Tensor Form Factors Research Articles

$$B_s\rightarrow D_s\ell \nu _\ell $$ B s → D s ℓ ν ℓ near zero recoil in and beyond the Standard Model

We compute the normalization of the form factor entering the Bs --> Ds l nu decay amplitude by using numerical simulations of QCD on the lattice. From our study with Nf=2 dynamical light quarks, and by employing the maximally twisted Wilson quark action, we obtain in the continuum limit G(1) = 1.052(46). We also compute the scalar and tensor form factors in the region near zero recoil and find f0(t0)/f+(t0)=0.77(2), fT(t0,mb)/f+(t0)=1.08(7), for t0=11.5 GeV^2. These latter results are useful for searching the effects of physics beyond the Standard Model in Bs --> Ds l nu decays. Our results for the similar form factors relevant to the non-strange case indicate that the method employed here can be used to achieve the precision determination of the B --> D l nu decay amplitude as well.

Energy–momentum tensor form factors of the nucleon within a π–ρ–ω soliton model

We investigate the energy–momentum tensor form factors (FFs) of the nucleon within the framework of a chiral soliton model, including the ρ and ω vector mesons. We examine the role of each meson degrees of freedom in these FFs. It is explicitly shown that the pion provides strong attraction whereas the ρ and ω yield repulsion in such a way that the soliton becomes stabilized. The results are discussed in comparison with those of other models.

In-medium modified energy-momentum tensor form factors

In this talk, we report a recent investigation on the energy-momentum tensor form factors of the nucleon in nuclear medium, based on the framework of the in-medium modified chiral soliton model. The model was constructed by taking into account the influence of the surrounding environment to the mesonic sector (π-, ρ- and ω-meson properties). We briefly discuss the results of the energy-momentum tensor form factors.

Radiative D(D s ) decays in the covariant light front approach

In the covariant light-front quark model, we investigate the D→V,A,T tensor form factors induced by c→u transition, which can contribute to radiative D(D s ) decays. The short distance contribution is much smaller than the experimental data, thus radiative D(D s ) decays is dominated by nonperturbative effect. We also include the weak annihilation contributions and the long distance contributions to D→Vγ. Our results for D→(K ∗0,ϕ)γ decays can approach the data and the other predictions should be checked with the BEPCII experiment.

Energy-Momentum Tensor Form Factors of the Nucleon in Nuclear Matter in the Chiral Soliton Model

In the present talk, we report a recent investigation on the nucleon form factors of the energy-momentum tensor in nuclear matter, based on the in-medium modified chiral soliton model. The results in free space are in agreement with those from other approaches. We have discussed the changes of the energy-momentum tensor form factors in nuclear matter and the modification of the soliton structure due to the surrounding nuclear environment.

Energy–momentum tensor form factors of the nucleon in nuclear matter

The nucleon form factors of the energy–momentum tensor are studied in nuclear medium in the framework of the in-medium modified Skyrme model. We obtain a negative D-term, in agreement with results from other approaches, and find that medium effects make the value of d1 more negative.

Anomalous Wtb coupling and forward–backward asymmetry of top quark production at the Tevatron

An influence of the anomalous Wtb coupling on forward–backward asymmetry in top quark pair production at the Tevatron is investigated taking into account decays of the top quarks to 6 fermion final states containing one charged lepton. To this end the most general effective Lagrangian of the Wtb interaction containing terms of dimension up to five is implemented into carlomat, a general purpose Monte Carlo program, which allows to compute automatically all necessary cross sections in the presence of anomalous vector and tensor form factors. A sample of results which illustrate little effect of the left- and right-handed tensor form factors on the tt¯ invariant mass dependent forward–backward asymmetry and the charge-signed rapidity distribution of the lepton originating from the W boson from top quark decay is shown.

