Leading logarithms of heavy quark masses in processes with light and heavy quarks

The matrix elements of operators containing both heavy quark (Q) and light quark (q) fields can contain large logarithms of the type ln(m_Q²/μ²), where μ is a typical QCD mass scale and m_Q is the heavy quark mass. We outline a method for summing leading logarithms of this type. We apply it to the decay constant f_M of a low lying pseudoscalar meson M with Q̄q flavor quantum numbers and predict the ratios of decay constants for mesons with different heavy flavors. We also apply it to a matrix element of a four-quark operator which is relevant for B⁰−B̄⁰ mixing.     

Semileptonic B<Subscript>s</Subscript>→D<Subscript>sJ</Subscript>(2460)lν decay in QCD

Using three point QCD sum rule methods, the form factors relevant to semileptonic B_s→D_sJ(2460)ℓν decay are calculated. The q² dependences of these form factors are evaluated and compared with the heavy quark effective theory predictions. The dependence of the asymmetry parameter α, characterizing the polarization of the D_sJ meson, on q² is studied. The branching ratio of this decay is also estimated, and it is shown that it can easily be detected at LHC.     

Effective meson lagrangian with chiral and heavy quark symmetries from quark flavor dynamics

By bosonization of an extended NJL model we derive an effective meson theory which describes the interplay between chiral symmetry and heavy quark dynamics. This effective theory is worked out in the low-energy regime using the gradient expansion. The resulting effective lagrangian describes strong and weak interactions of heavy B and D mesons with pseudoscalar Goldstone bosons and light vector and axial-vector mesons. Heavy meson weak decay constants, coupling constants and the Isgur-Wise function are predicted in terms of the model parameters partially fixed from the light quark sector. Explicit SU(3)_F symmetry breaking effects are estimated and, if possible, confronted with experiment.     

Hadronic decays of N and Δ resonances in a chiral quark model

π and η decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange. For the decay mechanism a modified version of the ³ P ₀ model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson exchange constituent quark model. We compare the predictions for π and η decay widths with experiment and also with results from a traditional one-gluon exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent quark models are outlined. We also discuss the sensitivity of the results on the parameterization of the meson wave function entering the ³ P ₀ model. Received: 11 May 2001 / Accepted: 17 September 2001     

Heavy-Quark Limit in a Relativistic Quark-Confinement Model

We have studied the weak decay constants and the Isgur-Wise form factors of the B and D mesons in the heavy-quark limit by employing a relativistic 2quark-confinement model. It is an attempt to improve our previous work within the same line of thinking, but by incorporating a couple of novel aspects. First, the infrared behaviour of the heavy quark is considered by modifying its conventional propagator in terms of a single parameter ν. Second, the mass difference between the heavy meson and heavy quark E = m _H – M _Q has been included. It is found that the weak decay constants depend strongly on this mass difference E with a relatively mild ν dependence. As for the Isgur-Wise function it is controlled more sensitively by the infrared parameter ν, leading to its suppression at maximum meson recoil. Received January 3, 1995; revised July 3, 1995; accepted for publication July 31, 1995     

DsJ (2317) meson production at RHIC

We study the production of D _sJ (2317) mesons in relativistic heavy ion collisions using the quark coalescence model. The predicted D _sJ (2317) abundance depends sensitively on the quark structure of the D _sJ (2317) meson. We have also evaluated the absorption cross sections of the D _sJ (2317) meson by π, ρ, kaon and K* in a phenomenological hadronic model. We find that the final yield of D _sJ (2317) mesons remains sensitive to its initial number produced from the quark-gluon plasma, providing thus the possibility of studying the quark structure of the D _sJ (2317) meson and its production mechanism in relativistic heavy ion collisions.     

Some two body non-leptonicB decays and estimation off D in the heavy quark effective theory

We have studied some of the two body nonleptonic decays ofB meson in the context of heavy quark effective theory using factorization hypothesis. Treatinga ₁ as a free parameter, we have obtained its value asa ₁=0.822±0.045, by correlating the experimental and predicted branching ratio for process. With this value ofa ₁ the branching ratios obtained for other decay channels are in good agreement with the experiment. The decay constant ofD meson is extracted to be 280.82 MeV. Heavy quark spin symmetry has also been tested.     

