Open Charm Cross Sections Research Articles

The multiple-charm hierarchy in the statistical hadronization model

In relativistic nuclear collisions the production of hadrons with light (u,d,s) quarks is quantitatively described in the framework of the Statistical Hadronization Model (SHM). Charm quarks are dominantly produced in initial hard collisions but interact strongly in the hot fireball and thermalize. Therefore charmed hadrons can be incorporated into the SHM by treating charm quarks as ‘impurities’ with thermal distributions, while the total charm content of the fireball is fixed by the measured open charm cross section. We call this model SHMc and demonstrate that with SHMc the measured multiplicities of single charm hadrons in lead-lead collisions at LHC energies can be well described with the same thermal parameters as for (u,d,s) hadrons. Furthermore, transverse momentum distributions are computed in a blast-wave model, which includes the resonance decay kinematics. SHMc is extended to lighter collision systems down to oxygen-oxygen and includes doubly- and triply-charmed hadrons. We show predictions for production probabilities of such states exhibiting a characteristic and quite spectacular enhancement hierarchy.

QCD predictions for open charm meson production at the LHCb in a fixed-target experiment

We investigate open charm meson production in fixed-target LHCb experiment at $\sqrt{s}=86.6$ GeV in $p+^4\!\mathrm{He}$ collisions. Theoretical calculations of charm cross section are done in the framework of the $k_{T}$-factorization approach. Its application in the kinematical range never examined before is carefully discussed. We consider different schemes for the calculations relevant for different unintegrated (transverse momentum dependent) parton densities in a proton. We include in the analysis both CCFM- and DGLAP-based models of unintegrated parton distributions appropriate for the considered kinematics. Integrated as well as differential cross sections as a function of $D^{0}$ meson rapidity and transverse momentum are shown and compared with the experimental data. As a reference point, predictions of next-to-leading order collinear approach are also presented and discussed. A very good agreement between the experimental data and the $k_{T}$-factorization predictions was obtained. Both the CCFM and the DGLAP-based frameworks for parton distributions in a proton are successfully used to explain the LHCb fixed-target open charm cross section.

New HERA Results on Diffraction

Four new measurements are presented in the area of diffractive and exclusive production at HERA. Preliminary results are available for isolated photons in diffractive photoproduction from ZEUS and open charm cross section in diffractive deep-inelastic scattering (DIS) regime from H1. ZEUS Collaboration has also measured the cross-section ratio σψ(2S)/σJ/ψ(1S) in exclusive DIS using full HERA data statistics. Finally, H1 Collaboration for the first time studied exclusive ρ0 meson photoproduction associated with a leading neutron at HERA.

Polarization effects in double open-charm production at LHCb

Double open-charm production is one of the most promising channels to disentangle single from double parton scattering (DPS) and study different properties of DPS. Several studies of the DPS contributions have been made. A missing ingredient so far has been the study of polarization effects, arising from spin correlations between the two partons inside an unpolarized proton. We investigate the impact polarization has on the double open-charm cross section. We show that the longitudinally polarized gluons can give significant contributions to the cross section, but for most of the considered kinematic region only have a moderate effect on the shape. We compare our findings to the LHCb data in the D0D0 final state, identify observables where polarization does have an impact on the distribution of the final state particles, and suggest measurements which could lead to first experimental indications of, or limits on, polarization in DPS.

Inclusive Open Charm Production in pp and Pb-Pb collisions with the ALICE Detector

ALICE is the dedicated heavy-ion experiment at the LHC. Its main physics goal is to study the properties of strongly-interacting matter at conditions of high energy density (>10 GeV/fm3) and high temperature (> 0.5 GeV) expected to be reached in central PbPb collisions. Charm and beauty quarks are powerful tools to investigate this high density and strongly interacting state of matter since they are produced in initial hard scatterings that are therefore generated early in the system evolution and probe its hottest, densest stage. The measurement of the charm production cross sections in pp collisions provides an interesting insight into QCD processes and is crucial as a reference for heavy ion studies. We present open charm cross section measurements in pp collisions at = 7 TeV and =2.76 TeV in the central rapidity region. In addition, the first measurement of nuclear modification factor of D-meson in Pb–Pb collisions at = 2.76 TeV is shown.

Observation of double charm production involving open charm in pp collisions at $ \sqrt {s} = {7}\;{\text{TeV}} $

Abstract The production of J/ψ mesons accompanied by open charm, and of pairs of open charm hadrons are observed in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 355 pb−1 collected with the LHCb detector. Model independent measurements of absolute cross-sections are given together with ratios to the measured J/ψ and open charm cross-sections. The properties of these events are studied and compared to theoretical predictions.

Recent charm measurements through hadronic decay channels with STAR at RHIC in 200 GeV Cu+Cu collisions

We report on the measurements of D 0 and D s meson production in 200 GeV Cu+Cu collisions at the STAR at RHIC experiment. Results are discussed with reference to pQCD predictions of the open charm cross-section as well as the statistical hadronization model.

