Search

The UA2 experiment at CERN is currently upgrading its apparatus to take advantage of the higher accelerator luminosity to be provided from November 1987. The first large particle tracking detector using scintillating optical fibres will form a major part of this upgrade. The detector is built by the Cambridge, CERN and Saclay groups. The Scintillating Fibre Detector is a cylinder of radius 38 to 44 cm, composed of 60000 plastic optical fibres of length over 2 m. The 1 mm diameter fibres are optically clad and aluminised, and are arranged in 24 layers. The detector will be used to track charged particles produced in pp interactions, and also contains a lead converter to cause neutral and charged electromagnetic particles to shower. The signals from the fibres are amplified, multiplexed and digitised by 32 readout chains. These consist of: • —A large aperture, de-magnifying image intensifier, providing a gain of ∼ 40000. Extremely fast phosphors are employed for the three stages, to match the short time (4 ps) between particle interactions; • —Charge-coupled devices (CCDs) converting the optical image into a single train of electrical pulses for 2000 fibres. A novel use of the anti-blooming electrode of the CCD enables unwanted images to be cleared in • —A Fastbus digitiser, which processes the video signal, providing a large degree of data reduction. A full-scale prototype of 960 fibres with readout has been tested in a particle beam. It has demonstrated a good spatial resolution of the tracks (

A large scintillating fibre detector for the UA2 experiment at the CERN p p Collider is under construction. It will be used for tracking and electron identification. The performance of a full scale test module containing 960 fibres of 2.1 m length and 1 mm diameter is described.

Results on the production cross sections ofW andZ bosons detected in the UA2 experiment are given based on a large sample ofW→eν andZ→e + e − decays. The measured cross sections are σ = 660±15(stat)±37(syst)pb, σ = 70.4±5.5(stat)±4.0(syst)pb and their ratioR=9.38 −0.72 +0.82 (stat)±0.25(syst). In the framework of the Standard Model, the measured value ofR is used to determine the total width of theW, Γ(W)=2.30±0.19(stat)±0.06(syst) GeV.

Photon imaging is an increasingly important technique for the measurement and analysis of chemiluminescence and bioluminescence. New high-performance low-light level imaging systems have recently become available for the life science. These systems use advances in camera design and digital image processing and are now being used for a wide range of luminescence applications. They offer good sensitivity for photon detection and large dynamic range, and are suitable for quantitative analysis. This is achieved using a range of software techniques including image arithmetic, histogramming or summing regions of interest, feature extraction and multiple image processing for kinetics or assay screening. Improvements in imageprocessing hardware and software have increased the usefulness of these systems in the biosciences. Low-light imaging is a rapid and non-invasive method for the sensitive detection and analysis of luminescent assays. As such it offers a powerful and sensitive tool for investigating processes, both at the cellular level (luc and lux reporter genes, intracellular signalling) and for measurement of macro samples (immunoassays, gels and blots, tissue sections).

A search for supersymmetric decays of the Z boson into a pair of scalar electrons or winos (partners of the electron and W boson) has been made with the upgraded UA2 experiment at the CERN p p collider at s = 630 GeV . The analysis of the sample of electron pairs, corresponding to an integrated luminosity of 7.4 pb −1 , shows no evidence for such exotic decays. The 90% confidence level lower mass limits obtained exclude selectron masses up to e40 GeV/ c 2 in the case of a light photino, and wino masses up to 45 GeV/ c 2 in the case of a light scalar neutrino.

The upgraded UA 2 detector has collected data corresponding to a total integrated luminosity of 7.5 pb−1 from\(\bar pp\) collisions at a centre of mass energy of 630 GeV during 1988 and 1989. A search has been performed for the production and decay of the top quark (t) or a member of a hypothetical fourth family (b′). No evidence has been found for such processes. Using the expected rates for production and decay branching ratios from the Standard Model, this implies that the top quark mass is greater than 69(71) GeV/c2, and that theb′ mass is greater than 54(57) GeV/c2, at 95(90)% confidence.

The construction of a KL0 beam for the CERN 2 m hydrogen bubble chamber and the derivation of the beam momentum spectrum are described. Cross sections are presented for the reaction KL0+p → KS0+π++π−+p for KL0 momenta up to 17 GeV/c. The reacti is seen to be dominated, particularly at the highest momenta, where there are no previous data, by the production of the Q0-Q0 system. The shapes of the t-distributions for Q0 and Q0 prodcution are found to be different in a sense opposite to that expected from the pion-exchange Deck model. A model in which the observed effect is ascribed to the addition of a K∗ exchange Deck graph is found to be incompatible with the data. The data are, however, consistent with a model in which the Q0-Q0 system is largely resonant and the sense of the cross-over is determined by the s-channel quantum numbers.