Generalized form factors and spin structures of the kaon

We investigate the spin structure of the kaon, based on the nonlocal chiral quark model from the instanton vacuum. We first revisit the electromagnetic form factors of the pion and kaon, improving the results for the kaon. We evaluate the generalized tensor form factors of the kaon in order to determine the probability density of transversely polarized quarks inside the kaon. We consider the effects of flavor SU(3) symmetry breaking, so that the probability density of the up and strange quarks are examined in detail. It is found that the strange quark behaves differently inside the kaon in comparison with the up quark.

Spin structures of the pion and nucleon

We present recent studies on the transverse spin densities of the pion and nucleon within the framework of the chiral quark-(soliton) model, based on the calculation of the electromagnetic and tensor form factors of the pion and the nucleon. The results for the transverse spin densities of the quark inside a pion are in good agreement with the recent lattice data, while those of the nucleon show similar features to the lattice results. We also present the first results of the transverse spin densities of the strange quark inside a nucleon.

Nucleon tensor form factors induced by isovector and isoscalar currents in QCD

Using the most general form of the nucleon interpolating current, we calculate the tensor form factors of the nucleon within light cone QCD sum rules. A comparison of our results on tensor form factors with those of the chiral--soliton model and lattice QCD is given.

Matrix elements of the electromagnetic operator between kaon and pion states

We compute the matrix elements of the electromagnetic (EM) operator (\bar{s} F{\mu \nu} \sigma{\mu \nu} d) between kaon and pion states, using lattice QCD with maximally twisted-mass fermions and two flavors of dynamical quarks (Nf = 2). The operator is renormalized non-perturbatively in the RI'/MOM scheme and our simulations cover pion masses as light as 270 MeV and three values of the lattice spacing from ~ 0.07 up to ~ 0.1 fm. At the physical point our result for the corresponding tensor form factor at zero-momentum transfer is fT{K\pi}(0) = 0.417 (14_stat) (5_syst), where the systematic error does not include the effect of quenching the strange and charm quarks. Our result differs significantly from the old quenched result fT{K\pi}(0) = 0.78 (6) obtained by the SPQcdR Collaboration with pion masses above 500 MeV. We investigate the source of this difference and conclude that it is mainly related to the chiral extrapolation. We also study the tensor charge of the pion and obtain the value fT{\pi\pi}(0) = 0.195 (8_stat) (6_syst) in good agreement with, but more accurate than the result fT{\pi\pi}(0) = 0.216 (34) obtained by the QCDSF Collaboration using higher pion masses.

Tensor form factors of nucleon in QCD

We extract the isovector tensor nucleon form factors, which play an important role in understanding the transverse spin structure of the nucleon when related to the quark helicity-flip generalized parton distributions via their first moments. We employ the light-cone QCD sum rules to leading order in QCD and include distribution amplitudes up to twist 6 in order to calculate the three tensor form factors HT, ET and H˜T. Our results agree well with those from other approaches in the low and high momentum-transfer regions.

Spin structure of the pion from the instanton vacuum

We investigate the spin structure of the pion within the framework of the nonlocal chiral quark model from the instanton vacuum. We first evaluate the tensor form factors of the pion for the first and second moment (n=1,2) and compare it with the lattice data. Combining the tensor form factor of the pion with the electromagnetic one, we determine the impact-parameter dependent probability density of transversely polarized quarks inside the pion. It turns out that the present numerical results for the tensor form factor as well as those for the probability density are in good agreement with the lattice data. We also discuss the distortion of the spatial distribution of the quarks in the transverse plane inside the pion.

Tensor form factors of [formula omitted] transition from QCD light cone sum rules

The tensor form factors of B into p-wave axial vector meson transition are calculated within light cone QCD sum rules method. The parametrizations of the tensor form factors based on the series expansion are presented.

