QCD analysis of quark recombination for leading particle effect

Abstract

The quark recombination mechanism is proposed to explain the asymmetry between production rates of D + and of D − in their inclusive productions, and also asymmetries for other charmed hadrons. These asymmetries are observed in experiment and are called as leading particle effects. In this work we give a general analysis for contributions of quark recombination to these asymmetries. The contributions consist of a perturbative-and nonperturbative part. We perform two types of factorization by considering the produced hadron with large transverse momentum and by taking charm quark as a heavy quark, respectively. In the case of large transverse momentum the effect of quark recombination is the standard twist-4 effect. We find that the contributions are parameterized with four nonperturbative functions, defined with four quark operators at twist-4, for initial hadrons without polarization. By taking charm quark as a heavy quark the factorization can be performed with the heavy quark effective theory(HQET). The effect of quark recombination is in general parameterized by eight nonperturbative parameters which are defined as integrals with matrix elements of four quark operators defined in HQET. For unpolarized hadrons in the initial state, the parameters can effectively be reduced to four. Perturbative parts in the two types of factorization are calculated at tree-level.

Λc+/Λc−andLai1, Leibovich2 2015Phys. Rev. D

“…The asymmetry is huge (∼ 50%). We believe that our An appealing feature of the heavy quark recombination mechanism is that it has its basis in perturbative QCD and thus is model-independent [18]. However, it should be emphasized that the heavy quark recombination mechanism is not the only possible way to give rise to production asymmtries of heavy hadrons at the LHC.…”

“…The cross section is factored into a perturbatively calculable piece dσ and a nonperturbative factor η[(Qq) n → Λ Q ] encoding the probability for the quark pair with quantum number n to hadronize into a final state including a Λ Q . η[(Qq) n → Λ Q ] can be expressed as a matrix element of a HQET operator [18]. Equations (3) and (4) must then be convoluted with the proton parton distribution functions to get the final hadronic cross section.…”

Flavor physics of leptons and dipole moments

“…The present limits B(B 0 d → eμ) < 1.7 × 10 −7 [975] determined by Belle and B(B 0 s → eμ) < 6.1 × 10 −6 [976] from CDF are of interest since they place bounds on the masses of two Pati-Salam leptoquarks [361] (see below). Both measurements are almost background free so significant improvements should be expected from these experiments.…”

$D^*$ meson production in jet from combination of charm quark with light one

“…It has been pointed out that, in hadronic interaction, the asymmetry of D meson in forward direction can be explained by the the combination of the initial parton with the charm quark produced in the hard interaction. Such a leading particle effect has been studied in [10][11][12][13], both in the approximation m c → ∞. In such an approximation, the light quark has vanishing momentum, hence, qualitatively, the momentum of the D meson is approximately that of the charm quark, so that not possible to probe the momentum of the light quark, but leaving a non relativistic combination matrix.…”

“…The combination matrix elements there depend on three variables z 1 , z 2 , z 3 , seem not corresponding to the momentum fraction of the valence partons. However, starting from Equation (4) in [13], by taking into account the space-time transition invariance, we get the combination matrix elements with two variables corresponding to the momentum fraction of the charm and the light quarks, which is like those in the above section:…”