Heavy Quark Production Cross Section Research Articles

Heavy flavor production under a strong magnetic field

The magnetic field created in high energy nuclear collisions will affect the QCD dynamical processes, such as the heavy quark production which happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section of the process gg→QQ¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ gg\ o Q\\overline{Q} $$\\end{document} at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the rotational invariance is broken in a magnetic field, the production becomes anisotropic.

Proton Structure Functions at Next-to-Leading Order in the Dipole Picture with Massive Quarks.

We predict heavy quark production cross sections in deep inelastic scattering at high energy by applying the color glass condensate effective theory. We demonstrate that, when the calculation is performed consistently at next-to-leading order accuracy with massive quarks, it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both the light and heavy quark production data at small x_{Bj}. Furthermore, we show how the heavy quark cross section data provides additional strong constraints on the extracted nonperturbative initial condition for the small-x_{Bj} evolution equations.

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, $k_T$ factorization including low-$x$ resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at $7$ TeV and at $13$ TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from $10\%$ to $50 \%$ at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

Search for Single Production of Vector-like Quarks Coupling to Light Generations in 4.64 fb−1 of ATLAS Data at = 7 TeV

This analysis presents a search for singly-produced vector-like quarks (VLQs) coupling to light quark generations in events with a W or Z boson produced in association with two or more high transverse momentum jets. The vector boson produced in the VLQ decay is reconstructed in the W → ℓν or Z → ℓℓ modes, where ℓ is an electron or a muon. No evidence of VLQs is observed above the expected background in 4.64 fb−1 of data taken in 2011 by the ATLAS experiment at the LHC at a centre-of-mass energy of 7 TeV. A fit to the distribution of the invariant mass of the system composed of the vector boson and the highest transverse momentum jet is used to set limits on the heavy quark production cross section times branching ratio, and mass bounds are obtained for three flavors of VLQs.

CHARMONIUM PRODUCTION IN Pb–Pb COLLISIONS AT ALICE: FROM SUPPRESSION TO REGENERATION?

Heavy quarkonium states are considered as one of the key observables for the study of the phase transition from a system made of hadrons towards a Quark–Gluon Plasma (QGP). In the last 25 years, experiments at CERN and Brookhaven have studied collisions of heavy ions looking for a suppression of charmonia/bottomonia, considered as a signature of the phase transition. After an introduction to the main concepts behind these studies and a short review of the SPS and RHIC results, I will describe the results obtained in Pb – Pb collisions by the ALICE experiment at the LHC. The ALICE findings will be critically compared to those of lower energy experiments, to CMS results, and to model calculations. The large cross-sections for heavy-quark production at LHC energies are expected to induce a novel production mechanism for charmonia in heavy-ion collisions, related to a recombination of [Formula: see text] pairs along the history of the collision and/or at hadronization. The occurrence of such a process at the LHC will be discussed. Finally, prospects for future measurements will be shortly addressed.

Measurement of nuclear modification of lepton production from heavy flavour decays in Pb-Pb collisions with ALICE at the LHC

The heavy quark production cross-section and its nuclear modification factor can be measured by identifying single leptons from semi-leptonic heavy flavour hadron decays. In 2010, pp collisions at = 7 TeV and Pb-Pb collisions at = 2.76 TeV have been recorded by ALICE at the LHC. We present the preliminary results of lepton pt spectra (electrons in |η| < 0.8 and muons in 2.5 < η < 4.0) from heavy flavour hadron decays in pp collisions and their nuclear modification factor in Pb-Pb collisions with both the central barrel and forward muon detectors of ALICE.

Photon plus heavy-quark production in high-energy collisions within the target rest frame formalism

We apply the target rest frame formalism to photon + heavy quark production cross section in hadronic collisions at high energies. We investigate the dependence of the production cross section on the photon and quark rapidities and transverse momenta. It is shown that the photon transverse momentum spectrum is a sensitive probe of color dipole scattering amplitude. The theoretical results are compared to Tevatron measurements of the differential \gamma + c + X and \gamma + b + X production cross sections at 1.96 TeV. An analysis for proton-proton and proton-lead collisions at the LHC regime is also performed.

Heavy quark production in deep inelastic electron-nucleus scattering

Heavy quark production has been very well studied over the last years both theoretically and experimentally. Theory has been used to study heavy quark production in $e p$ collisions at HERA, in $pp$ collisions at Tevatron and at RHIC, in $pA$ and $dA$ collisions at RHIC and in $AA$ collisions at CERN-SPS and at RHIC. However, to the best of our knowledge, heavy quark production in $eA$ has received almost no attention. With the possible construction of a high energy electron-ion collider, updated estimates of heavy quark production are needed. We address the subject from the perspective of saturation physics and compute the heavy quark production cross section with the dipole model. We isolate shadowing and non-linear effects, showing their impact on the charm structure function and on the transverse momentum spectrum.

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.

