Neutral strange particle production inK + p interactions at 32 GeV/c

The production properties ofK _s ⁰ , \(\bar \Lambda\) andK ⁺ p interactions at 32 GeV/c are investigated using the final statistics of the experiment. We present total and semi-inclusive cross sections and aver-age multiplicities. Estimates are given of the diffractive dissociation contributions to total and differential cross sections. Thex-,p _T ^?, and transverse mass dependence of inclusive and semi-inclusive distributions is discussed as well as properties of “prompt”K _s ⁰ 's. The ratio of “prompt”K ₈₉₀ ⁺ (K ₈₉₀ ⁰ ) to “prompt”K ⁰ cross sections is measured to be 1.03±0.12 (0.98±0.17). From a comparison of \(\bar \Lambda\) production inK ^± p interactions at 32 GeV/c, we estimate a strange sea-quark suppression of 0.26 ±0.02. The double differential cross sections ofK _s ⁰ 's is studied as a function of Feynman-x andp _T ² , and a Triple-Regge fit performed. The data are compared in detail to versions of the Lund-model for low-p _T hadronic collisions.     

Single photon production and event structure in hadronic interactions at large pT

We have calculated within the QCD frame-work the inclusive one and two particle production cross sections triggering on a photon or a π⁰ for incident protons and antiprotons. The results are compared and shown to be in good agreement with all pertinent experimental data, provided a hard gluon structure function is used. The γ/π⁰ ratio as well as the ratio of bremsstrahlung to directly produced γ's are examined as a function of rapidity andp _T. Results are presented for c.m. energies \(\sqrt s = 62\) and 800 GeV     

Inclusive Λ(1,520) production in 100 GeVp Be interactions

The reactionpBe→Λ(1,520)X has been measured at 100 GeV incident momentum in the kinematic range 0.15<x<0.35 \((x = 2p_\parallel ^{c.m} /\sqrt s )\) andP _T <1 GeV. The invariant cross section is compatible with that measured forpp interactions at the CERN-ISR. The differential cross sectiondσ/dp _T ² is fitted to an exponentiale ^?αp _T ² with α=2.7 GeV^?2.     

The holographic bubble chamber experiment and the determination of the effective charmed quark mass and theK-factor for hadronic charm production

In the first holographic bubble chamber experiment — the HOBC experiment — we have accumulated a total of 40000 holograms with particle interactions. We have determined the total charm pair cross section inpN collisions to be 23.3 _?7.7 ⁺¹⁰ μb and 3.6 _?1.7 ^+2.3 μb for 360 and 200 GeV/c incident protons respectively. We have assumed a linear dependence of the cross section on the atomic number of the target. This experiment has demonstrated the feasibility of holographic recording in small bubble chambers. Assuming that the charm cross section can be described by the standard QCD factorized expression with gluon fusion and quark-antiquark annihilation, we have used our measured charm cross sections with other measurements to determine the effective charmed quark mass to be 1.8 _?0.35 ^+0.25 GeV/c². TheK factor, which describes the importance of the higher order corrections, is calculated to be 9.8 _?6.9 ^+12.5 (See noted added in proof.)     

Higher order QCD corrections to the three-jet cross section: Bare versus dressed jets

We report results for the three-jet cross section to order α _s ² using a jet resolution criterion depending on the jet mass and study the sum of three-and four-jet cross sections inO(α _s ² ) as a function of the resolution parameters in order to obtain the limit of infinite resolution.     

A study of the production of high-p t π0 at the CERN intersecting storage rings

The inclusive cross-section for π⁰ production near 90° inpp collisions at the CERN Intersecting Storage Rings has been studied for thep _T range 3<p _T <16GeV/c at four different centre-of-mass energies ( \(\sqrt s = 30.6\) , 44.8, 52.7, and 62.8 GeV). In this experiment the two photons from the π⁰→yy decay were resolved and measured separately forp _T values up to 10 GeV/c. Results indicate an agreement with thep _T ^?8 behaviour for the lower values ofp _T and a slower decrease of the cross-section for the higher values ofp _T . The high-p _T data deviate from the scaling expressionp _T ^?n F(x _T ), which holds for the lowerp _T values (p _T <8GeV/c).     

Inclusive Λ production in\bar p p interactions at 3.0, 3.5, 4.0 and 4.5 GeV/c

Inclusive Λ production in \(\bar p\) p interactions at 3.0, 3.5, 4.0 and 4.5 GeV/c is studied. The inclusive cross sections for Λ and Λ \(\bar \Lambda \) production are measured. The differential cross sections as functions ofx, y, andP _T ² are given for each beam momentum. It is found that the contribution of indirect production of Λ from resonance decay is considerably enhanced in the region of higher missing mass against Λ. The negative polarization is observed for Λ with largerP _T and lower missing mass, and is found to be mainly from two body reactions. Inclusive cross sections for∑ ^±(1385) production and the fraction of indirect Λ from∑ ^±(1385) decay are measured. The ratio between the cross sections for∑ ⁺(1385) and∑ ^?(1385) productions is found to be almost constant for wide range of beam momenta.     

