Charm Quark Hadronization Research Articles

Investigation of charm-quark hadronization into baryons in hadronic collisions with ALICE

A comprehensive investigation into charm-baryon production provides insight into understanding charm-quark hadronization process. In this contribution, the charm-quark hadronization mechanism is discussed in terms of the production yield ratio between charm hadron species measured by ALICE Collaboration. Measurements of Λc+, ∑c0,+ +, Ξc0,+ and Ωc0 in pp collisions, Λc+ and Ξc0 in p–Pb collisions are presented, together with the Λc+ measurement in larger collision systems, Pb–Pb collisions. Furthermore, the charm-quark hadronization mechanism is discussed based on the fragmentation fractions computed for pp and p–Pb collisions. A preliminary result on ∑c0,+ + measurement with Run 3 data is also presented.

Observation of strangeness enhancement with charmed mesons in high-multiplicity pPb collisions at sNN=8.16 TeV

The production of prompt Ds+ and D+ mesons is measured by the LHCb experiment in proton-lead (pPb) collisions in both the forward (1.5<y*<4.0) and backward (−5.0<y*<−2.5) rapidity regions at a nucleon-nucleon center-of-mass energy of sNN=8.16 TeV. The nuclear modification factors of both Ds+ and D+ mesons are determined as a function of transverse momentum, pT, and rapidity. In addition, the Ds+ to D+ cross section ratio is measured as a function of the primary charged particle multiplicity in the event. An enhanced Ds+ to D+ production in high-multiplicity events is observed for the whole measured pT range, in particular at low pT and backward rapidity, where the significance exceeds six standard deviations. This constitutes the first observation of strangeness enhancement in charm quark hadronization in high-multiplicity pPb collisions. The results are also qualitatively consistent with the presence of quark coalescence as an additional charm quark hadronization mechanism in high-multiplicity proton-lead collisions. © 2024 CERN, for the LHCb Collaboration 2024 CERN

The dynamic hadronization of charm quarks in heavy-ion collisions

The Pythia8/Angantyr model for heavy ion collisions was recently updated with a mechanism for global colour reconnection. The colour reconnection model used is QCD colour algebra inspired and enhances baryon production due to the formation of string junctions. In this paper, we present updates to the junction formation and string fragmentation mechanisms, connected to heavy quark fragmentation. This allows for the simulation of heavy quark fragmentation, using junction formation, in heavy ion collisions. The framework is validated for proton collisions, and we show results for charm baryon production in proton-lead collisions.

Measurements of charm quark production and hadronization at CMS

The study of charm quark hadrons is an important probe into the hadronization of heavy quarks. More specifically, we present results on the production of Λc baryon, the nuclear modification factors (RAA), and the Λc/D0 yield ratios at √SNN = 5.02 TeV in proton-proton (pp) collisions and in different centrality regions in lead-lead (PbPb) collisions, using data recorded with the CMS detector in 2017 and 2018, respectively. The reported RAA for Λc provides useful information regarding the energy loss mechanism and the hadronization processes of charm quark in the quark-gluon plasma. The transverse momentum (pT) dependence of the RAA is similar to that of other charm and beauty hadrons but with its minimum shifted towards higher pT. Comparing the Λc/D0 production ratio in pp and PbPb collisions suggests that coalescence as a hadronization process is not significant for pT > 10 GeV/c. The ratio becomes comparable to the measurements in e+e− collisions for pT > 30 GeV/c. We also present results of the Λc baryon and D0 meson production and their ratios in proton-lead (pPb) collisions at √SNN = 8.16 TeV as a function of pT and final-state multiplicity using the data recorded by the CMS experiment in 2016. We do not observe significant multiplicity dependence for the baryon over meson ratio for charm hadrons. Based on a previous study, the difference between the results from charm quarks and those from light quarks suggests coalescence processes for heavy quarks do not increase further with multiplicity, unlike light quarks.

