Heavy Quark Fragmentation Functions Research Articles

Excited state contributions to the heavy baryon fragmentation functions in a quark-diquark model

Spin dependent fragmentation functions for heavy flavor quarks to fragment into heavy baryons are calculated in a quark-diquark model. The production of intermediate spin 1/2 and 3/2 excited states is explicitly included. The resulting ${\ensuremath{\Lambda}}_{b}$ production rate and polarization at CERN LEP energies are in agreement with experiment. The ${\ensuremath{\Lambda}}_{c}$ and ${\ensuremath{\Xi}}_{c}$ functions are also obtained. The spin independent ${f}_{1}(z)$ is compared to data. The integrated values for production rates agree with the data.

Compatibility of various approaches to heavy-quark fragmentation

We find that the definition of the heavy-quark fragmentation function given by Jaffe and Randall differs by a factor of the longitudinal-momentum fraction z from the standard Collins-Soper definition. Once this factor is taken into account, the explicit calculation of Braaten is found to be in agreement with the general analysis of Jaffe and Randall. We also examine the model of Peterson for heavy-quark fragmentation and find that the quoted values of the width and of the value of z at the maximum are in error. The corrected values are in agreement with the analysis of Jaffe and Randall.

Spin dependent fragmentation functions for heavy flavor baryons and single heavy hyperon polarization

Spin dependent fragmentation functions for heavy flavor quarks to fragment into heavy baryons are carculated in a quark-diquark model. The production of intermediate spin 1/2 and 3/2 excited states is explicity included. Λ b , Λc and Ξ c production rate and polarization at LEP energies are calculated and, where possible, compared with experiment. A different approach, also relying on a heavy quark-diquark model, is proposed for the small momentum transfer inclusive production of polarized heavy flavor hyperons. The predicted Λc polarization is roughly in agreement with experiment.

A phenomenological study of heavy-quark fragmentation functions in e+e− annihilation

We consider the computation of D and B fragmentation functions in e + e − annihilation. We compare the results of fitting present data using the next-to-leading-logarithmic resummed approach, versus the O(α s 2) fixed-order calculation, including also mass-suppressed effects. We also propose a method for merging the fixed-order calculation with the resummed approach.

A fixed-order calculation of the heavy-quark fragmentation function in e+e− collisions

We use a recently completed O(α s 2) fixed-order calculation of the heavy-flavour production cross section in e + e − collisions to compute the heavy-quark fragmentation function. We fit the result of our calculation, convoluted with a Peterson fragmentation function, to available data for charm production, and thus obtain a value for the parameter ϵ in the Peterson function. We discuss the relevance of mass effects and of subleading terms in our calculation.

THE HEAVY QUARK FRAGMENTATION FUNCTION AND THE MULTIPLICITY DIFFERENCE BETWEEN HEAVY AND LIGHT QUARK HADRONIC EVENTS IN e+e- ANNIHILATION IN THE LONGITUDINAL PHASE SPACE MODEL

The heavy quark fragmentation function and the multiplicity difference between heavy and light quark hadronic events are explained in a unified framework, namely the longitudinal phase space model. Good agreement of the predictions with data has been achieved.

Λb polarization in Z boson decays

In the framework of perturbative QCD and the diquark model of baryons we have obtained the fragmentation functions for heavy quarks that split into polarized Λ b baryons. We predict the longitudinal polarization asymmetry for prompt Λ b produced in e + e − annihilation at the Z resonance and estimate the spin-1/2 and spin-3/2 beauty baryon production rate.

Relativistic and binding energy corrections to heavy quark fragmentation functions

We calculate the fragmentation function for a charm quark to decay inclusively into $S$-wave charmonium states, including relativistic and binding energy corrections in powers of the quark relative velocity $v$. We also use these fragmentation functions to estimate their contribution to the production rate of ${\ensuremath{\eta}}_{c}$ and $J/\ensuremath{\psi}$ in ${Z}^{0}$ decay. These corrections contribute about $38$% to the integrated $c\ensuremath{\rightarrow}J/\ensuremath{\psi}+X$ fragmentation. For ${\ensuremath{\eta}}_{c},$ these corrections are found to be small.

