Quark Mass Corrections Research Articles

Quark mass corrections to the perturbative thrust and its effect on the determination of αs

We consider the effects of quark masses to the perturbative thrust in $e^+e^-$ annihilation. In particular we show that perturbative power corrections resulting from non-zero quark masses considerably alters the size of the non-perturbative power corrections and consequently, significantly changes the fitted value of $\alpha_s$.

Strange quark mass from the invariant mass distribution of Cabibbo-suppressed tau decays

Quark mass corrections to the tau hadronic width play a significant role only for the strange quark, hence providing a method for determining its mass. The experimental input is the vector plus axial-vector strange spectral function derived from a complete study of tau decays into strange hadronic final states performed by ALEPH. New results on strange decay modes from other experiments are also incorporated. The present analysis determines the strange quark mass at the Mtau mass scale using moments of the spectral function. Justified theoretical constraints are applied to the nonperturbative components and careful attention is paid to the treatment of the perturbative expansions of the moments which exhibit convergence problems. The result obtained, m_s(Mtau^2) = (120 +- 11_exp +- 8_Vus +- 19_th) MeV = (120^+21_-26) MeV, is stable over the scale from Mtau down to about 1.4 GeV. Evolving this result to customary scales yields m_s(1 GeV^2) = (160^+28_-35) MeV and m_s(4 GeV^2) = (116^+20_-25) MeV.

An interacting parton model for quark and anti-quark distributions in the baryon

In this paper we study a 1+1 dimensional relativistic parton model for the structure of baryons. The quarks and anti-quarks interact through a linear potential. We obtain an analytic formula for the isospin averaged valence quark distribution in the chiral and large N c limits. The leading 1 N c and non-zero current quark mass corrections are estimated. Then we extend this model to include `sea' and anti-quarks. We find that the anti-quark content is small at a low value of Q 2. Using these distributions as initial conditions for Q 2 evolution, we compare with experimental measurements of the structure function xF 3( x, Q 2) and find reasonable agreement. The only parameters we can adjust are the fraction of baryon momentum carried by valence quarks and the initial scale Q 0 2.

Heavy quark1/mQcontributions in semileptonicBdecays to orbitally excitedDmesons

Exclusive semileptonic decays of B mesons to orbitally excited D mesons are considered beyond the infinitely heavy quark limit in the framework of the relativistic quark model based on the quasipotential approach. This model agrees with the structure of heavy quark mass corrections predicted by the heavy quark effective theory and allows the determination of corresponding leading and subleading Isgur-Wise functions. It is found that both relativistic and 1/m_Q contributions significantly influence the decay rates. Thus, relativistic transformations of the meson wave functions (Wigner rotation of the light quark spin) already contribute at leading order of the heavy quark expansion and result in a suppression of B\to D^{*}_0e\nu and B\to D^{*}_1e\nu decay rates. On the other hand, the vanishing of the decay matrix elements at zero recoil of a final D^{**} meson in the infinitely heavy quark mass limit makes the 1/m_Q corrections to be very important, and their account results in a substantial enhancement of B\to D_1e\nu and B\to D^{*}_0e\nu decay rates.

The strange quark mass dependence of Rτ, S

The perturbative quark mass corrections to the tau hadronic width are studied to O( α 3 s m 2 q ). Using present data on R τ, S and including up to dimensions four corrections, we get m s (4 GeV 2) = (143 ± 42) MeV[ m s (1 GeV 2) = (193 ± 59 MeV] in the MS scheme. Possible improvements to reduce the theoretical uncertainty are pointed out.

The Quadrupole Oscillations of Strange‐Quark Stars

We study the relativistic quadrupole oscillations (l=2) of strange-quark stars by calculating their quasi-normal modes, and we thus explore the possibility of using these oscillation frequencies and damping times to differentiate among relativistic polytropic stars, neutron stars, pure light-quark stars, and hybrid neutron stars with quark cores. We found that, whereas the general features of the w-mode spectra of quark stars and hybrid neutron stars are very similar to those of relativistic polytropes, they differ in the higher mode frequencies for both axial and polar oscillations. The profiles of f-modes for quark stars are different from those of realistic neutron stars, and from that we conclude that quark and strange-quark stars are more efficient gravitational-waves radiators than pure neutron stars. Also, the damping times of various modes are rather sensitive to the details of the quark model, such as the Bag constant, quark-gluon interactions, and quark mass corrections.

