Heavy Flavor Research Articles

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.

Formula omitted]) polarized heavy flavor corrections to deep-inelastic scattering at Q2 ≫ m2

We calculate the quarkonic O(αs2) massive operator matrix elements ΔAQg(N),ΔAQqPS(N) and ΔAqq,QNS(N) for the twist–2 operators and the associated heavy flavor Wilson coefficients in polarized deeply inelastic scattering in the region Q2≫m2 to O(ε) in the case of the inclusive heavy flavor contributions. The evaluation is performed in Mellin space, without applying the integration-by-parts method. The result is given in terms of harmonic sums. This leads to a significant compactification of the operator matrix elements and massive Wilson coefficients in the region Q2≫m2 derived previously in [1], which we partly confirm, and also partly correct. The results allow to determine the heavy flavor Wilson coefficients for g1(x,Q2) to O(αs2) for all but the power suppressed terms ∝(m2/Q2)k,k≥1. The results in momentum fraction z-space are also presented. We also discuss the small x effects in the polarized case. Numerical results are presented. We also compute the gluonic matching coefficients in the two–mass variable flavor number scheme to O(ε).

Perturbative and non-perturbative interactions between heavy quarks and quark-gluon plasma within a unified approach

While perturbative QCD is sufficient for understanding the color, mass and energy dependences of parton energy loss and jet quenching at large transverse momentum in heavy-ion collisions, a simultaneous description of heavy flavor nuclear modification factor RAA and elliptic flow coefficient v2 at low and intermediate pT still remains a challenge due to the effects from non-perturbative interactions. In this work, we extend the linear Boltzmann transport model by implementing a generalized Cornell-type potential that incorporates both short-range Yukawa interaction and long-range color confining interaction between heavy quarks and the QGP medium. Combining our new approach for heavy-quark-QGP interaction with a (3+1)-dimensional hydrodynamic model CLVisc for the QGP evolution and a hybrid fragmentation-coalescence model for heavy quark hadronization, we obtain a satisfactory description of heavy meson RAA and v2 from low to intermediate to high pT observed at both RHIC and the LHC. By model-data-comparison, we obtain for the first time the in-medium heavy quark potential from open heavy flavor measurements; the result is in agreement with the lattice QCD calculation. Our study indicates that while jet quenching at high pT is dominated by perturbative QCD interactions, non-perturbative interactions are indispensible for understanding heavy flavor quenching and flow at low and intermediate pT.

The investigations of the P-wave Bs states combining quark model and lattice QCD in the coupled channel framework

Combining the quark model, the quark-pair-creation mechanism and B(*) overline{K} interaction, we have investigated the near-threshold P-wave Bs states in the framework of the Hamiltonian effective field theory. With the heavy quark flavor symmetry, all the parameters are determined in the Ds sector by fitting the lattice data. The masses of the bottom-strange partners of the {D}_{s0}^{ast }(2317) and {D}_{s1}^{ast }(2460) are predicted to be {M}_{B_{s0}^{ast }}={5730.2}_{-1.5}^{+2.4} MeV and {M}_{B_{s1}^{ast }}={5769.6}_{-1.6}^{+2.4} MeV, respectively, which are well consistent with the lattice QCD component. The two P-wave Bs states are the mixtures of the bare overline{b}s core and B(*) overline{K} component. Moreover, we find a crossing point between the energy levels with and without the interaction Hamiltonian in the finite volume spectrum in the 0+ case, which corresponds to a CDD (Castillejo-Dalitz-Dyson) zero in the T-matrix of the Boverline{K} scattering. This CDD zero will help deepen the insights of the near-threshold states and can be examined by future lattice calculation.

PHENIX Probing QCD Matter Through Heavy Flavor and Quarkonium at RHIC

Recent results from the PHENIX experiment on heavy flavors and quarkonia production in p + Al, p + Au, d + Au, and Au + Au collision systems at √ SNN = 200 GeV are summarized. The results are carried out by the measurements of the nuclear modification factors and elliptic flow. The nuclear modification factors measurements give insight into the energy loss of heavy quarks in the quark-gluon plasma medium along their path lengths. The elliptic flow measurements are a good tool to investigate the coupling of heavy quarks with the medium. The measurements are presented as a function of centrality, rapidity, and transverse momentum. The interpretations of the results in light of our current theoretical models, and comparison to LHCb and ALICE measurements are presented.

Recent Results from PHENIX

We present results from the heavy-ion physics program of the PHENIX experiment at RHIC. These results include jet substructure, open heavy flavor, charmonium, strangeness, electromagnetic probes, femtoscopy, and flow.