Light-front zero-mode contribution to the tensor form factors for the exclusive rare [formula omitted] decays

We study the light-front zero-mode contribution to the tensor form factors Ti (i=1,2,3) for the exclusive rare P→Vℓ+ℓ− decays using a covariant fermion field theory model in (3+1) dimensions. While the zero-mode contribution in principle depends on the form of the vector meson vertex Γμ=γμ−(2k−PV)μ/D, the three tensor form factors Ti(i=1,2,3) are found to be free from the zero mode if the denominator D contains the term proportional to the light-front energy or the longitudinal momentum fraction factor (1/x)n of the struck quark with the power n>0. Since the denominator D used in the light-front quark model (LFQM) has the power n=1/2, the three tensor form factors Ti (i=1,2,3) can be computed in LFQM safely without involving any complicate zero-mode contribution. The lack of zero-mode contribution benefits the phenomenology with LFQM.

Erratum:B→V,A,Ttensor form factors in the covariant light-front approach: Implications on radiativeBdecays [Phys. Rev. D81, 114006 (2010)

We reanalyze the $B\to M$ tensor form factors in a covariant light-front quark model, where $M$ represents a vector meson $V$, an axial-vector meson $A$, or a tensor meson $T$. The treatment of masses and mixing angles in the $K_{1A,1B}$ systems is improved, where $K_{1A}$ and $K_{1B}$ are the $^3P_1$ and $^1P_1$ states of the axial-vector meson $K_1$, respectively. Rates of $B\to M\gamma$ decays are then calculated using the QCD factorization approach. The updated $B\to K^*\gamma$, $B\to K_1(1270)\gamma$, $K_1(1400)\gamma$ and $K_2\gamma$ rates agree with the data. The $K_1(1270)$--$K_1(1400)$ mixing angle is found to be about $51^\circ$. The sign of the mixing angle is fixed by the observed relative strength of $B\to K_1(1270)\gamma$ and $K_1(1400)\gamma$. The formalism is then applied to $B_s\to M$ tensor form factors. We find that the calculated $B_s\to \phi\gamma$ rate is consistent with experiment, though in the lower end of the data. The branching fractions of $B_s\to f_1(1420)\gamma$ and $f'_2(1525)\gamma$ are predicted to be of order $10^{-5}$ and it will be interesting to search for these modes. Rates on $B_s\to f_1(1285)\gamma$, $h_1(1380)\gamma$, $h_1(1170)\gamma$, $f_2(1270)\gamma$ decays are also predicted.

Anomalous tensor magnetic moments and form factors of the proton in the self-consistent chiral quark-soliton model

We investigate the form factors of the chiral-odd nucleon matrix element of the tensor current. In particular, we aim at the anomalous tensor magnetic form factors of the nucleon within the framework of the SU(3) and SU(2) chiral quark-soliton model. We consider $1/N_c$ rotational corrections and linear effects of SU(3) symmetry breaking with the symmetry-conserving quantization employed. We first obtain the results of the anomalous tensor magnetic moments for the up and down quarks: $\kappa_{T}^{u}=3.56$ and $\kappa_{T}^{d}=1.83$, respectively. The strange anomalous tensor magnetic moment is yielded to be $\kappa_{T}^{s}=0.2\sim -0.2$, that is compatible with zero. We also calculate the corresponding form factors $\kappa_{T}^{q}(Q^{2})$ up to a momentum transfer $Q^{2}\leq 1\,\mathrm{GeV}^{2}$ at a renormalization scale of $0.36\,\mathrm{GeV}^{2}$.

Tensor charges and form factors of SU(3) baryons in the self-consistent SU(3) chiral quark-soliton model

We investigate the tensor form factors of the baryon octet within the framework of the chiral quark-soliton model, emphasizing those of the nucleon, taking linear 1/N_c rotational as well as linear m_s corrections into account, and applying the symmetry-conserving quantization. We explicitly calculate the tensor form factors H_{T}^{q}(Q^{2}) corresponding to the generalized parton distributions H_{T}(x,\xi,t). The tensor form factors are obtained for the momentum transfer up to Q^{2}\leq1\,\mathrm{GeV}^{2} and at a renormalization scale of 0.36\,\mathrm{GeV}^{2}. We find for the tensor charges \delta u=1.08, \delta d=-0.32, \delta s=-0.01 and discuss their physical consequences, comparing them with those from other models. Results for tensor charges for the baryon octet are also given.