Strange quark mass dependence of the Tau hadronic Width

The perturbative quark mass corrections to the tau hadronic width are studied to O( α s 3 m q 2). Including up to dimension four corrections, we get m s (4 GeV] 2) = (143 ± 42) MeV [ m s (1 GeV 2) (193 ± 59) MeV]. Possible improvements to reduce the theoretical uncertainty are pointed out.

Determining the strange quark mass in Cabibbo-suppressed τ lepton decays

In this work radiative corrections in the total hadronic decay rate of the τ lepton and some moments of its differential distributions are studied employing perturbative QCD and the operator product expansion. We calculate quadratic quark mass corrections in the strange mass to the decay rate ratio R τ to the order O(α s 3m 2) and find that they contribute appreciably to the Cabibbo-suppressed decay modes of the τ lepton. Using the results of a recent experimental analysis, we obtain m s (1 GeV) = 200 ± 40 exp ± 30 th MeV.

Higher twist distribution amplitudes of vector mesons in QCD: Formalism and twist 3 distributions

We present a systematic study of twist 3 light-cone distribution amplitudes of vector mesons in QCD, which is based on conformal expansion and takes into account meson and quark mass corrections. A complete set of distribution amplitudes is constructed for ϱ, ω, K ∗ and φ mesons, which satisfies all (exact) equations of motion and constraints from conformal expansion. Nonperturbative input parameters are calculated from QCD sum rules, including an update of SU(3) breaking corrections in the leading twist distributions.

Perturbative quark mass corrections to the tau hadronic width

The perturbative quark-mass corrections to the $\tau$ hadronic width are analysed to $O(\alpha_s^3 m_q^2)$, using the presently available theoretical information. The behaviour of the perturbative series is investigated in order to assess the associated uncertainties. The implications for the determination of the strange quark mass from $\tau$ decay data are discussed.

Chiral corrections to vector meson decay constants

We calculate the leading quark mass corrections of order $m_q\log(m_q)$, $m_q$ and $m_q^{3/2}$ to the vector meson decay constants within Heavy Vector Meson Chiral Perturbation Theory. We discuss the issue of electromagnetic gauge invariance and the heavy mass expansion. Reasonably good fits to the observed decay constants are obtained.

Sum rule for the twist four longitudinal structure function

We investigate the twist four longitudinal structure function $F_{L}^{\tau=4}$ of deep inelastic scattering and show that the integral of ${F_{L}^{\tau=4} \over x}$ is related to the expectation value of the fermionic part of the light-front Hamiltonian density at fixed momentum transfer. We show that the new relation, in addition to providing physical intuition on $F_{L}^{\tau=4}$, relates the quadratic divergences of $F_{L}^{\tau=4}$ to the quark mass correction in light-front QCD and hence provides a new pathway for the renormalization of the corresponding twist four operator. The mixing of quark and gluon operators in QCD naturally leads to a twist four longitudinal gluon structure function and to a new sum rule $ \int dx {F_L \over x}= 4 {M^2 \over Q^2}$, which is the first sum rule obtained for a twist four observable. The validity of the sum rule in a non-perturbative context is explicitly verified in two-dimensional QCD.

Baryon magnetic moments in chiral perturbation theory

We consider the chiral expansion of the octet baryon magnetic moments in heavy baryon chiral perturbation theory including all terms which are of order q 4. These terms are formally of quadratic order in the quark masses. We show that despite the large non-analytic quark mass corrections to the Coleman-Glashow relations at order q 3, including all analytic and non-analytic corrections at order q 4, which in total are of moderate size, allows for a fit to the measured magnetic moments due to the appearance of counter terms with free coupling constants of natural size. In this scheme, the ΛΣ 0 transition moment is predicted to be μ ΛΣ 0 = (1.40 ± 0.01) μ N .

