Baryon yields, isospin effects and strangeness production in elementary hadronic interactions

New NA49 data from hadron+proton and hadron+Pb interactions are used to extract detailed information on projectile isospin effects and baryon, baryon pair and strangeness production. Consequences for the interpretation of hadron production and strangeness enhancement in nuclear collisions are discussed.     

Charmed particle production in hadron-hadron collisions

In the framework of Quark-Gluon-String Model developed recently in ITEP we calculate spectra of charmed particlesD,D _s,Λ_c,Ξ_c,Ω_c in hadron-hadron collisions taking into account the decays ofS-wave resonances like D^*,D_s ^*,Σ_c,Σ_c ^*,Ξ_c ^*,Ξ_c ^′, and Ω_c ^*. We describe the bulk of the existing data onD, D^*, adΛ _c production in πp andpp collisions and predict the yield of charmed particlesin Σ^?p and Ξ^?p reactions at hyperon beam energies of 340 GeV/c and 600 GeV/c. Because of significant production of baryon resonances our predictions for unfavored fragmentation differ from predictions of other models which do not take resonance production into account.     

Baryon production in QCD jets

Recent data from several sources—Υ decays, high energy deep inelastic scattering,e ⁺ e ^? annihilation at PETRA—reveal substantial baryon production in QCD jets. We discuss the likely mechanisms within the context of QCD, and formulate experimental tests to distinguish amongst them.     

Baryon number transfer in hadronic interactions

The process of baryon number transfer due to string junction propagation in rapidity space is analyzed. It has a significant effect on the net baryon production in pp collisions at mid-rapidities and an even larger effect in the forward hemisphere in the cases of and interactions. The results of numerical calculations in the framework of the quark-gluon string model are in reasonable agreement with the data. Received: 14 December 2001 / Revised version: 24 April 2002 Published online: 16 October 2002 RID="a" ID="a" Permanent address: Yerewan Physics Institute, Armenia and JINR, Dubna, Russia e-mail: argev@jerewan1.yerphi.am RID="b" ID="b" e-mail: Alphonse.Capella@th.u-psud.fr RID="c" RID="d"     

Multifractal thermodynamics of hadron-hadron and hadron-nucleus interactions

It is shown that the constant-specific-heat approximation is applicable to multifractal thermodynamics of hadron-hadron and hadron-nucleus interactions at high energies. Moreover, the constant specific heats calculated from experimental data on hadron-hadron and hadron-nucleus interactions have approximately the same value for both these types of multifractal multiproduction. Thus this parameter may turn out to be an universal characteristic of the hadron-hadron and hadron-nucleus interactions. Some relationship of this phenomenon to multifractal thermodynamics at the onset of chaos is briefly discussed. Received: 16 December 1997 / Revised version: 2 April 1998     

Measurement of the hadron structure function in hadron-hadron interactions

Previously published data on low-p _T π⁺/K ⁺/p?p interactions at 250 GeV/c are used to analyze the rapidity charge distribution and hadron structure function for the projectile hadrons. It is shown that the rapidity charge distribution for projectile hadrons can be approximated by a Gauss distribution, and their structure functions are found.     

Observation of exclusive electron-positron production in hadron-hadron collisions

We present the first observation of exclusive e(+)e(-) production in hadron-hadron collisions, using pp[over] collision data at (square root) s = 1.96 TeV taken by the run II Collider Detector at Fermilab, and corresponding to an integrated luminosity of 532 pb(-1). We require the absence of any particle signatures in the detector except for an electron and a positron candidate, each with transverse energy E(T) > 5 GeV and pseudorapidity |eta| < 2. With these criteria, 16 events are observed compared to a background expectation of 1.9+/-0.3 events. These events are consistent in cross section and properties with the QED process pp[over] --> p + e(+)e(-) + p[over] through two-photon exchange. The measured cross section is 1.6(-0.3)(+0.5)(stat) +/- 0.3(syst) pb. This agrees with the theoretical prediction of 1.71+/-0.01 pb.     

Baryon production in the string fragmentation picture

An improved version of the “pop-corn” model for baryon production in quark and gluon jets is presented. With a reduced number of parameters the model reproduces well both production rates for different baryon species and baryon momentum distributions. Predictions are presented for a set of baryon-antibaryon correlations.     

Baryon production by primordial black holes

The evaporation of primordial black holes (PBH's) by the Hawking process can produce an excess of baryons over anti-baryons. Assuming a power-law form of the initial mass spectrum of PBH's and taking into account the observational constraints on that spectrum we calculate the baryon excess produced. We find that if the spectrum is steep ($\text{α?3.5}$) or cut off for masses above ～ 10⁹ g, the observed baryon/photon ratio of ～ 10^?9 can be produced by PBH evaporations.     

Baryon production in lepton-nucleon scattering and diquark fragmentation

We study baryon production in deep inelastic scattering using an extended version of the Lund jet model. There are two contributing sources. The first is baryon production in the target fragmentation. In a scheme related to our earlier work on lowp _hu baryon fragmentation we present some details of the fragmentation of a diquark into baryons and mesons. A non-negligible baryon-antibaryon production is observed ine ⁺ e ^? annihilation. In a previous paper we developed a model for this production, and the same mechanism should also give fast baryons in leptoproduction. In this paper we discuss those features of baryon production which can be more easily studied in a leptoproduction experiment.     

A spontaneously broken quintet Baryon model for strong interactions

A gauge type model of quantum field theory for strong interactions based on a quinted of observed fields, namely the proton, neutron, , _c and _b baryon fields is proposed. Gauging the resulting global symmetry groupK= SU(3)×¹ U(1)ײ U(1)׳ U(1) for matter fields, one obtains boson-fermion field theory with eleven gauge bosons. The analysis of admissible Higgs sector indicates that the Higgs multiple consists of one adjoint and two fundamental representationsSU(3) and three scalar representations of¹ U(1),² U(1) and³ U(1). The structure of the Higgs sector implies that the original symmetry group extends to the groupK×U(2). Breaking spontaneously the obtained field theory, one converts gauge bosons into the eleven massive vector bosons which can be identified with the observed , K^*, ¯K^*, , , J/ and Y vector mesons. The surviving global symmetry is isomorphic with the symmetry groupSU(2)× ⁰ U(1)× ×¹ U(1)ײ U(1)׳ U(1) corresponding to the isospin, strangeness, baryon number, charm and beauty conservation observed in strong interactions. The surviving Higgs scalars have the same quantum numbers as , K, ¯K, , S, , , and _b mesons. The model gives a newSU(3) classification scheme for baryons without charm and beauty in terms of triplets, sextets and 15-plets. These multiplets can be identified with the observed baryons; the scheme also includes the observed Z₀ and Z₁ baryons (the experimental evidence of which is, nevertheless, still weak). The model predicts the existence and the specific quantum numbers of new mesons and baryons with charm and beauty, and provides a very simple framework for the dibaryon analysis. Since all final physical fields are massive, this model is free from infrared divergences.Invited talk presented at the International Conference Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 23–27, 1986.