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R. Vogt

Publications and source records attributed to R. Vogt.

At least 109 records · Page 6Linked to original sources
arXiv1998

Energy loss effects on heavy quark production in heavy-ion collisions at $\sqrt{s} = 5.5$ $A$TeV

We study the effect of energy loss on charm and bottom quarks in high-energy heavy-ion collisions including hadronization, longitudinal expansion and partial thermalization. We consider in detail the detector geometry and single lepton energy cuts of the ALICE and CMS detectors at the Large Hadron Collider (LHC) to show the large suppression of high $p_T$ heavy quarks and the consequences of their semileptonic decays.

hep-ph↗
arXiv1998

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.

nucl-th↗
arXiv1997

Charm Quark Production in Non-central Heavy Ion Collisions

The effect of gluon shadowing on charm quark production in large impact parameter ultrarelativistic heavy ion collisions is investigated. Charm production cross sections are calculated for a range of non-central impact parameters which can be accurately inferred from the global transverse energy distribution. We show that charm production is a good probe of the local parton density which determines the effectiveness of shadowing. The spatial dependence of shadowing can only be studied in heavy ion collisions.

nucl-th↗
arXiv1997

A microscopic calculation of secondary Drell-Yan production in heavy ion collisions

A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The contributions from meson-baryon interactions, small in hadron-nucleus interactions, are found to be substantial in nucleus-nucleus collisions at low dilepton masses. Preresonance collisions of partons may further increase the yields.

hep-ph↗
arXiv1997

Intrinsic Charm at High-Q^2 and HERA Data

We compute the predictions of intrinsic charm for deep-inelastic scattering at high-Q^2 and compare to HERA data. With the inclusion of constraints from low-energy data, enhancements beyond the predictions of standard structure functions are very modest, but peaking in the leptoquark mass variable is present near 200 GeV. Ultimately, the ability of HERA to probe the intrinsic charm hypothesis could be very substantial.

hep-ph↗
arXiv1997

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.

hep-ph↗
arXiv1996

Determining the existence and nature of the quark-gluon plasma by Upsilon suppression at the LHC

Minijet production in $\sqrt{s} = 5.5$ TeV Pb+Pb collisions at the LHC is expected to produce a gluon-dominated plasma with large initial temperatures and energy densities. We discuss the implications of the high initial temperatures on the screening mass and on the relative suppression of members of the $Υ$ family. We demonstrate that $p_T$-dependence of the $Υ'/Υ$ ratio is only expected if a quark-gluon plasma with significant energy density is present, and that the precise dependence of this ratio will strongly constrain the QGP models. We also propose that the $p_T$ spectra of the $Υ$ resonances themselves will provide valuable information by comparing these spectra to that of the $Z$ boson, which should not be influenced by plasma production.

hep-ph↗
arXiv1996

$J/ψ$ and $ψ'$ suppression by comovers in Pb+Pb collisions

Measurements of $ψ$ and $ψ'$ production at the CERN SPS are compared to predictions based on a hadronic model of charmonium suppression. Detailed information is presented to facilitate comparison to other analyses. Sensitivity of these conclusions to the model parameters is discussed.

nucl-th↗
arXiv1996

Charmonium Suppression by Comover Scattering in Pb+Pb Collisions

The first reports of $ψ$ and $ψ'$ production from experiment NA50 at the CERN SPS are compared to predictions based on a hadronic model of charmonium suppression. Data on centrality dependence and total cross sections are in good accord with these predictions.

hep-ph↗
arXiv1996

Charm and Bottom Quark Production Cross Sections Near Threshold

The cross sections for charm and bottom quark production in the threshold region are discussed. We consider the effects of an all order resummation of initial state soft-plus-virtual gluon radiation on the total cross sections compared to the order $α_s^3$ results.

hep-ph↗
arXiv1996

How To Find Charm in Nuclear Collisions at RHIC and LHC

Measurements of dilepton production from charm decay and Drell-Yan processes respectively probe the gluon and sea quark distributions in hadronic collisions. In nucleus-nucleus collisions, these hard scattering processes constitute a `background' to thermal contributions from the hot matter produced by the collision. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to dilepton production in nuclear collisions at RHIC and LHC at next to leading order in perturbative QCD. Invariant mass, rapidity and transverse momentum distributions are presented. We compare these results to optimistic hydrodynamic estimates of the thermal dilepton production. We find that charm production from hard scattering is by far the dominant contribution. Experiments therefore can measure the gluon distribution in the nuclear target and projectile and, consequently, can provide new information on gluon shadowing. We then illustrate how experimental cuts on the rapidity gap between the leptons can aid in reducing the charm background, thereby enhancing thermal information.

