Strange Final States Research Articles

HFLAV $τ$ branching fractions fit and measurements of Vus with $τ$ lepton data

We report the status of the Heavy Flavour Averaging Group (HFLAV) averages of the \tauτ lepton measurements We then update the latest published HFLAV global fit of the \tauτ lepton branching fractions (Spring 2017) with recent results by . We use the fit results to update the Cabibbo-Kobayashi-Maskawa (CKM) matrix element \left|V_{us}\right||Vus| measurements with the \tauτ branching fractions. We combine the direct \tauτ branching fraction measurements with indirect predictions using kaon branching fractions measurements to improve the determination of \left|V_{us}\right||Vus| using \tauτ branching fractions. The \left|V_{us}\right||Vus| determinations based on the inclusive branching fraction of \tauτ to strange final states are about 3\sigma3σ lower than the \left|V_{us}\right||Vus| determination from the CKM matrix unitarity.

Predicting the τ strange branching ratios and implications for V us

Hadronic tau decays provide several ways to extract the Cabbibo-Kobashi-Maskawa (CKM) matrix element V_{us}. The most precise determination involves using inclusive tau decays and requires as input the total branching ratio into strange final states. Recent results from B-factories have led to a discrepancy of about 3.4 sigma from the value of V_{us} implied by CKM unitarity and direct determination from Kaon semi-leptonic modes. In this paper we predict the three leading strange tau branching ratios, using dispersive parameterizations of the hadronic form factors and taking as experimental input the measured Kaon decay rates and the tau -> K pi nu_tau decay spectrum. We then use our results to reevaluate V_{us}, for which we find |V_{us}|=0.2207 \pm 0.0027, in better agreement with CKM unitarity.

TAU PHYSICS FROM B FACTORIES

Some recent τ-physics results are presented from the BaBar and Belle experiments at the SLAC and KEK B factories, which produce copious numbers of τ-lepton pairs. Measurements of the tau mass and lifetime allow to test lepton universality and CPT invariance, while searches for lepton-flavour violation in tau decays are powerful ways to look for physics beyond the Standard Model. In semihadronic, non-strange tau decays, the vector hadronic final state is particularly important in helping determine the hadronic corrections to the anomalous magnetic moment of the muon, while studies of strange final states are the best available ways to measure the CKM matrix element V us and the mass of the strange quark.

Measurement of the Strangeness Spectral Function and the Mass of the Strange Quark with the Opal Detector at LEP

Tau lepton decays with open strangeness in the final state are measured with the Opal detector at LEP to determine the strange hadronic spectral function of the τ lepton and the mass of the strange quark. The decays τ − → ( K π ) − ν τ , ( K π π ) − ν τ and ( K π π π ) − ν τ with final states consisting of neutral and charged kaons and pions, have been studied. The invariant mass distribution of 93.4% of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining 6.6% and for the strange final states including η mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the τ lepton. The moments of the spectral function which are important input parameters for theoretical analyses, are determined. From the CKM weighted difference of strange and non-strange spectral moments, the mass of the strange quark has been measured to be m s ( m τ 2 ) = ( 84 ± 14 exp ± 6 V us ± 17 theo ) MeV . Furthermore, the branching fractions B ( τ − → K − π 0 ν τ ) = ( 0.471 ± 0.064 stat ± 0.021 sys ) % and B ( τ − → K − π + π − ν τ ) = ( 0.415 ± 0.059 stat ± 0.031 sys ) % have been measured.

Measurement of the strange spectral function in hadronic $\tau$ decays

Tau lepton decays with open strangeness in the final state are measured with the OPAL detector at LEP to determine the strange hadronic spectral function of the tau lepton. The decays tau(-) -->(Kpi)(-)nu(tau)(Kpipipi)(-)nu(tau) and (Kpipipi)(-)nu(tau) with final states consisting of neutral and charged kaons and pions have been studied. The invariant mass distributions of 93.4% of these final states have been experimentally determined. Monte Carlo simulations have been used for the remaining 6.6% and for the strange final states including eta mesons. The reconstructed strange final states, corrected for resolution effects and detection efficiencies, yield the strange spectral function of the tau lepton. The moments of the spectral function and the ratio of strange to non-strange moments, which are important input parameters for theoretical analyses, are determined. Furthermore, the branching fractions B(tau(-) --> K(-)pi(o)nu(tau)) = (0.471 +/- 0.059(stat) +/- 0.023(sys))% and B(tau(-) --> K(-)pi(+)pi(-)nu(tau)) = (0.415 +/- 0.053(stat) +/- 0.040(sys))% have been measured.

Experimental puzzles in heavy flavor decays. Anomalously high η′ appearance in charmless strange B decays — flavor SU(3) breaking in charm decays

Simple experimental tests are proposed which can clarify the origin for the anomalously high η′ appearance in charmless strange final states in B decays and can investigate the the nature of SU(3) symmetry-breaking in weak heavy flavor decays.

Study of $\tau$ decays involving kaons, spectral functions and determination of the strange quark mass

All ALEPH measurements of branching ratios of \(\tau\) decays involving kaons are summarized including a combination of results obtained with \(K^0_S\) and \(K^0_L\) detection. The decay dynamics are studied, leading to the determination of contributions from vector \(K^*(892)\) and \(K^*(1410)\), and axial-vector \(K_1(1270)\) and \(K_1(1400)\) resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the \(K\overline{K}\pi\) mode is compared with the corresponding cross section for low energy \(e^+e^-\) annihilation, yielding an axial-vector fraction of \((94^{\,+6}_{\,-8})\%\) for this mode. The branching ratio for \(\tau\) decay into all strange final states is determined to be \(B(\tau^-\to X^-(S=-1)\nu_\tau)=(28.7\pm1.2)\times 10^{-3}\). The measured mass spectra of the strange \(\tau\) decay modes are exploited to derive the \(S=-1\) spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result \(m_s(M_\tau^2)=(176^{\,+46}_{\,-57})\) MeV/\(c^2\). The evolution down to 1 GeV gives \(m_s(1 {\rm GeV}^2) = (234^{\,+61}_{\,-76}){\rm MeV}/c^2\).