First measurement of prompt and non-prompt D⁎+ vector meson spin alignment in pp collisions at [formula omitted] TeV

This letter reports the first measurement of spin alignment, with respect to the helicity axis, for D⁎+ vector mesons and their charge conjugates from charm-quark hadronisation (prompt) and from beauty-meson decays (non-prompt) in hadron collisions. The measurements were performed at midrapidity (|y|<0.8) as a function of transverse momentum (pT) in proton–proton (pp) collisions collected by ALICE at the centre-of-mass energy s=13TeV. The diagonal spin density matrix element ρ00 of D⁎+ mesons was measured from the angular distribution of the D⁎+→D0(→K−π+)π+ decay products, in the D⁎+ rest frame, with respect to the D⁎+ momentum direction in the pp centre of mass frame. The ρ00 value for prompt D⁎+ mesons is consistent with 1/3, which implies no spin alignment. However, for non-prompt D⁎+ mesons an evidence of ρ00 larger than 1/3 is found. The measured value of the spin density element is ρ00=0.455±0.022(stat.)±0.035(syst.) in the 5<pT<20GeV/c interval, which is consistent with a Pythia 8 Monte Carlo simulation coupled with the EvtGen package, which implements the helicity conservation in the decay of D⁎+ meson from beauty mesons. In non-central heavy-ion collisions, the spin of the D⁎+ mesons may be globally aligned with the direction of the initial angular momentum and magnetic field. Based on the results for pp collisions reported in this letter it is shown that alignment of non-prompt D⁎+ mesons due to the helicity conservation coupled to the collective anisotropic expansion may mimic the signal of global spin alignment in heavy-ion collisions.

Open heavy flavour production in small systems with ALICE

Charm and beauty production measurements in proton–proton (pp) collisions are an important test of perturbative QCD calculations, based on the factorisation approach, which assumes universal fragmentation functions among different collision systems. Recent measurements of charm baryon production at midrapidity in small systems show a baryon-to-meson ratio significanlty higher than that in e+e− and e−p collisions: this observation suggests that charm fragmentation is not universal across different collision systems. Therefore, measurements of charm baryon production are fundamental to characterise the charm quark hadronisation in pp and proton–lead (p–Pb) collisions at the LHC energies. In these proceedings, the latest measurements of D0, D+ and Ds+ mesons, the new measurements of Λc+, Ξc0,+, Σc0,++, the first measurement of Ωc0 baryons and of the non-prompt Λc+, performed with the ALICE detector at midrapidity in pp collisions at s=5.02 and s=13TeV are presented. Furthermore, the recent Λc+/D0 yield ratio, measured down to pT=0 in pp and p–Pb collisions will be discussed together with the measurements of the charm fragmentation fractions into hadrons in pp and p–Pb collisions at sNN=5.02TeV. This rich set of experimental results challenges existing theoretical calculations.

Charm-baryon enhancement and charm fragmentation fractions in small systems measured with ALICE

Recent measurements of charm-baryon production at midrapidity by the ALICE collaboration show baryon-to-meson yield ratios significantly higher than those measured in e+e− collisions, suggesting that the charm fragmentations are not universal across different collisions systems. Thus, measurements of charm-baryon production are crucial to study the charm quark hadronisation in proton–proton (pp) collisions. In proton–lead (p–Pb) collisions, the measurements of charm baryons provide important information about cold nuclear matter effects and help to understand how the possible presence of collective effects could modify the production of heavy-flavour hadrons. In this contribution, the most recent results on open charm-hadron production in pp and p–Pb collisions measured by ALICE are discussed.

Charm-baryon enhancement and charm fragmentation fractions in small systems measured with ALICE

Recent measurements of charm-baryon production at midrapidity by the ALICE collaboration show baryon-to-meson yield ratios significantly higher than those measured in e+e− collisions, suggesting that the charm fragmentations are not universal across different collisions systems. Thus, measurements of charm-baryon production are crucial to study the charm quark hadronisation in proton–proton (pp) collisions. In proton–lead (p–Pb) collisions, the measurements of charm baryons provide important information about cold nuclear matter effects and help to understand how the possible presence of collective effects could modify the production of heavy-flavour hadrons. In this contribution, the most recent results on open charm-hadron production in pp and p–Pb collisions measured by ALICE are discussed.