Inclusive prompt photon production inpp and\bar p p interactions

High transverse momentum (p _T ) production of pions and photons in proton-proton and proton-antiproton interactions are studied within the QCD framework and compared with the presently available experimental data. Scaling violation effects are included, and shown to be important at largep _T . Predictions are made for the γ/π⁰ ratio at collider energies. The possibility of extricating the gluon distribution function from the invariant cross section data for the process \(\bar p\) +p→γ+X is suggested.     

Pulsed ESR on the organic ion radical salt: 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-[TCNQ]2

We present firstT _1e ^?1 andT _2e ^?1 measurements on the organic ion radical salt 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-(TCNQ)₂ as function of temperature and of orientation. The electronic spin diffusion constant could be determined directly by the electron spin echo field gradient technique:D (300 K)=0.03±0.02 cm²/sec. Pulsed ESR experiments have — in comparison to conventional cw-ESR — the advantage to monitor viaT _1e ^?1 andT _2e ^?1 the spectral density of dynamical processes at different frequencies. This is shown in a general manner on 3,3′-diethyl-4,4′-dimethyl-2,2′-thiazolocyanine-(TCNQ)₂. Between 300 and 60 K,T _1e ^?1 andT _2e ^?1 are close in amplitude and have a similar temperature dependence. At 60 K their degeneracy is lifted, yielding a quantitative value for the effective spin exchange between localized spinsτ _ex ^?1 sec^?1 and via the absolute value of the relaxation an average distance of the localized centers of about 12 Å. The dynamical data as evaluated above cannot be correlated with the conductivity, clearly indicating that the conduction electrons are a minority, not being monitored by the ESR-experiments.     

Inclusive∑ ± production in\bar pp interactions at 12 GeV/c

Inclusive production of∑ ^±(1385) resonances is studied in \(\bar pp\) interactions at 12 GeV/c. The cross sections for∑ ⁺(1385)+cc and∑ ^? are determined to be 251±38 μb and 123±30 μb, respectively. The inclusive spectra are presented as a function of Feynman x, c.m. rapidity and the squared transverse momentump _T ² . Significant differences with the correspondingpp data are found in the longitudinal momentum distributions. The qualitative features of the production can be explained by simple quark ideas.     

Production of charmed hadrons in neutrino proton and antineutrino proton charged current interactions

Usind data from avp and \(\bar v\) p experiment with BEBC at CERN, the rates for inclusive production ofD ^*+,Λ _c ⁺ andD ⁰ invp scattering and ofD ^*? in \(\bar v\) p scattering are measured. Some examples of the exclusive production ofD ^*+,Λ _c ⁺ and∑ _c ⁺⁺ are given. The cross section for the reactionvp→μ ^? _c ⁺⁺ is estimated.     

Two-jet cross section ine + e − annihilation

We calculate the two-jet cross section in order α _s ² in the framework of massless perturbative QCD, using for jet resolution the jet mass. We derive results for two different approaches. One approach is based on the singularity structure of the various contributions. The other one is adjusted to the methods used in three- and four-jet calculations so that the total cross section can be reconstructed.     

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of π⁰ mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of ?s = 91.2 GeV. Neutral pions are reconstructed using photons measured in the electromagnetic calorimeter and photons from conversion pairs. The inclusive π⁰ momentum spectrum is measured in the range 0.025 < x _p = p/p _beam < 1. In this range the number of π⁰ per hadronic Z is found to be 4.80 ± 0.07(stat) ± 0.31(sys). The differential inclusive π⁰ cross section is also measured as a function of transverse momentum with respect to the event plane (p _T ⁱⁿ and p _T ^out ).     

Two-particle production inK + p interactions at 32 GeV/c

Results are presented on two-particle inclusive production inK ⁺ p interactions at 32 GeV/c. We study thex _1,2=x ₁+x ₂ dependence of invariant structure functions of (ππ)-pairs and compare them to single particle inclusive distributions in the fragmentation regions. Distributions of particles observed at Feynmanx ₂ in association with various “trigger” particles or systems atx ₁ in the same hemisphere are dicussed in terms of the reduced variable \(\tilde x_2 = x_2 /(1 - |x_1 |)\) . We further present absolute production rates and production ratios of π⁺'s and π^?'s associated with π^±,K _s ⁰ , Λ, \(\bar \Lambda \) ,K ^*+ (890), (K _s ⁰ π⁺), and (π⁺ π^?)-triggers, and compare them with qualitative predictions of the quark recombination model. Forwardbackward correlations between (K _s ⁰ π^±), (K _s ⁰ ,p), (Λ, π^?), \((\bar \Lambda \pi ^ \pm )\) , and (p, π^?) pairs are also discussed.     

