[Paper Review] B Physics at the Tevatron Run II

K. Yip|ArXiv.org|May 13, 2004

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents B physics results from the CDF and DØ experiments at Fermilab's Tevatron Run II, focusing on precise measurements of B hadron masses and lifetimes, B mixing, the X(3872) particle, rare decays, CP violation, and spectroscopy. Key contributions include the world's best measurements of $ M(B_s) = 5365.50 \pm 1.29\ \text{MeV}/c^2 $ and $ \tau(B^+)/\tau(B^0) = 1.093 \pm 0.021 $, along with stringent limits on rare decays such as $ \text{Br}(B_s \to \mu^+\mu^-) < 5.8 \times 10^{-7} $ at 90% CL.

ABSTRACT

We present the B physics results from the CDF and DØ experiments at the Tevatron Run II at Fermilab and their future prospect. This includes various B mass and lifetime measurements, B mixing, the confirmation of the discovery of the X particle, rare decays, CP violation and spectroscopy.

Motivation & Objective

• To measure B hadron masses and lifetimes with high precision using data from CDF and DØ at the Tevatron Run II.
• To study B mixing, particularly $ \Delta m_d $ and the prospects for measuring $ \Delta m_s $, which are critical for testing the Standard Model.
• To confirm the discovery of the X(3872) particle and investigate its prompt and long-lived production components.
• To set stringent limits on rare decays such as $ B_s \to \mu^+\mu^- $, which are sensitive to new physics beyond the Standard Model.
• To probe CP violation through unitary triangle angles and self-tagging decays, and to study spectroscopy via resonant states in $ B \to \mu\nu D^{*+}X $ decays.

Proposed method

• CDF and DØ used upgraded detectors with silicon vertex trackers, muon systems, and calorimeters to reconstruct B hadron decays with high resolution and efficiency.
• Lifetime measurements were performed using proper decay length distributions, with systematic corrections applied via full detector simulations and K-factors for reconstruction efficiency.
• For $ \Delta m_d $, DØ used opposite-side muon tagging in semi-leptonic decays to measure the oscillation frequency with a tagging efficiency of 4.8% and purity of 73.0%.
• Rare decay limits were obtained through blind analysis techniques to avoid bias, using optimized selection criteria and background modeling.
• Spectroscopy studies used invariant mass reconstruction of $ D^{*+} \pi^- $ systems in $ B \to \mu\nu D^{*+}X $ decays to identify resonant contributions from $ D_1^0 $ and $ D^{*0}_2 $ states.
• Theoretical ratios such as $ \tau(B^+)/\tau(B^0) $ were extracted directly from event yield ratios as a function of visible decay length, minimizing systematic uncertainties.

Experimental results

Research questions

• RQ1 What are the most precise measurements of $ M(B_s) $, $ M(\Lambda_b) $, and $ \tau(B^+) $ at the Tevatron Run II?
• RQ2 How accurately can $ \Delta m_d $ and $ \Delta m_s $ be measured, and what are the prospects for $ \Delta m_s $ with future data?
• RQ3 What is the production behavior of the X(3872) particle in terms of prompt vs. long-lived components across different rapidity regions?
• RQ4 What are the most stringent limits on rare decays like $ B_s \to \mu^+\mu^- $, and how do they constrain new physics models?
• RQ5 What is the resonant contribution to $ B \to \mu\nu D^{*+} \pi^- X $ decays from $ D_1^0 $ and $ D^{*0}_2 $ states, and how can it be isolated?

Key findings

• CDF measured the world’s best $ M(B_s) = 5365.50 \pm 1.29\ (\text{stat}) \pm 0.94\ (\text{syst})\ \text{MeV}/c^2 $ using 80 pb⁻¹ of data.
• CDF measured $ M(\Lambda_b) = 5620.4 \pm 1.6\ (\text{stat}) \pm 1.2\ (\text{syst})\ \text{MeV}/c^2 $ with 70 pb⁻¹ of data.
• The ratio $ \tau(B^+)/\tau(B^0) = 1.093 \pm 0.021\ (\text{stat}) \pm 0.022\ (\text{syst}) $ was measured with 250 pb⁻¹, representing one of the most precise lifetime ratio measurements.
• DØ measured $ \Delta m_d = 0.506 \pm 0.055\ (\text{stat}) \pm 0.049\ (\text{syst})\ \text{ps}^{-1} $, consistent with the world average.
• CDF set the most stringent limit on $ \text{Br}(B_s \to \mu^+\mu^-) < 5.8 \times 10^{-7} $ at 90% confidence level.
• DØ observed a resonant contribution of $ 0.280 \pm 0.021\ (\text{stat}) \pm 0.088\ (\text{syst})\ \% $ to $ B \to \mu\nu D^{*+} \pi^- X $ decays from $ D_1^0 $ and $ D^{*0}_2 $ states.