Charm Quark Mass Research Articles

NNLO QCD counterterm contributions to [formula omitted] for the physical value of mc

One of the most important O(αs2) corrections to the B¯→Xsγ branching ratio originates from interference of contributions from the current–current and photonic dipole operators. Its value has been estimated using an interpolation in the charm quark mass between the known results at mc=0 and for mc≫12mb. An explicit calculation for the physical value of mc is necessary to remove the associated uncertainty. In the present work, we evaluate all the ultraviolet counterterm contributions that are relevant for this purpose.

Inclusive semi-leptonic B meson decay structure functions from lattice QCD

We propose a method to non-perturbatively calculate the forward-scattering matrix elements relevant to inclusive semi-leptonic B meson decays. Corresponding hadronic structure functions at unphysical kinematics are accessible through lattice QCD calculation of four-point correlation functions. The unphysical kinematical point may be reached by analytic continuation from the physical differential decay rate. A numerical test is performed for the B_s -> X_c l nu mode in the zero-recoil limit. We use lattice ensembles generated with 2+1 dynamical quark flavors. The valence charm quark mass is tuned to its physical value, while the bottom quark mass is varied in the range (1.56-2.44)m_c. From the numerical results we can identify the contributions of the ground state D_s^(*) meson as well as those of excited states or continuum states.

Charm quark mass with calibrated uncertainty

We determine the charm quark mass hat{m}_c from QCD sum rules of the moments of the vector current correlator calculated in perturbative QCD at mathcal{O} (hat{alpha }_s^3). Only experimental data for the charm resonances below the continuum threshold are needed in our approach, while the continuum contribution is determined by requiring self-consistency between various sum rules, including the one for the zeroth moment. Existing data from the continuum region can then be used to bound the theoretic uncertainty. Our result is hat{m}_c(hat{m}_c) = 1272 pm 8 MeV for hat{alpha }_s(M_Z) = 0.1182, where the central value is in very good agreement with other recent determinations based on the relativistic sum rule approach. On the other hand, there is considerably less agreement regarding the theory dominated uncertainty and we pay special attention to the question how to quantify and justify it.

Continuum limit of the D meson, Ds meson, and charmonium spectrum from Nf=2+1+1 twisted mass lattice QCD

We compute masses of $D$ meson, ${D}_{s}$ meson, and charmonium states using ${N}_{f}=2+1+1$ Wilson twisted mass lattice QCD. All results are extrapolated to physical light quark masses, to physical strange and charm quark masses, and to the continuum. Our analysis includes states with spin $J=0$, 1, 2, parity $\mathcal{P}=\ensuremath{-},+$, and in case of charmonium also charge conjugation $\mathcal{C}=\ensuremath{-},+$. Computations are based on a large set of quark-antiquark meson creation operators. We investigate and quantify all sources of systematic errors, including fitting range uncertainties, finite volume effects, isospin breaking effects, and the choice of the fitting ansatz for the combined chiral and continuum extrapolation such that the resulting meson masses can be compared directly and in a meaningful way to experimental results. Within combined statistical and systematic errors, which are between below 2 per mille and 3%, our results agree with available experimental results for most of the states. In the few cases where we observe discrepancies, we discuss possible reasons.

Charm quark mass determined from a pair of sum rules

In this paper, we present preliminary results of the determination of the charm quark mass [Formula: see text] from QCD sum rules of moments of the vector current correlator calculated in perturbative QCD at [Formula: see text]. Self-consistency between two different sum rules allow to determine the continuum contribution to the moments without requiring experimental input, except for the charm resonances below the continuum threshold. The existing experimental data from the continuum region is used, then, to confront the theoretical determination and reassess the theoretic uncertainty.

Prompt atmospheric neutrino fluxes: perturbative QCD models and nuclear effects

We evaluate the prompt atmospheric neutrino flux at high energies using three different frameworks for calculating the heavy quark production cross section in QCD: NLO perturbative QCD, $k_T$ factorization including low-$x$ resummation, and the dipole model including parton saturation. We use QCD parameters, the value for the charm quark mass and the range for the factorization and renormalization scales that provide the best description of the total charm cross section measured at fixed target experiments, at RHIC and at LHC. Using these parameters we calculate differential cross sections for charm and bottom production and compare with the latest data on forward charm meson production from LHCb at $7$ TeV and at $13$ TeV, finding good agreement with the data. In addition, we investigate the role of nuclear shadowing by including nuclear parton distribution functions (PDF) for the target air nucleus using two different nuclear PDF schemes. Depending on the scheme used, we find the reduction of the flux due to nuclear effects varies from $10\%$ to $50 \%$ at the highest energies. Finally, we compare our results with the IceCube limit on the prompt neutrino flux, which is already providing valuable information about some of the QCD models.