D-meson production in Pb–Pb collisions with ALICE at the LHC

Heavy quarks, like charm and beauty, are sensitive probes to investigate the colour-deconfined medium created in high-energy heavy-ion collisions, the Quark–Gluon Plasma (QGP). The ALICE Collaboration measured the production of D0, D+, D*+ and D+s in Pb–Pb collisions at sNN=5.02TeV. The measurement of the nuclear modification factor (RAA) provides information on the in-medium parton energy loss. In addition, the comparison between D+s and the non-strange D-meson RAA allows to investigate possible modifications of the charm-quark hadronisation mechanism in the QGP. The most recent results for these observables, which were obtained by analysing the latest 2018 data sample of Pb–Pb collisions as well as the comparison with theoretical model calculations, are presented.

Open-Charm Hadron Measurements in Au+Au Collisions at √sNN = 200 GeV by the STAR Experiment

Study of the open-charm hadron production in heavy-ion collisions is crucial for understanding the properties of the Quark-Gluon Plasma. In these papers, we report on a selection of recent STAR measurements of open-charm hadrons in Au+Au collisions at s NN = 200 GeV , using the Heavy-Flavor Tracker. In particular, the nuclear modification factors of D 0 and D ± mesons, elliptic and directed flow of D 0 mesons, D s /D 0 and Λ c / D 0 yield ratios are discussed. The observed suppression of D 0 and D ± mesons suggests strong interactions of the charm quarks with the QGP. The measured elliptic flow of D 0 mesons is large and follows the NCQ scaling, suggesting that charm quarks may be close to thermal equilibrium with the QGP medium. Both D s /D 0 and Λ c / D 0 yield ratios are found to be enhanced in Au+Au collisions. The enhancement can be explained by models incorporating coalescence hadronization of charm quarks. In addition, the directed flow of the D 0 mesons is measured to be negative and larger than that of light-flavor mesons which is in a qualitative agreement with hydrodynamic model predictions with a tilted QGP bulk.

Formula omitted] production in Pb–Pb collisions at [formula omitted] TeV

A measurement of the production of prompt Λc+ baryons in Pb–Pb collisions at sNN=5.02 TeV with the ALICE detector at the LHC is reported. The Λc+ and Λ‾c− were reconstructed at midrapidity (|y|<0.5) via the hadronic decay channel Λc+→pKS0 (and charge conjugate) in the transverse momentum and centrality intervals 6<pT<12 GeV/c and 0–80%. The Λc+/D0 ratio, which is sensitive to the charm quark hadronisation mechanisms in the medium, is measured and found to be larger than the ratio measured in minimum-bias pp collisions at s=7 TeV and in p–Pb collisions at sNN=5.02 TeV. In particular, the values in p–Pb and Pb–Pb collisions differ by about two standard deviations of the combined statistical and systematic uncertainties in the common pT interval covered by the measurements in the two collision systems. The Λc+/D0 ratio is also compared with model calculations including different implementations of charm quark hadronisation. The measured ratio is reproduced by models implementing a pure coalescence scenario, while adding a fragmentation contribution leads to an underestimation. The Λc+ nuclear modification factor, RAA, is also presented. The measured values of the RAA of Λc+, Ds+ and non-strange D mesons are compatible within the combined statistical and systematic uncertainties. They show, however, a hint of a hierarchy (RAAD0<RAADs+<RAAΛc+), conceivable with a contribution from coalescence mechanisms to charm hadron formation in the medium.

Measurement of azimuthal correlations of D mesons with charged particles in pp collisions at √s=13$\sqrt s = 13$ TeV with ALICE at the LHC

The ALICE (A Large Ion Collider Experiment) detector at the LHC (Large Hadron Collider) is dedicated to the study of the properties of the hot and dense QCD matter (Quark–Gluon Plasma) produced in the nucleus-nucleus collisions at high energy. Heavy quarks (charm and beauty), having large masses, are produced in the hard-parton scattering in the early stages of the collision. Therefore, they experience the whole evolution of the hot and dense medium, representing an important tool for its characterization. The study of angular correlations between D mesons and charged particles in Pb–Pb collisions gives insight about the energy loss of charm quarks and the medium-induced modification of its fragmentation into jets. Moreover, pp collisions help to understand the production mechanisms, fragmentation and hadronization of charm quarks and acts as a reference for p–Pb and Pb–Pb measurements. In this article, the measurement of azimuthal correlations between D0 meson and charged particles in pp collisions at $\sqrt s = 13$ TeV is presented. The collisional energy dependence of the correlations is extracted from the comparison with the results at $\sqrt s = 7$ TeV. The data are also compared with simulations performed with different event generators.

