Heavy quark production in parton model and in QCD

The cross sections of heavy quark production inpp collision and for their photo- and electroproduction are calculated in the framework of QCD. The virtual nature of the interacting gluons as well as their transverse motion and different polarizations are taken into account. The obtained cross sections exhibit more rapid growth with the initial energy than the parton model predictions and thep _T distributions of produced heavy quarks are more smooth.     

Charged particle spectra in αα and αp collisions at the CERN ISR

Momenta of charged particles produced in inelastic αα, αp, andpp collisions were measured using the Split-Field-Magnet detector at the CERN Intersecting Storage Rings. Inclusive and semi-in-clusive spectra are presented as a function of rapidityy, Feynman-x, and transverse momentump _T . The inclusivey distributions agree well with predictions of the dual parton model; the highest particle densities are reached aty?0 and the momenta of leading protons decrease significantly for increasing total multiplicity. ‘Temperatures’ are equal in αα, αp, andpp interactions. Thep _T distributions depend weakly on the multiplicity.     

Correlation with large transverse momentum photons and the gluon structure function

The inclusive two-particle cross section for the production of largep _T photons and opposite side charged hadrons in proton-proton collisions is examined in detail in the framework of QCD. The model, with the parametrization as in our previous work, agrees with the measured single photon spectra. Quantitative predictions are made for two-particle distributions to be measured at the ISR. The contributions due to the photon bremsstrahlung and the effects coming from the intrinsic constituent motion are estimated. It is shown that indeed the direct subprocess gluon+quark→photon+quark gives the dominant contribution in the experimentally relevant region of phase space, and that direct information about the gluon structure function can be obtained from such measurements.     

QCD predictions for jet transverse momentum in leptoproduction

QCD predictions for distributions in the jet variable Σ_T  [Σ_hadp_T|]² are calculated for incident ν, $\text{ν}$ and μ. Estimates of the nonperturbative background are constructed.     

Perturbative quantum chromodynamics

A large variety of modern perturbative aspects of QCD is critically reviewed from a theoretical as well as phenomenological point of view. The first part of this review is devoted to the classical more formal approach of summing leading logs: After a brief discussion of the basic concepts of renormalization theory, we review the renormalization group and its predictions for the effective (running) coupling constant in any field theory (asymptotic freedom as well as ‘fixed point’ theories). Using, in addition, the operator product expansion for deep inelastic scattering we calculate scaling violations of structure functions and show how to compare these results with experiment. Furthermore, dynamical calculations of parton distributions are discussed, as well as σ_L/σ_T, jets in leptoproduction and subleading corrections. We then proceed to show how these renormalization group improved results can be also derived using a simple perturbative language (Kogut-Susskind; Altarelli-Parisi) or by summing parton (Bethe-Salpeter) ladders. The universal validity (process independence) of the resulting Q² dependencies of parton distributions is emphasized and their factorization from the uncalculable non-perturbative piece (infrared divergences) is discussed. These latter results enable us to make rather unambiguous predictions for processes other than deep inelastic scattering, to which the remainder of this review is devoted. The hard scattering processes discussed indetail include hadronic (Drell-Yan) production of lepton pairs as well as their transverse momenta, the hadronic production of heavy quark flavors, semi-inclusive processes and fragmentation functions, high-p_T reactions and some recent topics and problems of jet production in e⁺e^? annihilation.     

An experimental check of the quark-model relations for inclusive reactions

The quark-model relations for inclusive reactions obtained in the previous paper by two of the authors are compared with existing experimental data. The x and p_T² distributions are considered for hadrons produced as a result of fragmentation of an incident meson or nucleon, with the kinematics of the resonance decay being taken into account. The predictions of the quark model are in a reasonable agreement with experiment, both in the shape of spectra and in the absolute magnitude of cross sections. A number of predictions is obtained for cross sections of some inclusive reactions which are not yet measured.     

