kT-factorization Approach Research Articles

Deep-inelastic heavy-quark production at the HERA collider within the QCD semihard approach

Deep-inelastic heavy-quark production in electron-proton interactions at the HERA collider energies is considered within the QCD semihard (kT-factorization) approach. The dependence of the total and differential cross sections for the production of b quarks (and for muons arising in the subsequent semileptonic decay of B mesons) on the choice of unintegrated distributions of gluons in the proton is investigated. In particular, the gluon distributions obtained by solving the Catani-Ciafaloni-Fiorani-Marchesini evolution equation and the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi-Balitsky-Fadin-Kuraev-Lipatov combined equation are used in numerical calculations. The results of the theoretical calculations are compared with latest experimental data obtained by the H1 and ZEUS Collaborations at the HERA collider.

Prompt photon hadroproduction at high energies in the kT-factorization approach

We consider the prompt photon production at high energy hadron colliders in the framework of the kT-factorization approach. The unintegrated quark and gluon distributions in a proton are determined using the Kimber–Martin–Ryskin prescription. The conservative error analysis is performed. We investigate both inclusive prompt photon and prompt photon and associated muon production rates. In a standard model such events occur mainly due to the Compton scattering process where the final heavy (charm or bottom) quark produces a muon. The theoretical results are compared with recent experimental data taken by the D∅ and CDF collaborations at Fermilab Tevatron. Our analysis also covers the azimuthal correlations between the produced prompt photon and muon which can provide an important information about non-collinear parton evolution in a proton. Finally, we extrapolate the theoretical predictions to CERN LHC energies.

Deep inelastic beauty production at HERA in thekT-factorization approach

We calculate the cross section of beauty production in electron-proton deep inelastic scattering at HERA collider in the framework of the kt-factorization approach. The unintegrated gluon distributions in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber-Martin-Ryskin prescription. We investigate different production rates and study the b-quark contribution to the inclusive proton structure function F2(x,Q2) at small x and at moderate and high values of Q2. Our theoretical results are compared with the recent experimental data taken by the H1 and ZEUS collaborations. We demonstrate the importance of leading ln 1/x contributions in description of the HERA data.

Unintegrated parton distributions and pion production in pp collisions at RHIC energies

We compare the results of the 2 → 1 kt-factorization approach (often called BFKL multi-Regge factorization) with Kwieciński unintegrated parton distribution functions (UPDF) and the standard collinear-factorization approach at RHIC and slightly smaller energies. Our approach contains only one free parameter responsible for internal parton motion in nucleons. In contrast to recent works in the literature, our kt-factorization approach also includes quark degrees of freedom in addition to purely gluonic terms. Both mid- and forward-rapidity regions are considered. We discuss uncertainties due to fragmentation functions. In general, the kt-factorization approach gives a much better description of the pt∼ 1–4 GeV region than the leading order collinear approach both at mid- and forward-rapidity regions. Our approach leads to asymmetry in the production of π+ and π−, very similar to that observed very recently by the BRAHMS Collaboration.

Unintegrated gluon distributions in D*± and dijet associated photoproduction at HERA

We consider the photoproduction of D*± mesons associated with two hadron jets at HERA collider in the framework of the kT-factorization approach. The unintegrated gluon densities in a proton are obtained from the full CCFM, from unified BFKL-DGLAP evolution equations as well as from the Kimber–Martin–Ryskin prescription. Resolved photon contributions are reproduced by the initial-state gluon radiation. We investigate different production rates and make a comparison with the recent experimental data taken by the ZEUS collaboration. Special attention is given to the specific dijet correlations which can provide unique information about non-collinear gluon evolution dynamics.

Hadroproduction of High-Transverse-Momentum B c mesons within the k T -Factorization approach

With the kT-factorization approach, the transverse-momentum spectra of Bc mesons at the energies of the Tevatron and LHC hadron colliders are calculated on the basis of the fusion and fragmentation models. In the fusion model, the calculations are performed under the assumption of charm excitation in the proton.