New feature of low p_{T} charm quark hadronization in pp collisions at sqrt{s}=7 TeV

Treating the light-flavor constituent quarks and antiquarks whose momentum information is extracted from the data of soft light-flavor hadrons in pp collisions at sqrt{s}=7 TeV as the underlying source of chromatically neutralizing the charm quarks of low transverse momenta (p_{T}), we show that the experimental data of p_{T} spectra of single-charm hadrons D^{0,+}, D^{*+}D_{s}^{+}, varLambda _{c}^{+} and varXi _{c}^{0} at mid-rapidity in the low p_{T} range (2lesssim p_{T}lesssim 7 GeV/c) in pp collisions at sqrt{s}=7 TeV can be well understood by the equal-velocity combination of perturbatively created charm quarks and those light-flavor constituent quarks and antiquarks. This suggests a possible new scenario of low p_{T} charm quark hadronization, in contrast to the traditional fragmentation mechanism, in pp collisions at LHC energies. This is also another support for the exhibition of the soft constituent quark degrees of freedom for the small parton system created in pp collisions at LHC energies.

Heavy Quark Dynamics toward thermalization: RAA, υ1, υ2, υ3

We describe the propagation of Heavy quarks (HQs) in the quark-gluon plasma (QGP) within a relativistic Boltzmann transport (RBT) approach. The interaction between heavy quarks and light quarks is described within quasi-particle approach which is able to catch the main features of non-perturbative interaction as the increasing of the interaction in the region of low temperature near TC. In our calculations the hadronization of charm quarks in D mesons is described by mean of an hybrid model of coalescence plus fragmentation. We show that the coalescence play a key role to get a good description of the experimental data for the nuclear suppression factor RAA and the elliptic flow υ2(pT) at both RHIC and LHC energies. Moreover, we show some recent results on the direct flow υ1 and triangular flow υ3 of D meson.

Measurements of charm hadron production and anisotropic flow in Au+Au collisions at 200 GeV with the STAR experiment at RHIC

Heavy flavor quarks, owing to their large masses, are predominantly produced through initial hard parton scatterings in heavy-ion collisions, and thus are excellent probes to study properties of the strongly coupled Quark Gluon Plasma (sQGP) medium produced in these collisions. Measurements of anisotropic flow harmonics of heavy flavor hadrons can provide information on the properties of the medium, including the heavy flavor transport coefficient. Charm quark hadronization mechanism in the sQGP medium can be studied through measurements of yields of different charm hadrons. In these proceedings we report on the measurements of elliptic and triangular flow harmonics of D0 mesons as well as the yield ratios of D±s/D0 and Λ±c/D0 in Au+Au collisions at [see formula in PDF] = 200 GeV at RHIC with the STAR detector. These measurements use the STAR Heavy Flavor Tracker (HFT) to reconstruct charm hadrons via their hadronic decay channels. Results are compared to model calculations and the implications on the understanding of charm quark dynamics in the medium are discussed.

Measurements of D+ production in pp, p—Pb and Pb—Pb collisions with ALICE at the LHC

ALICE has measured D+ production at mid-rapidity in pp (√8 =7 TeV), p-Pb (√8NN = 5.02 TeV) and Pb-Pb (√8NN =2.76 TeV) collisions, through the hadronic decay channel D+s⟶ϕΠ+⟶K+ K-Π+. The study of the D+s-meson production could reveal important details about charm-quark hadronisation in the Quark-Gluon Plasma (QGP). The measured D+ yields in pp and p-Pb collisions and the nuclear modification factors for central and semi-central Pb-Pb collisions will be shown here as a function of transverse momentum.