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 Λ p→ Λ p π + π − for the first time above 5 GeV c .

We have made a search for charmed particles among strange particle production events in neutron-proton interactions up to 24 GeV/ c . We have found no evidence of long-lived ‘cascade’ decays not of statistically significant peaks in effective mass distributions, and have quoted upper limits on the production cross sections of such particles in the mass range 1.5 to 5.0 GeV/ c 2 .

We have studied the inclusive production of K/sup asteriskplus-or-minus/(890) and Y/sup asteriskplus-or-minus/(1385) in pp, ..pi../sup +/p, and K/sup +/p interactions at 147 GeV/c. The experiment used the Fermilab 30-inch hydrogen bubble chamber with the hybrid spectrometer system. Results are based on a sample of 1916 observed K/sub S/ and 932 observed ..lambda... Inclusive cross sections are given for K/sup asteriskplus-or-minus/ and Y/sup asteriskplus-or-minus/ production from the three beams, and comparisons are made with experiments at other energies. Feynman-x and transverse-momentum-squared distributions are also calculated. The results suggest that the K/sup asterisk-/ is entirely produced in the central region, while the K/sup asterisk+/ includes a component from beam fragmentation. Comparisons are made with the additive quark model.

We report on an experiment in which the SLAC 40-in. hybrid facility was exposed to an 8.8-GeV/c antiproton beam. Using external detectors we have identified a large fraction of nonannihilation events and thus obtained a clean sample of annihilation data. Using proton interactions taken in the same detector at the same energy we have made a detailed study of ($\overline{p}p\ensuremath{-}pp$) differences and explored their relationship to $\overline{p}p$ annihilations.

We present results from a high statistics (46 events/μ;b) experiment on K−p interactions in the Argonne 12 foot bubble chamber. In particular we make a systematic search for Ξ ∗ resonances. We confirm recent evidence of a Ξ(2370), and see a number of other well established states. We also give cross sections for various exclusive and inclusive reactions, including those in which θ− are produced.

Multiplicity distributions of charged particles for inelastic, non single-diffractive events in proton-antiproton collisions at a centre of mass energy of 540 GeV are presented for various pseudorapidity (Δη) intervals. The widths of the multiplicity distributions, scaled to their means, increase as Δη is made smaller, and the deviation from a Poisson distribution becomes progressively more pronounced. It is found that the data are remarkably well described by a negative binomial distribution. The parameters of the distributions vary smoothly with the size of the acceptance interval.

We present data on the inclusive γ, λ 0 and K S spectra produced forward direction by interactions of 23.85 GeV/ c protons in a copper target. The Λ 0 spectra are compared with the predictions of the Hagedorn-Ranft model.

We derive cross-sections for the inclusive productiion in pp interactions at 100 GeV /c of π 0 , K S 0 and Λ 0 Λ 0 of 91.5±5.7 mb, 5.2±0.4 mb and 4.8±0.4 mb respectively, which are all higher than pp cross-sections at energy. We find indications that these differences can be attributed to “annihilation” processes.

We have investigated the reactions p p π + π − a and p p a p p 2π + 2π − at 100 GeV /c . The p p π + π − final state is dominated by diffractive production of a p π + π − ( or p π + π − ) system which shows a strong tendency to form Δ ++ π − ( or Δ ++ π + ) . The process p p a Δ ++ Δ ++ is also observed in this reaction, indicating an energy dependence of s−1.5±0.1. The p p 2π + 2π − channel shows less single diffraction, and has a doubly diffractive component consistent with pomeron factorization. Strong Δ++(Δ++) production is agoain seen, but in contrast to the p p π + π − channel we also observe considerable ϱ0 production.

Results are presented from the first p p colliding beam runs at the CERN ISR, using the UA5 streamer chamber detector. p p interactions at s = 53 GeV are compared with pp data taken in the same experiment. The results are in good agreement with extrapolations of low-energy p p data.

We present results of an experiment on strange particle production in np interactions below 24 GeV/c. We derive cross sections in 25 exclusive channels, and compare them with lower energy data. We see evidence for a significant diffractive contributions to the lower multiplicity processes. We also obtain information about the inclusive production of Λ0, Ξ−, Σ±(1385) and K±(890).

Results on the charged multiplicity distribution in π−d interactions at 21 GeV/c are presented. The effects due to the two-nucleon structure of the deuteron target are analysed and the contribution of double scattering processes is estimated as a function of charged multiplicity. The evidence against simple cascade models is discussed.