Jet cross sections in leptoproduction from QCD

We have calculated the longitudinal and other polarization dependent cross sections for jet production in deep inelasticep, vp, and \(\bar vp\) scattering up to order α _s of the quark-gluon coupling constant. Fragmentation of final state partons into hadrons is taken into account. Distributions in thrust,p ₂ ^{T in} andp ₂ ^{T out} are predicted for all three reactions and various values ofW andQ.     

Gluon tagging in hard proton-proton interactions at the ISR

Events obtained by triggering on a single particle with high transverse momentump _T show a four-jet structure. The two transverse jets are due to the fragmentation of point-like scattered partons. Experimental evidence is presented that highp _T K ^? mesons and their associated jets are produced by hard scattering and subsequent fragmentation of flavour neutral partons with a rather soft structure function. Hence, gluons are a natural source of highp _T K ^? mesons which do not share any valence quark with the incoming protons. The analysis is based upon measurements of short-range quantum number correlations within the trigger jet and of long-range correlations between different jets. The data were obtained at \(\sqrt s\) =62 GeV GeV with the Split Field Magnet Detector (SFM) at the CERN ISR.     

General features of\bar pp interactions at 7.3 GeV/c

Absolute inclusive cross sections for \(\bar pp\) interactions at 7.3 GeV/c are given. The data cover prong cross sections,V ⁰, γ production and inclusive charged particle (p/π) production. Separation has been made into annihilation and non-annihilation components. Inclusive π⁺, π^? production in the processes of \(\bar pp\) annihilation and non-annihilation are compared with simple quark models.     

Influence of cone algorithm parameters on efficiency and characteristics of reconstructed jets in p-p interactions at \sqrt s = 200 GeV

The influence of the cone algorithm parameters (E _cut, E _seed, R) on efficiency and characteristics of reconstructed jets in p-p collisions at the energy $\sqrt s $ = 200 GeV is studied. Event generation was carried out using the Monte Carlo code PYTHIA. The fraction of dijet event production as a function of transverse momentum of the hard process $\hat p_ \bot $ for different algorithm parameters is studied. The dependence of energy and parton direction reconstruction accuracy for dijet events and two leading jets in N-jet (N _Jet ≥ 2) events on the algorithm parameters is found. The results of jet modeling are compared with predictions obtained in the framework of z-scaling and experimental data obtained at RHIC. It is proved that the slope parameter of the scaling function is independent of the algorithm parameters in the transverse jet energy range E _T ^Jet = 25–60 GeV. It is shown that in the region E _T ^Jet < 25 GeV, strong dependence of invariant cross sections and the slope of the scaling function on the algorithm parameters is observed, and this dependence is enhanced with decreasing E _T ^Jet .     

A computational study of entropy rules for charged fullerenes

Thermochemical data on fullerenes are relatively scarce. However, some thermochemical information can be derived from gas-phase experiments using the Knudsen cell mass spectrometry method. The third-law treatment can be carried out on the observed data, though one has to make the crucial presumption that the change in the thermodynamic potential ΔΦ _T ^o in the course of the reactions considered is negligible: ΔΦ _T ^o =0. It would be difficult to check the presumption directly in the experiment, but it can be checked computationally. Model reactions like C₆₀+ ₇₀ ^? = ₆₀ ^? +₇₀ are selected. The change in the thermodynamic potential ΔΦ _T ^o and the change in the standard entropy ΔS _T ^o are computed. For example, at a temperature of T=1000 K, the standard changes for the reaction evaluated using the SAM1 method are ΔΦ _T ^o =1.513 cal/(mol K) and ΔS _T ^o =?0.054 cal/(mol K). Overall, the computations support the critical thermodynamic presumption.     

Inclusive production of neutral strange particles in\bar pp interactions at 70 GeV/c

The inclusive production ofK _s ⁰ , Λ and \(\bar \Lambda \) particles is investigated in 70 GeV/c \(\bar pp\) interactions in an experiment performed at CERN using BEBC equipped with a TST. Differential cross-sections are studied and compared with corresponding data at surrounding energies. Differences withpp data obtained at the same energy allow an estimate of theK _s ⁰ , production cross-section in annihilation processes. Evidence is also given for central \(\Lambda \bar \Lambda \) production.