Single- and central-diffractive production of open charm and bottom mesons at the LHC: Theoretical predictions and experimental capabilities

We discuss diffractive production of open charm and bottom mesons at the LHC. The differential cross sections for single- and central-diffractive mechanisms for $c\bar c$ and $b\bar b$ pair production are calculated in the framework of the Ingelman-Schlein model corrected for absorption effects. In this approach one assumes that the pomeron has a well defined partonic structure, and that the hard process takes place in a pomeron-proton or proton-pomeron (single diffraction) or pomeron-pomeron (central diffraction) processes. Here, leading-order gluon-gluon fusion and quark-antiquark anihilation partonic subprocesses are taken into consideration, which are calculated within standard collinear approximation. Both pomeron flux factors as well as parton distributions in the pomeron are taken from the H1 Collaboration analysis of diffractive structure function and diffractive dijets at HERA. The extra corrections from subleading reggeon exchanges are explicitly calculated and are also taken into consideration. Several quark-level differential distributions are shown. The hadronization of charm and bottom quarks is taken into account by means of fragmentation function technique. Predictions for single- and central-diffractive production in the case of inclusive $D$ and $B$ mesons, as well as $D\bar D$ pairs are presented, including detector acceptance of the ATLAS, CMS and LHCb Collaborations. The experimental aspects of possible standard and dedicated measurements are carefully discussed.

Yield correlations andpTdependence of charmed hadrons in Pb + Pb collisions atsNN=2.76TeV

Recently the ALICE Collaboration has published a few data of charm hadrons in Pb + Pb collisions at the CERN Large Hadron Collider (LHC). We extend the quark combination to the charm sector and point out that the measurement of charm hadron yields can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios, e.g. $D^{*+}/D^0$, $D_s^+/D^+$ and $\Lambda_c^+/D_s^+$, to measure various properties of low $p_T$ charm quark hadronization. We argue that ratios $D_s^+/D^0$ and $2D_s^+/(D^0+D^+)$ as the function of transverse momentum can serve as good probes for the dynamics of charm quark hadronization. We further make predictions for the yields and $p_T$ spectra of identified charm hadrons in central Pb + Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV.

Single- and Central-diffractive Production of Open Charm and Bottom Mesons at the LHC

We discuss diffractive production of open charm and bottom mesons at the LHC. The differential cross sections for single- and central-diffractive mechanisms for $c\bar c$ and $b\bar b$ pair production are calculated in the framework of the Ingelman-Schlein model corrected for absorption effects. The LO gluon-gluon fusion and quark-antiquark anihilation partonic subprocesses are taken into consideration, which are calculated within standard collinear approximation. The extra corrections from reggeon exchanges are taken into account. The hadronization of charm and bottom quarks is taken into account by means of fragmentation functions. Predictions for single- and central-diffractive production in the case of $D$ and $B$ mesons, as well as $D\bar D$ pairs are presented, including detector acceptance of the ATLAS, CMS and LHCb Collaborations.

D meson-hadron angular correlations in pp and p-Pb collisions with ALICE at the LHC

The comparison of angular correlations between charmed mesons and charged hadrons produced in pp, p-Pb and Pb-Pb collisions can give insight into charm quark energy loss mechanisms in the hot nuclear medium formed in heavy-ion collisions and can help to spot possible modifications of charm quark hadronization induced by the presence of the medium. The analysis of pp and p-Pb data and the comparison with predictions from pQCD calculations, besides constituting the necessary baseline for the interpretation of Pb-Pb results, can provide relevant information on charm production and fragmentation processes.We present a study of azimuthal correlations between D0 and D*+ mesons and charged hadrons measured by the ALICE experiment in pp collisions at = 7 TeV and p-Pb collisions at = 5.02 TeV. D mesons were reconstructed from their hadronic decays at central rapidity and in the transverse momentum range 2 < pT < 16 GeV/c, and they were correlated to charged hadrons reconstructed in the pseudorapidity range |η| < 0.8. The current status of the analysis in pp and p-Pb collisions and the prospects for Pb-Pb collisions are discussed.