The UA5 Monte Carlo program, consisting of a non-diffractive event generator GENCL, a diffractive event generator DIFFR and a tracking program are described. The inputs to the event generators are explained in detail. Their outputs are compared to available data from the S p pS Collider, and the agreement is shown to be good. The importance of some features of the generators are discussed. It is shown that cluster production and leading baryons are necessary to describe non-diffractive phenomena.

Data on the reaction ppπ+π− in the momentum range 2–25 GeV/c are analysed for features indicating double pomeron exchange (DPE). The moments of the ππ angular distributions are examined in the quasi three-body frame of reference which is analogous to the s-channel helicity frame for quasi two-body processes. Inequality constraints on the moments are shown to suggest the presence of both S and P waves of the ππ system in the relevant pp(ππ) kinematic region, arguing against the dominance of DPE. The energy dependence of cross sections for selected events in different ranges of ππ mass is shown to be in accord with the predictions of a double Regge exchange model incorporating pomeron-reggeon exchange and not DPE. Both the cross sections and the ππ angular distributions are also examined in the light of a reggeized one-pion exchange model.

We give cross sections for annihilation and non-annihilation reactions in pp interactions at 8.8 GeV. The non-annihilation data are compared with pp data from the same experiment. We compare data on resonance production and on the impact parameter structure of the final states in pp annihilation and non-annihilation and pp interactions. We investigate the charge structure of the 2π+ 2π− π0 final state, and find it consistent with a simple quark model.

We discuss a number of features of π − p interactions at 100 GeV/ c , and in particular we attempt to understand the differences between π − p and p p interactions using p p data from the same experiment. The optics considered include the rates of strange particle production, charge transfer distributions, the partition of energy among various particle species and inclusive meson production in beam and target fragmentation regions, with special reference to constituent models of hadrons.

We present an analysis of 3 π coherent production in the reaction π − d→ π − π − π + d at 21 GeV/ c , using a sample of 4552 events. We find the cross section for the process is 517 ± 27 μ b, and discuss the effective-mass distributions of the 3 π , 2 π and d π systems. The 3 π mass distribution is dominated by the A 1 enhancement, with no evidence for A 2 production and only a shoulder at the A 3 . The (2 π ) 0 mass distributions are dominated by ϱ and f production. The d ∗ effect is seen only in the (beam-like) d π − combination, and does not behave like a genuine resonance. A three-particle partial-wave analysis (Ascoli type) of the data confirms previous observations that although the A 1 and A 3 can be associated with single spin states, their resonance character is not established. The A 2 state does not occur, and this provides evidence in favour of the Gribov-Morrison rule.

Results are presented from a study of inclusive neutral strange particle production by a 147 GeV/c tagged π+/K+/p beam in the Fermilab 30-inch hydrogen bubble chamber. The experiment made use of the proportional hybrid spectrometer system. Results are based on 995 KS0, 485 Λ, and 83 Λ found in a sample of 132 000 pictures. Cross sections are given for inclusive production of these particles by each of the three beam particles, and comparisons are made with measurements at other energies. Topological cross sections are also calculated, and KNO multiplicity scaling is investigated. Distributions are presented of invariant cross sections as functions of the Feynman scaling variable x and c.m. rapidity y. The transverse momentum-squared distributions with their fitted slopes are also given. Comparisons are made of the production characteristics for the three beam types.

The effect of double scattering is extracted from experimental data on π − D interactions at 12 GeV/ c . Multiplicity, rapidity y , x F and p ⊥ distributions for double scattering process are presented. It is found that double scattering occurs in 16% of π − D interactions at this energy: its relative importance increases with the charged multiplicity N , and the largest absolute contribution is at N = 4 and 6. The multiplicity distribution for double scattering has mean value 〈 N − 〉 = 1.76 ± 0.03 and dispersion D − = 0.88 ± 0.04. The distributionsin rapidity, x F and p ⊥ are similar to those of single scattering processes, but the relative importance of double scattering increases at large p ⊥ and low x F or y . The distributions are similar at all multiplicities, and for π + and π − .

A spin-parity analysis is performed of the low-mass ( .. (p..pi../sup -/) p using new data at 13 GeV/c and 20 GeV/c. In the context of a Deck-plus-resonances model a good fit to the p..pi../sup -/ angular moments is found only if the Gribov-Morrison parity-change rule does not hold and spin states up to j = 5/2 are included. In particular the presence of a considerable fraction of spin-parity 1/2/sup -/ state is indicated. (AIP)

Results are presented on the topological cross sections obtained for antiproton-proton interactions from an exposure of the Fermilab 30-inch bubble chamber to a 100 GeV/ c negative beam enriched in p 's. The p p inelastic cross section is found to be σ inel = 34.6 ± 0.4 mb, and the average inelastic charged particle multiplicity to be 〈 n 〉 = 6.74 ± 0.05.

