[Paper Review] Combined results on b-hadron production rates and decay properties

Aleph, Opal+4 more|ArXiv.org|Dec 19, 2001

Particle physics theoretical and experimental studies18 citations

TL;DR

This paper presents a global combination of b-hadron production rates, decay properties, and oscillation parameters from ALEPH, CDF, DELPHI, L3, OPAL, and SLD experiments using data from summer 2000. It provides precise averages for b-hadron lifetimes, B⁰_d and B⁰_s oscillation frequencies, and charm quark production rates, enabling a stringent determination of the CKM unitarity triangle parameters within the Standard Model.

ABSTRACT

Combined results on b-hadron lifetimes, b-hadron production rates, B^0_d - \bar{B^0_d} and B^0_S - \bar{B^0_s} oscillations, the decay width difference between the mass eigenstates of the B^0_s - \bar{B^0_s} system, the average number of c and \bar{c} quarks in b-hadron decays, and searches for CP violation in the B^0_d - \bar{B-0_d} system are presented. They have been obtained from published and preliminary measurements available in Summer 2000 from the ALEPH, CDF, DELPHI, L3, OPAL and SLD Collaborations. These results have been used to determine the parameters of the CKM unitarity triangle.

Motivation & Objective

• To combine experimental results on b-hadron production rates, lifetimes, and decay properties from multiple high-energy physics collaborations.
• To improve the precision of key parameters in the Standard Model, particularly those related to the CKM matrix and the unitarity triangle.
• To reduce theoretical uncertainties in |V_cb| and |V_ub| by combining inclusive and exclusive measurements with improved experimental inputs.
• To test the consistency of the Standard Model through constraints on B⁰_s oscillations, decay width differences, and CP violation in B⁰_d systems.
• To provide updated inputs for lattice QCD and future B-factory experiments by refining measurements of b-hadron production and decay characteristics.

Proposed method

• Systematic combination of published and preliminary measurements from ALEPH, CDF, DELPHI, L3, OPAL, and SLD collaborations collected in summer 2000.
• Application of weighted averaging techniques to combine b-hadron lifetime, production rate, and oscillation frequency measurements, accounting for statistical and systematic uncertainties.
• Use of inclusive and exclusive semileptonic decay rates to extract |V_cb|, with corrections for D** and D* resonances and non-perturbative QCD effects.
• Incorporation of constraints from CP violation measurements in the B⁰_d system and from the kaon system to constrain the unitarity triangle.
• Use of theoretical inputs from lattice QCD and HQET to interpret experimental results and reduce theoretical uncertainties in |V_ub| and |V_cb|.
• Evaluation of theoretical uncertainties in V_cb and V_ub determinations, including quark masses, higher-order corrections, and shape functions in inclusive decays.

Experimental results

Research questions

• RQ1 What are the combined values of b-hadron lifetimes, production rates, and decay properties across multiple experiments?
• RQ2 How precisely can the B⁰_d and B⁰_s oscillation frequencies be determined from combined data?
• RQ3 What constraints do the combined measurements place on the CKM unitarity triangle parameters (ρ̄, η̄, α, β, γ)?
• RQ4 How do the measured charm quark production rates in b-hadron decays compare with theoretical expectations?
• RQ5 What is the combined experimental limit on the decay width difference ΔΓ_B⁰_s / Γ_B⁰_s, and how does it compare to theory?

Key findings

• The average b-hadron lifetime is determined with high precision, serving as a key input for inclusive |V_cb| determinations.
• The B⁰_d mass difference Δm_d is measured with a relative precision of approximately 3%, providing a strong constraint on the unitarity triangle.
• The B⁰_s production rate in b-jets is measured at 10% with a 12% uncertainty, crucial for B⁰_s oscillation searches.
• The combined limit on the decay width difference ΔΓ_B⁰_s / Γ_B⁰_s remains significantly below theoretical expectations, indicating room for new physics or improved theoretical modeling.
• The average number of c and c̄ quarks produced per b-hadron decay is consistent with Standard Model predictions, with no evidence for large new physics contributions.
• The global average of |V_cb| is dominated by theoretical uncertainties, particularly in inclusive decays, highlighting the need for improved theoretical control.