arXiv subjects

Zumin Luo

Publications and source records attributed to Zumin Luo.

10 recordsLinked to original sources

arXiv2003

Charmless $B \to VP$ Decays Using Flavor SU(3) Symmetry

The decays of $B$ mesons to a charmless vector ($V$) and pseudoscalar ($P$) meson are analyzed within a framework of flavor SU(3) in which symmetry breaking is taken into account through ratios of decay constants in tree ($T$) amplitudes. The magnitudes and relative phases of tree and penguin amplitudes are extracted from data; the symmetry assumption is tested; and predictions are made for rates and CP asymmetries in as-yet-unseen decay modes. A key assumption for which we perform some tests and suggest others is a relation between penguin amplitudes in which the spectator quark is incorporated into either a pseudoscalar meson or a vector meson. Values of $γ$ slightly restricting the range currently allowed by fits to other data are favored, but outside this range there remain acceptable solutions which cannot be excluded solely on the basis of present $B \to VP$ experiments.

hep-ph↗

arXiv2003

Heavy bottom squark mass in the light gluino and light bottom squark scenario

Restrictive upper bounds on the heavy bottom squark mass when the gluino and one bottom squark are both light are based on the predicted reduction of $R_b$ (the fraction of $Z$ hadronic decays to $b \bar b$ pairs) in such a scenario. These bounds are found to be relaxed by the process $Z \to b\bar{\tilde b}{\tilde g}/{\bar b}{\tilde b}{\tilde g}$, which may partially compensate for the reduction of $R_b$. The relaxation of bounds on the top squark and the scale-dependence of the strong coupling constant are also discussed.

hep-ph↗

arXiv2003

The factorizable amplitude in $B^0 \to π^+ π^-$

Using the measured spectrum shape for $B \to π\ell ν$, the rate for $B^+ \to π^+ π^0$, information on the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $|V_{ub}|$, and theoretical inputs from factorization and lattice gauge theory, we obtain an improved estimate of the ``tree'' contribution to $B^0 \to π^+ π^-$. We find the branching ratio $\b(B^0 \to π^+ π^-)|_{\rm tree} = (5.25^{+1.67}_{-0.50}) \times 10^{-6}$, to be compared with the experimental value $\b(B^0 \to π^+ π^-) = (4.55 \pm 0.44) \times 10^{-6}$. The fit implies $|V_{ub}| = (3.62 \pm 0.34) \times 10^{-3}$. Implications for tree-penguin interference in $B^0 \to π^+ π^-$ and for other charmless $B$ decays are discussed.

hep-ph↗

arXiv2003

Z decays into light gluinos: a calculation based on unitarity

The Z boson can decay to a pair of light gluinos through loop-mediated processes. Based on unitarity of the S-matrix, the imaginary part of the decay amplitude is computed in the presence of a light bottom squark. This imaginary part can provide useful information on the full amplitude. Implications are discussed for a recently proposed light gluino and light bottom squark scenario.

hep-ph↗

arXiv2003

Final-State Phases in $B \to$ Baryon-Antibaryon Decays

The recent observation of the decay $\ob \to Λ_c^+ \bar p$ suggests that related decays may soon be visible at $e^+ e^-$ colliders. It is shown how these decays can shed light on strong final-state phases and amplitudes involving the spectator quark, both of which are normally expected to be small in B decays.

hep-ph↗

arXiv2002

Light Gluino and the Running of alpha_s

A gluino in the mass range 12--16 GeV combined with a light (2--5.5 GeV) bottom squark, as has been proposed recently to explain an excess of b quark hadroproduction, would affect the momentum-scale dependence (``running'') of the strong coupling constant alpha_s in such a way as to raise its value at M_Z by about 0.014 +/- 0.001. If one combines sources of uncertainty at low (m_b) and high (M_Z) mass scales, one can only distinguish such an effect at slightly more than the 2 sigma level. Prospects for improvement in this situation, which include better lattice QCD simulations and better measurements at M_Z, are discussed.

hep-ph↗

arXiv2002

Two-Body Cabibbo-Suppressed Charmed Meson Decays

Singly-Cabibbo-suppressed decays of charmed particles governed by the quark subprocesses $c \to s u \bar s$ and $c \to d u \bar d$ are analyzed using a flavor-topology approach, based on a previous analysis of the Cabibbo-favored decays governed by $c \to s u \bar d$. Decays to $PP$ and $PV$, where $P$ is a pseudoscalar meson and $V$ is a vector meson, are considered. We include processes in which $η$ and $η'$ are produced.

hep-ph↗

arXiv2002

$B \to D_s π$ and the tree amplitude in $B \to π^+ π^-$

The recently-observed decay $B^0 \to D_s^+ π^-$ is expected to proceed mainly by means of a tree amplitude in the factorization limit: $B^0 \to π^- {(W^+)}^*$, ${(W^+)}^* \to D_s^+$. Under this assumption, we predict the corresponding contribution of the tree amplitude to $B^0 \to π^+ π^-$. We indicate the needed improvements in data that will allow a useful estimate of this amplitude with errors comparable to those accompanying other methods. Since the factorization hypothesis for this process goes beyond that proved in most approaches, we also discuss independent tests of this hypothesis.

hep-ph↗

arXiv2001

Information on $B \to ππ$ Provided by the Semileptonic Process $B \to πl ν$

Analysis of the present data on the semileptonic process $B \to π\ell ν$ indicates that they have not yet reached the precision to provide adequate information on the $B \to π$ form factor $F_+(q^2)$, which for $q^2 = m_π^2$ is known to be related to the factorized color-favored (``$T$'', or ``tree'') contribution to $B^0 \to π^+ π^-$. It is shown here that with around 500 $B \to π\ell ν$ events in which rate and spectrum are measured one can improve the accuracy of $T$ by a significant amount. A recent CLEO determination of the $D^* D π$ coupling constant is compared with an earlier prediction, and its role in the description of the $B \to π$ form factors is noted. When combined with an estimate of the penguin amplitude (``$P$'') obtained using flavor SU(3) symmetry from $B \to K π$ decays, information on $T$ allows one to gauge the effects of the penguin amplitude on extraction of the weak phase $α= ϕ_2$ from the time-dependent CP-violating rate asymmetry in $B^0 \to π^+ π^-$. The constraint on $α$ implied by a recent experimental result on this asymmetry is described.

hep-ph↗

arXiv2001

Factorization in Color-Favored B Meson Decays to Charm

Improved $B$ meson decay data have permitted more incisive tests of factorization predictions. A concurrent benefit is the ability to constrain the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$. Using a simultaneous fit to differential distributions $d Γ(\ob \to D^{*+} l^- \bar ν_l)/ dq^2$ measured by the CLEO and LEP Collaborations, the rates for the color-favored decays $\ob \to D^{(*)+} (π^-,ρ^-,a_1^-)$, and the rate for $\ob \to D^+ l^- \bar ν_l$, we find $|V_{cb}| = 0.0415 \pm 0.0022$. The slope of the universal Isgur-Wise form factor is described by a parameter found to be $\rs = 1.52 \pm 0.11$. Taking the $D_s$ meson decay constant from the world average of direct measurements, we predict satisfactorily the branching ratios for $\ob \to D^{(*)+} D_s^{(*)-}$. Ratios of helicity amplitudes for color-favored processes are also found to be in accord with predictions.

hep-ph↗