Koba-Nielsen-Olesen scaling

A correct version of Koba-Nielsen-Olesen (KNO) scaling is described in detail for multiplicity distributions. Some statements on the violation of KNO scaling that are based on an erroneous interpretation of experimental data are discussed. An accurate comparison with data is presented for the distributions of negatively charged particles originating from electron-positron annihilation at $\sqrt s = 3 - 161GeV$ , from inelastic proton-proton collisions at p _lab=4.5–520 GeV/c, and from nucleus-nucleus collisions at p _lab=4.5–520 GeV/c per projectile nucleon. Data on proton-antiproton interactions at $\sqrt s = 546GeV$ are also considered.     

Strangeness enhancement in sulphur—Nucleus collisions at 200 A GeV/c

The NA35 experiment used several independent methods to determine the strange particle production in p+S and S+A collisions. The different techniques show consistent results. Strangeness conservation in full phase space is used as an additional check of the consistency of the data. On the base of the analysis in full phase space it could be shown that strangeness conservation is fullfilled. The NA35K _S ⁰ in S+S and S+Ag are consistent with the NA44 results forK ⁺ andK ^?. The results of the NA36 collaboration for S+Pb collisions were extrapolated to full phase space. The comparison with the NA35 results shows more than two times lower yields. The ratio of Λ to $\bar \Lambda $ at midrapidity of NA36 is inconsistent with the high baryon density determind by NA35. The strange particle production is compared to the abundance of non strange particles, especially negatively charged pions which are measured in full phase space in the same experiment. A clear enhanced strange hadron production relative to σ^? is observed in S+Ag collisions compared to p+S reactions at the same energy. TheK _S ⁰ multiplicity in full phase space per negative hadron (h ^?) in S+S, S+Ag and Pb+Pb is enhanced by about a factor 1.6 compared to N+N and p+S collisions. The NA36 result for theK _S ⁰ multiplicity perh ^? in S+Pb is below the N+N value.     

Single decay-lepton angular distributions in polarizede + e − →\overline {tt} and simple angular asymmetries as a measure of CP-violating top dipole couplingsand simple angular asymmetries as a measure of CP-violating top dipole couplings

In the presence of an electric dipole coupling of $\overline {tt} $ to a photon, and an analogous ‘weak’ dipole coupling to the Z, CP violation in the process e⁺e^? → $\overline {tt} $ results in modified polarization of the top and the anti-top. This polarization can be analyzed by studying the angular distributions of decay charged leptons when the top or anti-top decays leptonically. Analytic expressions are presented for these distributions when eithert or $\overline t $ decays leptonically, including $\mathcal{O}$ (α_s) QCD corrections in the soft-gluon approximation. The angular distributions are insensitive to anomalous interactions in top decay. Two types of simple CP-violating polar-angle asymmetries and two azimuthal asymmetries, which do not need the full reconstruction of thet or $\overline t $ , are studied. Independent 90% CL limits that may be obtained on the real and imaginary parts of the electric and weak dipole couplings at a linear collider operating at √ s = 500 GeV with integrated luminosity 500 fb^? and also at √s = 1000 GeV with integrated luminosity 1000 fb^? have been evaluated. The effect of longitudinal electron and/or positron beam polarizations has been included.     

Characteristics of charged particle production in relativistic heavy-ion collisions

Inclusive spectra of charged particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } = 130$ GeV and 200 GeV were measured with the STAR detector at RHIC. The measured mean transverse momentum 〈p _T 〉 shows a characteristic dependence on charged particle multiplicity and beam energy in Au+Au collisions that is distinctly different from pp, $p\bar p$ and e⁺e^? collisions. A 32%±3%(syst) increase in 〈p _T 〉 from pp to Au+Au collisions was observed at 200 GeV. While the charged multiplicity was found to increase by 19%±5%(syst) from $\sqrt {s_{NN} } = 130$ GeV to 200 GeV, no significant difference in 〈p _T 〉 was found between the two energies. A comparison with model predictions is discussed.     

K S 0 , Λ and ≡ production at intermediate to high pT from Au+Au collisions at \sqrt {s_{NN} } = 39, 11.5 and 7.7 GeV

We report on the p _T dependence of nuclear modification factors (R _CP) for K _S ⁰ , ??, ?? and the $\bar NK_S^0 $ ratios at mid-rapidity from Au+Au collisions at $\sqrt {s_{NN} } $ = 39, 11.5 and 7.7 GeV. At $\sqrt {s_{NN} } $ = 39 GeV, the R _CP data show a baryon/meson separation at intermediate p _T and a suppression for K _S ⁰ for p _T up to 4.5 GeV/c; the $\bar \Lambda K_S^0 $ shows baryon enhancement in the most central collisions. However, at $\sqrt {s_{NN} } $ = 11.5 and 7.7 GeV, R _CP shows less baryon/meson separation and $\bar NK_S^0 $ shows almost no baryon enhancement. These observations indicate that the matter created in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 or 7.7 GeV might be distinct from that created at $\sqrt {s_{NN} } $ = 39 GeV.     

