kT-factorization Approach Research Articles

Isolated prompt photon pair production at hadron colliders with k T -factorization

In the framework of the kt-factorization approach, the isolated prompt photon pair production in pp and p \bar p collisions at high energies is studied. The consideration is based on the quark-antiquark annihilation, quark-gluon scattering and gluon-gluon fusion subprocesses, where the non-zero transverse momenta of incoming partons are taken into account. The unintegrated quark and gluon densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The numerical analysis covers the total and differential production cross sections and extends to specific angular correlations between the produced prompt photons. Theoretical uncertainties of our evaluations are studied and comparison with the NLO pQCD calculations is performed. The numerical predictions are compared with the recent experimental data taken by the D0, CDF, CMS and ATLAS collaborations at the Tevatron and LHC energies.

Measurement of the differential [formula omitted]-jet cross section and the ratio of differential [formula omitted] and [formula omitted] cross sections in [formula omitted] collisions at [formula omitted

We present measurements of the differential cross section dσ/dpTγ for the associated production of a c-quark jet and an isolated photon with rapidity |yγ|<1.0 and transverse momentum 30<pTγ<300 GeV. The c-quark jets are required to have |yjet|<1.5 and pTjet>15 GeV. The ratio of differential cross sections for γ+c to γ+b production as a function of pTγ is also presented. The results are based on data corresponding to an integrated luminosity of 8.7 fb−1 recorded with the D0 detector at the Fermilab Tevatron pp¯ Collider at s=1.96 TeV. The obtained results are compared to next-to-leading order perturbative QCD calculations using various parton distribution functions, to predictions based on the kT-factorization approach, and to predictions from the sherpa and pythia Monte Carlo event generators.

Prompt photon and associated heavy quark production at hadron colliders with k T -factorization

In the framework of the kt-factorization approach, the production of prompt photons in association with a heavy (charm or beauty) quarks at high energies is studied. The consideration is based on the O(\alpha \alpha_s^2) off-shell amplitudes of gluon-gluon fusion and quark-(anti)quark interaction subprocesses. The unintegrated parton densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The analysis covers the total and differential cross sections and extends to specific angular correlations between the produced prompt photons and muons originating from the semileptonic decays of associated heavy quarks. Theoretical uncertainties of our evaluations are studied and comparison with the results of standard NLO pQCD calculations is performed. Our numerical predictions are compared with the recent experimental data taken by the D0 and CDF collaborations at the Tevatron. Finally, we extend our results to LHC energies.

PromptJ/ψproduction at the LHC: New evidence for thekTfactorization

In the framework of the kt-factorization approach, the production and polarization of prompt J/Psi mesons in pp collisions at the LHC energy 7 TeV is studied. Both the direct production mechanism as well as feed-down contributions from chic1, chic2 and psi' decays are taken into account. Our consideration is based on the color singlet model supplemented with the off-shell matrix elements for the corresponding partonic subprocesses. The unintegrated gluon densities in a proton are determined using the CCFM evolution equation as well the Kimber-Martin-Ryskin prescription. We compare our numerical predictions with the first experimental data taken by the CMS, ATLAS and LHCb collaborations. The estimation of all polarization parameters which determine J/Psi spin density matrix is performed.

Drell-Yan lepton pair production at high energies in the k T -factorization approach

In the framework of the kt-factorization approach, the production of unpolarized Drell-Yan lepton pair at high energies is studied. The consideration is based on the O(alpha) and $O(alpha alpha_s) off-shell partonic matrix elements with virtual photon and Z boson exchange. The calculations include leptonic decays of Z bosons with full spin correlations as well as gamma - Z interference. The unintegrated parton densities in a proton are determined by the Kimber-Martin-Ryskin prescription. Our numerical predictions are compared with the data taken by the D0, CDF and CMS collaborations at the Tevatron and LHC energies. Special attention is put on the specific angular distributions measured very recently by the CDF collaboration for the first time.

