Relativistic correction to gluon fragmentation function into pseudoscalar quarkonium

Inspired by the recent measurements of the ηc meson production at LHC experiments, we investigate the relativistic correction effect for the fragmentation functions of gluon/charm quark fragmenting into η_c, which constitute the crucial nonperturbative element for the ηc production at high p_T. Employing three distinct methods,we calculate the next-to-leading-order(NLO) relativistic correction to g →η_c fragmentation function in the NRQCD factorization framework, as well as verifying the existing NLO result for the c →η_c fragmentation function. We also study the evolution behavior of these fragmentation functions with the aid of the DGLAP equation.     

Precise evaluation of h→c■ and axion-like particle production

We study the decay of the SM Higgs boson to a massive charm quark pair at the next-to-next-to-leading order QCD and next-to-leading order electroweak.At the second order of QCD coupling,we consider the exact calculation of flavour-singlet contributions where the Higgs boson couples to the internal top and bottom quark.Helpful information on the running mass effects related to Yukawa coupling may be obtained by analyzing this process.High precision production for h→cc within the SM makes it possible to search for new physics that may induce relatively large interactions related to the charm quark.As an example,we evaluate the axion-like particle associate production with a charm quark pair in the Higgs decay and obtain some constraints for the corresponding parameters under some assumptions.     

First lattice QCD calculation of semileptonic decays of charmed-strange baryonsΞc

While the standard model is the most successful theory to describe all the interactions and constituents of elementary particle physics,it has been constantly scrutinized for over four decades.Weak decays of charm quarks can be used to measure the coupling strength between quarks in different families and serve as an ideal probe for CP violation.As the lowest charm-strange baryons with three different flavors,Ξ;baryons(composed of csu or csd)have been extensively studied in experiments.In this study,we use state-of-the-art lattice QCD techniques to generate 2+1 clover fermion ensembles with two lattice spacings,a=(0.108,0.080 fm).Then,we present the first ab-initio lattice QCD calculation of the Ξ;→Ξ form factors.Our theoretical results for the Ξc→Ξl;v;decay widths are consistent with and approximately two times more precise than the latest measurements by the ALICE and Belle collaborations.Based on the latest experimental measurements,we independently obtain the quark-mixing matrix element |V;|,which is in good agreement with results from other theoretical approaches.     

Investigation of Z-boson decay into Ξbc and Ξbb baryons within the NRQCD factorization approach

Z-boson decay provides a good opportunity to search for the Ξ_bQ baryon because a large number of its events can be collected at high energy colliders.In this paper,we perform a complete investigation of the indirect production of the Ξ_bc and Ξ_bb baryons via the Z-boson decay process Z→Ξ_bQ+■+■ with a Q=(c,b) quark under the NRQCD factorization approach.After considering the contribution from the diquark states ■,■ and ■,the calculated branching fraction...     

Decay rates of charmonia within a quark-antiquark confining potential

In this work, we investigate the spectroscopy and decay rates of charmonia within the framework of the non-relativistic Schro¨dinger equation by employing an approximate inter quark-antiquark potential. The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are employed to compute the spectroscopy of the excited S states and a few low-lying P and D waves. The resultant wave functions at zero interquark separation as well as some finite separations are employed to predict the di-gamma, di-leptonic and di-gluon decay rates of charmonia states using the conventional Van Royen-Weisskopf formula. The di-gamma and di-leptonic decay widths are also computed by incorporating the relativistic corrections of order v4 within the NRQCD formalism.We have observed that the NRQCD predictions with their matrix elements computed at finite radial separation yield results which are found to be in better agreement with experimental values for both di-gamma and di-leptonic decays.The same scenario is seen in the case when di-gamma and di-leptonic decay widths are computed with the Van RoyenWeisskopf formula. It is also observed that the di-gluon decay width with the inclusion of binding energy effects are in better agreement with the experimental data available for 1S-2S and 1P. The di-gluon decay width of 3S and 2P waves waves are also predicted. Thus, the present study of decay rates clearly indicates the importance of binding energy effects.     

Theory for quarkonium: from NRQCD factorization to soft gluon factorization

We demonstrate that the recently proposed soft gluon factorization(SGF)is equivalent to the nonrelativistic QCD(NRQCD)factorization for heavy quarkonium production or decay,which means that,for any given process,these two factorization theories are either both valid or both violated.We use two methods to arrive at this conclusion.In the first method,we apply the two factorization theories to the physical process J/ψ→e^+e^-.Our explicit calculation shows that both SGF and NRQCD can correctly reproduce the low energy physics of full QCD,and the two factorizations are thus equivalent.In the second method,by using equations of motion,we successfully deduce SGF from NRQCD effective field theory.By identifying SGF with NRQCD factorization,we establish relations between the two factorization theories and prove the generalized Gremm-Kapustin relation as a byproduct.Compared with the NRQCD factorization,the advantage of SGF is that it resums the series of relativistic corrections originating from kinematic effects to all powers,yielding better convergence of the relativistic expansion.     

