Constituent Interchange Research Articles

Possible molecular states in B(*)B(*) scatterings

We present that, if unitarizing the $B^{(*)}B^{(*)}$ scattering amplitudes in the constituent interchange model, one can find two bound state poles for $(I_{tot},S_{tot})=(0,1)$ $BB^*$ and $B^*B^*$ system, which corresponds to two $I(J^P)=0(1^+)$ doubly bottomed molecular states. Furthermore, it is noticed that the virtual states in $(1,0)$ $BB$, $(1,1)$ $BB^*$, $(1,0)$ $B^*B^*$, and $(1,2)$ $B^*B^*$ systems could produce enhancements of the module squares of the scattering $T$-matrix just above the related thresholds, which might correspond to $I(J^P)=1(0^+)$, $1(1^+)$, and $1(2^+)$ doubly bottomed molecular states, respectively. The calculation may be helpful for searching for the doubly bottomed molecular state in future experiments.

Do glueballs contribute in heavy-ion collisions?

In heavy-ion collision simulations many hadron states and/or parton degrees of freedom are included in order to obtain the observables. Meson spectroscopy, for example, considers the 0++ meson as a mixture of and glue. This fact is usually not considered in heavy-ion collision physics. In the present work, we consider two extreme possibilities for the constitution of the 0++ meson, either as a pure glueball or as meson. The scattering amplitude and cross sections with constituent interchange are determined for the two situations. The comparison showed that the glueball–glueball elastic scattering cross section for a colour singlet state is between one to two orders of magnitude smaller than the corresponding state. The 2++ glueball–glueball interaction is also evaluated with similar behaviour. Thus, glueball–glueball scattering is not very likely to introduce significant changes in heavy-ion collision observables.

Charmonium cross-sections and the QGP

In this short review we summarize experimental information and theoretical results for the low-energy dissociation cross sections of charmonia by light hadrons. These cross sections are required for the simulation of charmonium absorption through collisions with comovers in heavy ion collisions, which competes with quark-gluon plasma production as a charmonium-suppression mechanism. If the cross sections are sufficiently large these dissociation reactions may be misinterpreted as an effect of quark-gluon plasma production. Theoretical predictions for these RHIC-related processes have used various methods, including a color-dipole scattering model, meson exchange models, constituent interchange models and QCD sum rules. As the results have been largely unconstrained by experiment, some of the predictions differ by orders of magnitude, notably in the near-threshold regime that is most relevant to QGP searches.

Drug discovery by dynamic combinatorial libraries.

Dynamic combinatorial chemistry is a recently introduced supramolecular approach that uses self-assembly processes to generate libraries of chemical compounds. In contrast to the stepwise methodology of classical combinatorial techniques, dynamic combinatorial chemistry allows for the generation of libraries based on the continuous interconversion between the library constituents. Spontaneous assembly of the building blocks through reversible chemical reactions virtually encompasses all possible combinations, and allows the establishment of adaptive processes owing to the dynamic interchange of the library constituents. Addition of the target ligand or receptor creates a driving force that favours the formation of the best-binding constituent--a self-screening process that is capable, in principle, of accelerating the identification of lead compounds for drug discovery.

Hadronic molecules and scattering amplitudes from the nonrelativistic quark model

This report summarizes recent calculations of low-energy hadron-hadron scattering amplitudes in the nonrelativistic quark potential model, which assume that the scattering mechanism is a single interaction (usually OGE) followed by constituent interchange. We refer to the scattering diagrams as «quark Born diagrams». For the cases chosen to isolate this mechanism,I=2ππ,I=3/2 Kπ, KN andNN, the results are usually in good agreement with experimentalS-wave scattering amplitudes given standard potential- model parameters. These calculations also lead to predictions of vector-vector bound states, one of which may be the ϑ(1710). This assignment can be tested by searches for $$K\bar K\pi \pi $$ and φπ0γ decay modes of the ϑ(1710).

NN core interactions and differential cross sections from one gluon exchange.

We derive nonstrange baryon-baryon scattering amplitudes in the nonrelativistic model using the quark Born diagram formalism. This approach describes the scattering as a single interaction, here the one-gluon-exchange (OGE) spin-spin term followed by constituent interchange, with external nonrelativistic baryon wavefunctions attached to the scattering diagrams to incorporate higher-twist wavefunction effects. The short-range repulsive core in the NN interaction has previously been attributed to this spin-spin interaction in the literature; we find that these perturbative constituent-interchange diagrams do indeed predict repulsive interactions in all I,S channels of the nucleon-nucleon sytem, and we compare our results for the equivalent short-range potentials to the core potentials found by other authors using nonperturbative methods. We also apply our perturbative techniques to the NDelta and Delta Delta systems: Some Delta Delta channels are found to have attractive core