Exclusive production of [formula omitted] meson and its measurement in the [formula omitted] channel

We report on the results of a theoretical study of the central exclusive production of scalar χc(0+) meson via χc0→π+π− decay in high-energy hadron collisions at the RHIC, Tevatron and LHC. The corresponding amplitude for exclusive double-diffractive χc0 meson production was obtained within the kt-factorization approach including virtualities of active gluons and the cross section is calculated with unintegrated gluon distribution functions (UGDFs) known from the literature. The four-body pp→ppπ+π− reaction constitutes an irreducible background to the exclusive χc0 meson production. We include the absorption effects due to proton-proton interaction and pion-pion rescattering. Several differential distributions for pp(p¯)→pp(p¯)χc0 process, including the absorptive corrections, were calculated. The influence of kinematical cuts on the signal-to-background ratio is investigated.

Inclusive J/ψ and χ c meson production in pp collisions at RHIC

Inclusive cross sections for J/ψ and χc production in pp collisions were calculated in the kt-factorization approach for the RHIC energy. Several mechanisms were considered. Radiative χc decays and direct color-singlet contributions constitute the dominant mechanisms of J/ψ production. The results are compared with recent RHIC data.

Measurement of exclusive production of scalar [formula omitted] meson in proton–(anti)proton collisions via [formula omitted] decay

We consider a measurement of exclusive production of scalar χc(0++) meson in the proton–proton collisions at LHC and RHIC and in the proton–antiproton collisions at the Tevatron via χc0→π+π− decay. The corresponding amplitude for exclusive double-diffractive χc0 meson production was obtained within the kt-factorization approach including virtualities of active gluons and the corresponding cross section is calculated with unintegrated gluon distribution functions (UGDFs) known from the literature. The four-body pp→ppπ+π− reaction constitutes an irreducible background to the exclusive χc0 meson production. We include absorption effects due to proton–proton interaction and pion–pion rescattering. We calculate several differential distributions for pp(p¯)→pp(p¯)χc0 process including the absorptive corrections. The influence of kinematical cuts on the signal-to-background ratio is investigated. Corresponding experimental consequences are discussed.

PRODUCTION OF D AND B MESONS AND THEIR SEMILEPTONIC DECAYS

We have calculated the kinematical correlations between charged leptons from semileptonic decays of open charm/bottom as well as leptons produced in the Drell-Yan mechanism in proton-proton collisions at BNL RHIC. Presented production rates for open charm and bottom were estimated by a detailed analysis of so-called nonphotonic electrons. The distributions for charm and bottom quarks pairs are calculated in the kt-factorization approach with the help of the Kwieciński unintegrated parton distributions. The hadronization of heavy quarks is done by means of Peterson et al. fragmentation function. The semileptonic decay functions are found by fitting recent semileptonic data obtained by the CLEO and BABAR. We get good description of recent PHENIX data.

Heavy-flavor production in pp and heavy-ion collisions in QCD up-to-LHC energies

Charm production in pp collisions is considered in the framework of perturbative QCD. The values of two parameters, the charm quark mass mc and the QCD scale µ2, are determined from the comparison of the theoretical calculations with experimental data. The RHIC data on charm and beauty production are compared with the kT-factorization approach predictions and with standard NLO QCD. The calculated results underestimate the STAR Collaboration data. The role of possible nuclear effects is discussed. The predictions for LHC energies are also given.

Deep inelastic prompt photon production at HERA in thekT-factorization approach

We investigate the prompt photon production in deep inelastic scattering at HERA in the framework of kt-factorization QCD approach. Our study is based on the off-shell partonic amplitude e q* -> e gamma q, where the photon radiation from the leptons as well as from the quarks is taken into account. The unintegrated quark densities in a proton are determined using the Kimber-Martin-Ryskin prescription. The conservative error analisys is performed. We investigate both inclusive and jet associated prompt photon production rates. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. We demonstrate that in the kt-factorization approach the contribution from the quark radiation subprocess (QQ mechanism) is enhanced as compared to the leading-order collinear approximation.

Exclusive photoproduction of ϕ meson in [formula omitted] and [formula omitted] reactions

The amplitude for γp→ϕp is calculated in a pQCD kT-factorization approach. The total cross section for this process is compared with HERA data. Total cross section, as a function of photon–proton energy and photon virtuality, is calculated. We also discuss the ratio of σL/σT and the dependence on the mass of the strange quark. The amplitude for γp→ϕp is used to predict the cross section for exclusive photoproduction of ϕ meson in proton–proton collisions. Absorption effects are included. The results for RHIC, Tevatron and LHC energies are presented.