Using the UA5 detector, the inclusive central production of Ks0 and K± mesons has been measured in non-single-diffractive interactions at the CERN SPS p p Collider at a c.m. energy of 540 GeV. The average transverse momentum is found to be 〈pT〉 = 0.57±0.03 GeV/c in the rapidity range |y

New 100 GeV/c p p data are used to find moments of the difference between the p p and pp topological cross sections. The mean multiplicity for annihilations at 100 GeV/c is estimated to be 9.06 ± 0.56, and the value of the quantity 〈n〉/D to be 2.75 ± 0.33. It is shown that R n = {σ n ( p p) − σ n (pp)}/σ n (pp) appears at 100 GeV/c to have acquired an asymptotic form, Rn = s−αβn, with α and β constant.

We present data on photon production in non single-diffractivep % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiCayaara% aaaa!36FA! $$\bar p$$ -collisions at c.m. energies of 200 and 900 GeV. Besides the general properties of photon production, i.e. pseudorapidity distribution and average multiplicity, we also investigate photon-charged two-particle pseudorapidity and multiplicity correlations. We find for the average number of photons in non single-diffractivep % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiCayaara% aaaa!36FA! $$\bar p$$ -collisions 22.2±1.4±2.0 at 200 GeV and 41.4±2.1±3.5 at 900 GeV, where the first error is statistical and the second systematic. The analysis of photon-charged particle multiplicity correlations reveals strong positive correlations between the average number of photons and the number of simultaneously produced charged particles, as expected from FNAL and ISR studies and from our result at 546 GeV. We obtain for the correlation slope 0.95±0.08±0.11 at 200 GeV and 1.09±0.09±0.13 at 900 GeV (first error is statistical and the second systematic). The investigation of photon-charged two-particle pseudorapidity correlations shows that these correlations are of short range and compatible with the observed charged two-particle pseudorapidity correlations. These correlations and the results for the average number of photons as a function of the produced number of charged particles favour the conclusion that photon sources other than π0 s contribute significantly to the observed photon yield in non single-diffractivep % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGabmiCayaara% aaaa!36FA! $$\bar p$$ -collisions. For example, if all photons are assumed to come from π0 s and η mesons, a η/π0 ratio of about 20% is inferred.

Charged particle multiplicity distributions for the inelastic, non-single-diffractive component of p p reactions at 540 GeV CMS energy and of pp reactions above about 10 GeV are shown to be remarkably well described by a negative binomial distribution at each energy. The two parameters of the distribution depend on energy in a regular manner, which affords the possibility of predicting multiplicity distributions at high energies not yet experimentally available. In this description there is a complete absence of any tendency to approach asymptotic KNO scaling below 540 GeV. The approximate scaling in the CM energy range 10–62 GeV is shown, in this framework, to be accidental.

We have studied π−d interactions at 21 GeV/c with charged multiplicities of 9 or more. Cross sections, single-particle distributions and two-particle correlations are discussed. The evidence for double scattering effects is confirmed and analysed.

We present new data on charged particle production in p p interactions at 100 GeV/c. Comparisons are made between p p annihilations (estimated by differences) between corresponding p p and pp data samples) and e+e− annihilation into hadrons. A technique for separating the inclusive proton and pion spectra is described and the resulting pion spectra are studied in terms of Feynman x, rapidity and pT. Comparison with pp data allows us to estimate the pion spectra in p p annihilations and we find agreement with predictions of Mueller-Regge theory. We also present results on semi-inclusive π± and proton production, give updated topological cross sections and describe further attempts to isolate effects due to annihilations. Finally we investigate the diffractive excitation of the antiproton into low-mass states by studying events with a slow recoil proton.

A large scintillating-fibre detector consisting of ≈ 60 000 scintillating plastic fibres of 1 mm diameter and 2.4 m length has been used successfully as a tracking and preshower detector in the UA2 experiment at CERN. The detector readout and the results from the p p data-taking run are described.

We present data on two-particle pseudorapidity and multiplicity correlations of charged particles for non single-diffractive\(p\bar p - collisions\) at c.m. energies of 200, 546 and 900 GeV. Pseudorapidity correlations interpreted in terms of a cluster model, which has been motivated by this and other experiments, require on average about two charged particles per cluster. The decay width of the clusters in pseudorapidity is approximately independent of multiplicity and of c.m. energy. The investigations of correlations in terms of pseudorapidity gaps confirm the picture of cluster production. The strength of forward-backward multiplicity correlations increases linearly with ins and depends strongly on position and size of the pseudorapidity gap separating the forward and backward interval. All our correlation studies can be understood in terms of a cluster model in which clusters contain on average about two charged particles, i.e. are of similar magnitude to earlier estimates from the ISR.