Strange hadron production in d+Au collisions at RHIC

We report the centrality dependence of transverse mass (m _t ) spectra at mid-rapidity for the identified strange hadrons K _S ⁰ , ? $\Lambda + \bar \Lambda $ and $\Xi ^ - + \bar \Xi ^ + $ in d+Au collisions at RHIC. The measured transverse momentum (p _T ) covers 0.4<p _T <6.0 GeV/c for K _S ⁰ , ø, $\Lambda + \bar \Lambda $ and 0.6<p _T <5.0 GeV/c for $\Xi ^ - + \bar \Xi ^ + $ . The binary collision normalized nuclear modification factors R _CP of these hadrons indicate that the Cronin effect in d+Au collisions has a distinct particle-type dependence. the R _CP ratios show a distinct baryons versus mesons dependence: the R _CP for $\Xi ^ - + \bar \Xi ^ + $ follows that for $\Lambda + \bar \Lambda $ while the R _CP for the ? is close to that for the K _S ⁰ . Similar features have also been observed in Au+Au collisions. Initial parton scattering alone is not sufficient to explain this particle-type dependence. Hadronization processes are likely to be important for determining hadron properties in high-energy collisions as suggested by coalescence and recombination models.     

Benchmark cross sections forp \bar p collisions at 1.8 TeV

High-energyp \(\bar p\) collisions provide many quantitative tests of the standard model. Of particular interest are “hard scattering” processes, which test not only standard model matrix elements and higher order perturbative corrections, but also the distributions of quarks and gluons in the colliding hadrons. We present detailed comparisons of data from the CERNSp \(\bar p\) S collider with theory, incorporating up-to-date parton distributions derived from recent deep inelastic scattering data. Encouraged by the excellent agreement between data and theory at \(\sqrt s \) =630GeV, we present a complete set of “benchmark” predictions for the FNALp \(\bar p\) collider at \(\sqrt s \) =1.8TeV.     

First measurement of the strange particles R CP nuclear modification factors in heavy-ion collisions at the SPS

The NA57 experiment has measured the p _T distributions of K _S ^O , Λ, and $\bar \Lambda $ particles in fixed-target Pb?Pb interactions at √s _NN=17.3 GeV, as a function of the collision centrality. In this paper we study the central-to-peripheral nuclear modification factors and compare them to other measurements and to theoretical predictions.     

Quantitative assessment of target dependence of pion fluctuation in hadronic interactions – estimation through erraticity

Event-to-event fluctuation pattern of pions produced by proton and pion beams is studied in terms of the newly defined erraticity measures χ(p, q), $\chi_q^{\prime}$ and $\mu_q^{\prime}$ proposed by Cao and Hwa. The analysis reveals the erratic behaviour of the produced pions signifying the chaotic multiparticle production in high-energy hadron–nucleus interactions (π ^???–AgBr interactions at 350 GeV/c and p–AgBr interactions at 400 GeV/c). However, the chaoticity does not depend on whether the projectile is proton or pion. The results are compared with the results of the VENUS-generated data for the above interactions which suggests that VENUS event generator is unable to reproduce the event-to-event fluctuations of spatial patterns of final states. A comparative study of p–AgBr interactions and p–p collisions at 400 GeV/c from NA27, with the help of a quantitative parameter for the assessment of pion fluctuation, indicates conclusively that particle production process is more chaotic for hadron–nucleus interactions than for hadron–hadron interactions.     

Probing the QCD phase boundary with elliptic flow in relativistic heavy ion collisions at STAR

We present measurement of elliptic flow, v ₂, for charged and identified particles at midrapidity in Au+Au collisions at $\sqrt {s_{NN} } $ = 7.7?C39 GeV. We compare the inclusive charged hadron v ₂ to those from transport model calculations, such as the UrQMD model, AMPT default model and AMPT string-melting model. We discuss the energy dependence of the difference in v ₂ between particles and anti-particles. The v ₂ of ? meson is observed to be systematically lower than other particles in Au+Au collisions at $\sqrt {s_{NN} } $ = 11.5 GeV.     

Q^2 \to A\sqrt s Scaling law fore + e −→hadrons andpp collisions at high energy

It has been conjectured recently that multiparticle production in low momentum transfer hadronic collisions is due to gluon bremsstrahlung off highly virtual (mass \(\mu ^2 \sim \sqrt s \) ) quarks. The model gives a new scaling law: \(Q^2 \to A\sqrt s \) , for comparinge ⁺ e ^?→hadrons andpp non-diffractive inelastic data. The scaling law is tested for average multiplicities, plateau height and 〈p ₂ ^⊥ 〉. Fore ⁺ e ^? annihilation a parametrization of data based on perturbative QCD approach is used.     