hep-ph↗
arXiv1995

Charmed Hadron Asymmetries in the Intrinsic Charm Coalescence Model

Fermilab experiment E791, measuring charmed hadron production in $π^- A$ interactions at 500 GeV with high statistics, has observed a strong asymmetry between the hadroproduction cross sections for leading $D$ mesons which contain projectile valence quarks and the nonleading charmed mesons without projectile valence quarks. Such correlations of the charge of the $D$ meson with the quantum numbers of the beam hadron explicitly contradict the factorization theorem in perturbative QCD which predicts that heavy quarks hadronize through a jet fragmentation function that is independent of the initial state. The E791 experiment also measures $Λ_c/ \bar Λ_c$ and $D_s/\bar{D_s}$ production asymmetries as well as asymmetries in $D \bar D$ pair production. We examine these asymmetries and the fractional longitudinal momentum, $x_F$, distributions for single and pairs of charmed hadrons within a two-component model combining leading-twist $g g$ and $q \bar q$ fusion subprocesses with charm production from intrinsic heavy quark Fock states. A key feature of this analysis is intrinsic charm coalescence, the process by which a charmed quark in the projectile's Fock state wavefunction forms charmed hadrons by combining with valence quarks of similar rapidities.

hep-ph↗
arXiv1995

Reanalysis of the EMC charm production data with extrinsic and intrinsic charm at NLO

A calculation of the next-to-leading order exclusive extrinsic charm quark differential distributions in deeply inelastic electroproduction has recently been completed. Using these results we compare the NLO extrinsic contributions to the charm structure function $F_2(x,Q^2,m_c^2)$ with the corresponding NLO intrinsic contributions. The results of this analysis are compared with the EMC DIS charm quark data and evidence for an intrinsic charm component in the proton is found.

hep-ph↗
arXiv1995

Phenomenology of Charm and Bottom Production

We discuss the renormalization and factorization scale dependence of charm and bottom production both at fixed-target energies and at present and future colliders. We investigate whether distributions calculable at leading order can be extrapolated to next-to-leading order by a constant multiplicative factor.

hep-ph↗
arXiv1995

Intrinsic Charm Contribution to Double Quarkonium Hadroproduction

Double $J/ψ$ production has been observed by the NA3 collaboration in $πN$ and $p N$ collisions with a cross section of the order of 20-30 pb. The $ψψ$ pairs measured in $π^- $ nucleus interactions at 150 and 280 GeV$/c$ are observed to carry an anomalously large fraction of the projectile momentum in the laboratory frame, $x_{ψψ} \geq 0.6$ at 150 GeV$/c$ and $\geq 0.4$ at 280 GeV$/c$. We postulate that these forward $ψψ$ pairs are created by the materialization of Fock states in the projectile containing two pairs of intrinsic $c \overline c$ quarks. We calculate the overlap of the charmonium states with the $|\overline u d c \overline c c \overline c \rangle$ Fock state as described by the intrinsic charm model and find that the $π^- N \rightarrow ψψ$ longitudinal momentum and invariant mass distributions are both well reproduced. We also discuss double $J/ψ$ production in $pN$ interactions and the implications for other heavy quarkonium production channels in QCD.

hep-ph↗
arXiv1995

QCD Mechanisms for Double Quarkonium and Open Heavy Meson Hadroproduction

Double $J/ψ$ production on the order of 20-30 pb has been observed by the NA3 collaboration. These $ψψ$ pairs, measured in $π^- N$ interactions at 150 and 280 GeV$/c$ and in $pN$ interactions at 400 GeV$/c$, carry a large fraction of the projectile momentum, $x_{ψψ} \geq 0.6$ for the 150 GeV$/c$ beam and $\geq 0.4$ at 280 GeV$/c$. We examine several sources of $ψψ$ pair production within QCD, including ${\cal O}(α_s^4)$ $ψψ$ production, leading-twist $b \overline b$ production and decay, and the materialization of heavy-quark Fock states in the projectile. We estimate the production cross section and the single and double $J/ψ$ momentum and mass distributions for each, comparing the results with the NA3 data, and predict $ψψ$ production in $pN$ interactions at 800 GeV$/c$, accessible to current fixed-target experiments. We also discuss the observable implications of open heavy meson pair production from the intrinsic heavy quark Fock states.

hep-ph↗
arXiv1995

Quarkonium production in hadronic collisions

We summarize the theoretical description of charmonium and bottonium production in hadronic collisions and compare it to the available data from hadron-nucleon interactions. With the parameters of the theory established by these data, we obtain predictions for quarkonium production at RHIC and LHC energies.

hep-ph↗