Charmed Meson Production Research Articles

Physics performance studies for the ALICE inner tracker upgrade

During the second long shutdown of the LHC in 2018, the ALICE Collaboration plans to install an upgrade of the ALICE Inner Tracking System (ITS) in the central barrel with seven layers of silicon detectors starting at 2.2 cm radial distance from the interaction region and a material budget as low as 0.3 % radiation length per layer. A single-hit resolution of 4 μm and a readout rate capability of up to 50 kHz in Pb–Pb collisions will allow new and unique measurements in the heavy-quark sector, i.e. charm and beauty. Using detailed Monte Carlo simulations of pp and Pb–Pb collisions we study the performance for heavy-flavor detection with an upgraded ITS in the following benchmark analyses: Charm meson and baryon production, i.e. D0 → K−π+ and Λ+c → pK−p+, and beauty meson and baryon production, i.e. displaced vertices of B+ → D̄0π+ and Λb → Λ+cπ−.

Heavy Flavour Cross Section Measurements with the ATLAS Detector

ATLAS measurements of heavy flavour production cross sections are presented from proton-proton collisions at the LHC at a centre-of-mass energy of 7 TeV. These make use of b-hadron decays to D⁎μX, inclusive charm meson production, inclusive electron and muon production from semileptonic heavy flavour decays, and reconstruction of secondary decay vertices to tag b-jets. The results are compared with next-to-leading-order QCD calculations.

Inclusive charmed-meson production at the CERN LHC

We present predictions for the inclusive production of D mesons at the CERN LHC in the general-mass variable-flavor-number scheme at next-to-leading order. Detailed numerical results are compared to data where available, or presented in a way to ease future comparisons with experimental results. We also point out that measurements at large rapidity have the potential to pin down models of intrinsic charm.

Too many Xʼs, Yʼs and Zʼs?

A large number of new states have been reported during the last few years in charmonium spectroscopy above the charmed meson production threshold. They have been called Xʼs, Yʼs, and Zʼs. We reflect on the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge meson–meson molecules.

Heavy quark production at collider energies: Some selected topics

We discuss production of charm quarks and mesons as well as nonphotonic electrons in $pp$ scattering at RHIC. The distributions in rapidity and transverse momentum of charm and bottom quarks/antiquarks are calculated in the $k_t$-factorization approach. The hadronization of heavy quarks is done by means of fenomenological fragmentation functions. The semileptonic decay functions found by fitting semileptonic decay data measured by the CLEO and BABAR collaborations are used. Good description of the inclusive data at large transverse momenta of electrons is obtained and a missing strength at small transverse momenta of electrons is found. Furthermore we discuss kinematical correlations between charged leptons from semileptonic decays of open charm/bottom, leptons produced in the Drell-Yan mechanism as well as some other mechanisms not included so far in the literature. When calculating the Drell-Yan processes we include transverse momenta of $q$ and $\bar q$, using the Kwiecinski parton distributions. Reactions initiated by purely QED $\gamma^*\gamma^*$-fusion in elastic and inelastic $pp$ collisions as well as diffractive mechanism of exclusive $c \bar c$ production are included. A good description of the dilepton invariant mass spectrum measured by the PHENIX collaboration is achieved. Predictions for the dilepton pair transverse momentum distribution as well as distribution in azimuthal angle between electron and positron are presented.

Charmed Meson Production in Deep Inelastic e + A Scattering at Small-x

Based on the nuclear effects considered in the Glauber—Gribov approach, charmed meson production in high energy deep inelastic e+A scattering is investigated in the color dipole formalism. Using the Peterson fragmentation function and the KLR-AdS/CFT color dipole model, which reasonably well describes the HERA data for the inclusive structure functions at small Bjorken-x, we present the predictive results for the D-meson transverse spectra at EIC and LHeC energies. The theoretical results indicate that the x-independence phenomena at very small-x predicted by the KLR-AdS/CFT model are not seen in our calculation.

NLO QCD result for the gluon polarisation from open-charm D0 meson production at COMPASS

One of the main goals of the COMPASS experiment is the measurement of the gluon contribution to the nucleon spin. Among the processes studied by COMPASS, open-charm D0 meson production seems to be the cleanest channel for probing gluons in the energy range covered by the experiment. The gluon polarisation is related to the measured asymmetry for charmed meson production via the analyzing power (asymmetry at the partonic level) calculated in the perturbative QCD frame. The analyzing power for the "photon-gluon fusion" process corresponds to a LO QCD approximation. The significant improvement of the statistical precision and the new, final LO result are presented. The NLO QCD corrections to the partonic cross sections (unpolarised and polarised ones) are now also included into the analysis scheme since these higher order contributions are not negligible. The preliminary NLO QCD result on the gluon polarisation based on a set of measured D0 meson asymmetries in kinematical bins of the D0 energy and transverse momentum is presented.