Heavy quark production from colour glass condensate at RHIC

I consider production of heavy quarks in pA and AA collisions in the framework of the colour glass condensate. I discuss the heavy quark production in pA collisions in a classical approximation which takes into account all multiple rescatterings of a proton in a nucleus. For peripheral collisions, the heavy quark production cross section can be written in the kT-factorized form. The kT-factorization is used to construct a simple model which takes into account both classical and quantum effects in pA and AA collisions. I review the main result of calculation based on that model: open charm in the central rapidity region at RHIC gets suppressed as a function of rapidity. Although the numbers obtained for the suppression factor are model dependent, the very fact of suppression is the general feature of the colour glass condensate at RHIC kinematical region. It indicates the onset of quantum evolution effects in a nucleus and is universal for all inclusive processes.

Heavy quark production by a quasi-classical color field in proton–nucleus collisions

We calculate the inclusive heavy quark production cross section for proton–nucleus collisions at high energies. We perform calculation in a quasi-classical approximation (McLerran–Venugopalan model) neglecting all low-x evolution effects. The derived expression for the differential cross section can be applied for studying the heavy quark production in the central rapidity region at RHIC.

Heavy-quark production in p $$\bar p$$ collisions and unintegrated gluon distributions

The inclusive production of heavy (c and b) quarks in high-energy p\(\bar p\) collisions are considered within the semihard approach in QCD. The dependence of the cross section for heavy-quark production, σ(pT>p T min ), on unintegrated gluon distributions is studied. The results of this consideration are compared with experimental data obtained by the D0 and CDF Collaborations at Tevatron.

The high density effects in heavy-quark production at pA colliders

In this Letter we investigate the role of the high density effects in the heavy-quark production cross section in pA processes at RHIC and LHC. We use, as initial condition, a gluon distribution consistent with fixed target nuclear data and the Glauber–Mueller approach to describe the high density effects. We show that this process can be used as a probe of the presence of the high density effects. Moreover, we include these effects in the calculation of the heavy-quark production in AA collisions, verifying that they cannot be disregarded both in the estimates of quarkonium suppression and in the initial conditions of the quark–gluon plasma.

Soft-gluon resummation for heavy quark production in hadronic collisions

We discuss the heavy quark production cross section near partonic threshold in hadronic collisions, including the resummation of leading and next-to-leading logarithms arising from soft gluon emission. We show how to handle the complications due to the non-universal non-leading logarithms. We give analytical results for the $q {\bar q}$ partonic subprocess and numerical results in the DIS scheme for top quark production at the Fermilab Tevatron where the $q {\bar q}$ channel dominates.

Spatial Variation of Nuclear Structure Functions and Heavy Quark Production

We explore how nuclear modifications to the free nucleon structure functions (also known as shadowing) affect heavy quark production in collisions at different impact parameters. We assume that the nuclear modifications arise from a density dependent effect such as gluon recombination and are thus proportional to the local density. We calculate the dependence of charm and bottom quark production on impact parameter and show that density dependent modifications can lead to significant reductions in the heavy quark production cross sections in central relative to peripheral interactions.

Resummed heavy quark production cross sections to next-to-leading logarithm

We study how next-to-leading logarithms modify predictions from leading logarithmic soft-gluon resummation in the heavy quark production cross section near threshold. Numerical results are presented for top quark production at the Fermilab Tevatron and bottom quark production at fixed-target energies. {copyright} {ital 1997} {ital The American Physical Society}

Heavy quark production in soft pp-bar collisions at superhigh energies.

The heavy-quark production cross sections $\ensuremath{\sigma}(\frac{c}{\overline{c}})$, $\ensuremath{\sigma}(\frac{b}{\overline{b}})$, and $\ensuremath{\sigma}(\frac{t}{\overline{t}})$ in $\mathrm{pp}$ and $p\overline{p}$ collisions at superhigh energies are calculated in the framework of Reggeon phenomenology.

Heavy-quark correlations in hadron collisions at next-to-leading order

We present a calculation of the fully exclusive parton cross sections for heavy-quark production at order O( α S 3) in QCD. Our result includes the Born cross section for producing a Q Q pair, of order O( α S 2), the virtual corrections to the Born cross section, of order O( α S 3), and the cross section for producing a Q Q pair plus a light parton, of order O( α S 3). We can therefore compute distributions in which correlations among the heavy quarks (and, if present, the associated jet) are correctly taken into account up to order O( α S 3). We present some applications of phenomenological interest to top, bottom and charm production at hadron colliders.

The fragmentation function for heavy quarks in QCD

We present the results of a next-to-leading order QCD calculation of the fragmentation function for heavy quarks. Our formalism can be used to obtain the next-to-leading order inclusive heavy quark production cross section in any hard collisions, in the limit when the transverse momentum of the heavy quark is much larger than its mass. We apply our results to the inclusive production of heavy quarks in e +e − collisions, and present detailed formulas for the moments of the heavy quark fragmentation function in e +e − production processes.