Test for T-violating in N-N scattering

We make predictions for the angular distributions of nucleon-nucleon observables revealing T-violation, in the limit of very short-ranged T-violating mechanisms. Curves are shown for the observables P - a, and P_A - P_B, at 425 MeV for both p-p and n-p scattering.     

Accuracy of speech transmission index predictions based on the reverberation time and signal-to-noise ratio

This paper examines the accuracy of the speech transmission index (STI) calculated from the reverberation time (T) and signal-to-noise ratio (L_SN) of enclosed spaces. Differences between measured and predicted STIs have been analysed in two rooms (reverberant vs. absorbent), for a wide range of absorption conditions and signal-to-noise ratios (sixteen tests). The STI was measured using maximum length sequence analysis and predictions were calculated using either measured or predicted values of T and L_SN, the latter assuming diffuse sound field conditions. The results obtained for all the conditions tested showed that STI predictions based on T and L_SN tend to underestimate the STI, with differences between measured and predicted STIs always lower than 0.1 (on a 0.0–1.0 scale), and on average lower than 0.06. According to previous research, these differences are noticeable and therefore non-negligible, as 0.03 is the just noticeable difference in STI. The use of either measured or predicted values of T and L_SN provided similar STI predictions (i.e. non-noticeable changes), with differences between predictions that are on average lower than 0.03 for the absorbent room, and lower than 0.01 for the reverberant room.     

Heavy-quark hadroproduction in k T -factorization approach with unintegrated gluon distributions

We consider the processes of heavy-quark production using the unintegrated gluon distributions. The numerical predictions for high-energy nucleon-nucleon and photon-nucleon collisions of the k _T -factorization approach (semihard theory) are compared with the experimental data from the Tevatron collider and HERA. The total production cross sections and pT distributions are considered and they are in reasonable agreement with the data for reasonable values of QCD scale. The text was submitted by the authors in English.     

On the hadron-parton reciprocity relation

The possibility of an equality between the distributions of partons inside hadrons and the distributions of hadrons in parton fragmentation is studied. It is consistent with existing electroproduction data when the momentum fractions involved are not too small. Implications for current-hadron interactions, large p_T hadronic cross sections and heavy lepton pair production in hadron-hadron collisons are discussed.     

Model for inclusive production of protons,anti-protons pions and kaons with large transverse momenta

The production of particle with large transverse momenta P_T and other unexpected features observed with CERN ISR are explained on the basis of a model which traces their origin to a small class of events, called central collisions, involving “core-core” interactions. In each central collision, two massive fire balls, moving slowly in the C.M. system, are produced and they decay according to Fermi's statistical theory. The model makes specific predictions like a correlations between large P_T, high multiplicities and production of antiprotons.     

Hadron production at large transverse momentum and QCD

The predictions of a QCD-based hardscattering model for large p_T hadronic processes are investigated. Not only quark-quark scattering but all contributions in lowest order are considered. At low x_T, gluon-gluon and quark-gluon scattering are found to dominate the quark-quark term. At present energies the QCD predictions lie below the data but already come very close at the highest ISR energy. Predictions for higher p_T values and higher energies are made.     

Large-pT production of single and double photons in proton-proton and pion-proton collisions

Quantum chromodynamic (QCD) predictions are made for the large transverse momentum production of single and double photons in proton-proton, proton-antiproton, and pion-proton collisions. In π^?p collisions at center-of-mass energy W = 27.4 GeV and p_T = 4.0 GeV, it is estimated that about 0.3% of the 90° single photon triggers will be balanced on the “away-side” by a single photon with roughly the same transverse momentum. In π⁺p collisions this fraction drops to about 0.09%. These fractions increase with p_T. In addition to the pure QED annihilation term $\text{q}\text{q}\text{→γγ}$, it is found that the QCD-induced subprocess gg→γγ provides an important source of double photons. Photon bremsstrahlung contributions are also examined. Experimental study of the systematics of single and double photon production in hadron-hadron collisions will provide information on the size of the strong interaction coupling constant, α_s(Q), and on the charges of the quarks. Knowledge of the gluon distributions within hadrons and of the effective transverse momentum of partons in hadrons can also be gained.     

