Longitudinal Polarization Fraction Research Articles

Branching ratios, CP asymmetries and polarizations of Brightarrow psi (2S) V decays

We analyze the non-leptonic decays B/B_srightarrow psi (2S) V with V=(rho , omega , K^{*}, phi ) by employing the perturbative QCD (pQCD) factorization approach. Here the branching ratios, the CP asymmetries and the complete set of polarization observables are investigated systematically. Besides the traditional contributions from the factorizable and non-factorizable diagrams at the leading order, the next-to-leading order (NLO) vertex corrections could also provide considerable contributions. The pQCD predictions for the branching ratios of the B_{(s)}rightarrow psi (2S)K^{*}, psi (2S)phi decays are consistent with the measured values within errors. As for Brightarrow psi (2S) rho , psi (2S) omega decays, the branching ratios can reach the order of 10^{-5} and could be measured in the LHCb and Belle-II experiments. The numerical results show that the direct CP asymmetries of the considered decays are very small. Thus the observation of any large direct CP asymmetry for these decays will be a signal for new physics. The mixing-induced CP asymmetries in the neutral modes are very close to sin 2beta _{(s)}, which suggests that these channels can give a cross-check on the measurement of the Cabbibo–Kobayashi–Maskawa (CKM) angle beta and beta _s. We find that the longitudinal polarization fractions f_0 are suppressed to sim 50% due to the large non-factorizable contributions. The magnitudes and phases of the two transverse amplitudes mathcal {A}_{parallel } and mathcal {A}_{perp } are roughly equal, which is an indication for the approximate light-quark helicity conservation in these decays. The overall polarization observables of Brightarrow psi (2S) K^{*0} and B_srightarrow psi (2S) phi channels are also in good agreement with the experimental measurements as reported by LHCb and BaBar. Other results can also be tested by the LHCb and Belle-II experiments.

Charmless B_{(s)}rightarrow VV decays in factorization-assisted topological-amplitude approach

Within the factorization-assisted topological-amplitude approach, we studied the 33 charmless B_{(s)} rightarrow VV decays, where V stands for a light vector meson. According to the flavor flows, the amplitude of each process can be decomposed into eight different topologies. In contrast to the conventional flavor diagrammatic approach, we further factorize each topological amplitude into decay constant, form factors and unknown universal parameters. By chi ^2 fitting 46 experimental observables, we extracted 10 theoretical parameters with chi ^2 per degree of freedom around 2. Using the fitted parameters, we calculated the branching fractions, polarization fractions, CP asymmetries and relative phases between polarization amplitudes of each decay mode. The decay channels dominated by tree diagram have large branching fractions and large longitudinal polarization fraction. The branching fractions and longitudinal polarization fractions of color-suppressed decays become smaller. Current experimental data of large transverse polarization fractions in the penguin dominant decay channels can be explained by only one transverse amplitude of penguin annihilation diagram. Our predictions of the not yet measured channels can be tested in the ongoing LHCb experiment and the Belle-II experiment in the future.

Revisiting B→K*(→Kπ)νν¯ decays

The rare decay $B\to K^\ast( \to K\pi) \nu\bar{\nu}$ is expected to play an important role in searches for physics beyond the Standard Model at the near future $B$-physics experiments. We investigate resonant and non-resonant backgrounds that arise beyond the narrow-width approximation for the $K^\ast$. Non-resonant $B\to K\pi \nu\bar{\nu}$ decays are analyzed in the region of low hadronic recoil, where $B \to K \pi$ form factors from Heavy-Hadron-Chiral-Perturbation Theory are available. In a Breit-Wigner-type model interference-induced effects in the $K^*$ signal region are found to be sizable, as large as $20\%$ in the branching ratio. Corresponding effects in the longitudinal polarization fraction $F_L$ are smaller, at most around few \%. Effects of the broad scalar states $K_0^\ast$ and $\kappa$ are at the level of percent in the branching fraction in the $K^\ast$ signal region and negligible in $F_L$. Since the backgrounds to $F_L$ are small this observable constitutes a useful probe of form factors calculations, or alternatively, of right-handed currents in the entire $q^2$-region. The forward-backward asymmetry in the $K \pi$-system, $A_{\rm FB \, L}^K$, with normalization to the longitudinal decay rate probes predominantly S,P-wave interference free of short-distance coefficients and can therefore be used to control the resonant and non-resonant backgrounds.