Mass of the bottom quark from Upsilon(1S) at NNNLO: an update

We update our perturbative determination of M̅S̅ mass m̅b(m̅b), by including the recently obtained four-loop coefficient in the relation between the pole and M̅S̅ mass. First the renormalon subtracted (RS or RS’) mass is determined from the known mass of the Y(1S) meson, where we use the renormalon residue Nm obtained from the asymptotic behavior of the coefficient of the 3-loop static singlet potential. M̅S̅ mass is then obtained using the 4-loop renormalon-free relation between the RS (RS’) and M̅S̅ mass. We argue that the effects of the charm quark mass are accounted for by effectively using Nf = 3 in the mass relations. The extracted value is m̅b(m̅b) = 4222(40) MeV, where the uncertainty is dominated by the renormalization scale dependence.

Short-distance charmonium correlator on the lattice with Möbius domain-wall fermion and a determination of charm quark mass

We calculate charmonium correlators on the lattice with 2+1-flavors of sea quarks and charm valence quark both described by the M\"obius domain-wall fermion. Temporal moments of the correlators are calculated and matched to perturbative QCD formulae to extract the charm quark mass $m_c(\mu)$ and strong coupling constant $\alpha_s(\mu)$. Lattice data at three lattice spacings, 0.044, 0.055, and 0.080~fm, are extrapolated to the continuum limit. The correlators in the vector channel are confirmed to be consistent with the experimental data for $e^+e^-\to c\bar{c}$, while the pseudo-scalar channel is used to extract $m_c(\mu)$ and $\alpha_s(\mu)$. We obtain $m_\mathrm{c}(3 \mathrm{\ GeV})$ = 1.003(10)~GeV and $\alpha_s^{\bar{\mathrm{MS}}(4)}(3\mathrm{\ GeV})$ = 0.253(13). Dominant source of the error is the truncation of perturbative expansion at $\alpha_s^3$.

Quark masses and strong coupling constant in2+1flavor QCD

We present a determination of the strange, charm and bottom quark masses as well as the strong coupling constant in 2+1 flavor lattice QCD simulations using highly improved staggered quark action. The ratios of the charm quark mass to the strange quark mass and the bottom quark mass to the charm quark mass are obtained from the meson masses calculated on the lattice and found to be $m_c/m_s=11.871(91)$ and $m_b/m_c=4.528(57)$ in the continuum limit. We also determine the strong coupling constant and the charm quark mass using the moments of pseudoscalar charmonium correlators: $\alpha_s(\mu=m_c)=0.3697(85)$ and $m_c(\mu=m_c)=1.267(12)$ GeV. Our result for $\alpha_s$ corresponds to the determination of the strong coupling constant at the lowest energy scale so far and is translated to the value $\alpha_s(\mu=M_Z,n_f=5)=0.11622(84)$.

A determination of m c (m c ) from HERA data using a matched heavy-flavor scheme

The charm quark mass is one of the fundamental parameters of the Standard Model Lagrangian. In this work we present a determination of the $$ \overline{\mathrm{MS}} $$ charm mass from a fit to the inclusive and charm HERA deep-inelastic structure function data. The analysis is performed within the xFitter framework, with structure functions computed in the FONLL general-mass scheme as implemented in APFEL. In the case of the FONLL-C scheme, we obtain m c (m c ) = 1.335 ± 0.043(exp) − 0.000 + 0.019 (param) − 0.008 + 0.011 (mod) − 0.008 + 0.003 (th) GeV. We also perform an analogous determination in the fixed-flavor-number scheme at next-to-leading order, finding m c (m c ) = 1.318 ± 0.054(exp) − 0.010 + 0.011 (param) − 0.004 + 0.015 (mod) − 0.004 + 0.045 (th) GeV, compatible with the FONLL-C value. Our results are consistent with previous determinations from DIS data as well as with the PDG world average.

