Semi-inclusive Processes Research Articles

Back-to-back jets in QCD

We give a procedure for calculating in QCD (in terms of quark decay functions d A a (z) ) the cross section for the semi-inclusive process e + + e − → A + B + X. The procedure is useful at high energy in the back-to-back region 0 ⩽ θ ⪡ 1, where θ is the angle between P A and − P B .

Renormalization group for many-particle exclusive and exclusive semi-inclusive processes

In this paper it is shown that in quantum chromodynamics a new set of high-energy processes is calculable. Firstly, many meson exclusive processes are shown to be controllable. Secondly, a new type of exclusive semi-inclusive meson process (for example ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}_{\mathrm{cone}}+\mathrm{anything}$, where $\ensuremath{\pi}$ is unaccompanied in phase space) is shown to be controllable by the renormalization-group approach. Possible experimental confrontation is discussed.

Seven Topics in Perturbative QCD

The following topics of perturbative QCD are discussed: (1) Deep inelastic scattering; (2) Higher order corrections to e+e- annihilation, to photon structure functions and to quarkonia decays; (3) Higher order corrections to fragmentation functions and to various semi-inclusive processes; (4) Higher twist contributions; (5) Exclusive processes; (6) p⊥ effects; (7) Jet and photon physics.

Energy dependence of inclusive and semi-inclusive processes in the quark-cascade jet model

We consider here the energy dependence of different inclusive and semi-inclusive processes in the quark-cascade jet model for hadron production. The corresponding integral equations for inclusive quark fragmentation functions are derived. The energy dependence of individual multiplicities for quark-antiquark jets is also discussed. The results are calculated with different primordial quark fragmentation functions and compared with experiments. It is further suggested that the diffractive dissociation of mesons may also be possible examples of hadronization of high-energy quark-antiquark pairs corresponding to the invariant mass of the dissociated hadrons and this hypothesis is examined in the context of the present model. There is general agreement with the experimental results when the energies are not too high.

QCD effects in semi-inclusive neutrino processes

We present quantitative predictions for effects in semi-inclusive deep inelastic neutrino scattering which result from first-order QCD calculations. These are done for finite energies and reasonable kinematic cuts to allow their direct comparison with the data when they become available. Non-perturbative effects arising from long-range confinement forces are estimated. We show that a reliable quantity, from both theoretical and experimental points of view, for testing QCD in these processes is the mean square momentum component normal to the leptonic plane.

On the possibility of extracting pion-structure functions from semi-inclusive deep inelastic neutrino scattering

and in the case of a 7:target the structure functions E~ ~have valence contributions while only sea quarks contribute to 1 ,~ (the opposite is true for ~+). Moreover the y distl ibution (where as usual y = 1 E ~ / E L ~ ~,/EL) should contain both a constant term and a term varying as (1--y)~ in equal amounts, since /7~ and ~a '~ should approximately be zero. An experimental test of these predictions, in the absence of pion targets, can be obtained measuring semi-inclusive processes, such as

Hard semi-inclusive processes in QCD

We present formulae resulting from a complete perturbative analysis of differential cross sections of (i) massive lepton pair production in hadron collisions, (ii) leptoproduction of a particle from the current fragmentation region, (iii) production of two particles from opposite jets in e +e − annihilation into hadrons. A new effective double logarithmic quark form factor is derived, which manifests itself in these processes. Experimental investigation of two-particle angle correlations in e +e − annihilation provides a possibility to measure directly this form factor and thus to make a nice test of QCD.

Average transverse momenta in semi-inclusive processes

The average transverse momenta in semi-inclusive and associated semi-inclusive distributions are investigated as a function of the prong number. The predictions of the statistical chain model of hadron clusters are compared with 40 GeV/c π − p data and good agreement is found.

Limiting fragmentation and pulverization in bilocal current algebra

Predictions are made for the limiting behaviour of the single particle distribution ( E/ σ T)(d 3 σ/d 3 p) and the average multiplicity 〈η〉 for the deep inelastic semi-inclusive processes ep → ehx and (ν, ν) p → μ hx where h is a ps eudo-scalar or vector meson. Technique used is a generalisation of free quark bilocal algebra and the assumption is its validity in the entire longitudinal phase space of h. Our analysis shows that the single particle distribution in the fragmentation regions scales as a function of Bjorken variable ω and the Feynman variable x = 2p ∥/√s ∗ . It also suggests that the production mechanism in the central region is not related to pionization in purely hadronic collisions, but rather to ‘pulverization’ proposed by Chou and Yang.

Internal symmetries and an analysis of bilocal operators and partons with three-triplet currents

Three-triplet quark currents for the weak and electromagnetic interactions are examined in the context of different internal symmetry groups. Parton models constructed out of these currents are then applied to investigate the usual deep inelastic region of eN→μN and\(\left( {\nu ,{\mathbf{ }}\bar \nu } \right)\mathcal{N} \to \mu X\). The relevant bilocal current algebra on the light-cone is examined and correspondence with parton models demonstrated. To test these hypotheses of internal symmetries and the full bilocal current algebra based on them, we study the semi-inclusive processes lH→l’(l+l−)X (l, l’ are leptons, l+, l− the lepton pair and H is any hadron target) in a generalized Bjorken limit. In particular, sum rules are derived to test the symmetries in the process eN→e(μ+μ−)X. The implications of these hypotheses on π0→2ψ, e+e−→ hadrons, e+e−→(p, n)X, and deep inelastic ψp→(μ+μ−)X are also discussed.