Studying the Fourth Generation Quark Contributions to the Double Charm Decays B ( s ) → D ( s ) ( ∗ ) D s ( ∗ ) $B_{(s)} \to D_{(s)}^{(*)} D_{s}^{(*)}$

Almost all branching ratios and longitudinal polarization fractions of the double charm decays $B_{(s)} \to D_{(s)}^{(*)} D_{s}^{(*)}$ have been measured, and the experimental central value of $f_{L}({B^{0}_{s}}\to D^{*+}_{s}D^{*-}_{s})$ is quite small comparing to its Standard Model prediction. We study the fourth generation quark contributions to the double charm decays $B_{(s)} \to D_{(s)}^{(*)} D_{s}^{(*)}$ . We find that the loop diagrams involving the fourth generation quark t′ have great effects on all branching ratios and CP asymmetries, which are very sensitive to the fourth generation parameter $\lambda ^{s}_{t^{\prime }}$ and $\phi _{t^{\prime }}$ . Nevertheless, the experimental measurements of all branching ratios can not give effective constraints on relevant new physics parameters. In addition, they have no obvious effect on the relevant polarization fractions. These results could be used to search for the fourth heavy quark t′ via its indirect manifestations in loop diagrams.

Shedding light on diphoton resonances

The experimental and theoretical implications of heavy digauge boson resonances that couple to, or are comprised of, new charged and strongly interacting matter are investigated. Observation and measurement of ratios of the resonant digauge boson channels $WW$, $ZZ$, $\gamma \gamma$, $Z \gamma$, and $gg$ in the form of dijets, provide a rather direct -- and for some ratios a rather robust -- probe of the gauge representations of the new matter. For a spin-zero resonance with the quantum numbers of the vacuum, the ratios of resonant $WW$ and $ZZ$ to $\gamma \gamma$ channels, as well as the longitudinal versus transverse polarization fractions in the $WW$ and $ZZ$ channels, provide probes for possible mixing with the Higgs boson, while di-Higgs and ditop resonant channels, $hh$ and $tt$, provide somewhat less sensitivity. We present a survey of possible underlying models for digauge boson resonances by considering various limits for the mass of the new charged and strongly interacting matter fields as well as the confinement scale of new hypergauge interactions under which they may also be charged. In these limits, resonances may be included as elementary weakly coupled spin-zero states or can correspond to hyperglueballs, hyperonia, or pseudoscalar hypermesons. For each of these cases, we make predictions for additional states that could be resonantly or pair produced and observed at the Large Hadron Collider or in future collider experiments. Heavy digauge boson resonances can provide a unified explanation for a number of small discrepancies and excesses in reported data from the Large Hadron Collider.

Study of the Υ(1S) → BcDs∗ decay with pQCD approach

The [Formula: see text] weak decay is studied with the perturbative QCD approach firstly. It is found that (1) main contributions to branching ratio come from the longitudinal and parallel helicity amplitudes, (2) branching ratio, longitudinal and parallel polarization fractions are sensitive to the wave functions of the [Formula: see text] meson, (3) branching ratio for the [Formula: see text] decay can reach up to [Formula: see text], which might be promisingly measured by the future experiments.

Angular analysis and differential branching fraction of the decay: B → K⁎μ+μ−

Measurements of rare B meson decay properties provide an alternative approach to direct searches for physics beyond the Standard Model. These decays, which proceed through flavor-changing neutral currents, can have interferences from new physics through loop diagrams and hence an excellent probe. In particular, the angular distribution of the decay B→K⁎μ+μ− can be measured to estimate the forward-backward asymmetries of the muons, the longitudinal polarization fractions of K⁎ and the differential branching fractions, as a function of the dimuon invariant mass. Results based on data recorded by the CMS experiment at centre-of-mass energy of 7 TeV are presented.