Dependence of |V ub/Vcb| on Fermi momentump F in ACCMM model

The Gaussian width of Fermi momentum,p _F, is the most important parameter of the ACCMM model, and its value is essential in the determination of |V _ub/V_cb| because the experimental analysis is allowed only at the end-point region of inclusive semileptonicB-decay spectrum. We extract the value of |V _ub/V_cb| as a function ofp _F. We also calculate the parameterp _F in the relativistic quark model using the variational method, and obtainp _F=0.54 GeV which is much larger than the commonly used value, ∼0.3 GeV, in experimental analyses. When we usep _F=0.5 GeV instead of 0.3 GeV, the value of |V _ub/V_cb| from ACCMM model is increased by a factor 1.81, and can give a good agreement with Isgur et al. model.     

Semileptonic B decays into even parity charmed mesons

By using a constituent quark model we compute the form factors relevant to semileptonic transitions of the B mesons into low-lying p-wave charmed mesons. We evaluate the q² dependence of these form factors and compare them with other model calculations. The Isgur–Wise functions τ_1/2 and τ_3/2 are also obtained in the heavy quark limit of our results. PACS 13.25.Hw; 12.39.Hg; 12.39.Jh     

Two body nonleptonic decays of Λb involving proton

We study some nonleptonic decays of Λ_b-baryon involving transition of a heavy to light quark, using nonrelativistic quark model for form factors. The decay rates for two such decays are consistent with the data available. Also these decays can give us information on the CKM matrix element |V_Ub|.     

A relativistic quark model for mesons with an instanton-induced interaction

We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the U _A(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like π⁺/K ⁺↦e ⁺υ_eγ and 0^-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the K _?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data. Received: 28 August 2000 / Accepted: 12 September 2000     

x-dependence of the quark distribution functions in the χCQM<Subscript>config</Subscript>

Chiral constituent quark model with configuration mixing (χCQM_config) is known to provide a satisfactory explanation of the “proton spin problem” and related issues. In order to enlarge the scope of χCQM_config, we have attempted to phenomenologically incorporate x-dependence in the quark distribution functions. In particular, apart from calculating valence and sea quark distributions q_val(x) and q̄(x), we have carried out a detailed analysis to estimate the sea quark asymmetries d̄(x)-ū(x), d̄(x)/ū(x) and as well as spin independent structure functions F₂ ^p(x)-F₂ ⁿ(x) and F₂ ⁿ(x)/F₂ ^p(x) as functions of x. We are able to achieve a satisfactory fit for all the above mentioned quantities simultaneously. The inclusion of effects due to configuration mixing have also been examined in the case F₂ ^p(x)-F₂ ⁿ(x) and F₂ ⁿ(x)/F₂ ^p(x) where the valence quark distributions dominate and it is found that it leads to considerable improvement in the results. Further, the valence quark structure has also be tested by extrapolating the predictions of our model in the limit x→1 where data is not available.     

Weak decays of heavy mesons in the instantaneous Bethe Salpeter approach

In the framework of the instantaneous Bethe Salpeter equation we investigate weak decays ofB andD mesons. Mesons are described asq $\bar q$ states interacting via a mixture of a scalar and a vector confining kernel and a one gluon exchange. The model parameters are fixed by a fit to the meson mass spectrum including also the light mesons. We calculate form factors and compare our results to the pole dominance hypothesis. From a fit to ARGUS and CLEO data onB→D ^*?v semileptonic decay we extract the Cabbibo Kobayashi Maskawa matrix element to beV _cb =(0.032 ± 0.003)(1.49ps/τ _b )^1/2 The Isgur Wise function is calculated utilizing the heavy quark mass limit. Finally, we give some results on nonleptonic decays.     

Covariant trace formalism for heavy mesons-wave top-wave transitions

Heavy meson,s- top-wave, weakb→c transitions are studied in the context of the heavy quark effective theory using covariant meson wave functions. We use the trace formalism to evaluate the weak transitions. As expected from heavy quark symmetry, the eight transitions betweens- andp-wave states are described in terms of only two universal form factors which are given in terms of explicit wave function overlap integrals. We present our results in terms of both invariant and helicity amplitudes. Using our helicity amplitude expressions we discuss rate formulae, helicity structure functions and joint angular decay distributions in the decays \(\bar B \to D^{**} ( \to (D,D^* ) + \pi ) + W^ - ( \to l^ - \bar v_l )\) . The heavy quark symmetry predictions for the one pion transitionsD ^**→(D,D ^*)+π are similarly worked out by using trace techniques.     

