Elastic scattering of antiprotons on protons at 5 GeV/c evidence for a backward peak

Antiproton-proton elastic scattering has been measured at 5 GeV/c. A total of 30 000 events were observed in the angular range 17° < θ_cm < 136°, corresponding to 0.3 < −t < 7.7 (GeV/c²). In addition to the known dip at −t = 0.5 (GeV/c)², we observe a structure at about −t = 2 (GeV/c)² and a backward peak with a slope4.1 ± 0.6 (GeV/c)². The extrapolated differential cross-section at u = 0 is 1.3 ± 0.8 μb/(GeV/c)².     

Polarized target asymmetry for pi-zero photoproduction at 4 GeV

The polarized target asymmetry parameter has been measured for single π^o photoproduction from hydrogen at 4 GeV and values of four-momentum transfer squared between −0.15 (GeV/c)² and −1.8 (GeV/c)².     

Measurement of Large-angle πp elastic scattering at 5 GeV/c

The differential cross-section for 5 GeV/cπ⁺p and π⁻p elastic scattering have been measured in the c.m. angular region 27° < θ_cm < 130° corresponding to 0.5 < |t| < 7.8 (GeV/c)². Dips are observed in both reactions at −t = 2.8 and 4.8 (GeV/c)² where the cross-sections are approximately 0.1 μb/(GeV/c)².     

The behaviour in terms of angular variables of the inclusive reactions Kp → KX and Kp → KπX at 5.0 and 8.2 GeV/c

The inclusive reactions K⁺p → K⁰ + X⁺⁺ at 5.0 and 8.2 GeV/c and K⁺p → K⁰ + π⁺ + X⁺ at 8.2 GeV/c are analysed in terms of angular variables θ and ø. The data are compared and found consistent with various theoretical bounds on the s-dependence of the inclusive reaction cross sections. Experimental evidence is presented that dσ/dcos θ = a exp (−b sinθ) with b ∼ √s and a increasing with energy. Correlations between the angular variables and between the variable ø and the K⁰ and π⁺ momenta in the c.m.s. are observed and discussed.     

Measurement of the polarization in the forward peak of π−p→K0λ at 5 GeV/c

The π^?p→K⁰λ polarization has been measured at 5 GeV/c in the range 0<?t<1.4 (GeV/c)². The polarization is small for ?t?0.4 (GeV/c)², becoming negative at the higher values of ?t.     

Missing-mass spectra observed in π + p → p + X at 25 and 40 GeV/c

Missing-mass spectra were obtained in the reaction π⁻p → p X⁻ at 25 and 40 GeV/c at the Serpukhov Accelerator. At low masses a strong peak at 1.3 and a smaller one near 1.7 GeV are observed. In the mass region above 2 GeV no structure exceeding 3μb/(geV/c² is seen.     

Spin dependence of inclusive reactions from proton-proton collisions at 7.9 GeV/c

The spin dependence of inclusive proton and pion production by 7.9 GeV/c protons has been measured using a polarized proton target, for nominal values of x = p_L^cm/p_max^cm = 0.7 in the transverse momentum range 0.4 GeV/c <pp_t < 1.2 GeV/c, and for p_t = 0.4 GeV/c in the range 0.1 < x < 0.96. The results indicate a positive asymmetry of +5% over this kinematic region, which corresponds to fragmentation of the unpolarized proton.     

Antiproton-proton elastic scattering at 6.2 GeV/c

Antiproton-proton elastic scattering data at 6.2 GeV/c in the range 0.3 (GeV/c)² ? ?t ? 10.0 (GeV/c)² is presented. The experiment, using spark chambers and proportional chambers, was performed at the CERN Proton Synchroton.The dip at about ?t = 0.5 and the structure at about ?t = 2.2 (GeV/c)² are equally strong at 6.2 GeV/c as they are at 5.0 GeV/c. The differential cross sections around 90° c.m. are not very different at 5.0 GeV/c and at 6.2 GeV/c, whereas in the backward region there is a decrease of the order of one magnitude.     

K−p elastic scattering at 14.3 GeV/c

Results are presented of a bubble chamber experiment on K^?p elastic scattering at 14.3 GeV/c, in four-momentum transfer range 0.04 < |t| < 2.74 GeV² using an initial set of 40 000 events. The total elastic cross section is (2.96 ± 0.10) mb. The results are compared with K⁺p elastic scattering data at 13.8 GeV/c, and the effective Regge trajectory is calculated using K^?p data from 5 to 100 GeV/c.     

Measurement of np elastic scattering at high energies and very small momentum transfers

The np elastic differential cross section has been measured for incident neutron momenta 100–400 GeV/c in the |t| range 6 · 10^?6 ? 5 · 10^?1 (GeV/c)². The np data of this experiment provide a first direct measurement of the hadronic amplitude for |t| < 10^?2 (GeV/c)², which is consistent with the extrapolations from higher |t| values. Our data for |t| < 10^?4 (GeV/c)² are consistent with a rise which can be attributed to Schwinger scattering, caused by the interaction of the neutron magnetic moment with the proton.     

A measurement of direct photon production at large pT at the CERN ISR

We have measured direct photon production in pp collisions at the CERN intersecting storage rings for c.m. energies 31 < √s < 63 GeV and transverse momenta up to 9GeV/c, using segmented lead/liquid-argon calorimeters. The ratio of direct photon to π⁰ production is significantly larger than zero, starting at p_T ≈ 4 GeV/c and increasing to values of about 0.4 at 9GeV/c. No significant √s dependence is seen.     