Measurement of the open charm cross-section in GeV Cu+Cu collisions at the STAR experiment at RHIC

A measurement of the charm cross-section in Cu+Cu collisions at GeV was performed using the solenoidal tracker at RHIC (STAR) detector at the relativistic heavy ion collider (RHIC), through the direct reconstruction of the D0 meson (and of the associated anti-particle) in the hadronic decay channel D0 → π+ + K−. The preliminary measured value of mb (stat) is consistent with a scaling of the cross-section with the number of binary collisions (Nbin).

QCD factorization in diffraction

I present measurements of dijet and open charm cross-sections in diffractive DIS and photoproduction taken with the H1 and ZEUS detectors at the HERA accelerator. Diffractive events were identified by a rapidity gap selection. The resulting differential cross sections are compared to QCD calculations in NLO, based on parton densities extracted from inclusive diffraction. Additionally a fit of diffractive parton densities to the combined data sets of the inclusive F2D measurement and the dijet data was performed. This leads to reduced uncertainties for the gluon density.

Charm, beauty and charmonium production at HERA-B

is a fixed target experiment working on the 920 GeV proton beam of the HERA accelerator at the DESY laboratory in Hamburg. During the last data taking period (2002-2003), about 150 million dilepton triggers, 220 million minimum bias events and 35 million hard photon triggers were acquired. These large statistics allow detailed studies on the production of charmonium states in proton-nucleus p-A collisions, which extend for the first time into the negative Feynman-x () region. Measurements of the inclusive , $\Upsilon$ and open charm cross sections are also ongoing. After a brief discussion of the detector and of the data samples, we report on preliminary results obtained on these physics topics.

Open charm and charmonium production at relativistic energies

We calculate open charm and charmonium production in $Au+Au$ reactions at $\sqrt{s}$ = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from $pN$ and $\pi N$ reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm ($D+\bar{D}$ pairs) is included dynamically. The 'comover' dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength $M_0^2$, that is fitted to the $J/\Psi$ suppression data for $Pb+Pb$ collisions at SPS energies. As a novel feature we implement the backward channels for charmonium reproduction by $D \bar{D}$ channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is comparable to the dissociation by 'comoving' mesons. This leads to the final result that the total $J/\Psi$ suppression at $\sqrt{s}$ = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the 'comover' dissociation is substantial and the backward channels play no role. Furthermore, even in case that all directly produced $J/\Psi$ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the $D+\bar{D} \to J/\Psi$ + meson channels in central collisions of $Au+Au$ at $\sqrt{s}$ = 200 GeV which, however, is lower than the $J/\Psi$ yield expected from binary scaling of $pp$ collisions.

Diffractive charm and jet production at HERA

A new high precision inclusive measurement of the diffractive production of D ∗±(2010) mesons in deep inelastic scattering (DIS) in the kinematic region Q 2>1.5 GeV 2, 0.02< y <0.7, χ IP < 0.035 as well as differential dijet cross sections in low-| t| diffractive photoproduction (PHP) process in the kinematic region Q 2 <0.01 GeV 2, 165< W <240 GeV 2, χ IP < 0.03 are presented. Diffractive parton densities extracted using a NLO DGLAP QCD fit are used for comparisons with diffractive DIS and PHP dijet and open charm cross sections at HERA and the Tevatron, thus testing the factorization properties of hard diffraction.

Open charm production in relativistic nucleus–nucleus collisions

We calculate excitation functions for open charm mesons in Au +Au reactions from AGS to RHIC energies within the HSD transport approach which is based on string, quark, diquark (q, q ̄ ,qq, q ̄ q ̄ ) and hadronic degrees of freedom. The open charm cross sections from pN and πN reactions are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. From our dynamical calculations we find an approximate m T -scaling for pions, kaons, D mesons and J/Ψ — when discarding final-state elastic scattering of kaons and φ mesons with pions — in central collisions of Au +Au at 160 A GeV (with an apparent slope of 176 MeV) without employing the assumption of a Quark–Gluon Plasma (QGP). We demonstrate that this result is essentially due to a relative m T -scaling in pp collisions at s ≈17.3 GeV. At lower bombarding energies of 25 A GeV a suppression of D mesons by a factor of ∼10 relative to a global m T -scaling with slope 143 MeV is expected. However, when incorporating attractive D-meson self-energies as suggested by QCD sum rules, an approximate m T -scaling is regained even at 25 A GeV. The effects of D-meson rescattering and charmonium absorption are discussed, furthermore, with respect to rapidity and transverse mass distributions in central collisions of Au +Au at 25, 160 A GeV and 21.3 A TeV.

Study of charm photoproduction mechanisms

This paper presents results on charm photoproduction in the energy interval 40 to 160 GeV, obtained from the high-statistics charm samples of the NA 14/2 experiment at CERN. We measure the charm cross-section, the distributions inx F andp T2 and various production ratios and charge asymmetries. The total non-diffractive open-charm cross-section per nucleon is measured to be\(\sigma _{(\gamma N \to c\bar cX)} \) at 〈E γ〉 =100 GeV. We discuss the photoproduction of charm in terms of theoretical and phenomenological models. We compare the measuredp T2 andx F distributions with first-order QCD calculations of photon-gluon fusion and obtain a value for the charm-quark mass ofm c =1.5 −0.1+0.2 GeV/c2.