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Register a new userThe lightest flavor--singlet qqq baryons as witnesses to color
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We present a new computation in a field-theoretical model of Coulomb gauge QCD of the first radial and angular excitations of a qqq system in a SU(3) flavor singlet state, Lambda_S. The traditional motivation for the study is that the absence of flavor singlets in the lowest-lying spectrum is a direct consequence of the color degree of freedom. (The calculation is tested with decuplet baryons Delta(1232) and Omega(1672).) We also analyze decay branching fractions of the flavor singlet baryon for various masses with the simplest effective Lagrangians.
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We demonstrate how to efficiently expand cross sections for color-singlet production at hadron colliders around the kinematic limit of all final state radiation being collinear to one of the incoming hadrons. This expansion is systematically improvable and applicable to a large class of physical observables. We demonstrate the viability of this technique by obtaining the first two terms in the collinear expansion of the rapidity distribution of the gluon fusion Higgs boson production cross section at next-to-next-to leading order (NNLO) in QCD perturbation theory. Furthermore, we illustrate how this technique is used to extract universal building blocks of scattering cross section like the N-jettiness and transverse momentum beam function at NNLO.
We study the triply heavy baryons $Omega_{QQQ}$ $(Q=c, b)$ in the QCD sum rules by performing the first calculation of the next-to-leading order (NLO) contribution to the perturbative QCD part of the correlation functions. Compared with the leading order (LO) result, the NLO contribution is found to be very important to the $Omega_{QQQ}$. This is because the NLO not only results in a large correction, but also reduces the parameter dependence, making the Borel platform more distinct, especially for the $Omega_{bbb}$ in the $overline{rm{MS}}$ scheme, where the platform appears only at NLO but not at LO. Particularly, owing to the inclusion of the NLO contribution, the renormalization schemes ($bar {MS}$ and On-Shell) dependence and the scale dependence are significantly reduced. Consequently, after including the NLO contribution to the perturbative part in the QCD sum rules, the masses are estimated to be $4.53^{+0.26}_{-0.11}$ GeV for $Omega_{ccc}$ and $14.27^{+0.33}_{-0.32}$ GeV for $Omega_{bbb}$, where the results are obtained at $mu=M_B$ with errors including those from the variation of the renormalization scale $mu$ in the range $(0.8-1.2) M_B$. A careful study of the $mu$ dependence in a wide range is further performed, which shows that the LO results are very sensitive to the choice of $mu$ whereas the NLO results are considerably better. In addition to the $mu=M_B$ result, a more stable value, (4.75-4.80) GeV, for the $Omega_{ccc}$ mass is found in the range of $mu=(1.2-2.0) M_B$, which should be viewed as a more relevant prediction in our NLO approach because of $mu$ dependence.
It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of the color-flavor locking at high baryon density by using the Nambu-Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between the color-flavor locked phase and the spin polarized phase is the first order by means of the second order perturbation theory.
Aiming at relativistic description of gluons in hadrons, the renormalization group procedure for effective particles (RGPEP) is applied to baryons in QCD of heavy quarks. The baryon eigenvalue problem is posed using the Fock-space Hamiltonian operator obtained by solving the RGPEP equations up to second order in powers of the coupling constant. The eigenstate components that contain three quarks and two or more gluons are heuristically removed at the price of inserting a gluon-mass term in the component with one gluon. The resulting problem is reduced to the equivalent one for the component of three quarks and no gluons. Each of the three quark-quark interaction terms thus obtained consists of a spin-dependent Coulomb term and a spin-independent harmonic oscillator term. Quark masses are chosen to fit the lightest spin-one quarkonia masses most accurately. The resulting estimates for bbb and ccc states match estimates obtained in lattice QCD and in quark models. Masses of ccb and bbc states are also estimated. The corresponding wave functions are invariant with respect to boosts. In the ccb states, charm quarks tend to form diquarks. The accuracy of our approximate Hamiltonian can be estimated through comparison by including components with two gluons within the same method.
Amplitude Analysis of two photon production of $pipi$ and ${overline K}K$, using S-matrix constraints and fitting all available data, including the latest precision results from Belle, yields a single partial wave solution up to 1.4 GeV. The two photon couplings of the $sigma/f_0(500)$, $f_0(980)$ and $f_2(1270)$ are determined from the residues of the resonance poles.
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