Heavy Quark Production Research Articles

LONGITUDINALLY POLARIZED HADRO- AND PHOTOPRODUCTION OF HEAVY QUARKS

Measurements of double-spin asymmetries for single-inclusive heavy flavor production and for heavy quark correlations are expected to provide valuable information about the spin structure of the nucleon, in particular, the elusive gluon polarization. We discuss progress towards a versatile parton-level Monte-Carlo code for the production and decay of heavy quarks in longitudinally polarized hadron-hadron and photon-hadron collisions at next-to-leading order accuracy of QCD. Phenomenological studies are presented for BNL-RHIC and COMPASS.

Recent results from the Relativistic Heavy Ion Collider (RHIC)

The most recent physics results obtained at the Relativistic Heavy Ion Collider (RHIC) are surveyed. The survey is devoted to considering p + p, Cu + Cu, and Au + Au systems of colliding nuclei at c.m. energies of √sNN = 200, 62.4, and 22.4 GeV. The results obtained within the first years of collider operation are discussed. New data on the production of high-transverse-momentum particles are presented. Manifestations of collective flows, such as the radial and elliptic flows, as well as the formation of a shock wave and a ridge, are considered. The results concerning heavy-quark production are also discussed.

Probing the gauge content of heavy resonances with soft radiation

The use of energy flow is investigated as a diagnostic tool for determining the color SU(3) representation of new resonances. It is found that the pattern of soft gluon radiation into a rapidity gap depends on color flow in the hard scattering, and reflects the gauge content of new physics. The massive soft anomalous dimension matrix for rapidity gap events is introduced for describing soft gluon emission analytically in heavy quark pair production. A gap fraction is used for quantifying the amount of soft radiation into the gap region. In general, the results illustrate that radiation is greater for a singlet resonance than for an octet. Especially, it is found that the quantitative difference is quite distinguishable for spin-1 resonances, depending on the gauge content in the new sector.

Open Heavy Flavor Production at Forward Rapidity in [formula omitted] Cu+Cu Collisions

The first measurement of the nuclear modification factor, R A A , for single muons produced in Cu+Cu collisions at s N N = 200 GeV is presented, which is the first measurement of the nuclear modification factor for open heavy flavor production made at forward angles in heavy ion collisions. Single muons are used to tag heavy flavor quark production via semi-leptonic decay of open heavy flavor mesons. With its muon arms, PHENIX has a unique ability to measure single muons at forward rapidity ( 1.2 < | η | < 2.2 ) .

Threshold resummation for top-pair hadroproduction to next-to-next-to-leading log

We derive the threshold-resummed total cross section for heavy quark production in hadronic collisions accurate to next-to-next-to-leading logarithm, employing recent advances on soft anomalous dimension matrices for massive pair production in the relevant kinematic limit. We also derive the relation between heavy quark threshold resummations for fixed pair kinematics and the inclusive cross section. As a check of our results, we have verified that they reproduce all poles of the color-averaged $q\overline{q}\ensuremath{\rightarrow}t\overline{t}$ amplitudes at two loops, noting that the latter are insensitive to the color-antisymmetric terms of the soft anomalous dimension.

NLO predictions for t-channel production of single top and fourth generation quarks at hadron colliders

We present updated NLO predictions for the electroweak t-channel production of heavy quarks at the Tevatron and at the LHC. We consider production of single top and fourth generation t' starting from both 2 to 2 and 2 to 3 Born processes. Predictions for tb' and t'b' cross sections at NLO are also given for the first time. A thorough study of the theoretical uncertainties coming from parton distribution functions, renormalisation and factorisation scale dependence and heavy quark masses is performed.

Associated production of Higgs bosons and heavy quarks at the LHC: Predictions with thekT-factorization approach

In the framework of the ${k}_{T}$-factorization approach, we study the production of Higgs bosons associated with a heavy (beauty or top) quark pair at the CERN LHC collider conditions. Our consideration is based mainly on the off-shell gluon-gluon fusion subprocess ${g}^{*}{g}^{*}\ensuremath{\rightarrow}Q\overline{Q}H$. The corresponding matrix element squared has been calculated for the first time. We investigate the total and differential cross sections of $b\overline{b}H$ and $t\overline{t}H$ production taking into account also the non-negligible contribution from the $q\overline{q}\ensuremath{\rightarrow}Q\overline{Q}H$ mechanism. In the numerical calculations we use the unintegrated gluon distributions obtained from the Ciafaloni-Catani-Fiorani-Marchesini evolution equation. Our results are compared with the leading predictions of the collinear factorization of QCD.

