Isospin Violation Research Articles

DirectCPviolation forB¯s0→K0π+π−decay in QCD factorization

In the framework of QCD factorization, based on the first order of isospin violation, we study direct CP violation in the decay of $\bar{B}_{s}^{0} \to K^{0}\rho^{0}(\omega)\to K^{0}\pi^{+}\pi^{-}$ including the effect of $\rho-\omega$ mixing. We find that the CP violating asymmetry is large via $\rho-\omega$ mixing mechanism when the invariant mass of the $\pi^{+}\pi^{-}$ pair is in the vicinity of the $\omega$ resonance. For the decay of $\bar{B}_{s}^{0} \to K^{0}\rho^{0}(\omega)\to K^{0}\pi^{+}\pi^{-}$, the maximum CP violating asymmetries can reach about 46%. We also discuss the possibility to observe the predicted CP violating asymmetries at the LHC.

Isospin violation, light quark masses, and all that

Isospin violation is driven through the light quark mass difference and electromagnetic effects. I review recent progress in extracting the light quark mass difference and tests of the chiral dynamics of Quantum Chromodynamics in various reactions involving light as well as heavy quarks.

Isospin violating mechanisms in quarkonium hadronic decays

We analyze the ϕ meson production in e+e− → ωπ0 as a probe for studying the isospin violation mechanisms. By clarifying the dynamic sources causing the isospin violation, we succeed in quantifying those mechanisms with the help of the recent KLOE data. Hence, the ϕ → ωπ0 branching ratio is extracted. We find that apart from the electromagnetic (EM) transitions, the strong transition via intermediate kaon loops plays an important role in understanding the cross section and its lineshape.

Custodial isospin violation in the Lee-Wick standard model

We analyze the tension between naturalness and isospin violation in the Lee-Wick Standard Model (LW SM), by computing tree-level and fermionic one-loop contributions to the post-LEP electroweak parameters and the Zbb coupling. The model is most natural when the LW partners of the gauge bosons and fermions are light, but small partner masses can lead to large isospin violation. The post-LEP parameters yield a simple picture in the LW SM: the gauge sector contributes to Y and W only, with leading contributions arising at tree-level, while the fermion sector contributes to S-hat and T-hat only, with leading corrections arising at one loop. Hence, W and Y constrain the masses of the LW gauge bosons to satisfy M1, M2 > 2.4 TeV at 95% CL. Likewise, experimental limits on T-hat reveal that the masses of the LW fermions must satisfy Mq, Mt > 1.6 TeV at 95% CL if the Higgs mass is light and tend to exclude the LW SM for any LW fermion masses if the Higgs mass is heavy. Contributions from the top-quark sector to the Zbb coupling can be even more stringent, placing a lower bound of 4 TeV on the LW fermion masses at 95% CL.

Isospin violation in low-energy pion–nucleon scattering revisited

We calculate isospin breaking in pion–nucleon scattering in the threshold region in the framework of covariant baryon chiral perturbation theory. All effects due to quark mass differences as well as real and virtual photons are consistently included. As an application, we discuss the energy dependence of the triangle relation that connects elastic scattering on the proton π ± p → π ± p with the charge exchange reaction π − p → π 0 n .

Reanalysis of pion–pion phase shifts from [formula omitted] decays

We re-investigate the impact of isospin violation for extracting the s-wave ππ scattering phase shift difference δ0(MK)−δ2(MK) from K→ππ decays. Compared to our previous analysis in 2003, more precise experimental data and improved knowledge of low-energy constants are used. In addition, we employ a more robust data-driven method to obtain the phase shift difference δ0(MK)−δ2(MK)=(52.5±0.8exp±2.8theor)°.

Measurement of the isospin-filtering dd $ \rightarrow$ 4HeK+K- reaction at Q = 39 MeV

The total cross-section for the dd $ \rightarrow$ 4HeK + K - reaction has been measured at a beam momentum of 3.7GeV/c, corresponding to an excess energy of 39MeV, which is the maximum possible at the Cooler Synchrotron COSY-Julich. A deuterium cluster-jet target and the ANKE forward magnetic spectrometer, placed inside the storage ring, have been employed in this investigation. We find a total cross-section of $ \sigma_{{{\rm tot}}}^{}$ < 14 pb, which brings into question the viability of investigating the dd $ \rightarrow$ 4Hea 0(980) reaction as a means of studying isospin violation.