Renormalization group study of the minimal Majoronic dark radiation and dark matter model

We study the 1-loop renormalization group equation running in the simplest singlet Majoron model constructed by us earlier to accommodate the dark radiation and dark matter content in the universe. A comprehensive numerical study was performed to explore the whole model parameter space. A smaller effective number of neutrinos △ Neff∼ 0.05, or a Majoron decoupling temperature higher than the charm quark mass, is preferred. We found that a heavy scalar dark matter, ρ, of mass 1.5–4 TeV is required by the stability of the scalar potential and an operational type-I see-saw mechanism for neutrino masses. A neutral scalar, S, of mass in the 10–100 GeV range and its mixing with the standard model Higgs as large as 0.1 is also predicted. The dominant decay modes are S into bb̄ and/or ωω. A sensitive search will come from rare Z decays via the chain Z → S+ ff̄, where f is a Standard Model fermion, followed by S into a pair of Majoron and/or b-quarks. The interesting consequences of dark matter bound state due to the sizable Sρ ρ-coupling are discussed as well. In particular, shower-like events with an apparent neutrino energy at Mρ could contribute to the observed effective neutrino flux in underground neutrino detectors such as IceCube.

Charm-Quark Production in Deep-Inelastic Neutrino Scattering at Next-to-Next-to-Leading Order in QCD.

We present a fully differential next-to-next-to-leading order calculation of charm-quark production in charged-current deep-inelastic scattering, with full charm-quark mass dependence. The next-to-next-to-leading order corrections in perturbative quantum chromodynamics are found to be comparable in size to the next-to-leading order corrections in certain kinematic regions. We compare our predictions with data on dimuon production in (anti)neutrino scattering from a heavy nucleus. Our results can be used to improve the extraction of the parton distribution function of a strange quark in the nucleon.

Heavy flavour precision physics from Nf = 2 + 1 + 1 lattice simulations

We present precision lattice calculations of the pseudoscalar decay constants of the charmed sector as well as determinations of the bottom quark mass and its ratio to the charm quark mass. We employ Nf=2+1+1 dynamical quark gauge configurations generated by the European Twisted Mass Collaboration, using data at three values of the lattice spacing and pion masses as low as 210 MeV. Strange and charm sea quark masses are close to their physical values.

Fragmentation contributions to hadroproduction of promptJ/ψ,χcJ, andψ(2S)states

We compute fragmentation corrections to hadroproduction of the quarkonium states $J/\psi$, $\chi_{cJ}$, and $\psi(2S)$ at leading power in $m_c^2/p_T^2$, where $m_c$ is the charm-quark mass and $p_T$ is the quarkonium transverse momentum. The computation is carried out in the framework of nonrelativistic QCD. We include corrections to the parton-production cross sections through next-to-leading order in the strong coupling $\alpha_s$ and corrections to the fragmentation functions through second order in $\alpha_s$. We also sum leading logarithms of $p_T^2/m_c^2$ to all orders in perturbation theory. We find that, when we combine these leading-power fragmentation corrections with fixed-order calculations through next-to-leading order in $\alpha_s$, we are able to obtain good fits for $p_T\geq 10$ GeV to hadroproduction cross sections that were measured at the Tevatron and the LHC. Using values for the nonperturbative long-distance matrix elements that we extract from the cross-section fits, we make predictions for the polarizations of the quarkonium states. We obtain good agreement with measurements of the polarizations, with the exception of the CDF Run II measurement of the prompt $J/\psi$ polarization, for which the agreement is only fair. In the predictions for the prompt-$J/\psi$ cross sections and polarizations, we take into account feeddown from the $\chi_{cJ}$ and $\psi(2S)$ states.

New Charm and Bottom Quark Mass Determinations from QCD Sum Rules

In this talk we discuss results of a new extraction of the MS‾ charm quark mass using relativistic QCD sum rules at O(αs3) based on moments of the vector and the pseudoscalar current correlators, and using the available experimental measurements from e+e− collisions and lattice results, respectively. The analysis of the perturbative uncertainties is based on different implementations of the perturbative series and on independent variations of the renormalization scales for the mass and the strong coupling, following a work we carried out earlier. Accounting for the perturbative series that result from this double scale variation is crucial, since some of the series can exhibit extraordinarily small scale dependence, if the two scales are set equal. The new aspect of the work reported here addresses the problem that double scale variation might also lead to an overestimate of the perturbative uncertainties. We supplement the analysis by a convergence test that allows to quantify the overall convergence of QCD perturbation theory for each moment, and to discard series that are artificially spoiled by specific choices of the renormalization scales. We also apply the new method to an extraction of the MS‾ bottom quark mass using experimental moments that account for a modeling uncertainty associated to the continuum region where no experimental data is available. We obtain mc(m‾c)=1.288±0.020 GeV and m‾b(m‾b)=4.176±0.023 GeV.