Transverse momentum of jets in electroproduction from quantum chromodynamics

Detailed predictions of QCD on transverse momentum distributions of jets in leptoproduction are presented. The average p_⊥² is found to be asymptotically proportional to W² (the hadronic invariant mass squared) with a coefficient function that depends little on x and y. Contributions from gluons in the nucleon are relatively smaller than for σ_L/σ_T.     

Quantum number effects in events with a charged particle of large transverse momentum: (I). Leading particles in single and diquark jets

In an experiment performed with the SFM facility at the CERN ISR, we have studied events with a large-p_T particle (π⁺, π^-, K^-, p) produced at polar angle settings of 20° and 45°. The longitudinal momentum distributions of leading fragments in the spectator jet of the same rapidity hemisphere as the trigger are strongly correlated to the nature of the trigger particle involved. These distributions are compared with predictions from dimensional counting rules, if parton scattering via vector gluon exchange is assumed for the large-p_T process. Given slight modifications of the original counting rules, we observe a fair agreement. As to the fastest particle (jet leader) in the “away” jet, its average charge is about $\text{1}\text{3}$ independent of the charge of the trigger; this value is expected for the case of three valence quarks participating in the hard scattering process. From the analysis of the trigger jet we find ?⁰/π⁺ and ?⁰/π^- production ratios near unity at a value of the transverse momentum of about 2 GeV/c.     

Low p T phenomena in A+A and p+A collisions at mid-rapidity

CERN experiment NA44 measures pion and kaon distributions at p _T = 0–320 MeV/c at midrapidity in p+A and A+A collisions at 450 and 200A GeV/c, respectively. Pion production from p+Pb and A+A is slightly enhanced at low p _T relative to p+Be, but less than observed at target rapidity. The low p _T behavior can be understood in the context of the RQMD model as arising from baryonic resonance decays.     

Energy flow in ultra-relativistic nucleus-nucleus collisions and comparison between models

We calculate the cross sections of transverse and neutral energy production in the nucleus-nucleus collisions using the additive quark model (AQM) and the wounded nucleon model (WNM). In the case of α?α collisions, the experimental data of the transverse energy (E _T ) distribution favor the WNM, whereas those of the total neutral energy and the transverse neutral energy distributions favor the AQM. We predict theE _T distributions in the heavy ion collisions using these two models. The AQM and the WNM give the different results.     

On Spatially Homogeneous Solutions of a Modified Boltzmann Equation for Fermi–Dirac Particles

The paper considers a modified spatially homogeneous Boltzmann equation for Fermi–Dirac particles (BFD). We prove that for the BFD equation there are only two classes of equilibria: the first ones are Fermi–Dirac distributions, the second ones are characteristic functions of the Euclidean balls, and they can be simply classified in terms of temperatures: T>2/5T _F and T=2/5T _F , where T _F denotes the Fermi temperature. In general we show that the L ^∞-bound 0≤f≤ 1/ε derived from the equation for solutions implies the temperature inequality T≥2/5T _F , and if T>2/5T _F , then f trend towards Fermi–Dirac distributions; if T=2/5T _F , then f are the second equilibria. In order to study the long-time behavior, we also prove the conservation of energy and the entropy identity, and establish the moment production estimates for hard potentials.     

Enhancement of the B11 nuclear relaxation in CrB2 near the antiferromagnetic transition

Measurements of B¹¹ nuclear spin-lattice relaxation as a function of temperature in the itinerant antiferromagnet CrB₂ are reported. T^-1₁ shows a divergent behavior near T_N and it approaches a constant value well above T_N. The results are compared with the different theoretical predictions of Moriya and Ueda obtained either from the RPA or from the renormalized spin fluctuation approach.     

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.