Breakdown of [formula omitted]-factorization and [formula omitted] production in dA collisions

In spite of the sweeping coherence effects in high energy hadron and nuclei collisions, k T -factorization can be recovered for the inclusive gluon production in pA collisions at the leading logarithmic order. In open charm production at RHIC k T -factorization holds numerically with about 10–20% accuracy. This allows to extrapolate the cold nuclear matter effect observed in light and charm meson production in dA collisions to that in AA ones. Unlike the open charm, the breakdown of factorization in J / ψ production is severe. Indeed, already at the lowest order in gluon density the main contribution to the inclusive cross section is proportional to the square of gluon density in the nucleus. As a consequence, one cannot infer the cold nuclear matter effect on J / ψ production in AA collisions from that in dA. We present the calculation of J / ψ multiplicity in the framework of the CGC (color glass condensate)/saturation and show that it agrees with the experimental data.

Open charm and beauty production in hadron reactions

The production of charmed and beauty hadrons in proton-proton and proton-antiproton collisions at high energies is analyzed within the modified quark-gluon string model (QGSM) including the internal motion of quarks in colliding hadrons. It is shown that using both the QGSM and NLO QCD one can describe the experimental data rather successfully in a wide region of transverse momenta. We also present some predictions for the future experiments on the beauty baryon production in $pp$ collisions at LHC energies and on the charmed meson production in ${\bar p}p$ reactions at GSI energies.

The role and detectability of the charm contribution to ultra high energy neutrino fluxes

It is widely believed that charm meson production and decay may play an important role in high energy astrophysical sources of neutrinos, especially those that are baryon-rich, providing an environment conducive to pp interactions. Using slow-jet supernovae (SJS) as an example of such a source, we study the detectability of high-energy neutrinos, paying particular attention to those produced from charmed-mesons. We highlight important distinguishing features in the ultra-high energy neutrino flux which would act as markers for the role of charm in the source. In particular, charm leads to significant event rates at higher energies, after the conventional (π,K) neutrino fluxes fall off. We calculate event rates both for a nearby single source and for diffuse SJS fluxes for an IceCube-like detector. By comparing muon event rates for the conventional and prompt fluxes in different energy bins, we demonstrate the striking energy dependence in the rates induced by the presence of charm. We also show that it leads to an energy dependant flux ratio of shower to muon events, providing an additional important diagnostic tool for the presence of prompt neutrinos. Motivated by the infusion of high energy anti-electron neutrinos into the flux by charm decay, we also study the detectability of the Glashow resonance due to these sources.

Neutrino fluxes from astrophysical sources, the role of neutrinos from charmed meson production and decay

We show that charm production gives significant enhancement to a flux of very high energy neutrinos from astrophysical sources with jets driven by central engines, such as gamma ray bursts or supernovae with jets. We demonstrate that neutrino flux from semi-leptonic decays of charmed mesons is subject to much less hadronic and radiative cooling than the conventional flux from pion and kaon decays. We discuss implications of our results for future ultrahigh energy neutrino experiments.

Production of excited charm and charm-strange mesons at HERA

The production of excited charm, D_1(2420)^0 and D_2^*(2460)^0, and charm-strange, D_{s1}(2536)^+-, mesons in ep collisions was measured with the ZEUS detector at HERA using an integrated luminosity of 126 pb^-1. Masses, widths and helicity parameters were determined. The measured yields were converted to the rates of c quarks hadronising as a given excited charm meson and to the ratios of the dominant D_2^*(2460)^0 and D_{s1}(2536)^+- branching fractions. A search for the radially excited charm meson, D^{*'}(2640)^+-, was also performed. The results are compared with those measured previously and with theoretical expectations.

Measurement of the Gluon Polarization of the Nucleon at COMPASS

The determination of the gluon polarization Δ G / G represents one of the main goals of the COMPASS Collaboration at CERN. This quantity is experimentally accessible by selecting photon gluon fusion (PGF) events in the scattering of a polarized 160 GeV muon beam off a polarized 6 LiD target. At COMPASS the PGF mechanism is tagged by means of three different channels: charmed meson production and high- p T hadron pairs in either electro-production ( Q 2 > 1 GeV 2 ) or quasi-real photo-production ( Q 2 1 GeV 2 ). The status of the different analyses and the Δ G / G results obtained from the 2002-04 data samples are presented. The most precise measurement comes from the hight- p T quasi-real photo-production, yielding a small gluon polarization.