Study of

All ALEPH measurements of branching ratios of $\tau$ decays involving kaons are summarized including a combination of results obtained with $K^0_S$ and $K^0_L$ detection. The decay dynamics are studied, leading to the determination of contributions from vector $K^*(892)$ and $K^*(1410)$ , and axial-vector $K_1(1270)$ and $K_1(1400)$ resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the $K\overline{K}\pi$ mode is compared with the corresponding cross section for low energy $e^+e^-$ annihilation, yielding an axial-vector fraction of $(94^{\,+6}_{\,-8})\%$ for this mode. The branching ratio for $\tau$ decay into all strange final states is determined to be $B(\tau^-\to X^-(S=-1)\nu_\tau)=(28.7\pm1.2)\times 10^{-3}$ . The measured mass spectra of the strange $\tau$ decay modes are exploited to derive the $S=-1$ spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result $m_s(M_\tau^2)=(176^{\,+46}_{\,-57})$ MeV/ $c^2$ . The evolution down to 1 GeV gives $m_s(1 {\rm GeV}^2) = (234^{\,+61}_{\,-76}){\rm MeV}/c^2$ .

Strange decays of nonstrange baryons

The strong decays of excited nonstrange baryons into the final states $\ensuremath{\Lambda}K,$ $\ensuremath{\Sigma}K,$ and for the first time into $\ensuremath{\Lambda}(1405)K,$ $\ensuremath{\Lambda}(1520)K,$ $\ensuremath{\Sigma}(1385)K,$ $\ensuremath{\Lambda}{K}^{*},$ and $\ensuremath{\Sigma}{K}^{*},$ are examined in a relativized quark pair creation model. The wave functions and parameters of the model are fixed by previous calculations of $N\ensuremath{\pi}$ and $N\ensuremath{\pi}\ensuremath{\pi},$ etc., decays. Our results show that it should be possible to discover several new negative parity excited baryons and confirm the discovery of several others by analyzing these final states in kaon production experiments. We also establish clear predictions for the relative strengths of certain states to decay to $\ensuremath{\Lambda}(1405)K$ and $\ensuremath{\Lambda}(1520)K,$ which can be tested to determine if a three-quark model of the $\ensuremath{\Lambda}(1405)K$ is valid. Our results compare favorably with the results of partial wave analyses of the limited existing data for the $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K$ channels. We do not find large $\ensuremath{\Sigma}K$ decay amplitudes for a substantial group of predicted and weakly established negative-parity states, in contrast to the only previous work to consider decays of these states into the strange final states $\ensuremath{\Lambda}K$ and $\ensuremath{\Sigma}K.$

FSI rescattering in B± decays via states with η, η′ ω and φ

New results going beyond those obtained from isospin and flavor symmetry and subject to clear experimental tests are obtained for effects of FSI in $B^\pm$ decays to charmless strange final states containing neutral flavor-mixed mesons like $\omega$, $\phi$, $\eta$ and $\eta'$. The most general strong-interaction diagrams containing arbitrary numbers of quarks and gluons are included with the assumptions that any $q \bar q$ pair created by gluons must be a flavor singlet, and that there are no hairpin diagrams in which a final meson contains a $q \bar q$ pair from the same gluon vertex. The smallness of $K^- \eta$ suggests that it might have a large CP violation. A sum rule is derived to test whether the large $K^- \eta'$ requires the addition of an additional glueball or charm admixture. Further analysis from $D_s$ decay systematics supports this picture of FSI and raises questions about charm admixture in the $\eta'$.

τ decays into strange particles and QCD

New results from ALEPH on τ decay modes into strange final states have been presented at this workshop. Together with already published results they provide strong constraints on several interesting questions which are of relevance for understanding low-energy QCD. The measurements of the branching ratios for τ → ν τ K − π + π − , τ → ν τ K S o K L o π − and τ → ν τ K S o K S o π − allows a determination of the vector and axial fractions in the KK¯ π hadronic system. The DMO sum rule is saturated by ρ and K* spectral functions; however the measured non-strange contribution at higher masses need a strange counterpart. In this context, vector and axial resonance contributions are discussed and a branching ratio of (4.9 ± 1.3) × 1.3) × 10 −3 is derived for τ → ν τ K A *(1270). Finally, the total strange hadronic contribution is determined, R τ,S = 0.1560 ± 0.0064, and is used in the context of the OPE QCD expansion to derive a measurement of the strange quark mass: m s ( m τ ) = 212 −35 −5 +30 +1 MeV/c 2 in qualitative agreement with previous theoretical estimates.

Evidence for a Kπ π resonance

Four body strange particle final states produced by a 3.0-Bev/c meson ( pi /sup -/) beam in a bubble chamber seem to indicnte a resonance in the K pi pi system. The resonance appears to be produced in association with both hyperons ( LAMBDA ) and ( SIGMA ) in the final states pi /sup -/ + p yields pi pi K LAMBDA and pi /sup -/ p yields pi pi K SIGMA . (C.E.S.)