Heavy-quark pair production in polarized photon-photon collisions at next-to-leading order: Fully integrated total cross sections

We consider the production of heavy-quark pairs in the collisions of polarized and unpolarized on-shell photons and present, in analytic form, the fully integrated total cross sections for total photon spins J{sub z}=0, {+-}2 at next-to-leading-order in QCD. Phenomenological applications include bb production, which represents an irreducible background to standard-model intermediate-mass Higgs-boson production, as well as tt production.

Mixed heavy quark hybrid mesons, decay puzzles, and RHIC

We estimate the energy of the lowest charmonium and upsilon states with hybrid admixtures using the method of QCD sum rules. Our results show that the ${\ensuremath{\Psi}}^{\ensuremath{'}}(2S)$ and $\ensuremath{\Upsilon}(3S)$ states both have about a 50% admixture of hybrid and meson components. From this we find explanations of both the famous $\ensuremath{\rho}\ensuremath{-}\ensuremath{\pi}$ puzzle for charmonium and the unusual pattern of $\ensuremath{\sigma}$ decays that have been found in $\ensuremath{\Upsilon}$ decays. Moreover, this picture can be used for predictions of heavy quark production with the octet model for RHIC.

Two-Loop Soft Anomalous Dimensions and Next-to-Next-to-Leading-Logarithm Resummation for Heavy Quark Production

I present results for two-loop soft anomalous dimensions for heavy quark production which control soft-gluon resummation at next-to-next-to-leading-logarithm accuracy. I derive an explicit expression for the exact result and study it numerically for top quark production via e(+)e(-)-->tt, and I construct a surprisingly simple but very accurate approximation. I show that the two-loop soft anomalous dimensions with massive quarks display a simple proportionality relation to the one-loop result only in the limit of vanishing quark mass. I also discuss the extension of the calculation to single top and top pair production in hadron colliders.

Functional equations for one-loop master integrals for heavy-quark production and Bhabha scattering

The method for obtaining functional equations, recently proposed by one of the authors [O.V. Tarasov, Phys. Lett. B 670 (2008) 67, arXiv:0809.3028 [hep-ph]], is applied to one-loop box integrals needed in calculations of radiative corrections to heavy-quark production and Bhabha scattering. We present relationships between these integrals with different arguments and box integrals with all propagators being massless. It turns out that functional equations are rather useful for finding imaginary parts and performing analytic continuations of Feynman integrals. For the box master integral needed in Bhabha scattering, a new representation in terms of hypergeometric functions admitting one-fold integral representations is derived. The hypergeometric representation of a master integral for heavy-quark production follows from the functional equation.

The massive soft anomalous dimension matrix at two loops

We study two-loop anomalous dimension matrices in QCD and related gauge theories for products of Wilson lines coupled at a point. We verify by an analysis in Euclidean space that the contributions to these matrices from diagrams that link three massive Wilson lines do not vanish in general. We show, however, that for two-to-two processes the two-loop anomalous dimension matrix is diagonal in the same color-exchange basis as the one-loop matrix for arbitrary masses at absolute threshold and for scattering at 90 degrees in the center of mass. This result is important for applications of threshold resummation in heavy quark production.

Strongly coupled fourth generation at the LHC

We study extensions of the standard model with a strongly coupled fourth generation. This occurs in models where electroweak symmetry breaking is triggered by the condensation of at least some of the fourth-generation fermions. With focus on the phenomenology at the LHC, we study the pair production of fourth-generation down quarks, D4. We consider the typical masses that could be associated with a strongly coupled fermion sector, in the range (300--600) GeV. We show that the production and successive decay of these heavy quarks into final states with same-sign dileptons, trileptons and four leptons, can be easily seen above background with relatively low luminosity. On the other hand, in order to confirm the presence of a new strong interaction responsible for fourth-generation condensation, we study its contribution to D4 pair-production, and the potential to separate it from standard QCD-induced heavy quark production. We show that this separation might require large amounts of data. This is true even if it is assumed that the new interaction is mediated by a massive colored vector boson, since its strong coupling to the fourth generation renders its width of the order of its mass. We conclude that, although this class of models can be falsified at early stages of the LHC running, its confirmation would require high integrated luminosities.