New formalism for the nuclear Drell-Yan process

A more systematic derivation of the new formalism for Drell-Yan processes on nuclear targets is developed by expanding the nuclear tensor in terms of the nucleon tensor. As explained previously, the new formalism which is compatible with the factorization theorem is very different from the commonly used procedure in two aspects. First, not the target-quark distribution function alone, but the product of projectile and target-quark distribution functions is convoluted with the nucleon-momentum distribution function. Second, since Drell-Yan cross sections are expressed in the centre-of-mass system, the transformation from the projectile-nucleus to-nucleon centre-of-mass systems introduces an additional nuclear effect through kinematical factors inherent in the Drell-Yan tensor. The new formulae agree with those obtained from the constituent interchange model. Using the new formalism, the nuclear effect is investigated by proton scattering off a 184W target and is found stronger than the naive expectation based on the free-nucleon target would have indicated. The difference from the conventional result is dependent both on the heavy-lepton mass and the Feynman variable.

Further studies of the interactions between thick film resistors and dielectrics

Previous work has demonstrated that there is an interchange of constituents between the films when thick films are fired on dielectric layers. This paper extends the study from ruthenium dioxide based resistors to those based on barium ruthenate. It shows that, here also, the reactions are much less marked on the filled glaze DP 9950 than on the crystallising DP 9429 and that electrical changes have a similar relationship. Plots are given of the change of chemical constitution over the cross sections of several different resistors/dielectric combinations.

Regge theory and QCD in large-angle scattering

We argue that exclusive processes whose cross-sections are determined by Regge pole trajectory exchanges, α(t), at small momentum transfers (t), are controlled by these same exchanges at very large |t| too. The analysis is based on a Reggeized version of the constituent interchange model (CIM), which predicts that α(t)→−1 ast→−∞, and that the asymptotic form of the Regge residues is fixed by the dimensional counting rules and CIM constraints. Between the two regimes of soft and hard scattering there is an intermediate region where Regge cuts are important, but these higher-twist effects die away as |t| is increased. We show that this hypothesis is consistent with high energy nucleon-nucleon and pion-nucleon scattering at all angles.

Exclusive production of heavy mesons in photon-photon collisions: The double scattering mechanism

We present two mechanisms which can compete with constituent interchange in the exclusive production at wide angle of heavy mesons in photon-photon collisions. We show that they have the same energy behaviour as constituent interchange, and that their amplitudes are free from large logarithms. We exploit this to calculate the double-scattering diagrams numerically. We find that while constituent interchange dominates at 90°, double scattering becomes dominant for angles less than about 45°.

Hadron and hadron-pair production at large transverse momentum in [formula omitted] and pp interactions at the ISR

We have measured the production of one and two large transverse momentum hadrons in p p and pp interactions in the range 2 < p T < 6 GeV/ c for the central rapidity region |y| < 0.9 at s = 63 and 31 GeV . No statistically significant difference between p p and pp collisions is observed. The results are in accordance with lowest order QCS perturbative calculations and rule out a large contribution of Constituent Interchange Model (CIM), di-quark of quark-fusion subprocesses in this kinematic range.

Quark interchange and spin observables in high-energy large-angle nucleon-nucleon scattering

The differential cross-section and spin correlation parameters in high-energy large-angle nucleon-nucleon scattering are studied in the spin core parton model. The model is an adaptation to exclusive processes of the constituent interchange approach. It is based on the factorization between the hadronic binding mechanism, described by a two-body nucleon wave function of a quark correlated with a core, and the reaction mechanism, described by quark interchange. The initial version of the core model, discussed in the literature, is considerably enhanced by an account of the spin-isospin structure and of the normalization. Detailed predictions are presented for the proton-proton and neutron-proton systems in the interesting regimes of transverse momenta pT2 ≲ 10 (GeV/c)2 for the scattered nucleon.

Quark interchange and deuteron electromagnetic form factors at large transfers

The elastic electromagnetic form factors of the proton, neutron and deuteron at momentum transfers Q 2 ⩽ 10 ( GeV c ) 2 are discussed in the parton light-cone approach. The framework is an adaptation of the constituent interchange model to exclusive processes based on the factorization of the hadronic binding mechanisms described in terms of wave functions from the reaction mechanisms described by simple interchange of constituents. The constituent description for the deuteron is examined at two levels: the conventional level where one resolves the proton-neutron compositeness and the quark level where one resolves the quark compositeness of the nucleon constituents. Associated with the first level are the impulse approximation form factors which we describe in the nucleon parton approach. The light-cone description of the deuteron-neutron-proton (dnp) vertex is examined from a dynamical standpoint, the main emphasis being however on a phenomenological construction of wave functions. Predictions using such constructs are presented. The discussion of deuteron form factors at the quark level bears on the quark interchange mechanism between quarks in different nucleons. To prepare for this discussion we examine the core parton model of the nucleon based on a simplified two-particle representation in terms of an active quark correlated to a passive core. The initial version of the core model is considerably enhanced by an account of the spin-isospin structure and of the normalization. The predictions for the nucleon form factors and structure functions are used to test the model and gauge its various parameters. We then proceed without parameter adjustment to a discussion of the quark interchange deuteron form factors. The calculations are performed in a simplified factorization approximation for the dnp vertex. The quark interchange mechanism stands out as a serious competitor to the impulse approximation matching better the shape of the Q 2 dependence at large Q 2.