General scan in flavor parameter space in models with vector quark doublets and an enhancement in the B→X_sγ process

In models with vector-like quark doublets, the mass matrices of up and down type quarks are related.Precise diagonalization of the mass matrices has become an obstacle in numerical studies. In this work we first propose a diagonalization method. As its application, in the Standard Model with one vector-like quark doublet we present the quark mass spectrum and Feynman rules for the calculation of B → X_sγ. We find that i) under the constraints of the CKM matrix measurements, the mass parameters in the bilinear term are constrained to a small value by the small deviation from unitarity; ii) compared with the fourth generation extension of the Standard Model, there is an enhancement to the B → X_sγ process in the contribution of vector-like quarks, resulting in a non-decoupling effect in such models.     

Distributions and correlations of constituent quarks in jets

In the frame of the quark recombination model, we study the momentum distributions and correlations of constituent quarks in jets by analyzing the final state hadrons generated by PYTHIA for the hard parton fragmentation processes in vacuum. Parameterizations for the distributions are tabulated.     

Quenched Charmed Meson Spectra Using Tadpole Improved Quark Action on Anisotropic Lattices

Charmed meson charmonium spectra are studied with improved quark actions on anisotropic lattices. We measured the pseudo-scalar and vector meson dispersion relations for four lowest lattice momentum modes with quark mass values ranging from the strange quark to charm quark with three different values of gauge coupling β and four different values of bare speed of light v. With the bare speed of light parameter v tuned in a mass-dependent way, we study the mass spectra of D, Ds, ηc, D^＊, D^＊s and J/ψ mesons. The results extrapolated to the continuum limit are compared with the experiment, and a qualitative agreement is found.     

Lepton number violation in D meson decay

The lepton number violation(LNV) process can be induced by introducing a fourth generation heavy Majorana neutrino,which is coupled to the charged leptons of the Standard Model(SM). There have been many previous studies on the leptonic number violating decay processes with this mechanism. We follow the trend to study the process: D→Kllπ with the same-sign dilepton final states. We restrict ourselves to certain neutrino mass regions,in which the heavy neutrino could be on-shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the narrow width approximation(NWA),we found that the upper limit for the branching fractions for D0→ K-l+l+π-are generally at the order of 10-12 to 10-9,if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constraints,which is competitive compared to the LNV B decays,on the mixing matrix element |VeN|2 based on the upper limit of D0→ K-e+e+π-estimated from the Monte-Carlo(MC) study at BESⅢ. Although the constraints are worse than the ones from(0νββ) decay in the literature,the future experiment at the charm factory may yield more stringent constraints.     

THE QUARK MASS EFFECT OF THE DISTRIBUTION AMPLITUDES IN γγ-EXCLUSIVE PROCESSES

In this paper we have analyzed the γ^*π°→γ, γγ→ππ and γγ→ρρ processes by using the sum rules of the distribution amplitude ФM(xi,Q²), which are obtained from the π°→γγ and the π→μν decay processes. Since the angular distributions of the γγ→π°π° and γγ→ρ_⊥ρ_⊥ amplitudes are sensitive to the shape of the distribution amplitude ФM(xi,Q²), there is a possibility to investigate the effect of the quark mass from the angular distributions of γγ→MM exclusive processes.     

Production Rate of Ds+Ds- at φ(4030)

By using a generalized relativistic quark pair creation model (QPCM), the hadronic decay processes of φ(4030), assigned as the 3S state of cc, are investigated. The relative rates of φ(4030) → DD, DD^*+DD^*, D^*D^*,and in particular D_s⁺D_s^- are calculated and compared with data. The nodes of the radially excited wavefunctions of charmonium states are found to be significant for these decay processes. Considering the SU(3) suppression factor of ~3 for the s quark pair creation relative to the u and d quarks, we obtain σ(e⁺e^- → φ4(4030) → D_s⁺D_s^-) ~ 0.9 nb.     

Formation of charmonium states in heavy-ion collisions and thermalization of charm

We examine the possibility to utilize in-medium charmonium formation in heavy-ion interactions at collider energy as a probe of the properties of the medium. This is possible because the formation process involves recombination of charm quarks which imprints a signal on the resulting normalized transverse momentum distribution containing information about the momentum distribution of the quarks. We have contrasted the transverse momentum spectra of J/ψ, characterized by 〈p _T ²〉, which result from the formation process in which the charm quark distributions are taken at opposite limits with regard to thermalization in the medium. The first uses charm quark distributions unchanged from their initial production in a pQCD process, appropriate if their interaction with the medium is negligible. The second uses charm quark distributions which are in complete thermal equilibrium with the transversely expanding medium, appropriate if a very strong interaction between charm quarks and medium exists. We find that the resulting 〈p _T ²〉 of the formed J/ψ should allow one to differentiate between these extremes, and that this differentiation is not sensitive to variations in the detailed dynamics of in-medium formation. We include a comparison of predictions of this model with preliminary PHENIX measurements, which indicates compatibility with a substantial fraction of in-medium formation.     