A new study of Kπ scattering between 0.7 and 2 GeV/c2

We present new data on the reaction K⁺d → K⁺π^?p(p), at 5.44 GeV/c. This reaction is dominated by absorbed pion exchange and we have used the data to study K⁺π^? scattering between 0.7 and 2 GeV/c². We find the $\text{I=}\text{1}\text{2}$ s-wave Kπ phase shift increases approximately linearly with mass up to 1.45 GeV/c², and have evidence for a more rapid variation of the s-wave amplitude in the region of 1.5 GeV/c². The so-called “up” branches in the region of the K¹(890) and K¹(1400) are excluded, save for the possibility of narrow s-wave resonances of width <10 MeV/c². We have explained quantitatively every aspect of the data up to 2 GeV/c² with s-, p-, d- and f-waves, finding an f-wave resonance at a mass of ≈1.76 GeV/c² and with a width ≈300 MeV/c². We have obtained new resonance parameters for the K¹(1400) which differ substantially from the currently accepted values.     

K−p and pp elastic scattering at 10.1 GeV/c

The differential cross sections for K^?p and $\text{p}$p elastic scattering have been measured over the range of four-momentum transfer squared 0.18<?t<3.3 (GeV/c)². The K^?p data decrease smoothly as a function of ?t, whereas, the $\text{p}\text{p}$ data shows a break at ?t = 0.6 (GeV/c)² followed by a fast drop to ?t ? 1.6 (GeV/c)² where the differential cross section levels off and stays constant out to ?t = 3 (GeV/c)².     

Elastic backward scattering of negative pions on neutrons at 23 and 40 GeV/c

The differential cross sections of the elastic backward scattering reaction π⁻n→nπ⁻ has been measured at 23 and 40 GeV/c in the u-interval −0.07 ? u ? 0.01 (GeV/c)².     

Spin dependence of the inclusive reaction p + p (polarized) → π0 + X at 24 GeV/c for high-pTπ0 produced in the central region

The spin dependence of π⁰ inclusive production by 24 GeV/c protons has been measured using a polarized target for Fhe Feynman x near 0 in the transverse momentum range 1.0 < p_T < 2.5 GeV/c. The results indicate a negative updown asymmetry growing strongly with p_T and greater than 50% in absolute value for p_T greater than 2 GeV/c.     

Missing mass analysis of the A−2 at 6.0 GeV/c

The missing mass spectrum in the region of the A^?₂ has been measured in the reaction π^?p→X^?p at 6.0 GeV/c in the interval 0.27 <|t|<0.42 (GeV/c)², with an optical spark chamber system which simultaneously observed the decay X^?→ηπ^?. A signal of 230 events above background per five MeV interval is observed at the A₂ peak, with a signal-to-background ratio of greater than 1:1. A single D-wave Breit-Wigner distribution with a quadratic background gives a good fit to the data, yielding the parameters M₀=(1.324±0.003) GeV/c² and Γ₀=(0.104±0.009) GeV/c². The spectrum is incompatible with a dipole shape.     

An amplitude analysis of ππ scattering from new data on the reaction π−p→π+π−n

We have carried out a partial-wave analysis of ππ scattering in the mass range 1.0 to 2.08 GeV/c². We find solutions similar to those obtained in previous analyses below 1.8 GeV/c² but, in addition, we obtain a new solution which does not suffer from violations of unitarity and is compatible with data from other channels. This solution, when continued to 2.08 GeV/c², shows a g meson with mass and width of 1.734± 0.010 GeV/c²and 0.322±0.035 GeV/c² respectively, and an h meson with mass 1.935±0.013 GeV/c²and width 0.263±0.057 GeV/c². The L = 2 partial wave contains the f meson and an additional resonance with parameters m = 1.502±0.025 Gev/c², Γ = 0.165±0.042 GeV/c²and x = 0.19±0.03. If we associate this state with the f′(1514), our ππ branching fraction is considerably higher than previous determinations. An SU(3) fit to the 2⁺ nonet yields a mixing angle of 38.4± 1.3°.     

Measurement of K production in the reaction Kp → Kp

The K^∗− spectrum in the reaction K⁻+p → K^∗−+p has been measured at beam momenta 10.9, 13.4 and 15.9 GeV/c using the missing mass technique. Production of the L(1770), and a Q-K^∗(1420) enhancement are observed. Differential cross sections in the range of momentum transfer 0.12 < | t_pp | < 0.40 (GeV/c)² are given. The L meson is observed with a width Γ = 100 ± 26 MeV. The mass spectrum between the L and 2.5 GeV does not show significant structure.     

Nuclear mass number dependence of inclusive pion production by pions and protons at 4.3GeV/c

The inclusive production of π⁺ for 0.4≤p_T<1.0 GeV/c in pion-nucleus and proton-nucleus collisions at 4.3 GeV/c was measured. A strong A-dependence of the cross sections at high p_T is observed to be persistent in the low energy region. The ratio of the cross sections for proton-nucleus and pion-nucleus collisions is also observed to be compatible with the quark-parton picture, for p_T>0.6 GeV/c.     

Study of Δ production in the reaction πp→ππp at 13.1 GeV/c

We have measured the production and decay angular distributions of the reaction π⁺p→π^OΔ⁺⁺ at 13.1 GeV/c incident momentum. For −t > 0.1 (GeV/c)² the data is well described by M1 ?-exchange models, the best results being obtained from a weak cut model with a wrong signature nonsense zero. For −t < 0.1 (GeV/c)² there is evidence for the existence of other exchange mechanisms.