We present results on inclusive Δ++ (1236) production in 100 GeV/c pp interactions. In the region |t| < 1 GeV2 we find a cross section of 1.29 ± 0.15 mb. Comparisons with pp interactions at high energies show Δ++ production in pp and pp interactions to be very similar. The decay angular distributions of the Δ++ are consistent with production predominantly through pion-exchange and the properties of the system recoiling from the Δ++ are similar to those of real π+p interactions. However, the pπ+ background is found to show qualitatively similar behaviour. In contrast to the indications of Δ++ production through pion exchange we also find evidence that events proceeding through diffraction dissociation are more likely to contain Δ++ than other events. We present results on the forward production of Δ++ in association with Δ++ and protons.

A detailed analysis ofK 0 production in $$\bar pp$$

We present data on the inclusive neutron spectra produced in the forward direction by the interactions of 23.85 GeV/ c protons in a copper target. The results are in good agreement with the predictions of the triple-Regge model.

We present evidence for a narrow Y∗ with a mass of 3.17 GeV and a width ⩽ 20 MeV decaying to ΣKK + pions, ΛKK + pions and ΞK + pions. The data come from two high statistics K−p bubble chamber experiments with a sensitivity of ≈100 eV/μb at 8.25 GeV/c and ≈ 45 eV/μb at 6.5 GeV/c.

We present a study of the reactions pp→ppπ0, pp→pnπ+, and pp→ npπ− at 8.8 GeV/c. Cross sections for the reactions are given, and the main features of the data are shown. The data are compared with the predictions of the Deck model, and evidence is presented for the presence of baryon exchange in the Deck amplitude.

We have investigated the inclusive production of $\ensuremath{\gamma}$, ${K}_{S}^{0}$, ${\ensuremath{\Lambda}}^{0}$, and ${\overline{\ensuremath{\Lambda}}}^{0}$ in 100-GeV/c $\overline{p}p$ interactions in the 30-in. hydrogen bubble chamber at Fermilab. We present various inclusive distributions and compare them with corresponding distributions in 100-GeV/c $\mathrm{pp}$ interactions and lower-energy $\overline{p}p$ interactions. We find some evidence for $\ensuremath{\Sigma}(1385)$ production but none for ${K}^{*}(890)$ production. We find evidence for a nonzero ${\ensuremath{\Lambda}}^{0}$ polarization of -0.45 \ifmmode\pm\else\textpm\fi{} 0.21.

We have made the first observations of Ξ− production in pp interactions at √s=540 GeV. In a sample of 6964 non single-diffractive events we observe 17 Ξ− decays with an estimated background of less than one event. This corresponds to 0.04 ± 0.01 Ξ− per event in the transverse momentum range pt>1.0 GeV/c and in the pseudorapidity range |η| < 3.5. Assuming an exponential pt distribution, we find 〈pt〉=1.1−0.2+0.3 GeV/c.

Inclusive cross sections for π0, Ks0, Λ0 and Λ0 production in 100, 200 and 360 GeV/c π−p interactions are presented and compared with data at other energies. Invariant cross sections for γ, Ks0, Λ0 and Λ0 production are presented in terms of Feynman x, the rapidity y, and transverse momentum squared, pT2. A comparison of the observed γ spectrum is made with the spectra computed assuming that the π0 momentum distribution is identical to that of the observed π+ orπ−.

Cross-sections for diffractive particle production and pseudorapidity distributions of the decay products of diffractive states are presented. The data were obtained with the UA 5 streamer chamber detector at the CERNpp Collider operated in a new pulsed mode yieldingpp interactions at c.m. energies of 900 and 200 GeV. Data recorded with a special trigger designed to select a sample of events enriched in single-diffractive interactions clearly favour apt-limited fragmentation of diffractive states. The cross-section for single-diffractive particle production ϊ was found to be 7.8±0.5±1.1 mb at 900 GeV and 4.8±0.5±0.8 mb at 200 GeV (first error statistical, second systematic). From the pseudorapidity distribution of diffractive states we deduce the average number of charged particles to be 6.5±1.0 at 900 GeV and 4.1±1.1 at 200 GeV. Furthermore we report on our estimates for the cross-section of double-diffractive particle production at both Collider energies.

First results from the UA5 detector on charged particle production at √s = 540 GeV in the pseudorapidity range ∣ν∣