Form Factors for Exclusive Semileptonic B Decays

We investigate the form factors for exclusive semileptonic decays of B meson to D, D*, based on the parton picture and helped by the results of the HQET. We obtain the numerical results for the slope of the Isgur–Wise function, which is consistent with the experimental results, and we extract the dependence of hadronic form factors on q2 by varying the input heavy quark fragmentation function without the nearest pole dominance ansätze.

Charmed meson fragmentation functions

Fragmentation functions for heavy-light mesons, like the charmed $D$, ${D}^{*}$ mesons, are proposed. They rest on next-to-leading QCD perturbative fragmentation functions for heavy quarks, with the addition of a nonperturbative term describing phenomenologically the quark $\ensuremath{\rightarrow}$ meson transition. The cross section for production of large ${p}_{T}$ $D$, ${D}^{*}$ mesons at the Fermilab Tevatron is evaluated in this framework.

Non-perturbative corrections to heavy quark fragmentation in e+e− annihilation

We estimate the non-perturbative power-suppressed corrections to heavy flavour fragmentation and correlation functions in e + e − annihilation, using a model based on the analysis of one-loop Feynman graphs containing a massive gluon. This approach corresponds to the study of infrared renormalons in the large- n f limit of QCD, or to the assumption of an infrared-finite effective coupling at low scales. We find that the leading corrections to the heavy quark fragmentation function are of order λ M , where λ is a typical hadronic scale (λ ∼ 0.4 GeV) and M is the heavy quark mass. The inclusion of higher corrections corresponds to convolution with a universal function of M(1 − x) concentrated at values of its argument of order λ, in agreement with intuitive expectations. On the other hand, corrections to heavy quark correlations are very small, of the order of (λ Q) p , where Q is the centre-of-mass energy and p ≥ 2.

Heavy quark fragmentation into double heavy baryons in the quark-diquark model

In the framework of nonrelativistic QCD and the quark-diquark model of baryons we have obtained the fragmentation functions for heavy quarks that split into spin- 1 2 and spin- 3 2 double heavy baryons. We predict the production rates as well as the shape of the energy spectra for cc- and bc-baryons in the region of the Z 0 peak at the LEP collider.

A derivation of the heavy quark fragmentation function in annihilation

We extend the kinematic analysis on heavy quark fragmentation initiated by Bjorken and Suzuki to derive the fragmentation function of the heavy quarks. Considering the thrust axis is not necessarily along the relative momentum direction of the initial quark pair, indeed the contribution of the heavy hadrons which locate at non-leading rapidity positions may be as important to the results as those at the leading position. A quite good agreement between data and our prediction is achieved.

Heavy quark fragmentation functions in the heavy quark effective theory.

We calculate fragmentation functions for a b-quark to fragment into color-singlet P-wave bound states $\bar c b$ in the Heavy Quark Effective Theory with the exact account of $O(1/m_b)$ corrections. We demonstrate an agreement of the obtained results with the corresponding calculations carried out in quantum chromodynamics.

Heavy quark fragmentation functions for D-wave quarkonium and charmed b-flavored mesons.

At the large transverse momentum region, the production of heavy-heavy bound-states such as charmonium, bottomonium, and $\bar bc$ mesons in high energy $e^+e^-$ and hadronic collisions is dominated by parton fragmentation. We calculate the heavy quark fragmentation functions into the D-wave quarkonium and $\bar bc$ mesons to leading order in the strong coupling constant and in the non-relativistic expansion. In the $\bar b c$ meson case, one set of its D-wave states is expected to lie below the open flavor threshold. The total fragmentation probability for a $\bar b$ antiquark to split into the D-wave $\bar b c$ mesons is about $2 \times 10^{-5}$, which implies that only 2\% of the total pseudo-scalar ground state $B_c$ comes from the cascades of these orbitally excited states.