Understanding mass hierarchy in different energy loss mechanisms through heavy flavor data

The theoretical analysis of experimental observations, such as the mass hierarchy effect, often neglects some ingredients, which may have a significant impact. The forthcoming measurements at RHIC and LHC will generate heavy flavor data with unprecedented precision, providing an opportunity to utilize high-p⊥ heavy flavor data to analyze the interaction mechanisms in QGP. To this end, we use our recently developed DREENA framework based on the dynamical energy loss formalism. We present: i) How to disentangle the signature of different interaction mechanisms (radiative and collisional energy losses) at the same dataset. ii) Novel observables susceptible to these different mechanisms to be tested by future high-precision measurements. iii) Analytical and numerical extraction of the mass hierarchy effect in energy losses through this observable.

A silicon vertex detector with timing for the Upgrade II of LHCb

The LHCb Upgrade II aims at maximizing the potential for heavy flavour physics at high luminosity-LHC. The Vertex Locator (VELO) plays an important role in this task due to its excellent tracking and vertexing abilities. During Run 5 and 6, the detector will undergo through a substantial increase in data rate, pile-up and radiation damage. To achieve the same vertex reconstruction efficiency as the current Upgrade I detector, the introduction of timing and its possible implementations are discussed. Additional requirements for new sensor and ASIC technologies, introduced to cope with increased radiation damage, data rate and timing, are also presented. Finally, possible new detector layouts, adapted to expected conditions, are discussed and their impact on the RF-foil and vacuum tank geometries are treated.

Measurement of nonprompt and prompt D0 azimuthal anisotropy in Pb-Pb collisions at √SNN = 5.02 TeV

Heavy quarks are primarily produced via initial hard scatterings, and thus carry information about the early stages of the Quark-Gluon Plasma (QGP). Measurements of the azimuthal anisotropy of the final-state heavy flavor hadrons provide information about the initial collision geometry, its fluctuation, and more importantly, the mass dependence of energy loss in QGP. Due to the larger bottom quark mass as compared to the charm quark mass, separate measurements of charm and bottom hadron azimuthal anisotropy can shed new light on understanding the dependence of the heavy quark and medium interaction. Because of the high branching ratio and large D0 mass, measurements of D0 meson coming from bottom hadron decay (nonprompt D0) can cover a broad kinematic range and be a good proxy of the parent bottom hadrons results. In this talk, we report on the prompt D0 and the first nonprompt D0 measurements of the azimuthal anisotropy elliptic (v2) and triangular (v3) coefficients of nonprompt D0 in PbPb collisions at √SNN = 5.02 TeV. The measurements are performed as functions of transverse momentum pT, in three centrality classes, from central to midcentral collisions. Compared to the prompt D0 results, the nonprompt D0 v2 flow coefficients are systematically lower but have a similar dependence on pT and centrality. A non-zero v3 coefficient of the nonprompt D0 is observed. The obtained results are compared with theoretical predictions. The comparison could provide new constraints on the theoretical description of the interaction between heavy quarks and the medium.

Status and Performance of sPHENIX Experiment

sPHENIX is a state-of-the-art experiment at the Relativistic Heavy Ion Collider. Hard probes are to be measured in p+p, p+Au and Au+Au collisions to understand the properties of the quark-gluon plasma. sPHENIX covers a wide range of physics programs: jet correlations and substructure, upsilon spectroscopy, open heavy flavor and cold quantum chromodynamics. It provides unique opportunities in the low transverse momentum region and also offer kinematic overlap with the Large Hadron Collider experiments. In these proceedings, the scientific mission of sPHENIX, detector design and key performance parameters are described, and expected projections of some measurements under consideration are presented.

Screening of the quark charge and mixing effects on transition moments and M1 decay widths of baryons

Motivated by the precision measurements of heavy flavor baryon masses, we analyze the modification of quark charge by employing the screening effect inside the baryon. In addition, we calculate the isospin mass splitting up to charmed baryons employing isospin symmetry breaking. Consequently, we obtain the masses, magnetic moments, and transition moments of $J^P=\frac{1}{2}^+$ and $\frac{3}{2}^+$ baryons to predict radiative decay widths for $\frac{1}{2}^{\prime +} \to \frac{1}{2}^+$ and $\frac{3}{2}^+\to \frac{1}{2}^{(\prime)+}$ transitions. Finally, we include the effects of state mixing in flavor degenerate baryon magnetic and transition moments, as well as M1 transition decay widths.