LargeP T photoproduction in the hard scattering expansion

LargepT photoproduction is studied in the hard scattering expansion, including both three- and four-jet processes. The higher twist corrections (∝p T −6 andp T −8 ) to the basic QCD hard scattering process (∝p T −4 ) are estimated using the constituent interchange model and the various terms compared. Both single jet inclusive cross sections and single particle inclusive π0 cross sections are evaluated, the latter using scale violating fragmentation functions. We find that the higher twist terms are significant at present energies, particularly for three-jet events, though the four-jet anomalous photon contribution can be measured. Three-jet QCD processes require considerably higher energies to provide a significant contribution to the cross section. Methods of separating the different processes experimentally are discussed.

High transverse momentum pion and photon production in pp collisions at ISR energies

High transverse momentum ( p T) production of pions and prompt photons in proton-proton collisions is studied in a QCD model including “higher twist” contributions parametrized by constituent interchange model. QCD scaling violations are included and comparisons are made with ISR data on invariant cross sections and the γ π 0 ratio. Studies of the away-side jet and charge angular distributions are proposed in order to isolate the various subprocesses contributing to high p T production, in particular that involving the trigluon coupling of QCD.

Why the constituent interchange model does not predict the dimensional counting rule to any finite order in QCD

We demonstrate that the constitutent interchange diagram for nucleon nucleon elastic scattering contains a pinch singularity. This means that it predicts that\(\frac{{d\sigma }}{{dt}} \sim s^{ - 9} f\left( \theta \right)\) for high energy elastic scattering, at least to any finite order in QCD. We also show how the dimensional counting rule may perhaps be recovered by summing a suitable infinite series of graphs.

Large-angle elastic scattering of charged pions on protons at 20 and 30 GeV/c incident momenta

Elastic cross-section measurements are presented for π ±−p at 20 GeV/ c and π −−p at 30 GeV/ c incident momenta in the large angle region (50° to 90° in the c.m. system). The data are compared with published lower energy elastic cross sections. A test is made of the dimensional counting rules for π ±−p elastic scattering and some indication of a deviation from this rule is observed in the π −−p case. A comparison is also made with the predictions of the constituent interchange model. Although the broad features of the predictions are confirmed, there are some important discrepancies. Finally, the predictions of the model due to Preparata and Soffer are also compared with the new data.

Inclusive π0 electroproduction in the deep inelastic region

Using 20.5 GeV electrons on protons, we measured inclusive π 0's (of transverse momentum, p T, from 0 to 1.4 GeV/ c) produced by virtual photons of energy, ν, from 4 to 16.5 GeV and four-momentum squared, q 2, from −1.8 to −8.5 (GeV/ c) 2. Comparing with charged pion data, we find σ π0 = 1 2 (σ π + + σ π − ) , supporting the quark model. Photon knockout of a quark is favored as the interpretation of these data because of scaling in z = E π / ν and similarity in z-dependence of other pion production data. Consistent with this interpretation are the dependence of 〈 p T〉 on q 2, the azimuthal dependence, and fits to the constituent interchange model. We also observe a possible p T −4 dependence at large | q 2| over a limited p T range.

Infinite-momentum frame description of relativistic heavy ion processes

Relativistic heavy ion processes are discussed in a covariant model based on an infinite-momentum frame description. The model is an adaptation of the constituent interchange model (CIM) used in igh-energy hadronic processes. Various aspects of the model aare considered, especially those aspects concerning the connection between exclusive and inclusive processes and the implications on relativistic nuclear dynamics. We present theoretical predictions for single-particle inclusive spectra of pions and protons for proton-nucleus and nucleus-nucleus processes. The model is tested in various regions of spectra: fragmentation as well as central regions and small as well as finite transverse momentum regions. It is also tested with respect to its predictions for scaling and production of ultra-fast secondaries with energies beyond the kinematical limit. Comparison with data is on the whole quite satisfactory and provides convincing evidence for descriptions based on the infinite-momentum frame and the CIM. Discrepancies do show up (more significantly in transition regions from central to fragmentation spectra and also in large transverse momentum spectra). The question whether they originate from coherent scattering and/ or multichain cascading effects is left open.

Transverse momentum fluctuations and high p⊥ processes in quantum chromodynamics

We discuss the introduction of constituent transverse momentum fluctuations in the parton model and examine their effects on the transverse momentum spectra of pions, jets and dilepton pairs in proton-proton collisions. We show that, when exact constituent kinematics are respected, the quark and gluon subprocesses of quantum chromodynamics do not suffice to explain the data in the present p ⊥ region. A hard scattering expansion, including constituent interchange model contributions, gives satisfactory agreement with the data.