Measurements of cross section and asymmetry for e+e--->bb-bar and heavy quark fragmentation at KEK TRISTAN.

Using 773 muons found in hadronic events from 142 pb-1 of data at a c.m. energy of 57.8 GeV, we extract the cross section and forward-backward charge asymmetry for the e+e- --> bbBAR process, and the heavy quark fragmentation function parameters for the Peterson model. For the analysis of the e+e- --> bbBAR process, we use a method in which the behavior of the c quark and lighter quarks is assumed, with only that of the b quark left indeterminate. The cross section and asymmetry for e+e- --> bbBAR are found to be R(b) = 0.57 +/- 0.06(stat) +/- 0.08(syst) and A(b) = -0.59 +/- 0.09 +/- 0.09, respectively. They are consistent with the standard model predictions. For the study of the fragmentation function we use the variable [x(e)], the fraction of the beam energy carried by the heavy hadrons. We obtain [x(E)]c = 0.56(-0.05-0.03)+0.04+0.03 and [x(E)]b = 0.65(-0.04-0.06)+0.06+0.05, respectively. These are in good agreement with previously measured values.

Bc meson production at hadron colliders by heavy quark fragmentation.

We present a reliable estimate on the production rate of ${\mathit{B}}_{\mathit{c}}$ mesons in 1S and 2S states in the large transverse momentum region at hadron colliders using heavy quark fragmentation functions derived within the framework of perturbative QCD. We also present the transverse momentum distribution for the ${\mathit{B}}_{\mathit{c}}$ mesons. The production rate is large enough for the ${\mathit{B}}_{\mathit{c}}$ mesons to be identified at the Fermilab Tevatron. At the Superconducting Super Collider or the CERN Large Hadron Collider the rate is so large that their properties can be studied in detail.

The fragmentation function for heavy quarks in QCD

We present the results of a next-to-leading order QCD calculation of the fragmentation function for heavy quarks. Our formalism can be used to obtain the next-to-leading order inclusive heavy quark production cross section in any hard collisions, in the limit when the transverse momentum of the heavy quark is much larger than its mass. We apply our results to the inclusive production of heavy quarks in e +e − collisions, and present detailed formulas for the moments of the heavy quark fragmentation function in e +e − production processes.

Heavy-quark fragmentation functions in a simple string model

We model QCD confinement by using the massless relativistic string that decays according to a simple covariant Poisson law. We explore the implications of the model and arrive at a heavy-quark fragmentation function which depends on only one parameter. We compare the resulting fragmentation function with data and other models and show how, unlike other string-based model, it exhibits the limiting behavior expected from general kinematic arguments and perturbative QCD.

Determination of semi-muonic branching ratios and fragmentation functions of heavy quarks ine + e ? annihilation at $$\langle \sqrt s \rangle $$ =34.6 GeV

Muon inclusive multihadronic final states ine+e− annihilation at\(\langle \sqrt s \rangle \)=34.6 GeV, collected by the JADE detector at PETRA, have been analysed in terms of the semi-muonic branching ratios and fragmentation functions of heavy quarks. Defining the fragmentation variable, ζ, as\(z = \frac{{\left( {E + p_\parallel } \right)_{hadron} }}{{\left( {E + p} \right)_{quark} }}\) we find =(77±3±5)% and =(86±4±5)%. The corresponding semi-muonic branching ratios are measured to be BR(c→μvμX)=7.8±1.5±2)% and BR (b→μvμX)=(11.7±1.6±1.5)%. Defining ζ as\(x_E = \frac{{E_{hadron} }}{{E_{beam} }}\) we observe an expected softening effect in the fragmentation due mainly to gluon emission, but find that this definition leads to semi-muonic branching ratiomeasurements which are strongly affected by uncertainties in the fragmentation process and the WCD calculation.