Production of spin-3 mesons in diffractive DIS

We calculate the amplitudes of J PC = 3- - meson production in diffractive DIS within the kt-factorization approach, with particular attention paid to the $\rho_3(1690)$ meson. We find that at all Q2 the $\rho_3(1690)$ production cross section is 2-5 times smaller than the $\rho(1700)$ production cross section, which is assumed to be a pure D-wave state. Studying $\sigma_{\mathrm{L}}$ and $\sigma_{\mathrm{T}}$ separately, we observe domination of $\rho_3$ in $\sigma_{\mathrm{L}}$ and domination of $\rho(1700)$ in $\sigma_{\mathrm{T}}$ and offer an explanation of this behavior in simple terms. We also find very strong contributions - sometimes even domination - of the s-channel helicity violating amplitudes. The typical color dipole sizes probed in $\rho_3$ production are shown to be larger than those in the ground state $\rho$ production, and the energy dependence of $\rho_3$ cross section turns out to be much flatter than the $\rho$ production cross section. All the conclusions about the relative behavior of the $\rho_3(1690)$ and $\rho(1700)$ mesons are numerically stable against variations of the input parameters.

Higgs boson production at hadron collidersin the kT-factorization approach

We consider the Higgs boson production at high energy hadron colliders in the framework of the k_T-factorization approach. The attention is focused on the dominant gluon-gluon fusion subprocess. We calculate the total cross section and transverse momentum distributions of the inclusive Higgs production using unintegrated gluon distributions in a proton obtained from the full CCFM evolution equation. We show that k_T-factorization gives a possibility to investigate the associated Higgs boson and jets production. We calculate the transverse momentum distributions and study the Higgs-jet and jet-jet azimuthal correlations in the Higgs + one or two jet production processes. We demonstrate the importance of the higher-order corrections within the k_T-factorization approach. These corrections should be developed and taken into account in the future applications.

Electroproduction of D*± mesons at high energies

A comparative analysis of the predictions of the collinear parton model and the kT-factorization approach is performed for the case of the D*-meson electroproduction at the HERA ep collider. It is shown that, owing to effectively taking into account, in noncollinear distributions, next-order corrections in the strong coupling constant αs, the kT-factorization approach increases, in contrast to the predictions of the collinear parton model, the absolute value of the cross sections for charmed-meson electroproduction by approximately a factor of 1.5 to 2. As a result, the agreement with experimental data is improved. This is not so only for the pseudorapidity spectrum, whose shape differs considerably from the experimental one and depends greatly on the choice of parametrization of the noncollinear gluon distribution within the proton.

Heavy quark production at LHC as a test of the kT-factorization approach

We report on a calculation of the beauty quark production at the Tevatron and LHC in the framework of the kT-factorization. We consider the azimutal correlations between the b and b ¯ quarks (or between the muons from B and B ¯ meson decay), which serve as a powerful test for the different unintegrated gluon distributions. We present a comparison of the theoretical results to the data taken by DO and CDF collaborations and give theoretical predictions for the LHC energies.

Hadroproduction of direct J/ψ and ψ′ mesons in the fragmentation of gluons and c quarks at high energies

The transverse-momentum spectra of direct J/ψ and ψ′ mesons in pp interactions at the Tevatron collider energy of \(\sqrt s = 1.8\) TeV are calculated on the basis of nonrelativistic QCD, the fragmentation model, the kT-factorization approach, and the standard parton model. The contribution of gluon fragmentation is shown to exceed the contribution of c-quark fragmentation both within the parton model and within the kT-factorization approach. Experimental data of the CDF Collaboration agree with the assumption that gluon fragmentation plays a dominant role in the \(Q\bar Q[^3 S_1 ,8]\) octet state, with the nonperturbative matrix element taking approximately equal values in the parton model and in the kT-factorization approach.

Production of [formula omitted] mesons via fragmentation in the [formula omitted]-factorization approach

In the framework of the kT-factorization approach we have calculated in the fragmentation model the pT-spectra of Bc mesons at the energies of the Tevatron and the LHC Colliders and at the large pT domain. We compare the obtained results with the existing experimental data and with the predictions obtained in the collinear parton model.