Quark mass correction to the string potential.

A consistent method for calculating the interquark potential generated by the relativistic string with massive ends is proposed. In this approach the interquark potential in the model of the Nambu--Goto string with point--like masses at its ends is calculated. At first the calculation is done in the one--loop approximation and then the variational estimation is performed. The quark mass correction results in decreasing the critical distance (deconfinement radius). When quark mass decreases the critical distance also decreases. For obtaining a finite result under summation over eigenfrequencies of the Nambu--Goto string with massive ends a suitable mode--by--mode subtraction is proposed. This renormalization procedure proves to be completely unique. In the framework of the developed approach the one--loop interquark potential in the model of the relativistic string with rigidity is also calculated.

Tensor charges of the nucleon in the SU(3) chiral quark soliton model

The tensor charges of the nucleon are calculated in the framework of the SU(3) chiral quark soliton model. The rotational 1 N c and strange quark mass corrections are taken into account up to linear order. We obtain the following numerical values of the tensor charges: δu = 1.12, δd = −0.42, and δs = −0.008. In contrast to the axial charges, the tensor charges in our model are closer to those of the nonrelativistic quark model, in particular, the net number of the transversely polarized strange quarks in a transversely polarized nucleon δs is compatible with zero.

P11charmonium state decay intopp¯in QCD models including constituent quark mass corrections

Stimulated by the experimental observation, made by the E760 Collaboration at Fermilab, of the $^1\!P_1$ state of charmonium resonantly formed in $p\,\bar p$ annihilation, we perform a calculation of the decay width for the $^1\!P_1\to p\,\bar p$ process. To this end, we employ a phenomenological model which adds constituent quark mass corrections to the usual massless QCD models for exclusive processes. For massless models, in fact, the process under consideration is forbidden by the so-called helicity selection rules, while it is allowed in our extended model. We find $\Gamma(^1\!P_1\to p\,\bar p)$ to be in the range $1-10$ eV. We also compare our results with previous, indirect estimates, based on QCD multipole expansion models.

Quark mass corrections to the Z boson decay rates.

The results of perturbative QCD evaluation of the ~m_f^2/M_Z^2 contributions to the decay rates in Z--->bb and Z--->hadrons for the quark masses m_f << M_Z are presented. The recent results due to the combination of renormalization group constraints and the results of several other calculations are independently confirmed by the direct computation. Some existing confusion in the literature is clarified. In addition, the calculated O(alpha_s^2) correction to the correlation function in the axial channel is a necessary ingredient for the yet uncalculated axial part of the O(alpha_s^3) mass correction to the Z decay rates. The results can be applied to the \tau hadronic width.

Twist-2 contributions to polarized structure functions and new sum rules

The twist-2 contributions to the polarized structure functions in deep inelastic lepton-hadron scattering are calculated including the exchange of weak bosons and using both the operator product expansion and the covariant parton model. A new relation between two structure functions leading to a sequence of new sum rules is found. The light quark mass corrections to the structure functions are derived in lowest order QCD.

Quark model description of polarised deep inelastic scattering and the prediction of g2

We show how the operator product expansion evaluated in the approximation of ignoring gluons leads to the covariant formulation of the quark parton model. We discuss the connection with other formulations and show how the free quark model prediction, g 2 = 0, changes smoothly into the Wandzura-Wilczek (WW) relation for quark masses small relative to the nucleon mass. Previous contradictory parton model predictions are shown to follow from an inconsistent treatment of the mass shell conditions. The description is extended to include quark mass corrections.

Electromagnetic form factors of the SU(3) octet baryons in the semibosonized SU(3) Nambu-Jona-Lasinio model.

The electromagnetic form factors of the SU(3) octet baryons are investigated in the semibosonized SU(3) Nambu--Jona-Lasinio model (chiral quark-soliton model). The rotational 1/${\mathit{N}}_{\mathit{c}}$ and strange quark mass corrections in linear order are taken into account. The electromagnetic charge radii of the nucleon and magnetic moments are also evaluated. It turns out that the model is in remarkably good agreement with the experimental data. \textcopyright{} 1996 The American Physical Society.