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 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.

Multi-strange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We present the transverse mass distributions of negative particles, Λ' s , Λ ' s and Ξ − ' s produced in sulphur-tungsten interactions at 200 GeV/c per nucleon and give the corrected rations Λ /Λ, Ξ − /Λ and Ξ − / Λ . Our ratio Ξ − / Λ appears to be larger than that from pp interactions.

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.

Results from the WA85 Experiment at the CERN Ω Spectrometer are presented. A 200 A GeV/ c beam of 32 S ions was used with a tungsten target. The apparatus is used to detect V 0, s and charged tracks in the range p T > 0.9 GeV/ c and 2.3 Y lab Λ and negative hadrons all show a linear increase with rapidity density in the range 70–140 as expected from models based on a superposition of independent NN collisions.

We study the production of meson resonance at pT≥2 GeV/c in π- 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) and K*0 (892) are found free from HT effects with a good accuracy, as expected from HT estimates and QCD sum rules. The magnitudes of the f2(1270) and ρ0 mesons signals are found larger than expected from the standard Lund (LT) Monte Carlo and from information provided by e+ e- annihilation experiments. The possible connection of these excesses with HT physics is discussed. We also report the first evidence for the production of f0(975) mesons in hadronic experiments at large pT. © 1996 Springer-Verlag.

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 with pT≥2 GeV/c balancing the transverse momentum of a third high-pT 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. © 1994 Springer-Verlag.

We study the shape of the invariant mass spectra of several resonances produced at PT≧2.0 GeV/c and observed through two-particle final states, namely the f2(1270), K*(892), {Mathematical expression}, K*(1430), and {Mathematical expression} mesons. The data sample comes from π- Be interactions at Plab=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. © 1994 Springer-Verlag.

The transverse momentum distributions for {Mathematical expression} and φ{symbol} (1020) have been studied in the pt 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 function pt-n with n∼8. A sample of simulated events from the Lund Monte Carlo in the same experimental conditions reproduces well the data. © 1993 Springer-Verlag.

We have studied the reactions {Mathematical expression} where the {Mathematical expression} system is centrally produced, at 85 GeV/c and 300 GeV/c using the CERN Omega spectrometer. A spin-parity analysis of the KS0K±π∓ system shows the presence of a strong JPC=1++ signal which we identify as the E/f1 (1420) meson. We also find evidence for the decay E/f1(1420)→KS0KS0π0 which determines the C-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 the E/f1 (1420) to be IG(JPC)=0+(1+). © 1992 Springer-Verlag.

Multi-strange baryon and antibaryon production is expected to be a useful probe in the search for quark-gluon plasma formation. We present the transverse mass distributions of negative particles, LAMBDAs, LAMBDAs-BAR and XI-s produced in sulphur-tungsten interactions at 200 GeV/c per nucleon and give the corrected ratios LAMBDA-BAR/LAMBDA, XI-/LAMBDA and XI–BAR/LAMBDA-BAR. Our ratio XI–BAR/LAMBDA-BAR appears to be larger than that from pp interactions.

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 WA76 experiment performed at the Ω facility at CERN required a high precision measurement of the forward produced particle whose momentum was close to 300 GeV/c. A telescope made of 12 silicon microstrip detectors has been built and operated for such a purpose.

The production of ρ{variant}0 mesons in hadronic interactions is investigated at high transverse momentum (pT > 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{variant}0→π+π- with pT(pair) > 2 GeV/c to recoil against an opposite particle with pT (opposite) > 1 GeV/c. The signal/(signal + background) ratio of ρ{variant}0 production shows an increase of 38% as ξE = pT (opposite)/pT (pair) decreases from 0.5