The unpolarized and polarized single-mass three-loop heavy flavor operator matrix elements Agg,Q and ∆Agg,Q

We calculate the gluonic massive operator matrix elements in the unpolarized and polarized cases, Agg,Q(x, μ2) and ∆Agg,Q(x, μ2), at three-loop order for a single mass. These quantities contribute to the matching of the gluon distribution in the variable flavor number scheme. The polarized operator matrix element is calculated in the Larin scheme. These operator matrix elements contain finite binomial and inverse binomial sums in Mellin N-space and iterated integrals over square root-valued alphabets in momentum fraction x-space. We derive the necessary analytic relations for the analytic continuation of these quantities from the even or odd Mellin moments into the complex plane, present analytic expressions in momentum fraction x-space and derive numerical results. The present results complete the gluon transition matrix elements both of the single- and double-mass variable flavor number scheme to three-loop order.

Heavy Flavor Physics at the EIC with the ECCE detector

The proposed Electron-Ion Collider (EIC) will operate high-energy high-luminosity electron+proton and electron+nucleus collisions to solve several unresolved fundamental questions. Due to their large masses (mc,b > ΛQCD), heavy quarks and their hadron products are ideal probes to study the nucleon/nuclear parton distribution functions in the high Bjorken-x (xBJ > 0.1) region and explore the hadronization process within the unconstrained kinematic region. Recently, the Electron-Ion Collider Comprehensive Chromodynamics Experiment (ECCE) consortium detector conceptual design has been selected as the reference design for the EIC project detector. The precise momentum and spatial resolutions provided by the ECCE tracking detector enable a series of open heavy flavor and quarkonia measurements. The physics projections of these proposed heavy flavor measurements in simulation studies using the ECCE detector design will be presented.

Heavy Flavor and Quarkonia Physics at sPHENIX

The sPHENIX detector, being constructed at BNL’s Relativistic Heavy Ion Collider (RHIC), will begin measuring a plethora of Heavy Flavor and Quarkonia observables with unprecedented statistics and kinematic reach at RHIC energies starting in 2023. This includes the largest recorded sample of b-flavored hadron decays from Heavy Ion collisions at RHIC, allowing for precise probes of the QGP using charm and beauty quarks. These measurements are enabled by the excellent vertexing of the MAPS-based micro-VerTeX detector (MVTX), timing of the INTermediate silicon strip Tracker (INTT), precision tracking by the Time Projection Chamber (TPC), and the ElectroMagnetic and Hadronic Calorimetry systems (EMCal and HCal, respectively), the latter of which is deployed for the first time at RHIC. The sPHENIX collaboration has created the reconstruction software stack as well as realistic data simulations, which allow for testing and optimization of the software and physics selections.

Inclusive weak-annihilation decays and lifetimes of beauty-charmed baryons

Imbalanced beauty-charmed baryons $ \Xi_{bc}^{+,0} $ are of great significance to the development of heavy flavor physics. In this work, we study the inclusive weak-annihilation decays of $\Xi_{bc}^{+,0}$ and their contributions to the $\Xi_{bc}^{+,0}$ lifetimes. For the calculation of the inclusive $\Xi_{bc}^{+,0}\to X_{cs}$ decay width where $X_{cs}$ stands for the sum of the final states with charm number +1 and strange number -1, we work in the heavy diquark effective theory which provides us with a convenient technical tool to construct the operator product expansion. The $\Xi_{bc}^{+,0}$ is considered to be a superposition of two states with one containing a spin-0 $bc$ diquark and the other one containing a spin-1 $bc$ diquark. It is found that both the $\Xi_{bc}^{+,0}$ lifetimes and the $\Xi_{bc}^{+,0}\to X_{cs}$ branching ratios are very sensitive to the $bc$ spin in $\Xi_{bc}^{+,0}$. The $\Xi_{bc}^{+,0}\to X_{cd}$ results are also presented. As $\Xi_{bc}^+$ has a longer lifetime than $\Xi_{bc}^{0}$ and bigger branching ratios of similar decay channels, the exclusive decays $\Xi_{bc}^+\to D^{(*)+}\Lambda$, $\Xi_{bc}^+\to \Lambda_c^+\bar{K}^{(*)0}$, $\Xi_{bc}^+\to D^{(*)+}K^-p$, and $\Xi_{bc}^+\to D^{0}\bar{K}^{(*)0}p$ are more promising for experimental searches of $\Xi_{bc}^{+,0}$ at the LHC comparing with exclusive decay $\Xi_{b c} ^{0} \to D^0pK^-$.

