Pair production of pions with symmetric momenta in the range 0.5⩽pT⩽2.0 GeV/c In 70 GeV p-p collisions

The invariant cross-section slope of the pp→π⁺π^?+X process as a function of p_T is found to have a break near 1 GeV/c. Fitting the cross section by a sum of two exponents gives the values of powers (12.3±0.9)(GeV/c)^?1 and (8.7±0.6)(GeV/c)^?1. The experimental points at p_T?1 GeV/c are significantly higher than predictions based on hard scattering models such as QCD and CIM.     

A study of the reaction pp → π− π+ at 10 GeV/c

The reaction $\text{p}\text{p}\text{→ π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ has been studied at 10.1 GeV/c in the ?t interval from 0.15 to 1.5 (GeV/c)². A line-reversal comparison with backward elastic scattering π⁺p → pπ⁺ shows good agreement for ?t > 0.3 (GeV/c)².     

Cross section determination for the reaction K+p → K+pπ+π−π0 and K+π+π+π−n at 8.2 and 16 GeV/c

The cross sections for the reactions: (a) K⁺p → K⁺pπ⁺π^?π⁺ and (b) K⁺p → K⁺π⁺π⁺π^?n have been determined at 8.2 and 16 GeV/c with the following results:at 8.2 GeV/c: (a) 0.99 ± 0.07 mb, (b) 0.41 ± 0.04 mb;at 16 GeV/c: (a) 0.72 ± 0.05 mb, (b) 0.28 ± 0.05 mb.Using the available data at other energies, the cross-section dependence of these reactions on the incident momentum is discussed.     

Structure in momentum-transfer for (pπ−) systems produced in diffractive dissociation of neutrons on protons

The four-momentum transfer distribution of (pπ^?) systems produced in the neutron dissociation reaction n + p → (pπ^?) + p has substantial structure which depends strongly on the mass and on the angular decay properties of the produced (pπ^?) system. No significant energy dependence is observed in the data for incident neutrons in the momentum range between 50 GeV/c and 300 GeV/c. The results are compared with a Deck-type of model.     

The reaction π+p→π+pπ0π0 at 4 GeV/c: No evidence for a narrow ϵ

The Track Sensitive Target technique has been used to isolate 5000 events from the reaction π⁺p→π⁺pπ⁰π⁰ at 4 GeV/c. Channel cross sections are measured. The data agree with predictions from phase-shift analyses of π⁺π^? data: the effect of the S¹ is clearly seen. There is strong evidence against any narrow ? below 1 GeV/c².     

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.     

The reaction pp→pπ−π+p at 25 and 40 GeV/c

The reaction $\text{p}\text{p}\text{→}\text{p}\text{π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}\text{p}$ has been studied at 25 and 40 GeV/c at the Serpukhov proton synchroton using the CERN-IHEP spectrometer. The differential cross section has been determined as a function of four-momentum transfer to the proton (0.05–0.30 (GeV/c)²) and $\text{p}\text{ππ}$ mass (up to 2.2 and 2.6 GeV/c²). At both energies there is a broad low-mass maximum with an enhancement at 1.6–1.8 GeV/c². The cross section in a given mass band falls rapidly with |t|, with an exponential slope that decreases with increasing mass. In both the background and the 1.7 GeV/c² peak there is a strong $\text{Δ}{}^{\mathrm{??}}\text{π}{}^{\mathrm{+}}$ component. Possible spin-parity (J^P) contributions to it are discussed. Throughout the range 1.5–2.2 GeV there is at least one state of $\text{J ?}\text{3}\text{2}$ and there is interference between states of opposite P, |ΔJ| ? 1. At the peak there is a $\text{J ?}\text{5}\text{2}$ component. There are striking parallels between this reaction and the boson reactions π^?p→π^?π^?π⁺p and K^? → K^?π^?π⁺p.     

Evidence for high mass NN and NNπ enhancements observed in pd interactions at 5.55 GeV/c

Based on 4085 $\text{p}\text{n→Xπ}{}^{\mathrm{?}}$ events, X denoting a neutral $\text{N}$N or $\text{N}\text{Nπ}$ system, we present evidence for 5.1 and 3.1 standard deviation enhancements at the X mass of 2.85 and 3.05 GeV/c², respectively. The lower mass bump has a width of Λ ? 39 GeV/c² while the 3.05 GeV/c² is seen as a one bin accumulation (20 GeV/c² width). The relevance of these peaks is discussed.     

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.     