Study of B0→ρ+ρ−decays and implications for the CKM angleϕ2

We present a measurement of the branching fraction and the longitudinal polarization fraction of $B^{0}\rightarrow\rho^+\rho^-$ decays, as well as the time-dependent $CP$ violating parameters in decays into longitudinally polarized $\rho^{+}\rho^{-}$ pairs with Belle's final data set of $772\times 10^6$ $B\bar{B}$ pairs, at the $\Upsilon(4S)$ resonance, collected at the asymmetric-energy $e^+ e^-$ collider KEKB. We obtain ${\cal B}(B^0 \rightarrow \rho^+ \rho^-)=(28.3\pm 1.5\;(\rm stat) \pm 1.5\;(\rm syst))\times 10^{-6}$, $f_L = 0.988\pm 0.012\;(\rm stat ) \pm0.023\;(\rm syst)$, ${\cal A}_{CP} = 0.00\pm0.10\;(\rm stat ) \pm0.06\;(\rm syst)$, ${\cal S}_{CP} = -0.13\pm0.15\;(\rm stat ) \pm0.05\;(\rm syst).$ We perform an isospin analysis to constrain the CKM angle $\phi_2$ and obtain two solutions with \begin{eqnarray} \phi_{2} = (93.7\pm10.6)^{\circ},\nonumber \end{eqnarray} being most compatible with other Standard-Model based fits to the data.

Perturbative corrections to Λ b → Λ form factors from QCD light-cone sum rules

We compute radiative corrections to $\Lambda_b \to \Lambda$ from factors, at next-to-leading logarithmic accuracy, from QCD light-cone sum rules with $\Lambda_b$-baryon distribution amplitudes. Employing the diagrammatic approach factorization of the vacuum-to-$\Lambda_b$-baryon correlation function is justified at leading power in $\Lambda/m_b$, with the aid of the method of regions. Hard functions entering the factorization formulae are identical to the corresponding matching coefficients of heavy-to-light currents from QCD onto soft-collinear effective theory. The universal jet function from integrating out the hard-collinear fluctuations exhibits richer structures compared with the one involved in the factorization expressions of the vacuum-to-$B$-meson correlation function. Based upon the QCD resummation improved sum rules we observe that the perturbative corrections at ${\cal O}(\alpha_s)$ shift the $\Lambda_b \to \Lambda$ from factors at large recoil significantly and the dominant contribution originates from the next-to-leading order jet function instead of the hard coefficient functions. Having at hand the sum rule predictions for the $\Lambda_b \to \Lambda$ from factors we further investigate several decay observables in the electro-weak penguin $\Lambda_b \to \Lambda \, \ell^{+} \ell^{-}$ transitions in the factorization limit (i.e., ignoring the "non-factorizable" hadronic effects which cannot be expressed in terms of the $\Lambda_b \to \Lambda$ from factors), including the invariant mass distribution of the lepton pair, the forward-backward asymmetry in the dilepton system and the longitudinal polarization fraction of the leptonic sector.

Angular analysis of the decay B0 → K⁎0μ+μ− from pp collisions at [formula omitted

The angular distributions and the differential branching fraction of the decay B0→K⁎(892)0μ+μ− are studied using data corresponding to an integrated luminosity of 20.5 fb−1 collected with the CMS detector at the LHC in pp collisions at s=8 TeV. From 1430 signal decays, the forward–backward asymmetry of the muons, the K⁎(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the dimuon invariant mass squared. The measurements are among the most precise to date and are in good agreement with standard model predictions.