On the quark component in prompt photon and electroweak gauge boson production at high energies

In the framework of the kT-factorization approach, we study the production of prompt photons and electroweak gauge bosons in high-energy proton–(anti)proton collisions at modern colliders. Our consideration is based on the amplitude for the production of a single photon or W±/Z0 boson associated with a quark pair in the fusion of two off-shell gluons. The quark component is taken into account separately using the quark–gluon scattering and quark–antiquark annihilation QCD subprocesses. Special attention is given to the contributions from the quarks involved in the earlier steps of the evolution cascade. Using the Kimber–Martin–Ryskin formalism, we simulate this component and demonstrate that it plays an important role at both the Tevatron and LHC energies. Our theoretical results are compared with recent experimental data taken by the D∅ and CDF Collaborations at the Tevatron.

Elastic double diffractive production of axial-vector [formula omitted] mesons and the Landau–Yang theorem

We discuss exclusive elastic double diffractive axial-vector χc(1+) meson production in proton–antiproton collisions at the Tevatron. The amplitude for the process is derived within the kt-factorization approach with unintegrated gluon distribution functions (UGDFs). We show that the famous Landau–Yang theorem is not applicable in the case of off-shell gluons. Differential cross sections for different UGDFs are calculated. We compare exclusive production of χc(1+) and χc(0+). The contribution of χc(1+) to the J/Ψ+γ channel is smaller than that of the χc(0+) decay, but not negligible and can be measured. The numerical value of the ratio of the both contributions is much less dependent on the UGDFs modeling than the cross sections themselves.

SEMILEPTONIC DECAYS OF HEAVY MESONS AT RHIC

We discuss production of nonphotonic electrons in proton-proton scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the kt-factorization approach. The hadronization of heavy quarks is done by means of Peterson and Braaten et al. fragmentation functions. The semileptonic decay functions are found by fitting recent semileptonic data obtained by the CLEO and BABAR collaborations.

Polarization variables in inclusive J/Ψ production at HERA in the k t -factorization approach

In the framework of k t -factorization approach, the process of inclusive photoproduction of J/Ψ mesons at HERA conditions is considered. The spin density matrix elements are calculated, and the predictions are compared with recent experimental data.

Associated production of prompt photons and heavy quarks in off-shell gluon–gluon fusion

In the framework of the kT-factorization approach, we study the production of prompt photons associated with heavy (charm and beauty) quarks in hadron–hadron collisions at high energies. Our consideration is based on the amplitude for the production of a single photon associated with a quark pair in the fusion of two off-shell gluons. The total and differential cross sections are presented and the conservative error analysis is performed. Two sets of unintegrated gluon distributions in the proton have been used in numerical calculation: the one obtained from Ciafaloni–Catani–Fiorani–Marchesini evolution equation and the other from Kimber–Martin–Ryskin prescription. The theoretical results are compared with recent experimental data taken by the CDF collaboration at the Fermilab Tevatron. Our analysis extends to specific angular correlations between the produced prompt photons and muons originating from semileptonic decays of the final charmed or beauty quarks. We point out the importance of such observables, which can serve as a crucial test for the unintegrated gluon densities in a proton. Finally, we extrapolate the theoretical predictions to the CERN LHC energies.

Inclusive production of J/ψ in proton-proton collisions at RHIC

Inclusive cross sections for J/ψ production in proton-proton collisions were calculated in the kt-factorization approach for the RHIC energy. Several mechanisms were considered. Radiative Xc decays and direct color-singlet contributions constitute the dominant mechanisms of J/ψ production. The results are compared with recent RHIC data.

B → K Transition Form Factor with Tensor Current within the kTFactorization Approach

We apply the kT factorization approach to deal with the B → K transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain FTB→K(0) = 0.25 ± 0.01 ± 0.02, where the first error is caused by the uncertainties from the pionic wavefunctions and the second is from that of the B-meson wavefunctions. This result is consistent with the light-cone sum rule results obtained in the literature.

Hadroproduction of heavy quarkonia at high energies within the k T -factorization approach

On the basis of the kT-factorization approach, heavy-quarkonium \((c\bar c,b\bar b)\) hadroproduction at high energies is considered within nonrelativistic QCD in the leading order in αs and v. The pT spectra of various S-and P-wave quarkonium states at the Tevatron collider energies (run I and run II) are fitted, and sets of octet nonperturbative matrix elements are obtained for three different versions of the noncollinear gluon distribution in the proton.