Charmed meson production in deep inelastic scattering

Charmed meson production in semi-inclusive deep inelastic scattering is investigated in the color-dipole formalism. The transverse momentum distributions are calculated. We find good agreement with the H1 data using a hard fragmentation function.

Single spin asymmetry for charm mesons

We study single spin asymmetries of D0 and D- mesons in polarized proton–proton collisions. A two component model is used to describe charm meson production. The production of D mesons occurs by recombination of the constituents present in the initial state as well as by fragmentation of quarks in the final state. This model has proved to describe the production of charm. The recombination component involves a mechanism of spin alignment that ends up in a single spin asymmetry. Experimental measurements of single spin asymmetry for pions at RHIC are compared with the model. Predictions for the asymmetry in D mesons are presented.

Nonfactorizable contributions inBdecays to charmonium: The case ofB−→K−hc

Nonleptonic $B$ to charmonium decays generally show deviations from the factorization predictions. For example, the mode $B^- \to K^- \chi_{c0}$ has been experimentally observed with sizeable branching fraction while its factorized amplitude vanishes. We investigate the role of rescattering effects mediated by intermediate charmed meson production in this class of decay modes, and consider $B^- \to K^- h_c$ with $h_c$ the $J^{PC}=1^{+-}$ $\bar c c$ meson. Using an effective lagrangian describing interactions of pairs of heavy-light $Q{\bar q}$ mesons with a quarkonium state, we relate this mode to the analogous mode with $\chi_{c0}$ in the final state. We find ${\cal B}(B^- \to K^- h_c)$ large enough to be measured at the $B$ factories, so that this decay mode could be used to study the poorly known $h_c$.

B and c quark production at CDF, $\sqrt{s}$ = 1.96 TeV

Measurements of heavy quark production at the Tevatron have previously shown discrepancies with theoretical predictions The increased luminosity of Run 2 will allow CDF to investigate b and c quark production more precisely. In this review three measurements, based on a subset of current data, are presented: charm meson production; J/ψ production; production of an energetic photon in conjunction with a b or c quark jet. PACS: 12.38.Qk Experimental tests of Quantum Chromodynamics – 13.85.Ni Inclusive production with identified hadrons

Measurement of prompt charm meson production cross sections in pp collisions at square root s = 1.96 TeV.

We report on measurements of differential cross sections dsigma/dp(T) for prompt charm meson production in ppmacr; collisions at sqrt[s]=1.96 TeV using 5.8+/-0.3 pb(-1) of data from the CDF II detector at the Fermilab Tevatron. The data are collected with a new trigger that is sensitive to the long lifetime of hadrons containing heavy flavor. The charm meson cross sections are measured in the central rapidity region |y|</=1 in four fully reconstructed decay modes: D0-->K-pi(+), D(*+)-->D0pi(+), D+-->K-pi(+)pi(+), D(+)(s)-->phipi(+), and their charge conjugates. The measured cross sections are compared to theoretical calculations.

Open charm production at HERA

Inclusive charm meson production cross sections in the deep inelastic scattering and photoproduction regimes are compared with QCD leading and next-to-leading (NLO) calculations. The NLO predictions are significantly below the data in some parts of the measured kinematic range. Angular distributions of dijet events with charm show clear evidence for the existence of charm originating from the incoming photon. The charm fragmentation function is measured for the first time at HERA. Various fragmentation ratios and the fragmentation fractions of the low-lying charm hadrons are determined and compared to previous e+e- results.

Hadronic Spectral Function and Charm Meson Production

At the chiral restoration/deconfinement transition, most hadrons undergo a Mott transition from being bound states in the confined phase to resonances in the deconfined phase. We investigate the consequences of this qualitative change in the hadron spectrum on final state interactions of charmonium in hot and dense matter, and show that the Mott effect for D-mesons leads to a critical enhancement of the J/Psi dissociation rate. Anomalous J/Psi suppression in the NA50 experiment is discussed as well as the role of the Mott effect for the heavy flavor kinetics in future experiments at the LHC. The status of our calculations of hadron-hadron cross sections using the quark interchange and chiral Lagrangian approaches is reviewed, and an Ansatz for a unification of these schemes is given.