Study ofD**production and light hadronic states in theB¯0→D*+ωπ−decay

We report on the first observations of $\bar{B}^0 \to D_1(2430)^0 \omega$, $\bar{B}^0 \to D_1(2420)^0 \omega$ and $\bar{B}^0 \to D^*_2(2460)^0 \omega$ decays. The $\bar{B}^0 \to D^{*+} \rho(1450)^-$ decay is also observed. The branching fraction measurements are based on $(771.6 \pm 10.6)\times 10^6$ $B\bar{B}$ events collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The fractions of longitudinal polarization of the $D^{**}$ states as well as partial wave fractions of the $D_1(2430)^0$ are obtained. We also set a $90\%$ confidence level upper limit for the product of branching fractions of $\mathcal{B}(\bar{B}^0 \to D^{*+} b_1(1235)^-) \times \mathcal{B}(b_1(1235)^- \to \omega \pi^-)$. The measurements show evidence of nontrivial final-state interaction phases for the $\rho$-like amplitudes.

Measurement of CP asymmetries and polarisation fractions in B s 0 → K ∗ 0 K ¯ ∗ 0 $$ {B}_s^0\to {K}^{\ast 0}{\overline{K}}^{\ast 0} $$ decays

An angular analysis of the decay $B_s^0 \rightarrow K^{*0}\bar{K}{}^{*0}$ is performed using $pp$ collisions corresponding to an integrated luminosity of $1.0$ ${fb}^{-1}$ collected by the LHCb experiment at a centre-of-mass energy $\sqrt{s} = 7$ TeV. A combined angular and mass analysis separates six helicity amplitudes and allows the measurement of the longitudinal polarisation fraction $f_L = 0.201 \pm 0.057 {(stat.)} \pm 0.040{(syst.)}$ for the $B_s^0 \rightarrow K^*(892)^0 \bar{K}{}^*(892)^0$ decay. A large scalar contribution from the $K^{*}_{0}(1430)$ and $K^{*}_{0}(800)$ resonances is found, allowing the determination of additional $CP$ asymmetries. Triple product and direct $CP$ asymmetries are determined to be compatible with the Standard Model expectations. The branching fraction $\mathcal{B}(B_s^0 \rightarrow K^*(892)^0 \bar{K}{}^*(892)^0)$ is measured to be $(10.8 \pm 2.1 {\ \rm (stat.)} \pm 1.4 {\ \rm (syst.)} \pm 0.6 \ (f_d/f_s) ) \times 10^{-6}$.

Study ofB0→ρ0ρ0decays, implications for the CKM angleϕ2and search for otherB0decay modes with a four-pion final state

We present a study of the branching fraction of the decay B^0->rho0rho0 and the fraction of longitudinally polarized rho0 mesons in this decay. The results are obtained from the final data sample containing 772 million BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find 166 +- 59 B^0 -> rho0 rho0 events (including systematic uncertainties), corresponding to a branching fraction of B(B^0->rho0rho0) = (1.02 +- 0.30 (stat) +- 0.15 (syst)) x 10^{-6} with a significance of 3.4 standard deviations and a longitudinal polarization fraction fL = 0.21^{+0.18}_{-0.22} (stat) +- 0.15 (syst). We use the longitudinal polarization fraction to determine the Cabibbo-Kobayashi-Maskawa matrix angle phi_2 = (84.9 +- 13.5) degrees through an isospin analysis in the B->rhorho system. We furthermore find 149 +- 49 B^0->f0rho0 events, corresponding to B(B^0->f0rho0) x B(f0->pi+pi-) = (0.78 +- 0.22 (stat) +- 0.11 (syst)) x 10^{-6}, with a significance of 3.1 standard deviations. We find no other significant contribution with the same final state, and set upper limits at 90% confidence level on the (product) branching fractions, B(B^0->pi+pi-pi+pi-)<11.2 x 10^{-6}, B(B^0->rho0pi+pi-)<12.0 x 10^{-6}, B(B^0->f0pi+pi-) x B(f0->pi+pi-) <3.0 x 10^{-6} and B(B^0->f0f0) x B(f0->pi+pi-)^{2} < 0.2 x 10^{-6}.

