of the mass, width, branching ratio, and cross section upon the final-state c.m. momentum, P*, were studied. The mass and width were independent of P* with values of 782.4 +- 0.5 and 10.22 +- 0.43 MeV, respectively. The branching ratio GAMMA(..omega.. ..-->.. ..pi../sup 0/..gamma..)/GAMMA(..omega.. ..-->.. ..pi../sup +/..pi../sup -/..pi../sup 0/) was also constant, having a value of 0.084 +- 0.013. An upper limit of 0.18 was set on the branching ratio GAMMA(..omega.. ..-->.. ..pi../sup 0/..pi../sup 0/..gamma..)/GAMMA(..omega.. ..-->.. ..pi../sup 0/..gamma..). We observed a rapid fall in the cross section below P* = 100 MeV/c. This could not be explained in terms of S-wave production alone, but could be fitted by a resonant P wave plus a noninterfering S wave. (AIP)

We fitted the X0 production cross-section data using a N* modulation to introduce a rise in the cross-section at lowp *. The fit leads to several solutions, the best one being that having values for the parameters describing the Breit-Wigner resonance(E 0,Гel, Г0) = (1889.3, 1.3 -0.7 +5.8 , 1.2 -0.9 +9.2 ) MeV. Therefore, one can explain the behaviour of the X0 production cross-section in 7π~p scattering as being due to a narrow N* with mass near 1890 MeV and width ~ 2 MeV.

In a high-resolution missing mass experiment the total width of the η′ (958) meson has been measured to be 0.28 ± 0.10 MeV. Using the known γγ branching ratio the value Γ ( η ′ → γγ ) = 5.4 ± 2.1 keV is deduced. This is in good agreement with calculations based on fractional charge quarks and a pseudo-scalar mixing angle of 11°.

We present results from a high-momentum-resolution measurement of the π-p elastic differential and total cross-sections-at values of cos θ* between — 0.60 and 0.85 in the centre-of-mass system and at incident-beam momenta between 1.34GeV/c and 1.49 GeV/c—close to the X0 production threshold. There is no significant enhancement near the X0 production threshold. However, a small effect of ~ 3 standard deviations is present, having mass 1898.8 MeV and width ~5MeV, and appearing at an incident-pion momentum of 1435 MeV/c. In addition, a narrow ~ 5-standard-deviation effect atEc.m.= 1876 MeV appeared at an incident-pion momentum of 1389 MeV/c.

We report observation of the S* meson in the reaction π−+p→S*+n. The S* decays into ππ and KK and is seen most clearly in the 2π0 channel. A fit to the data gives a sheet-II pole at 987±7−i(24±7) MeV and a relative coupling gS→KKgS→ππ of 3.8 ± 1.0.

The mass spectrum of the A2 meson has been studied in the reaction π−+p → A2−+p, A2− → π − + neutrals near threshold. In contrast to our previous study of the channel A 2 →π + π − π − there is some evidence for structure within the resonance.

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.

We have measured the s, t and x dependence of the invariant cross section for the inclusive reaction p + p ⇒ p + X in the region 108

The meson mass spectrum near the X 0 (958) has been studied in the reaction π − + p → missing mass + n near threshold. A single peak, consistent with the X 0 , is seen. The mass obtained is 957.1 ± 0.45 MeV and the width is less than 1.9 MeV(95% C.L.).

The meson spectrum near the η′(958) is studied in the reaction π−p ⇒ nXo near threshold. Only the η′ is seen. A mass of 957.1 ± .45 MeV and a width < 1.9 MeV (95% CL) is found.

We have measured the s, t and x dependence of the invariant cross section for the inclusive reaction p + p ⇒ p + X in the region 108

A simple counter experiment is proposed to investigate the s and s/M{sup 2} dependence of the invariant cross section for the single particle inclusive reactions pp {yields} pX and pp {yields} nX in a limited region of phase space. 4 < s/M{sup 2} < 20, 40 < s < s{sub max}, 0.1 < |t| < 0.6 near the kinematic limit. The neutron reaction will be studied directly, using a hydrogen jet, and also by measuring the difference between pp {yields} pX and pD {yields} pX using a deuterium jet. The latter will provide information on the line reversed reaction pn {yields} pX. The proposed experiment will use the internal target and aims to provide information on specific theoretical issues in a very short time interval. These issues are: (1) relatively importance of PPP and PPR couplings in the triple Regge framework; and (2) diffractive versus triple Regge approaches to the understanding of single particle inclusive reactions.