Search

We study the production of meson resonance atpT≥2 GeV/c inπ− Be interactions at two beam energies (150 and 300 GeV/c). The motivation is to look for the higher twist (HT) production mechanism, expected to exist besides standard hadron production through the fragmentation process of scattered quarks and gluons, the so-called leading twist (LT) mechanism. We show that the φ, K*0 (892) andK*0 (892) are found free from HT effects with a good accuracy, as expected from HT estimates and QCD sum rules. The magnitudes of thef2(1270) andρ0 mesons signals are found larger than expected from the standard Lund (LT) Monte Carlo and from information provided bye+e− annihilation experiments. The possible connection of these excesses with HT physics is discussed. We also report the first evidence for the production off0(975) mesons in hadronic experiments at largepT.

We have performed a search for vector-vector final states centrally produced in the reaction pp→pf(VV)ps at 300 GeV/c using the CERN Ω spectrometer. Evidence is found for ωπ0, ωω, π0π0 and π+π- associated production. No evidence is found for ωϕ production.

We study the shape of the invariant mass spectra of several resonances produced atPT≧2.0 GeV/c and observed through two-particle final states, namely thef2(1270),K*(892),\(\bar K*(892)\),K*(1430), and\(\bar K*(1430)\) mesons. The data sample comes from π− Be interactions atPlab=150 GeV/c and 300 GeV/c which have been collected using the OMEGA spectrometer at CERN. We find that although these meson resonances have their masses and widths consistent with the corresponding world average values, their shapes are all subject to the same kind of distortion: their low-mass tail is enhanced while their high-mass tail is sharply cut. This observation indicates that meson resonances produced in the fragmentation of quarks and gluons are distorted by the same damping factor in a way which preserves their masses and lifetimes.

We present the analysis of data samples taken by the WA77 experiment for π- interactions at 300 and 150 GeV/c. The trigger selects a pair of oppositely charged particles withp T ≥2 GeV/c balancing the transverse momentum of a third high-p T track. The primary aim of this experiment was the search for higher-twist production, mainly that of vector mesons. Since there are definite predictions for the polarization of mesons produced in fragmentation and through the higher-twist mechanism, we study the polarization properties of clearly identified mesons, namely the Φ and f2(1270) mesons. The results are compatible with no polarization. This can be interpreted as a production dominantly due to parton fragmentation.

The transverse momentum distributions for\(\rho ^0 (770),f_2 (1270),K*^0 (892),\bar K*^0 (892)\) and ϕ (1020) have been studied in thept region between 2 and 4 GeV/c and central rapidity. The data analysed come from the WA77 experiment at CERN with a 300 GeV/c π− beam incident on a Be target. These distributions are well described by the functionpt−n withn∼8. A sample of simulated events from the Lund Monte Carlo in the same experimental conditions reproduces well the data.

We have studied the reactions $$({{\pi ^ + } \mathord{\left/ {\vphantom {{\pi ^ + } p}} \right. \kern-\nulldelimiterspace} p})p \to ({{\pi ^ + } \mathord{\left/ {\vphantom {{\pi ^ + } p}} \right. \kern-\nulldelimiterspace} p})(K\bar K\pi )p$$ where the $$K\bar K\pi $$ system is centrally produced, at 85 GeV/c and 300 GeV/c using the CERN Omega spectrometer. A spin-parity analysis of theK 0 K ± π ∓ system shows the presence of a strongJ PC=1++ signal which we identify as theE/f 1 (1420) meson. We also find evidence for the decayE/f 1(1420)→K 0 K 0 π 0 which determines theC-parity of this state to be positive. Alternative explanations of the data have been tested and ruled out. Hence we obtain the quantum numbers of theE/f 1 (1420) to beI G(JPC)=0+(1+).

Production of multi-strange baryons and antibaryons is expected to be a useful indicator in the search for Quark-Gluon Plasma formation. Production of Ξ− and Ξ − has been observed for the first time in ultra-relativistic heavy ion interactions by the WA85 Experiment. We describe the procedure used to select these cascade candidates and show that Ξ− and Ξ − decays can be identified. Preliminary ratios of Ξ/Ξ production in sulphur-tungsten and proton-tungsten interactions are also presented.