Angular analysis and branching fraction measurement of the decay [formula omitted

The angular distributions and the differential branching fraction of the decay B0→K⁎(892)0μ+μ− are studied using a data sample corresponding to an integrated luminosity of 5.2 fb−1 collected with the CMS detector at the LHC in pp collisions at s=7 TeV. From more than 400 signal decays, the forward–backward asymmetry of the muons, the K⁎(892)0 longitudinal polarization fraction, and the differential branching fraction are determined as a function of the square of the dimuon invariant mass. The measurements are in good agreement with standard model predictions.

Angular analysis ofB0→ϕK*decays and search forCPviolation at Belle

We report the measurements of branching fractions and CP violation asymmetries in $B^0 \to \phi K^{*}$ decays obtained in an angular analysis using the full data sample of $772 \times 10^6 B\bar{B}$ pairs collected at the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We perform a partial wave analysis to distinguish among scalar [$B^0 \to \phi(K\pi)^{*}_{0}$], vector [$B^0 \to \phi K^{*}(892)^{0}$] and tensor [$B^0 \to \phi K^{*}_{2}(1430)^{0}$] components, and determine the corresponding branching fractions to be $\mathcal{B}[B^0 \to \phi(K\pi)^{*}_{0}] = (4.3 \pm 0.4 \pm 0.4) \times 10^{-6}$, $\mathcal{B}[B^0 \to \phi K^{*}(892)^{0}] = (10.4 \pm 0.5 \pm 0.6) \times 10^{-6}$ and $\mathcal{B}[B^0 \to \phi K^{*}_{2}(1430)^{0}] = (5.5 ^{+0.9}_{-0.7} \pm 1.0) \times 10^{-6}$. We also measure the longitudinal polarization fraction $f_L$ in $B^0 \to \phi K^{*}(892)^{0}$ and $B^0 \to \phi K^{*}_{2}(1430)^{0}$ decays to be $0.499 \pm 0.030 \pm 0.018$ and $0.918 ^{+0.029}_{-0.060} \pm 0.012$, respectively. The first quoted uncertainties are statistical and the second are systematic. In total, we measure 26 parameters related to branching fractions, polarization and CP violation in the $B^0 \to \phi K^{*}$ system. No evidence for CP violation is found.

CharmlessBu,d,s→VTdecays in perturbative QCD approach

Motivated by the experimental data, we study charmless $B_{u,d,s}\to VT$ ($V$ and $T$ denote light vector and tensor mesons respectively) decays in the perturbative QCD approach. The predictions of branching ratios, polarization fractions and direct CP violations are given in detail. Specifically, within this approach we have calculated the polarization fractions and the branching ratios of $B\to \phi(K_2^{*-}, \bar K_2^{*0})$ which agree well with the observed experimental data, however the branching ratios of $B\to \omega(K_2^{*-}, \bar K_2^{*0})$ are hard to be explained, where the polarization fractions are well accommodated. The tree dominated channels with a vector meson emitted have longitudinal polarization fraction of 90%, while the penguin dominating ones have subtle polarization fractions. Fortunately, most branching ratios of $B_{u,d}$ decays are of the order $10^{-6}$, which would be straight forward for experimental observations. For the $B_s$ decays the branching ratios can reach the order of $10^{-6}$ in tree dominated decays, while in penguin dominated decays those are of order of $10^{-7}$ which require more experimental data to be observed.