Interactions between heavy quarks and tilted QGP fireballs in 200 A GeV Au+Au collisions* *Supported by the National Natural Science Foundation of China (11935007, 12175122, 2021-867), Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008), Natural Science Foundation of Hubei Province (2021CFB272), Education Department of Hubei Province of China with Young Talents Project (Q20212703), Open Foundation of Key Laboratory

Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor () and directed flow () and elliptic flow () coefficients of heavy mesons and their decayed electrons at an RHIC energy. We find that the counter-clockwise tilt of nuclear matter in the reaction plane results in a positive (negative) heavy flavor in the backward (forward) rapidity region, whose magnitude increases with the heavy quark transverse momentum. The difference in the heavy flavor between different angular regions is also proposed as a complementary tool to characterize the asymmetry of the medium profile. Our model results are consistent with currently available data at the RHIC and provide predictions that can be tested by future measurements.

Anisotropic Flows of Charmonium in the Relativistic Heavy-Ion Collisions

We review recent studies about anisotropic flows (v1,v2,v3) of charmonium in the quark-gluon plasma produced in relativistic heavy-ion collisions. Collective flows of the bulk medium are developed due to the anisotropic pressure gradient of the medium. Strongly coupled with the bulk medium, charm quarks carry collective flows from the expanding medium, which will be inherited by the regenerated charmonium via the coalescence process. In event-by-event collisions where nucleon positions fluctuate from the smooth distribution, there is triangularity in the medium initial energy density. Triangular flows of the bulk medium and heavy flavor particles can be developed due to the initial fluctuations. In the longitudinal direction, the rapidity-odd distribution of the initial energy density is induced by the rotation of the medium in non-central heavy-ion collisions. Charmonium suffers biased dissociation along positive and negative x-directions in forward (backward) rapidity. The directed flow of charmonium becomes non-zero. The directed, elliptic and triangular flows (v1,v2,v3) of charmonium come from the anisotropic initial distributions of the medium energy density in the transverse and longitudinal directions.

Establishing the heavy quark spin and light flavor molecular multiplets of the X(3872) , Zc(3900) , and X(3960)

Recently, the LHCb Collaboration reported a near-threshold enhancement, $X(3960)$, in the $D_s^+D_s^-$ invariant mass distribution. We show that the data can be well described by either a bound or a virtual state below the $D_s^+D_s^-$ threshold. The mass given by the pole position is $(3928\pm3)$ MeV. Using this mass and the existing information on the $X(3872)$ and $Z_c(3900)$ resonances, a complete spectrum of the $S$-wave hadronic molecules formed by a pair of ground state charmed and anticharmed mesons is established. Thus, pole positions of the partners of the $X(3872)$, $Z_c(3900)$ and the newly observed $D_s^+D_s^-$ state are predicted. Calculations have been carried out at the leading order of nonrelativistic effective field theory and considering both heavy quark spin and light flavor SU(3) symmetries, though conservative errors from the breaking of these symmetries are provided.

DREENA-A framework as a QGP tomography tool

QGP tomography aims to constrain the QGP parameters by exploiting both low and high-p⊥ theory and data. With this goal in mind, we present a fully optimised framework DREENA-A based on a state-of-the-art energy loss model. The framework can include any, in principle arbitrary, temperature profile within the dynamical energy loss formalism. Thus, “DREENA” stands for Dynamical Radiative and Elastic ENergy loss Approach, while “A” stands for Adaptive. DREENA-A does not adjust parameters within the energy loss model, allowing it to exploit differences in temperature profiles which are the only input in the framework. The framework applies to light and heavy flavor observables, different collision energies, and large and smaller systems. This, together with the ability to systematically compare data and predictions within the same formalism and parameter set, makes DREENA-A a unique multipurpose QGP tomography tool. The provided code allows researchers to use their own QGP evolution models to straightforwardly generate high-p⊥ predictions.

Heavy flavour production in pp collisions at LHCb

These proceedings summarise the recent heavy flavour production measurements in proton-proton (pp) collisions at the LHCb experiment. The production cross-sections of J/ψ mesons are measured at a centre-of-mass energy of s=5TeV. The ratio of the Bs0 and B0 fragmentation fractions, fs/fd, is obtained from the combined analysis of different B-decay channels measured by the LHCb experiment. The asymmetry between Λb0 and Λ¯b0 baryon production rates is measured at s=7 and 8TeV.