Charm quark–antiquark correlations in photon–proton scattering

Correlation of charm-quark–charm-antiquark in γp scattering are calculated in the kt-factorization approach. We apply different unintegrated gluon distributions (uGDF) used in the literature. The results of our calculations are compared with very recent experimental results from the FOCUS Collaboration. The CCFM uGDF developed recently by Kwieciński et al. gives a good description of the data. New observables are suggested for future studies. Predictions and perspectives for the HERA energies are presented.

Testing the kt-factorization approach with P-wave quarkonia production

A new qualitative test of the kt-factorization approach is proposed. We analyse the production of P-wave quarkonium states with different spins χ0, χ1 and χ2 in high energy proton–proton interactions. The predictions of the usual parton model and the kt-factorization approach are compared. We find that the shape of the transverse momentum distributions and, also, the ratio of the production rates σ(χ1)/σ(χ2) are qualitatively different in the considered models. The referred processes may serve as an essential test of the validity of the kt-factorization approach.

Kt-FACTORIZATION AND CCFM: THE SOLUTION FOR DESCRIBING THE HADRONIC FINAL STATES EVERYWHERE?

The basic ideas of kt-factorization and CCFM parton evolution is discussed. The unintegrated gluon densities, obtained from CCFM fits to the proton structure function data at HERA are used to predict hadronic final state cross-sections like jet production at HERA, but also comparisons with recent measurements of heavy quark production at the Tevatron are presented. Finally, the kt-factorization approach is applied to Higgs production at high energy hadron–hadron colliders and the transverse momentum spectrum of Higgs production at the LHC is calculated.

Deep inelastic J/ψ production at HERA in the kT-factorization approach and its consequences on the nonrelativistic QCD

In the framework of the kT-factorization approach, we analyse the inclusive and inelastic production of J/ψ particles in deep inelastic ep scattering. We take into account both colour-singlet and colour-octet production channels. We inspect the sensitivity of theoretical predictions to the choice of model parameters. Our theoretical results agree reasonably well with recent experimental data collected by the H1 collaboration at HERA.

Photoproduction of J/ψ mesons at high energies within the parton model and in the k T-factorization approach

The photoproduction of J/ψ mesons is considered on the basis of the parton model and in the k T-factorization approach in the leading order in α s . It is shown that, at specific values of the charmed-quark mass and the J/ψ-meson wave function at the origin, the predictions of the two approaches for the total cross section and z spectra of J/ψ mesons nearly coincide and agree with experimental data obtained at the HERA ep collider. At the same time, the parton model and the theory of semihard processes predict significantly different p T spectra of J/ψ mesons and significantly different transverse-momentum dependences of the ratio of the cross sections for the production of longitudinally and transversely polarized J/ψ mesons. It is expected that nontrivial effects of low-x physics will clearly manifest themselves in experimentally testing this fact.

On charmonia and charmed mesons photoproduction at high energy

We compare the predictions of the collinear parton model and the kT-factorization approach in J/Ψ and D★ meson photoproduction at HERA energies. It is shown that obtained D★ meson spectra over pT and η are very similar in the parton model and kT-factorization approach and they underestimate the experimental data. Opposite, the predictions of the both approaches for pT- and z-spectra in the J/Ψ photoproduction are very different as well as the prediction obtained for the spin parameter α(pT).

Charm hadroproduction within k T -factorization approach

In the problem of describing heavy-quark production in high-energy hadron collisions, a comparison is made between the theoretical status and numerical predictions of two approaches, the traditional parton model in the leading order (LO) and the k T-factorization approach. Basic assumptions underlying relevant calculations are discussed. A very simple gluon structure function and a fixed coupling constant are chosen for the calculations in order to highlight distinctions associated with the use of nonidentical matrix elements in these two approaches. It is shown that, in the k T-factorization approach, formal LO calculations performed with allowance for the Sudakov form factor include many terms usually treated as next-to-leading-order (NLO) contributions of the traditional parton model (or even contributions next to NLO ones, NNLO).