Towards the quark-gluon plasma Equation of State with dynamical strange and charm quarks

We present an ongoing project aimed at determining the thermodynamic Equation of State (EoS) of quark-gluon matter from lattice QCD with two generations of dynamical quarks. We employ the Wilson twisted mass implementation for the fermionic fields and the improved Iwasaki gauge action. Relying on T = 0 data obtained by the ETM Collaboration the strange and charm quark masses are fixed at their physical values, while the pion mass takes four values in the range from 470 MeV down to 210 MeV. The temperature is varied within a fixed-lattice scale approach. The values for the pseudocritical temperature are obtained from various observables. For the EoS we show preliminary results for the pure gluonic contribution obtained at the pion mass value 370 MeV, where we can compare with previously obtained results with Nf = 2 degenerate light flavours.

Spectrum of heavy baryons in the quark model

Single- and double- heavy baryons are studied in the constituent quark model. The model Hamiltonian is chosen as a standard one with two exceptions : (1) The color-Coulomb term depend on quark masses, and (2) an antisymmetric $LS$ force is introduced. Model parameters are fixed by the strange baryon spectra, $\Lambda$ and $\Sigma$ baryons. The masses of the observed charmed and bottomed baryons are, then, fairly well reproduced. Our focus is on the low-lying negative-parity states, in which the heavy baryons show specific excitation modes reflecting the mass differences of heavy and light quarks. By changing quark masses from the SU(3) limit to the strange quark mass, further to the charm and bottom quark masses, we demonstrate that the spectra change from the SU(3) symmetry patterns to the heavy quark symmetry ones.

Determination of mc and mb from quarkonium 1S energy levels in perturbative QCD

We update determination of the MS‾ masses of the charm and bottom quarks, from comparisons of the masses of the charmonium and bottomonium 1S states with their perturbative predictions up to next-to-next-to-next-to-leading order in ε expansion and using the MS‾ masses. Effects of non-zero charm-quark mass in the bottomonium masses are incorporated up to next-to-next-to-leading order. We obtain m‾c=1246±2(d3)±4(αs)±23(h.o.) MeV and m‾b=4197±2(d3)±6(αs)±20(h.o.)±5(mc) MeV, which agree with the current Particle Data Group values.

Fragmentation contributions toJ/ψphotoproduction at HERA

We compute leading-power fragmentation corrections to $J/\psi$ photoproduction at DESY HERA, making use of the nonrelativistic QCD factorization approach. Our calculations include parton production cross sections through order $\alpha_s^3$, fragmentation functions though order $\alpha_s^2$, and leading logarithms of the transverse momentum divided by the charm-quark mass to all orders in $\alpha_s$. We find that the leading-power fragmentation corrections, beyond those that are included through next-to-leading order in $\alpha_s$, are small relative to the fixed-order contributions through next-to-leading order in $\alpha_s$. Consequently, an important discrepancy remains between the experimental measurements of the $J/\psi$ photoproduction cross section and predictions that make use of nonrelativistic-QCD long-distance matrix elements that are extracted from the $J/\psi$ hadroproduction cross-section and polarization data.

Phenomenology of charmed mesons in the extended linear sigma model

We study the so-called extended linear sigma model for the case of four quark flavors. This model is based on global chiral symmetry and dilatation invariance and includes, besides scalar and pseudoscalar mesons, vector and axial-vector mesons. Most of the parameters of the model have been determined in previous work by fitting properties of mesons with three quark flavors. Only three new parameters, all related to the current charm quark mass, appear when introducing charmed mesons. Surprisingly, within the accuracy expected from our approach, the masses of open charmed mesons turn out to be in quantitative agreement with experimental data. On the other hand, with the exception of $J/\psi$, the masses of charmonia are underpredicted by about 10\%. It is remarkable that our approach correctly predicts (within errors) the mass splitting between spin-0 and spin-1 negative-parity open charm states. This indicates that, although the charm quark mass breaks chiral symmetry quite strongly explicitly, this symmetry still seems to have some influence on the properties of charmed mesons.