A test of light-cone bilocal algebra of currents in the unified theory of weak and electromagnetic interactions

Recently RIAZUDDIN and FAYYAZUDDIN (1) wrote down light-cone algebra for currents in the unified field theory of weak and electromagnetic interactions as proposed by SALA~ (2) and by W~INBERO (3) for the leptons and later extended by WEI~BEnO to hadrons. They used the said algebra to obtain some sum rules for the deep inelastic structure functions of ~J~-+~x in terms of e~->ex and ~2C-+~x. A distinguishing feature of this algebra in contrast with that of FRITZSCH and G~LL-MANN (4) is the appearance of weak neutral currents corresponding to the neutral massive vector boson Z. The strangeness-changing (AS ~ 0 ) part of the current is eliminated by incorporating the four-quark model of GLASH0W, ILLIOPOULOUS and MAIA~I (5). Assuming that the AS = 0 weak neutral current is not ruled out by the present experimental situation, we propose here the study of the deep inelastic semi-inclusive Z-production process e2Y'-+ eZx. This provides a circumstance where the cross-section is determined by a commutator of two commutators of local currents and therefore tests the bilocal algebra on the light-cone. Denoting the four-momenta of the initial electron, nucleon, final electron, detected neutral vector boson Z and the unobserved (~ anything,> by k l , p , b2, b, P , respectively, we introduce the invariant variables

Inelastice-PScattering Process Involving Detected Final Proton

A phenomenological and simple model based on a statistical assumption is proposed for the semi-inclusive process e+P~e+P+X and the inclusive one e+P~e+X. It is assumed that secondary pions in these processes are emitted with the Maxwell distribution. The gross feature of the electro-production is reproduced by calculating the multiple-particle phase space with the isotropical momentum cut in the c.m. frame of the r-P system. The param­ eters in the model are adjustable so as to fit the experimental data. § I. Introduction The deep inelastic electron proton scattering has been very extensively in­ vestigated from both experimentaPl and theoreti.caPl sides. Most of these, how­ ever, have been concerned with inclusive reactions observing only the :final elec­ tron (but not the :final hadrons) except for a few works.8l Recently, the prelimi­ nary experimental results on the reaction e + P~e + P+ X (anything except for the :final proton) have been reported by Brasse et al. at DESY ;4l the :final elec­ tron and proton are detected in coincidence for some :fixed directions at incident electron energy 6.5 GeV. We attempt to construct a very simple model which, on the one hand, well accounts for the cross section for the semi-inclusive process e + P~e + P+ X, and on the other, reproduces the gross feature of Bjorken's scal­ ing: the inelastic structure function v w3 is in order-of-magnitude agreement with the experimental data. We visualize the whole process as follows (Fig. 1): the target proton is excited by high energy virtual photon to form a hadron cluster. We assume that the hadron cluster is produced with a type of form factor F' 1/ ../Q. Sequentially it decays into a system of a number of mesons and a baryon. In this process it is assumed that the :final proton is a remnant of the hadron cluster after emitting a number of mesons (mainly pions) with small relative velocity and that the emission of pions is isotropic around the direction of mo­ tion of the hadron cluster. Therefore it appears that we may regard the direc­ tion of the :final proton as that of the hadron cluster. It is known from the experimental evidence5l that in high energy production processes hadrons are emitted in multiparticle system whose constituents have small relative velocity. We take advantage of this information and introduce the statistical consideration that mesons are emitted with the Maxwell distribution. 6l The momenta are characterized by a mean momentum of a few-hundred

Pomeron contributions to light-cone dominated and other processes

The presence of pomeron-generated correction terms in deep inelastic scattering is investigated in the non-perturbative parton model. There is shown to be no leading-order pomeron contribution to light-cone dominated processes, nor to semi-inclusive processes involving detected final state particles if the related inclusive process is light-cone dominated. A new class of semi-inclusive processes not of this form is described which does have diffractive corrections.

General Connections Between Inclusive and Exclusive Processes and Cluster Decomposition

General connections between exclusive and inclusive cross sections are studied by the generating-functional technique. Exclusive cross sections, inclusive cross sections, and correlation functions appear as coefficients of different Taylor series expansions of the same generating functional. Also studied are the connections between semi-inclusive processes where all charged particles in an event are observed and genuine inclusive processes with only some of the charged particles observed. No information on neutral particles enter in these connections for semi-inclusive processes. In special cases our results reproduce several seemingly unrelated aspects of inclusive processes treated by Mueller, Predazzi, and Veneziano and by Campbell and Chang. Our approach yields additional constraints and sum rules for inclusive cross sections. It is established that an infinite number of correlation functions are needed; and correlation in the pionization region necessarily exists if the multiplicity increases with energy and the transverse momenta of the final particles are limited. A brief comparison between exclusive and inclusive cluster decomposition is given. The question of diffraction dissociation is also very briefly discussed.