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.     

A spark chamber measurement of the reactions π + p → ϱ + p at 15 GeV/c

A new method, using spark chambers, for the study of the reactions π^± + p → ?^± + p is described. The charged pion and both γ rays from the π^± decay are detected. Differential and integrated cross sections σ_π⁺=50 ± 9 μb, σ_π⁻=47 ± 9 μb) for 0.0 ?|t|?1. (GeV/c)² and a laboratory momentum (p_Lab) of 15 GeV/c are presented. The momentum dependence of σ_γ^± is well fitted from 2.7 to 16 GeV/c by σ = Kp_Lab⁻ with n_γ⁺ = 1.80 ± 0.80 and n_γ⁻ = 1.87 ± 0.15.     

The π+p interaction at 1.2 GeV/c

Experimental results are presented for the available channels in the 1.2 GeV/cπ⁺p interaction. An isobaric model with incoherent addition of the amplitudes is used to determine the π, Δ and N¹ abundance rates in the π⁺π^op final state. The multipole parameters in the density matrix of the Δ⁺⁺ are determined as functions of its production angle.     

Negative pion production in proton-proton interactions at 69 GeV/c

Inclusive spectra of π^? production for pp interactions are discussed at 69 GeV/c both in the central and in the fragmentation region and are compared to data at lower and higher energies. The p_T dependence of the invariant structure function is also analysed.     

Study of multi-gamma final states from π−p interactions at 40 GeV/c with invariant mass above 2 GeV

Searching for new heavy particles, we have investigated the invariant mass spectra of neutral final states from π^?p interactions at 40 GeV/c incident momentum. No particles, in the mass region from 2 to 5 GeV, decaying in γ- rays, π⁰, η and X⁰ mesons, have been found to a level of about 10^?34 cm².     

Two-prong events in π− p interactions at 4.45 GeV/c

(π^?p → π^?p)_el, π^?p → π^?π⁺n and π^?p → π^?π^op reactions at p_π? = 4.45 GeV/c were studied in a 50 cm hydrogen bubble chamber. Cross sections σ_tot and dσ/dt were measured for these reactions and also for the ?^o, f^o and ?^? resonances. The elastic π^?π⁺ and π^?π^o scattering cross sections were calculated by the Chew-Low extrapolation method and with the pseudoperipheric approximation.     

Measurement of diffractive 3π production on a polarized target at 17 GeV/c

The reaction π^?p↑→π^?π⁺π^?p has been measured at 17 GeV/c using a polarized target. The data sample contains about 60 000 interactions on polarized protons. The nucleon polarization as a function of momentum transfer is very similar to elastic π^?p scattering and is nearly independent of the π mass, except for a possible structure around 1.2 GeV.Using the isobar model, we have performed a partial-wave analysis and extracted the 3π amplitudes. The generalized 3π density matrix elements agree with earlier determinations. Relative phases obtained from density matrix elements agree well with the ones obtained from transversity amplitudes. This proves the validity of the coherence assumption made in the interpretation of unpolarized target results. Our results confirm the existence of an A₁ resonance in the region 1.2–1.3 GeV.     

Λ production in K−p interactions at 32 GeV/c

Lambda production is studied in K^?p interactions at 32 GeV/c. The total Λ cross section is 2.31±0.03 mb. Using the measured Λγ combinations we find that (31±4)% of all Λ's are produced via the Σ⁰→Λγ decay. About 60% of the Λ's are associated with either a $\text{N}\text{N}\text{or K}\text{K}$ pair; about 40% of the Λ's are produced through the hypercharge annihiltion reaction K^?p→Λ+π'a. The two-peak structure of the invariant x distribution can be related to fragmentation processes. The Λ is found to be unpolarized in the target fragmentation region, whereas a transverse polarization is observed for forward produced Λ's. As a function of p⊥, a polarization effect is measured at medium p⊥.     

Partial-wave analysis of backwardly produced three-pion systems in K−p interactions at 4.2 GeV/c

We report on the results of a partial-wave analysis of the 3π system produced by baryon exchange in the reaction K^?p→Σ^?π⁺π⁺π^? at 4.2 GeV/c. We confirm the existence of an enhancement in the 1⁺S(?π) wave as previously established from a Dalitz plot analysis of the same data. The phase variation of this wave is found to be consistent with that expected for a resonance and thus the enhancement is identified with A₁ production. No clear signal for this state is found in either the reaction K^?p→Σ⁺π⁺π⁺π^?π^? or K^?p→Λπ⁺π^?π⁰. We also find production via baryon exchange of the A₂ in all three reactions and the ω and $\text{ω}{}^1$ (1975) in the third reaction.     

Pion spectra from the reaction p+p → π + anything at 28.5 GeV

The single-particle inclusive pion spectrum from the reaction p + p → π^± + anything at 28.5 GeV is presented in both tabular and graphical form. The data are from exposures in the BNL 203 cm bubble chamber. The emphasis of this paper is on exhibiting the single-particle spectra in sufficient detail so that the data will be useful to those interested in testing models and developing new concepts.     

Azimuthal correlations in 40 GeV/c π−p collisions and the independent cluster model

Data on azimuthal correlations and their rapidity dependence are presented in inclusive and semi-inclusive reactions π^?p → π⁺π⁺X,→ π^?π^?X and π⁺π^?X at 40 GeV/c. They show a long range as well as a short range effect. The short range effect, leading to different behaviour of dN/dφ near φ = 0 of like and unlike pion pairs is explained by identical and unidentical particle statistics. The predictions of the independent cluster model for the azimuthal asymmetry are in qualitative agreement with data of this experiment as well as those at 102 and 205 GeV/c.     