Study of isospin violating ϕ excitation in e+e− → ωπ0

We study the reaction e+e− → ωπ0 in the vicinity of the ϕ mass region. The isospin-violating ϕ excitation is accounted for by two major mechanisms. One is electromagnetic transition and the other is strong isospin violations. For the latter, we consider contributions from the intermediate hadronic meson loops and ϕ–ρ0 mixing as the major mechanisms via the t- and s-channel transitions, respectively. By fitting the recent KLOE data, we succeed in constraining the model parameters and extracting the ϕ → ωπ0 branching ratio. It shows that the branching ratio is sensitive to the ϕ excitation line shape and background contributions. Some crucial insights into the correlation between isospin violation and Okubo–Zweig–Iizuka rule evading transitions are also learned.

Dynamics behind the quark mass hierarchy

We introduce a new class of models describing the quark mass hierarchy. In this class, the dynamics primarily responsible for electroweak symmetry breaking (EWSB) leads to the mass spectrum of quarks with no (or weak) isospin violation. Moreover, the values of these masses are of the order of the observed masses of the down-type quarks. Then, strong (although subcritical) horizontal diagonal interactions for the t quark plus horizontal flavor-changing neutral interactions between different families lead (with no fine-tuning) to a realistic quark mass spectrum. In this scenario, many composite Higgs bosons occur. A concrete model with the dynamical EWSB with the fourth family is described in detail.

Isospin Mixing in Nuclei within the Nuclear Density Functional Theory

We present the self-consistent, nonperturbative analysis of isospin mixing using the nuclear density functional approach and the rediagonalization of the Coulomb interaction in the good-isospin basis. The unphysical isospin violation on the mean-field level, caused by the neutron excess, is eliminated by the proposed method. We find a significant dependence of the magnitude of isospin breaking on the parametrization of the nuclear interaction. A rough correlation has been found between the isospin-mixing parameter and the difference of proton and neutron rms radii.

Comprehensive calculations on the OZI-forbidden nonleptonic decays of orthoquarkonia [formula omitted

In this work, we calculate the decay rates of the OZI-forbidden processes J / ψ ( ϒ ) → π π , ρ π at the order of the leading-twist distribution amplitude. The process of J / ψ ( ϒ ) → π + π − violates isospin conservation and the amplitude is explicitly proportional to the isospin violation factor m u − m d , our numerical results on their decay rates are consistent with the data. The process J / ψ ( ϒ ) → ρ π violates the hadronic helicity conservation and should be suppressed, as indicated in literature, its decay rate can only be proportional to m q 2 at the order of leading twist. Our theoretical evaluation confirms this statement that the theoretical evaluation on Γ ( J / ψ ( ϒ ) → ρ π ) is almost one order smaller than the data unless the model parameters take certain extreme values. It may imply that the sizable branching ratio of J / ψ ( ϒ ) → ρ π should be explained by either higher twist contributions or other mechanisms.

Dynamical parton distributions of the nucleon

A new generation of (unpolarized) dynamical parton distribution functions of the nucleon is determined. After introducing basic elements of perturbative QCD, the dynamical model is discussed and compared with the approach to parton distributions used by most other groups ("standard"). Parton distributions sets (with uncertainties) at different orders (LO, NLO, NNLO), using different factorization schemes (\overline{MS}, DIS) and different treatments of heavy quark masses (FFNS, VFNS) are extracted and compared. The astrophysical implications of the dynamical predictions are outlined before focusing on collider phenomenology. There, the relevance and perturbative stability of the longitudinal structure function of the nucleon is studied, and the role of heavy quark flavors in high-energy colliders is analyzed. In addition, it is shown how isospin violations in the nucleon help to explain the so-called "NuTeV anomaly".

Isospin-breaking nuclear forces with delta degrees of freedom

I discuss the leading contributions to the isospin-violating (IV) two- and three-nucleon forces in effective field theory with explicit delta degrees of freedom.

Reanalysis of the (0+, 1+) States Bs0 and Bs1 with QCD Sum Rules

We calculate the masses and decay constants of the P-wave strange-bottomed mesons Bso and Bsi with the QCD sum rules, and observe that the central values of the masses Bs0 and Bs1 are smaller than the corresponding BK and B*K thresholds respectively, the strong decays Bso→ BK and Bs1 → B*K are kinematically forbidden. They can decay through the isospin violation processes Bs0 → Bsη → BaΠ° and Bs1 → Bs*η → Bins*π0. The bottomed mesons Bso and Bs1, just like their charmed cousins Dso(2317) and Ds1 (2460), may be very narrow.