Inclusive pion production in 360 GeV/cpp interactions

In a study of proton-proton interactions at \(\sqrt s = 26GeV\) , inclusive distributions of single pions and systems of pions of various charge combinations are presented, as well as the production ratio obtained in association with various trigger particles. The results are compared to current phenomenological models in an attempt to understand multiparticle productions in hadron collisions.     

Multi-strange baryon elliptic flow in Pb-Pb collisions at \sqrt {s_{NN} } = 2.76 TeV measured with the ALICE detector

We present the results on elliptic flow with multi-strange baryons produced in Pb-Pb collisions at $\sqrt {s_{NN} } $ = 2.76 TeV. The analysis is performed with the ALICE detector at LHC. Multi-strange baryons are reconstructed via their decay topologies and the v ₂ measurements are analyzed with the two-particle scalar product method. The p _T differential v ₂ values are compared to the viscous hydrodynamical (VISH2+1) model calculation and to the STAR measurements in Au-Au collisions at $\sqrt {s_{NN} } $ = 200 GeV. We found that the model describes ?? and ??v ₂ measurements within uncertainties. The differential v ₂ of ?? and ?? is similar to the STAR measurements at 200 GeV in Au-Au collisions.     

Role of the cascade interactions on the multiplicity distribution in hadron-nucleus collisions

Multiplicity distribution in proton-nucleus (p-A) collisions are investigated by the use of the Monte Carlo event generator MCMHA which has been developed based on the multi-chain model. The comparisons between the calculational results of MCMHA and the data are made through the parameters of negative binomial distributions. We can find nice agreement between them. The interpretation for the difference in the behaviour of 1/k in the backward hemisphere between \(p(\bar p) - p\) andp-A collisions is presented. In this connection, we also discuss the multiplicity ration 〈N〉 _pA /〈N〉 _pN .     

Phenomenological model for the \overline{{K}}N \rightarrow K \Xi reaction

A phenomenological model for the $ \overline{{K}}$ N $ \rightarrow$ K $ \Xi$ reaction is suggested. The model includes s and u channel exchanges by $ \Lambda$ , $ \Sigma$ , $ \Sigma$ (1385) , and $ \Lambda$ (1520) and s channel exchanges by above-threshold hyperonic resonances. The explicit expression for the propagator for a particle with spin 7/2 is presented. High-mass and high-spin resonances play a significant role in the process. We deal with the whole set of existing experimental data on the cross-sections and polarizations in the energy range from the threshold to 2.8GeV in the center-of-mass system and reach a good agreement with experiments. Applications of the model to other elementary reactions of $ \Xi$ production and to $ \Xi$ hypernuclear spectroscopy are briefly discussed.     

How to search for pentaquarks in high energy hadronic interactions

The strange-anticharmed Pentaquark is a uud $\bar c$ ;s or udd $\bar c$ s five-quark baryon that is expected to be either a narrow resonance, or possibly even stable against strong and electromagnetic decay. We describe this hyperon here, its structure, binding energy and lifetime, resonance width, production mechanisms, production cross sections, and decay modes. We describe techniques to reduce backgrounds in search experiments and to optimize the conditions for Pentaquark observation. Possibilities for enhancing the signal over background in Pentaquark searches are investigated by examining predictions for detailed momentum and angular distributions in multiparticle final states. We consider a loosely boundD _s ^? N molecule and also a strongly-bound five-quark system. Fermilab E791 data, currently being analyzed, may have marginal statistics for showing definitive signals. Future experiments in the spirit of the recent CHARM2000 workshop, such as FNAL E781 and CERN COMPASS with 10⁶–10⁷ reconstructed charmed baryon events, should have sensitivity to determine whether or not the Pentaquark exists.     

Leading-particle effects in the spectra of Λc and \bar \Lambda _c produced in Σ− p, pp, and π − p interactions

The spectra of leading and nonleading charmed baryons (Λ_c and $\bar \Lambda _c$ ) and the asymmetries between these spectra measured in Σ^? A, π ^? A, and pA collisions at p _L =600 GeV/c in the E781 experiment are simultaneously described within the framework of the Quark-Gluon String Model (QGSM). It is shown that the charmed baryon spectra can be fitted by QGSM curves calculated with the parameter of diquark fragmentation, $a_f^{\Lambda _c } = 0.006$ . It was found in this experiment that the asymmetry between the spectra of Λ_c and $\bar \Lambda _c$ in π ^? A collisions is of nonzero value. It might be described in our model only assuming that the string junction is transferred from target proton into the kinematical region of pion projectile fragmentation.