Chiral Extension of Standard Model and Rc,Rb Problems

The deviations of R_c, R_b fiom the standard model are discussed within our theory, the cbiral extension of standard model and its supersymmetrization. Combining R_c, R_b with the coupling constants gv, gA of Z⁰ decay, Γ(W⁺ → e⁺υ_e) of W⁺ and the Michel parameters p_γ of γ decay, the mixing angles between hadronic and leptonic quarks and the form factors of the leptonic axial currents are determined within experimental errors, from which it is found that the mass of down leptonic quark of the third generation is about twice the mass of top quark.     

ξ(2230) Is Likely to Be a Glueball

On the basis of the recent results of ξ(2230) → π⁺π^-, pp and ξ(2230) → K⁺K^-, K_sK_s, measured by the BES Collaboration in J/ψ radiative decays, combined with the PSI85 experiment of pp → ξ(2230) → KK we argue that because of its very narrow partial decay widths to nn and KK (less than 1 MeV), its large production rate in J/ψ radiative decays (BR(J/ψ → γξ> 2.3×10^-3), and its flavor-symmetric couplings to ππ and KK, the ξ(2230) is very likely to to be a J^PC= (even)⁺⁺ glueball.     

Gluonia and Charmonium Decays

We discuss the search for a 1^-- gluonium state, 0, in connection with a possible solution for the so-called ρπ, K^*K puzzle in the J/φ and φ' decays. Some issues are examined. In particular, we argue that the expected most favorable process φ → ππO can have an appreciable branching ratio (say 10^-3 ~ 10^-4) only if the O has a very narrow partial decay width to ρπ (say 1 ~ 10 MeV). For the 0^-+ system we deduce a relation that BR(η'_c → h) ≈ BR (η_c → h), where h denotes an exclusive light hadronic channel. This relation may be useful for the experimental search of the yet to be confirmed q: state, for which the branching ratios of φ' → η'_c → γKKπ, γηππ, γη'ππ are estimated to be about 1 × 10^-4 if the mass of η'_c is around 3600 MeV, and this relation may also serve as a criterion to determine whether there exist anomalous decays in the η_c and η'_c system, in particular in the VV decay channels, which might be related to the 0^-+ glueball-charmonium mixing. We emphasize that the bigluonium and the trigluonium may have very different effects on these decays.     

Wigner Distributions in Light-Front Quark Models

We discuss the quark Wigner distributions which represent the quantum-mechanical analogues of the classical phase-space distributions. These functions can be obtained through a Fourier transform in the transverse space of the generalized transverse momentum dependent parton distributions, which encode the most general one-body information of partons in momentum space. In particular, we present a study within light-front quark models. The quark orbital angular momentum is also obtained from the phase-space average of the orbital angular momentum operator weighted with the Wigner distribution of unpolarized quark in a longitudinally polarized nucleon. The corresponding results calculated within different light-front quark models are compared with alternative definitions of the quark orbital angular momentum as given in terms of generalized parton distributions and transverse momentum dependent parton distributions.     

Diffractive production of dijets at HERA

We investigate the production of a quark-antiquark pair in diffractive photon-proton scattering, approximating soft pomeron exchange by the exchange of two nonperturbative gluons. In deep inelastic scattering at HERA, events with two jets and the scattered proton in the final state are predicted to be observable, with an important contribution from charm production. For photoproduction of light quark jets with high transverse momentum we find that both exchanged gluons must have a large invariant mass, so that the cross section is very small, whereas for charm quarks it is quite appreciable. From our calculation we also extract the quark structure function of the pomeron for the scaling variablez no too close to 0 or 1, finding a strong flavour dependence and a behaviour somewhat harder thanz(1?z) for light quarks.     

Semileptonic decays of heavy quarks in quantum chromodynamics

We investigate the semileptonic decays of heavy quarks in the leading non-trivial order in quantum chromodynamics. Effects of gluon corrections and the initial quark Fermi motion on the semileptonic rates and decay distributions are calculated. The resulting lepton energy spectrum for the charm semileptonic decay is compared with data to extract the mass of the charm quark. This is combined with the semileptonic branching ratio to predict the charm-quark lifetime. We find the lepton energy spectrum very stable with respect to gluon corrections. Expected spectra from the semileptonic decays of bottom and top quarks are presented. We also study the semileptonic decay process Q → q?v_? + G, involving the emission of a single hard non-collinear gluon. This process should be observable with a branching ratio of a few percent in the decays of top (and heavier) quarks.     

Observation of polarization in bottomonium production at square root of s = 38.8 GeV

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at square root of s = 38.8 GeV. The angular distribution of the decay dimuons of the Upsilon(1S) state shows no polarization at small values of the fractional longitudinal momentum x(F) and transverse momentum p(T) but significant positive transverse production polarization for either p(T)>1.8 GeV/c or for x(F)>0.35. The Upsilon(2S+3S) (unresolved) states show a large transverse production polarization at all values of x(F) and p(T) measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.