Inclusive production of vector mesons in π+ p interactions at 250 GeV/c

We report on a study of ρ⁰, ρ⁺, ω, \(\bar K^{*0} (892)\) andK ^*0 (892) inclusive production in π⁺ p interactions at 250 GeV/c, for ρ⁺, \(\bar K^{*0} (892)\) for the first time in a π⁺ p experiment. The data are compared withK ⁺ p data in the same experiment, with results of other experiments and with quark-parton models. Interesting differences are found between ρ^+,0 and ω production.     

Forward-backward multiplicity correlations in σ+ p,K + p andpp collisions at 250 GeV/c

Forward-backward multiplicity correlations in σ⁺,K ⁺ p andpp collisions at 250 GeV/c ( \(\sqrt s \) =22 GeV) are given for all charges and for the different charge combinations. The correlations are found to be caused predominantly by centrally produced particles. It is demonstrated that this result is an agreement with observations at the ISR and the CERNp \(\bar p\) -Collider. The results are compared to expectations from LUND, DPM and FRITIOF Monte Carlo models and a geometrical picture relating correlations in hadron-hadron collisions toe ⁺ e ^? data in terms of impact parameters is tested.     

Direct soft photon production inK + p andπ + p interactions at 250 GeV/c

Inclusive production of direct soft photons is studied inK ⁺ p andK ⁺ π interactions at 250 GeV/c. Total cross sections, Feynman-x and transverse momentum distributions of direct γ's are presented. The measured cross sections are several times larger than expected from QED inner bremsstrahlung, indicating the presence of an anomalous soft photon source. The model of Lichard and Van Hove, based on the “cold quark-gluon plasma” picture, agrees with the data.     

Multiplicity structure of inclusive diffraction in À+ p andK + p interactions at 250 GeV/c

Results on the multiplicity structure of diffractively excited meson and proton systems in À⁺/K⁺ p interactions at 250 GeV/c are presented for diffractive masses up to about 9 GeV. The energy dependence of the average charge multiplicity and the shape of the multiplicity distribution in terms of KNO-scaling and negative binomial distribution are investigated. The diffractive systems are compared toe ⁺ e ^–,lh and non-diffractivehh final states as suggested by modern approaches of the Pomeron-hadron collision. Systematic differences are found between diffractive meson and proton systems but also between diffraction and the reactions compared to.     

Invariant mass dependence of particle correlations in π+ p andK + p interactions at 250 GeV/c

We study two- and three-particle correlations as a function of invariant mass. Using data on π⁺ p andK ⁺ p collisions at 250 GeV/c, we compare correlation functions and normalised factorial cumulants for various charge combinations. Strong positive correlations are observed only at small invariant masses. The normalised cumulants for “exotic” [(??), (++)] and “nonexotic” pairs (+?) and triplets decrease in power-like fashion with increasing invariant mass. The mass dependence is not incompatible with the power-law behaviour as expected in a Dual Mueller-Regge framework. Comparison with FRITIOF reveals strong disagreements, which are due to too large production rates of resonances, such as ρ⁰ and η, and the absence of a Bose-Einstein low-mass enhancement in JETSET.

     

Collective characteristics of hadron systems produced in beam fragmentation of π+ p collisions at 250 GeV/c

Collective characteristics are studied of hadrons produced in beam fragmentation of non-single-diffractive π⁺ p-interactions at 250 GeV/c. An attempt is made to obtain experimental information on the properties of leading cluster production and fragmentation. On average, the leading cluster carries 0.8±0.1 of the incident momentum, so that the mean value of the inelasticity coefficient of 〈k〉=0.2±0.1 is significantly smaller than that deduced from leading single hadron spectra. The momentum transfer distribution shows that nonsingle-diffractive processes are less peripheral than diffraction dissociation. The analysis of thrust and sphericity shows jet-like structure of pion fragmentation, that of the charge flow an average forward charge of 〈Q _f 〉=0.45±0.04, in agreement with the average charge of the beam valence quarks. Our data are compared to diffraction dissociation and to the Fritiof model.     

Neutral strange particle production inK + andπ + collisions with Al and Au nuclei at 250 GeV/c

Data are presented on inclusiveK _s ⁰ and production inK ⁺ and ⁺ collisions with Al and Au nuclei at 250 GeV/c. Results are given on total inclusive cross sections and theA dependence, as well as on distributions in Feynman-x _F , rapidityy and transverse momentum. Ratios ofK _S ⁰ and of to ⁺ production are presented. The data are compared with predictions of the quark-parton model FRITIOF.     

Influence of multiplicity and kinematical cuts on Bose-Einstein correlation inπ + p at 250 GeV/c

The correlation of negative particles at small momentum difference and its dependence on multiplicity and on kinematical cuts is studied in ⁺ p-interactions at 250 GeV/c. In terms of the Kopylov-Podgoretski parametrization, an average radius of the pion emitting region ofr _K =1.59±0.14 fm and a life-time (or emission depth) =0.83±0.25 fm are found. The Lorentz invariant parametrization of Goldhaber givesr _G =0.85±0.04 fm. Assuming two different sources of pions, their radii are estimated asr ₁=1.75±0.25 fm andr ₂=0.60±0.08 fm. An angular and multiplicity dependence of the space-time size of the source is observed. The source is elongated along the collision axis and has larger sizer _K at higher multiplicities. The radiusr _K decreases with increasing pion pair momentum. The size of the emitting region appears to be larger for low rapidity pions than for pions from the fragmentation region. No evidence is found for a unique reference frame, where the pion source is motionless for each ⁺ p collision, i. e. where the space-time size of the source is definitely smaller than in any other frame.Partially supported by grants from CPBP 01.06 and 01.09.     

π 0 andη meson production inπ + p andK + p collisions at 250 GeV/c

We report on a study of inclusiveπ ⁰ and η meson production inπ ⁺ p andK ⁺ p interactions at 250 GeV/c beam momentum. The Feynman-x spectrum ofπ ⁰ is very similar in shape and normalization to that of negatively charged particles produced in the same experiment. The results are compared with data at other energies and with FRITIOF model predictions. This model overestimates the η cross section by a factor of 2.5. It reproduces theπ ⁰ cross section correctly, but predicts a too hardπ ⁰ x distribution.     

Deuteron production in collisions of 250 GeV/c π+ andK + mesons with Al and Au nuclei

Experimental data are presented on deuteron production in the target fragmentation region for 250 GeV/c π⁺ interactions with Al and Au nuclei, and compared with analogous data on proton production. Indications are observed for narrow structures in the (dπ^-) effective mass system at ～2.04 and ～2.08 GeV.