The aim of this experiment is to search for non-qq mesons in the reaction pp→pf(XO)ps at 300 GeV/c incident momentum, where the XO system is a centrally produced meson. The θ/f2(1720), E/f1(1420) and a new state in the 2π+2π− channel are presented as candidate non-qq mesons.

Preliminary results from the WA85 Experiment at the CERN Omega Spectrometer are presented. A 200 A GeV/c beam of 22S ions was used with a tungsten target. The apparatus is used to detect V°s and charged tracks in the range PT > 0.9 GeV/c and 2.3 Λ, Λ and cascade particles is discussed. A study of the multiplicity dependence of Λ, Λ and hadron production is presented.

Production of oppositely charged particle pairs at largep T is studied, where both particles, are in the central rapidity region within one unit of rapidity and nearby in azimuth. The data sample, which comes fromπ − Be interactions obtained using the CERN OMEGA spectrometer, contains events with a pair of oppositely charged particles havingp T ≧2 GeV/c recoiling, against a third one withp T ≧1 GeV/c. Our data provide new information on short range correlations involving the production of the nine possible pairs made from (π +,K +,p) and $$(\pi ^ - ,K^ - ,\bar p)$$ . Comparison with Lund Monte Carlo predictions is made. Apart from proton yields, the model reproduces correctly our data. The main discrepancies observed with protons can be attributed to hard scattering of diquarks from the target nucleons.

Production of Ξ − and Ξ − has been observed for the first time in heavy ion interactions by the WA85 Experiment. Multistrange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We describe the procedure used to select these cascade candidates and show that Ξ − and Ξ − decays can be identified. The ratio of Ξ Ξ production, corrected for geometrical acceptances and reconstruction efficiencies, is 0.39 ± 0.07 for sulphur-tungsten interactions in the central rapidity interval 2.3 Y lab p T >1.1 GeV/ c .

The production of ϱ 0 mesons in hadronic interactions is investigated at high transverse momentum ( p T > 2 GeV/ c ). The data come from a sample of Π − N interactions at 300 GeV/ c obtained at the CERN OMEGA spectrometer, requiring a ϱ 0 →Π + Π − with p T (pair) > 2 GeV/ c to recoil against an opposite particle with p T (opposite) > 1 GeV/ c . The signal/(signal + background) ratio of ϱ 0 production shows an increase of 38% as x E = p T (opposite)/ p T (pair) decreases from 0.5 x E x E ⩽ 0.5. This increase is not compatible with a QCD model of parton scattering and subsequent fragmentation. It is interpreted as evidence for direct ϱ 0 production via QCD higher twist processes, in terms of which a quantitative agreement with the data is found.

The production of ϱ 0 mesons in hadronic interactions is investigated at high transverse momentum (p T > 2 GeV/c). The data come from a sample of π-N interactions at 300 GeV/c obtained at the CERN Omega Spectrometer, requiring at ϱ 0 → π + π − with p T (pair) > 2 GeV/c to recoil against an opposite particle with p T (opposite) > 1 GeV/c. The signal/(signal + background) ratio of ϱ 0 production shows an increase of 38% as ξ E = p T (opposite)/p T (pair) decreases from 0.5 ξ E ξ E ⩽ 0.5. This increase is not compatible with a QCD model of parton scattering and subsequent fragmentation, and gives a strong indication that direct ϱ 0 production has been observed. Data has now been taken at 150 GeV/c and additional signatures to be used to identify direct ϱ 0 production are discussed.

The production of glueball candidates ι and Θ in hadronic interactions is investigated at high transverse momenta. The data come from a sample of π − interactions at 300 GeV/ c on a beryllium target, obtained at the CERN Omega Spectrometer using a trigger and off-line selection requiring a system of charged particles with p T >2 GeV/ c recoiling against an opposite particle with p T >0.9 GeV/ c . Cross sections are given for known resonances (ϱ 0 , φ, f 0 ) and upper limits for the ι(1440) and Θ(1720). A co mparison is made with recent theoretical calculations.

The aim of this experiment is to search for gluonic mesons in the reaction pp → pf(X0)ps at 300 GeV/c incident momentum, where the X0 system is a centrally produced meson. Preliminary results are presented on the two‐body (π+π−, K+K−, K0SK0S, pp), three body (K0SK±π±) and four‐body (2π+2π−) decays of the X0 system.