Hadron production at transverse momenta from 0.5 up to 2.2 GeV/c in proton-proton collisions at 70 GeV

The cross sections for π^±, K^±, p, and $\text{p}$ production in pp collisions have been measured at transverse momenta from 0.48 up to 2.21 GeV/c at 70 GeV. The data are compared with results obtained at lower and higher proton energies and also with the quantum chromodynamics parton model (QPM) calculations. Common behaviour of the cross sections of the form $\text{g(p}{}_{\mathrm{\perp }}\text{)?(x}{}_{\mathrm{\perp }}\text{)}$ in the energy range above 200 GeV does not take place at lower energies. Qualitatively QPM fits the data and the best agreement is for π⁺/π^? and K⁺/π⁺ ratios.     

Measurement of polarization in K−p elastic scattering between 0.955 GeV/c and 1.272 GeV/c

The polarization parameter has been measured for K^?p elastic scattering at nine incident beam momenta between 0.955 and 1.272 GeV/c covering the c.m. angular range $\text{?0.9 < cos θ}{}^1\text{< + 0.9}$. Experimental results and coefficients of Legendre polynomial fits to the data are presented and compared with other measurements and a partial-wave analysis.     

Evidence for double dissociation in K-p interactions at 14.3 GeV/c

We have studied the reaction K^-p → K^-π⁺π^-π⁺π^-p at 14.3 GeV/c to search for evidence of the double dissociation process $\text{K}{}^{\mathrm{-}}\text{p}\text{→}\text{QN}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^1$. In the channel $\text{K}{}^{\mathrm{-}}\text{p}\text{→}\text{K}{}^{10}\text{(890)}$π₁^-π₂^-Δ⁺⁺ (1236) there is evidence for simultaneous production of low-mass enhancements in the $\text{K}{}^{10}\text{π}{}_1{}^{\mathrm{-}}$ and Δ⁺⁺(1236)π₂^- subsystems which correspond to the $\text{Q}\text{→}\text{K}{}^1\text{(890)π}$ and $\text{N}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^1\text{→ Δπ}$ decay modes. In this particular final state the double fragmentation system is produced with a cross section of the order of a few microbarns. Our data are consistent with the factorizable pomeron exchange model of double diffractive dissociation.     

Elastic backward scattering of negative pions on protons at 25 and 38 GeV/c

The backward elastic scattering reaction π^?p → pπ^? at momenta 25 and 38 GeV/c have been measured using a magnetic spectrometer with hybrid chambers. The experimental data on the dependence of the cross section dσ/du on the momentum transfer u as well as the energy dependence dσ/du at u = 0 are given.     

An inclusive study of π-, K0 and a production from pn reactions at 11.6 GeV/c

Cross sections, multiplicities and particle inclusive spectra are presented for π^-, K⁰ and Λ produced in pn reactions at 11.6 GeV/c beam momentum. The results are compared with the data from pp interactions in the same energy range. Correlations between two π^- are also discussed. The main results are: the π^-, K⁰ and Λ all behave similarly as a function of transverse momentum squared; π^- in the forward c.m. hemisphere have spectra in x and y consistent with that of pp interactions, whereas the spectra of π^- in the backward hemisphere fall off more slowly with ∥x∥ and ∥y∥ than those in the forward hemisphere, suggesting n-fragmentation effects. The K⁰ and Λ have x and y distribution roughly similar to those in pp interactions. The K⁰ and Λ are consistent with a modified form of KNO scaling.     

Backward elastic scattering and ϱ− production in π−p collisions at 10 GeV/c

The reactions π^?p → p π^? and π^?p → p?^? (?^? → π^?π⁰) at 10 GeV/c with the proton in the forward direction in the c.m.s. are discussed on the basis of 953 elastic scattering events and 2240 events of the reaction π^?p → pπ^?π⁰. The total backward cross sections are 0.52±0.10 and 1.52±0.28 μb, respectively. In both cases the production mechanism is compatible with the dominance of the baryonic Δ_δ Regge trajectory exchange. The ?^? decay angular distributions are studied in the u-channel helicity frame and the spin density matrix elements are presented as functions of u.     

Absorption model amplitude analysis for the reaction πp → ππn at 17.2 GeV/c

The absorptive OPE model readily explains the recent amplitude analysis of the π⁻p → π⁻π⁺n CERN-Munich experiment at 17.2 GeV/c if the full helicity dependence of absorption corrections is included. No evidence for appreciable A₂-exchange in the forward direction is found.     

New limits on D0 (1.865) production in proton-nucleus collisions at 400 GeV/c

We present final results of a sensitive search for new particles in π^±K^? effective mass spectra observed in proton-nucleus collisions at 400 GeV/c. We establish a limit for D⁰ (1.865) production B_π⁺π^? dσ/dy < 360 nb/nucleon at y_cm^≈ ?0.4. For D?⁰ → π^?K⁺ the limit is 290 nb/nucleon.     

Some examples of associated charged particle multiplicities in proton-proton collisions at 19 GeV/c

19 GeV collisions in the CERN 2 meter hydrogen bubble chamber have been investigated for the number of prongs associated with an observed p, Λ, π^? or K_s⁰ with specified cms momentum components. For p and Λ the associated charged particles have been classified according to their longitudinal direction relative to the observed p and Λ