B→V,A,Ttensor form factors in the covariant light-front approach: Implications on radiativeBdecays

We reanalyze the $B\ensuremath{\rightarrow}M$ tensor form factors in a covariant light-front quark model, where $M$ represents a vector meson $V$, an axial-vector meson $A$, or a tensor meson $T$. The treatment of masses and mixing angles in the ${K}_{1A,1B}$ systems is improved, where ${K}_{1A}$ and ${K}_{1B}$ are the $^{3}P_{1}$ and $^{1}P_{1}$ states of the axial-vector meson ${K}_{1}$, respectively. Rates of $B\ensuremath{\rightarrow}M\ensuremath{\gamma}$ decays are then calculated using the QCD factorization approach. The updated $B\ensuremath{\rightarrow}{K}^{*}\ensuremath{\gamma}$, $B\ensuremath{\rightarrow}{K}_{1}(1270)\ensuremath{\gamma}$, ${K}_{1}(1400)\ensuremath{\gamma}$, and ${K}_{2}\ensuremath{\gamma}$ rates agree with the data. The ${K}_{1}(1270)--{K}_{1}(1400)$ mixing angle is found to be about 51\ifmmode^\circ\else\textdegree\fi{}. The sign of the mixing angle is fixed by the observed relative strength of $B\ensuremath{\rightarrow}{K}_{1}(1270)\ensuremath{\gamma}$ and ${K}_{1}(1400)\ensuremath{\gamma}$. The formalism is then applied to ${B}_{s}\ensuremath{\rightarrow}M$ tensor form factors. We find that the calculated ${B}_{s}\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\gamma}$ rate is consistent with experiment, though in the lower end of the data. The branching fractions of ${B}_{s}\ensuremath{\rightarrow}{f}_{1}(1420)\ensuremath{\gamma}$ and ${f}_{2}^{\ensuremath{'}}(1525)\ensuremath{\gamma}$ are predicted to be of order ${10}^{\ensuremath{-}5}$ and it will be interesting to search for these modes. Rates on ${B}_{s}\ensuremath{\rightarrow}{f}_{1}(1285)\ensuremath{\gamma}$, ${h}_{1}(1380)\ensuremath{\gamma}$, ${h}_{1}(1170)\ensuremath{\gamma}$, ${f}_{2}(1270)\ensuremath{\gamma}$ decays are also predicted.

Erratum: Covariant light-front approach forB→K*γ,K1γ,K2γdecays [Phys. Rev. D69, 094007 (2004)

Exclusive radiative B decays, B to K* gamma, K_1(1270) gamma, K_1(1400) gamma and K*_2(1430) gamma, are studied in the framework of a covariant light-front quark model. The tensor form factor T_1(q^2) at q^2=0, which is relevant to the decay B to K* gamma, is found to be 0.24, substantially smaller than what expected from the conventional light-front model or light-cone sum rules. Taking into account the sizable next-to-leading order (NLO) corrections, the calculated branching ratio of B to K* gamma agrees with experiment, while most of the existing models predict too large B to K* gamma compared to the data. The relative strength of B to K_1(1270) gamma and B to K_1(1400) gamma rates is very sensitive to the sign of the K_1(1270)-K_1(1400) mixing angle. Contrary to the other models in which K_1(1270) gamma and K_1(1400) gamma rates are predicted to be comparable, it is found that one of them is strongly suppressed owing to a large cancellation between two different form factor terms. The calculated branching ratio of B to K*_2 gamma is in a good agreement with experiment and this may imply the smallness of NLO corrections to this radiative decay mode.