Scaling of semi-inclusive cross sections with respect to longitudinal and transverse momenta

The semi-inclusive one-particle transverse and longitudinal momenta spectra of π^± mesons have been studied in the centre-of-mass system for π^?p interactions at 40 GeV/c. These data are compared with similar data from pp interactions at 300 GeV/c and lower energies. Distributions in the variables p_T/〈p_T〉 and p_L/〈p_L〉 reveal scaling properties, which are found to be substantially independent of the nature of the projectile, of the incident energy and of the prong multiplicity. These spectra are reasonably described by universal functions.     

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 critical discussion of a prism plot analysis of the four-body reaction π−p → π−pπ+π− at 3.93 GeV/c

A multidimensional analysis of the reaction π^?p → π^?pπ⁺π^? at 3.93 GeV/c is presented. Its results are compared to those obtained with conventional methods and its limitations are discussed.     

Charged particle multiplicity distributions for 32 GeV/c K±p and pp interactions and for 50 GeV/c π±p interactions

Topological cross sections are presented for K⁺p, K^?p and $\text{p}\text{p}$ interations at 32 GeV/c and for π⁺p and π^?p interactions at 50 GeV/c observed in the 4.5 m Mirabelle hydrogen bubble chamber at Serpukhov. Parameters characterizing the behaviour of the multiplicity distributions, namely 〈n_c〉, D and f₂ and the normalized moments are given. The dependence of these parameters on the energy and the nature of the beam particle is discussed. The multiplicity distributions obtained cannot be described by a single function in the KNO variables.     

Λp interactions below 24 GeV/c

Λp interactions have been studied at momenta up to 24 GeV/c using a new bubble chamber technique. We find that the Λp elastic cross section has fallen to approximately 6 mb at the highest momentum. Results are presented on Λp→Λpπ⁺π^? for the first time above 5 $\text{GeV}\text{c}$.     

Search for a Ks0π±π+π− resonance near 2.6 GeV in 14.75 GeV/ c pp interactions

We present the results of a search for a resonance at 2.6 GeV decaying into K_S⁰π^±π⁺π^? in the six-prong plus K_S⁰ final state in 14.75 GeV/c$\text{p}\text{p}$ interactions. We do not find confirming evidence, and with 95% confidence we quote an upper limit of σ·BR < 21 ub.     

Particle composition at high transverse momenta in p-p-collisions in the central region at the CERN ISR

Preliminary measurements have been made at centre of mass energies √s = 31 and 44 GeV of the π, K and p production ratios at 90° for p_T between 2.0 and 3.5 GeV/c. The (K+p)/π ratio is given down to p_T = 1.4 GeV/c. No strong energy dependence is observed for these transverse momenta.     

Prediction of the one pion exchange contribution to the processπ − p→π − pω with the help of the Veneziano model

The one pion exchange contribution to the differentialπ ^? p→π ^? pω cross-section is calculated assuming that theπ→πω amplitude associated with one of the vertices is described by the Veneziano formula, and that only a trivial dependence of the latter on the mass of the exchanged pion needs to be taken into account. The remaining unknown overall constant is then fixed by considering the decayω→3π. A rough comparison with preliminary data from a 16 GeV/cπ ^? p experiment shows that the one pion exchange model could possibly describe the reactionπ ^? p→π ^? pω forπω masses above 1.4 GeV.     

Single-spin asymmetry of inclusive π 0-meson production in 40-GeV pion interactions with a polarized target in the target-fragmentation region

Data on the single-spin asymmetry (A _N) of inclusive π ⁰ production in 40-GeV pion interactions with a polarized target, π^? + _↑→π⁰+X, are presented for the target-fragmentation region. The result is A _N=(?13.8±3.8)% for ?0.8<x _Fp _T<2 GeV/c and is compatible with zero for ?0.4<x _Fp _T<1.5 GeV/c. At a π ⁰ momentum of about 1.7 GeV/c in the c.m. frame, the asymmetry becomes nonzero both in the central and in the target-fragmentation region. The behavior of the asymmetry is similar to that observed in the beam-fragmentation region of the E-704 (FNAL, 200 GeV) and STAR (BNL, 20 TeV) experiments, which employed a polarized proton beam.     

Electroproduction of neutral pions at energies above the resonance region

The reaction e p→e'pπ⁰ has been measured at W=2.55 GeV a fixed electron scattering angle of 10.3°. Two magnetic spectrometers and a lead glass hodoscope were used to detect all four final state particles. Electroproduction cross sections in the t range ?0.15 to ?1.4 (GeV/c)² at q² = ?0.22, ?0.55 and ?0.85 (GeV/c)² are presented. Above |t|=0.6 (GeV/c)² the cross sections are considerably smaller than those for photoproduction.