Investigation of heavy-quark production in proton-nucleus collisions with the HERA-B detector

Results obtained with the aid of the HERA-B detector, which operated at an internal target in a 920-GeV proton beam of the HERA storage ring at DESY (Hamburg, Germany), are discussed. About 164 million dilepton-triggered and 210 million minimum-bias events were collected over the data-taking time. These vast statistics made it possible to study in detail charmonium production in proton—nucleus collisions. Inclusive cross sections for open-charm, open-beauty, and ϒ-meson production weremeasured. The results are compared with the respective predictions of theoretical models.

Dilepton-tagged $Q\overline{Q}+\mathrm{jet}$ events at the LHC

We propose a new method for identifying and isolating $Q\overline{Q}+\mathrm{jet}$ events through semileptonic decays of the $Q\overline{Q}$ pair. Employing these decay dileptons to tag the jet in a specific kinematic region provides a clean signature of jets associated with heavy-quark production. The measurement, in both pp and heavy-ion collisions, is essential for addressing heavy-quark fragmentation in vacuum and in a dense medium. We present next-to-leading order calculations of $Q\overline{Q}$ production (leading order in $Q\overline{Q}+\mathrm{jet}$ production) in $\sqrt{s}=14$ TeV pp collisions at the LHC and discuss the feasibility of the measurement in heavy-ion collisions at $\sqrt{s_{NN}}=5.5$ TeV.

One-loop gluon amplitude for heavy-quark production at next-to-next-to-leading order

We compute the one-loop QCD amplitude for the process $gg\ensuremath{\rightarrow}Q\overline{Q}$ in dimensional regularization through order ${ϵ}^{2}$ in the dimensional regulator and for arbitrary quark mass values. This result is an ingredient of the next-to-next-to-leading order cross section for heavy-quark production at hadron colliders. The calculation is performed in conventional dimensional regularization using well-known reduction techniques as well as a method based on recent ideas for the functional form of one-loop integrands in four dimensions.

Prospects for the discovery of 4th family quarks with the ATLAS detector

The pair production of heavy fourth-generation quarks, which are predicted under the hypothesis of flavor democracy, is studied using tree-level Monte Carlo generators and fast detector simulation. Two heavy-quark mass values, 500 and 750$\gev$, are considered with the assumption that the fourth family mixes primarily with the two light families. It is shown that a clear signature will be observed in the data collected by the ATLAS detector, after the first year of low-luminosity running at the Large Hadron Collider.

Measurements of heavy-quark production via single leptons at PHENIX

The measurement of single leptons from the semi-leptonic decay of heavy-flavor hadrons has long been a means for studying heavy-quark production. PHENIX has measured single muons in pp collisions at forward rapidity and single electrons in both pp and AuAu collisions at mid-rapidity at . The most recent PHENIX single lepton results are presented in the context of state-of-the-art pQCD calculations. An updated azimuthal anisotropy, v2(pT), measurement for heavy-flavor single electrons in AuAu collisions is also presented.

Heavy quark production from jet conversions in a quark-gluon plasma

Recently, it has been demonstrated that the chemical composition of jets in heavy ion collisions is significantly altered compared to the jets in the vacuum. This signal can be used to probe the medium formed in nuclear collisions. In this study we investigate the possibility that fast light quarks and gluons can convert to heavy quarks when passing through a quark-gluon plasma. We study the rate of light to heavy jet conversions in a consistent Fokker-Planck framework and investigate their impact on the production of high-${p}_{T}$ charm and bottom quarks at the Relativistic Heavy Ion Collider and the Large Hadron Collider.

Single spin asymmetries in heavy quark and antiquark productions

The single transverse spin asymmetries in heavy quark and antiquark production from the quark–antiquark annihilation channel contribution is studied by taking into account the initial and final state interactions effects. Because of the different color charges, the final state interaction effects lead to about a factor of 3 difference in the spin asymmetry for heavy quark over that for the antiquark in the valence region of low energy pp collisions. The experimental study of this model-independent prediction shall provide a crucial test for the underlying mechanism for the single spin asymmetry phenomena.