Nonperturbative charming penguin contributions to isospin asymmetries in radiativeBdecays

Recent experimental data on the radiative decays B{yields}V{gamma}, where V is a light vector meson, find small isospin violation in B{yields}K*{gamma} while isospin asymmetries in B{yields}{rho}{gamma} are of order 20%, with large uncertainties. Using soft-collinear effective theory, we calculate isospin asymmetries in these radiative B decays up to O(1/m{sub b}), also including O(v{alpha}{sub s}) contributions from nonperturbative charming penguins (NPCP). In the absence of NPCP contributions, the theoretical predictions for the asymmetries are a few percent or less. Including the NPCP can significantly increase the isospin asymmetries for both B{yields}V{gamma} modes. We also consider the effect of the NPCP on the branching ratio and CP asymmetries in B{sup {+-}}{yields}V{sup {+-}}{gamma}.

Estimate of the branching fractionτ−→ηπ−ντ, thea0−(980), and nonstandard weak interactions

We consider the ``second-class current'' decay ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\eta}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ from several points of view. We first focus on the decay rate as expected within standard weak interaction and QCD due to isospin violation. The decay contributions divide into $P$- and $S$-wave parts. The former can be reliably estimated using the $\ensuremath{\rho}\ensuremath{\eta}\ensuremath{\pi}$ coupling inferred from the rates and Dalitz-plot distributions of $\ensuremath{\eta}\ensuremath{\rightarrow}3\ensuremath{\pi}$ decays. The somewhat larger $S$-wave part, which was previously computed using chiral perturbation theory, is estimated from a simple $\overline{q}q$ model. Both estimates of the $S$-wave part depend on whether the ${a}_{0}(980)$ scalar particle is a $\overline{q}q$ or some other (4-quark) state. Finally, we discuss genuinely new, non-$V\ensuremath{-}A$ scalar weak interactions. The ${\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\eta}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ decay provides information on this question, which nicely complements that from precision $\ensuremath{\beta}$ decay experiments. In summary, we discuss the possible implications of putative values of the branching fraction $\mathcal{B}({\ensuremath{\tau}}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\eta}{\ensuremath{\nu}}_{\ensuremath{\tau}})$. In the case of larger values, in particular, of the $S$-wave part, not only will detection of the decay be more likely and more reliable, its implications will be more far-reaching and interesting.

Subleading contributions to the width of the [formula omitted

We construct the effective chiral Lagrangian involving the D-mesons and Goldstone bosons at next-to-leading order taking into account strong as well as electromagnetic interactions. This allows us to disentangle—to leading order in isospin violation—the electromagnetic and the strong contribution to the D-meson mass differences. In addition, we also apply the interaction to the decay Ds0∗(2317)→Dsπ0 under the assumption that the Ds0∗(2317) is a hadronic molecule. We find (180±110) keV for the decay width Γ(Ds0∗(2317)→Dsπ0)—consistent with currently existing experimental constraints as well as previous theoretical investigations. The result provides further evidence that this decay width can serve as a criterion for testing the nature of the Ds0∗(2317).

Strong decays Bs0→Bsπ and Bs1→B* sπ with light-cone QCD sum rules

In this article, we calculate the strong coupling constants gBs0Bsη and gBs1B*sη with the light-cone QCD sum rules. Then we take into account the small η–π0 transition matrix according to Dashen’s theorem, and we obtain the small decay widths for the isospin violation processes Bs0→Bsη→Bsπ0 and Bs1→Bs *η→Bs *π0. We can search the strange-bottomed (0+,1+) mesons Bs0 and Bs1 in the invariant Bsπ0 and B* sπ0 mass distributions, respectively.

Triquark structure and isospin symmetry breaking in exoticDsmesons

The color antitriplet triquark $q\overline{q}\overline{q}$ is considered as a compact component in the tetraquark structure $cq\overline{q}\overline{q}$ of exotic ${D}_{s}$ mesons. We discuss the mass spectrum and the flavor mixing of the triquarks by using the instanton induced interaction and the one-gluon exchange potentials. As a characteristic property of the triquark, we investigate the isospin violation. It is shown that the flavor $\overline{\mathbf{3}}$ (isosinglet) and $\mathbf{6}$ (isotriplet) states may be strongly mixed and then are identified with ${D}_{s}(2632)$.

Isospin breaking in the vector current of the nucleon

Extraction of the nucleon's strange form factors from experimental data requires a quantitative understanding of the unavoidable contamination from isospin violation. A number of authors have addressed this issue during the past decade, and their work is reviewed here. The predictions from early models are largely consistent with recent results that rely as much as possible on input from QCD symmetries and related experimental data. The resulting bounds on isospin violation are sufficiently precise to be of value to on-going experimental and theoretical studies of the nucleon's strange form factors.