Mass spectrum of diquarks and mesons in the color–flavor locked phase of dense quark matter

The spectrum of meson and diquark excitations of dense quark matter is considered in the framework of the Nambu–Jona-Lasinio model with three types of massless quarks in the presence of a quark number chemical potential μ. We investigate the effective action of meson and diquark fields both at sufficiently large values of μ>μ_c≈  330 MeV, where the color–flavor locked (CFL) phase is realized, and in the chirally broken phase of quark matter (μ<μ_c). In the latter case all nine pseudoscalar mesons are Nambu–Goldstone (NG) bosons, whereas the mass of the scalar meson nonet is twice the dynamical quark mass. In the chirally broken phase the pseudoscalar diquarks are not allowed to exist as stable particles, but the scalar diquarks might be stable only at a rather strong interaction in the diquark channel. In the case of the CFL phase, all NG bosons of the model are realized as scalar and pseudoscalar diquarks. Moreover, it turns out that massive diquark excitations are unstable for this phase. In particular, for the scalar and pseudoscalar octets of diquark resonances a mass value around 230 MeV was found numerically. In contrast, mesons are stable particles in the CFL phase. Their masses lie in the interval 400–500 MeV for not too large values of μ>μ_c. PACS 11.30.Qc; 12.38.-t; 12.39.-x     

Quark–lepton complementarity with lepton and quark mixing data predict θ<Subscript>13</Subscript><Superscript>PMNS</Superscript>=(9<Superscript>+1</Superscript><Subscript>-2</Subscript>)°

The complementarity between the quark and lepton mixing matrices is shown to provide a robust prediction for the neutrino mixing angle θ₁₃ ^PMNS. We obtain this prediction by first showing that the matrix V_M, product of the CKM and PMNS mixing matrices, may have a zero (1,3) entry, which is favored by the experimental data. Hence models with bimaximal or tribimaximal forms of the correlation matrix V_M are quite possible. Any theoretical model with a vanishing (1,3) entry of V_M, which is in agreement with the quark data, and the solar and the atmospheric mixing angle leads to θ₁₃ ^PMNS=(9⁺¹ _-2)^°. This value is consistent with the present 90% CL experimental upper limit. PACS 14.60.Pq; 14.60.Lm; 96.40.Tv     

Quark potential in a quark–meson plasma

We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly coupled in the temperature region 1≤T/T _c≤3, with T _c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase transition point.     

The Nambu,Jona-Lasinio model and low energy effective meson Lagrangians

Using standard techniques, the Nambu-Jona-Lasinio Lagrangian with its chirally invariant four-fermion couplings is transformed into a bosonized form which includes scalar, pseudo-scalar, vector and axial-vector fields. Then, after eliminating the scalar and axialvector fields in an appropriate way, we obtain the Lagrangian given by Bando et al. based on the “hidden” local symmetry approach, except that in the present approach the free parametera of their model is now uniquely given by a=(1? M _V ² /M _A ² )^?1 in terms of the vector and axial-vector meson massesM _V andM _A. The value ofa=2, which led them to remarkable phenomenological successes is therefore directly connected with the Weinberg mass relation M_A=√2M_V in this model. The formal equivalence between the hidden symmetry approach and the massive Yang-Mills scheme is clearly demonstrated in the present approach, which derives an effective meson theory starting from a Lagrangian at the underlying quark level.     

Production of V0 pairs in the hyperon experiment WA89

We present a comprehensive study of the inclusive production of V⁰V⁰ pairs (V⁰=Λ, Λ̄ or K_S ) by Σ^- and π^- of 340 GeV/c momentum and neutrons of 260 GeV/c mean momentum in copper and carbon targets. In particular, the dependence of the x_F spectra on the combination of beam-particle and produced V⁰V⁰ pair is investigated and compared to predictions obtained from PYTHIA and QSGM calculations. The data and these predictions differ in many details, the agreement can at best be termed as qualitative. A signal from decays of the tensor meson f’₂(1525) was observed in the K_S K_S mass distribution and inclusive production cross sections were measured. No signal was found from the double-strange H-dibaryon decaying to ΛΛ.     

Is X(3872) really a molecular state?

After taking into account both the pion and sigma meson exchange potential, we have performed a dynamical calculation of the D⁰D̄^*0 system. The σ meson exchange potential is repulsive from heavy quark symmetry and numerically important for a loosely bound system. Our analysis disfavors the interpretation of X(3872) as a loosely bound molecular state if we use the experimental D^*Dπ coupling constant g=0.59 and a reasonable cutoff around 1 GeV, which is the typical hadronic scale. Bound state solutions with negative eigenvalues for the DD̄^* system exist only with either a very large coupling constant (twice the experimental value) or a large cutoff (Λ ∼ 6 GeV or β ∼ 6 GeV²). In contrast, there probably exists a loosely bound S-wave BB̄^* molecular state. Once produced, such a molecular state would be rather stable, since its dominant decay mode is the radiative decay through B^*→Bγ. Experimental search of these states will be very interesting. PACS  12.39.Pn; 12.40.Yx; 13.75.Lb