Precise measurement of the branching fractions forBs0→Ds(*)+Ds(*)−and first measurement of theDs*+Ds*−polarization usinge+e−collisions

We have made a precise measurement of the absolute branching fractions of Bs->Ds(*)+ Ds(*)- decays using 121.4 fb-1 of data recorded by the Belle experiment running on the Upsilon(5S) resonance. The results are B(Bs0->Ds+ Ds-) = (0.58 +0.11 -0.09 +-0.13)%, B(Bs0->Ds*+- Ds-+) = (1.8 +-0.2 +-0.4)%, and B(Bs0->Ds*+ Ds*-) = (2.0 +-0.3 +-0.5)%; the sum is B(Bs0->Ds(*)+ Ds(*)- = (4.3 +-0.4 +-1.0)%. Assuming Bs->Ds(*)+ Ds(*)- saturates decays to CP-even final states, the branching fraction constrains the ratio Delta(Gamma_s)/cos(phi_s), where Delta(Gamma_s) is the difference in widths between the two Bs0-Bs0bar mass eigenstates, and phi_s is the CP-violating phase in Bs0-Bs0bar mixing. For phi_s=0 we obtain Delta(Gamma_s)/Gamma_s = 0.090 +-0.009 (stat.) +-0.023 (syst.), where Gamma_s is the mean decay width. We also measure for the first time the longitudinal polarization fraction of Bs->Ds*+ Ds*-; the result is 0.12 +0.30 -0.28 +0.04 -0.05.

Rare B decays with the CMS detector

An angular analysis of the B 0 ! K 0 + decay is performed in pp collisions at p s = 7 TeV, with a data sample corresponding to an integrated luminosity of 5:2 fb 1 collected by the CMS experiment at the LHC. The forward-backward asymmetry of the muons AFB, the K 0 longitudinal polarization fraction FL, and the di erential branching fraction dB=dq 2 , are measured as function of the dimuon invariant mass squared, q 2 . The results are in good agreement with the standard model expectations.

Physics beyond the Standard Model through b → s μ + μ − transition

A comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b → sμ + μ− transition is performed. The effects of new vector–axial vector (VA), scalar–pseudoscalar (SP) and tensor (T) interactions on the differential branching ratios, forward–backward asymmetries (AFB’s), and direct CP asymmetries of \({\bar B}_{\rm s}^0 \to \mu^+ \mu^-\), \({\bar B}_{\rm d}^0 \to\)\( X_{\rm s} \mu^+ \mu^-\), \({\bar B}_{\rm s}^0 \to \mu^+ \mu^- \gamma\), \({\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-\), and \({\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-\) are examined. In \({\bar B}_{\rm d}^0\to {\bar{K}^*} \mu^+ \mu^-\), we also explore the longitudinal polarization fraction fL and the angular asymmetries \(A_{\rm T}^{(2)}\) and ALT, the direct CP asymmetries in them, as well as the triple-product CP asymmetries \(A_{\rm T}^{\rm (im)}\) and \(A^{\rm (im)}_{\rm LT}\). While the new VA operators can significantly enhance most of the observables beyond the Standard Model predictions, the SP and T operators can do this only for AFB in \({\bar B}_{\rm d}^0 \to {\bar K} \mu^+ \mu^-\).

Contribution of vector resonances to the $\bar{B}_{d}^{0}\to\bar {K}^{*0}\mu^{+}\mu^{-}$ decay

The fully differential angular distribution for the rare flavor-changing neutral current decay \(\bar{B}_{d}^{0} \to\bar{K}^{*0} (\to K^{-} \pi^{+}) \mu^{+}\mu^{-} \) is studied. The emphasis is placed on accurate treatment of the contribution from the processes \(\bar{B}_{d}^{0} \to\bar{K}^{*0} (\to K^{-} \pi^{+}) V \) with intermediate vector resonances V=ρ(770),ω(782),ϕ(1020),J/ψ,ψ(2S),… decaying into the μ + μ − pair. The dilepton invariant-mass dependence of the branching ratio, longitudinal polarization fraction f L of the \(\bar{K}^{*0}\) meson, and forward–backward asymmetry A FB is calculated and compared with data from Belle, CDF and LHCb. It is shown that inclusion of the resonance contribution may considerably modify the branching ratio, calculated in the SM without resonances, even in the invariant-mass region far from the so-called charmonia cuts applied in the experimental analyses. This conclusion crucially depends on values of the unknown phases of the B 0→K ∗0 J/ψ and B 0→K ∗0 ψ(2S) decay amplitudes with zero helicity.