Decay Λb Research Articles

The Λb lifetime in the light front quark model

The enhancement of the Λb decay width relative to B decay due to the difference in Fermi motion effects in Λband B is calculated in the light front quark model with the simplifying assumption that Λbconsists of a heavy quark and a light scalar diquark. In order to explain the large deviation from unity in the experimental result for τ(Λb)/τ(B), it is necessary that the diquark be light and the ratio of the squares of the Λb and B wave functions at the origin be ≲1.

Two body nonleptonic decays of Λb involving proton

We study some nonleptonic decays of Λb-baryon involving transition of a heavy to light quark, using nonrelativistic quark model for form factors. The decay rates for two such decays are consistent with the data available. Also these decays can give us information on the CKM matrix element ¦VUb¦.

Sum rule calculation of semi-leptonic decays of heavy A hyperons in full QCD

The semi-leptonic decay amplitudes of heavy A hyperons are calculated with sum rules in full QCD. The decay rate of the Λc → Λlv agrees in the errors with the experimental value. For the decay Λb — Λclv a substantial deviation from HQET is found in our approach.

$\Lambda_{\lc{b}}\rightarrow \Lambda+D^0(\bar D^0)$ DECAYS AND CP-VIOLATION

It is shown that interference of the amplitudes for the decays Λb→ΛD and [Formula: see text] gives rise to CP-violation.

Λb→ΛcP(V) NONLEPTONIC WEAK DECAYS

The two-body nonleptonic weak decays of Λb→ΛcP(V) (P and V represent pseudoscalar and vector mesons respectively) are analyzed in two models: Bethe–Salpeter (BS) model and hadronic wave function model. The calculations are carried out in the factorization approach. The obtained results are compared with other models' calculations.

Ratio of the color suppressed decays Λ b →ΛJ/ψ andB 0→KJ/ψ

Based on the factorization approximation, we have estimated the ratio of the branching fractions for the color suppressed nonleptonic decays Λ b →ΛJ/ψ andB 0→KJ/ψ. Treating thes-quark as heavy, we have used the HQET to calculate the hadronic matrix elements. The mesonic Isgur-Wise function is calculated in the quark model whereas for the baryonic IW function we have employed the bound state soliton picture. The results obtained agree very well with the recent CDF experimental data.

TWO-BODY NONLEPTONIC Λb DECAYS WITH 1/mQ CORRECTIONS

The two-body nonleptonic Λb decays are considered in the HQET with 1/mQ corrections and factorization approximation. The Isgur–Wise function is evaluated in the bound state soliton picture. The results obtained remain well below their previously predicted upper limit.

Role of four-quark operators in the inclusive Λb decays

We compute by QCD sum rules the matrix elements of the relevant four-quark operators appearing in the expression of the Λ b inclusive decay rates at the order 1 m b 3 . The results suggest that 1 m b 3 corrections are not responsible of the observed difference between the lifetime of Λ b and B d .

Angular distribution and polarization of photons in the inclusive decay Λb → Xsγ

We study the angular distribution of photons produced in the inclusive decay of a polarized Λ b , Λ b → X sγ , using the technique of heavy quark effective theory. Finite non-perturbative corrections are obtained relative to the free quark decay b → sγ. These corrections affect significantly the intensity and polarization of photons emitted at small angles relative to the Λ b spin direction.

Polarized-Λb decay and the weak current structure

Semileptonic decay of Λb polarized along its moving direction is studied in the framework of the heavy quark effective theory. The energy distribution of the produced lepton is calculated up to the O(Λ/mc) (Λ≅O(ΛQCD)) corrections for both V−A and V+A interactions.

Search for Lambda b-->J/ psi Lambda 0 in pp-bar collisions at sqrt s =1.8 TeV.

We have searched for the b-flavored baryon decay Λb→JψΛ0 in pp¯ collisions at s=1.8 TeV with the Collider Detector at Fermilab (CDF). In the JψΛ0 invariant-mass distribution we observe a flat distribution and a small number of events, consistent with no signal. Using the b-quark cross section measured by the CDF we put an upper limit on the b→Λb production fraction times the branching ratio F(Λb)B(Λb→JψΛ0) of 0.50×10−3 at 90% confidence level.Received 28 September 1992DOI:https://doi.org/10.1103/PhysRevD.47.R2639©1993 American Physical Society

Semileptonic Decays of Atomlike Hadrons in the Heavy Quark Effective Theory

Semileptonic decays of heavy flavored hadrons are analyzed in the heavy quark effective theory (HQET) with leading 1/mQ corrections. All existing data for B →D(*)lν and D →K(*)lν are re-produced well in virtue of 1/mQ corrections, while the value of |Vcb| derived by the HQET is almost independent of those corrections. In particular, 1/ms corrections are remarkable for D →K(*)lν. Semiloptonic decays of Λc and Λb are also discussed including the 1/mQ corrections.

Semileptonic Decays of Atomlike Hadrons in the Heavy Quark Effective Theory

Semileptonic decays of heavy flavored hadrons are analyzed in the heavy quark effective theory (HQET) with leading 1/mQ corrections. All existing data for B →D(*)lν and D →K(*)lν are re-produced well in virtue of 1/mQ corrections, while the value of |Vcb| derived by the HQET is almost independent of those corrections. In particular, 1/ms corrections are remarkable for D →K(*)lν. Semiloptonic decays of Λc and Λb are also discussed including the 1/mQ corrections.

Weak matrix elements and the determination of the weak mixing angles

In the limit of QCD where heavy quark masses go to infinity new symmetries appear which enable one to predict the hadronic form factors that occur in the semileptonic decays B → Deve, B → D∗eve and Λb → Λceve. These results may eventually improve our ability to extract the weak mixing angles from experimental data on B and Λb decay.