[Paper Review] B-meson production in p\\bar p collisions at Tevatron with k_T-factorization

S. P. Baranov, A. V. Lipatov+1 more|arXiv (Cornell University)|Feb 19, 2003

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper applies the $k_T$-factorization QCD approach to $b$-quark and $B$-meson production in $p\bar{p}$ collisions at the Tevatron, using unintegrated gluon distributions (UGDs) to model transverse momentum-dependent partonic subprocesses. It demonstrates good agreement with D\O and CDF data for $b$ quark, $B$ meson, and decay muon cross sections, particularly with the JB and KMS UGD parametrizations, and predicts muon-muon and muon-jet cross sections for the Tevatron and LHC.

ABSTRACT

In the framework of the k_T-factorization QCD approach we consider the production of b quark pairs in p\\bar p collisions at the Fermilab Tevatron. We investigate the dependence of the b quark, B meson and decay muon differential cross sections on the different forms of unintegrated gluon distributions. The analysis also covers the azimuthal correlations between the b and \\bar b quarks and their decay muons. Our theoretical results agree well with recent data taken by the D0 and CDF collaborations at Tevatron. Finally, we present our predictions for muon-muon and muon-jet cross sections at the Tevatron and CERN LHC conditions.

Motivation & Objective

• To address the long-standing discrepancy between next-to-leading-order (NLO) pQCD predictions and experimental data on $b$-flavor production at the Tevatron, which show a factor of two or more excess in cross sections.
• To investigate the impact of unintegrated gluon distributions (UGDs) with transverse momentum dependence on $b$-quark, $B$-meson, and decay muon differential cross sections.
• To analyze azimuthal correlations between $b\bar{b}$ quarks and their decay muons as a probe of production mechanisms and UGD properties.
• To provide theoretical predictions for muon-muon and muon-jet cross sections at Tevatron and CERN LHC energies, using realistic detector cuts.

Proposed method

• Employs the $k_T$-factorization approach based on the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution equation to resum large logarithms in $1/x$ and $\mu^2/\Lambda_{\text{QCD}}^2$, leading to $q_T$-dependent unintegrated gluon distributions (UGDs).
• Uses off-shell matrix elements with the polarization tensor $L^{\mu\nu} = q_T^\mu q_T^\nu / q_T^2$ to describe hard partonic subprocesses $gg \to b\bar{b}$ with transverse momentum dependence.
• Applies four different UGD parametrizations: JB, KMS, and two others (including a misprinted one from prior work), to assess sensitivity of results to UGD form.
• Performs numerical integration over phase space with kinematic cuts matching experimental conditions: $p_T^\mu > 6\,\text{GeV}$, $|y^\mu| < 2.5$, and $6 < m^{\mu\mu} < 35\,\text{GeV}$ for muon pairs.
• Compares theoretical differential cross sections $d\sigma/dp_T^{\mu}$, $dy^{\mu}$, and $d\sigma/d\Delta\phi^{\mu\mu}$ with D\O and CDF data.
• Predicts cross sections for muon-muon and muon-jet final states at $\sqrt{s} = 1.96\,\text{TeV}$ (Tevatron) and $14\,\text{TeV}$ (LHC), using ATLAS-like cuts.

Experimental results

Research questions

• RQ1 How do different unintegrated gluon distribution (UGD) parametrizations affect the $b$-quark, $B$-meson, and decay muon differential cross sections in $p\bar{p}$ collisions at the Tevatron?
• RQ2 To what extent do azimuthal correlations between $b\bar{b}$ quarks and their decay muons distinguish between $k_T$-factorization and leading-order pQCD predictions?
• RQ3 Which UGD model (JB, KMS, or others) best describes the D\O and CDF data on $b$-flavor production and muon correlations?
• RQ4 What are the predicted cross sections for muon-muon and muon-jet final states at the Tevatron and LHC, under realistic detector cuts?
• RQ5 How sensitive are the results to the choice of factorization scale $\mu^2 = q_T^2$ and $m_b = 4.75\,\text{GeV}$?

Key findings

• The $k_T$-factorization approach with JB and KMS unintegrated gluon distributions provides excellent agreement with D\O and CDF data for $b$-quark, $B$-meson, and decay muon differential cross sections.
• The $k_T$-factorization results for $d\sigma/dp_T^\mu$ and $dy^\mu$ in the forward region ($2.4 < |y^\mu| < 3.2$) match experimental data well, while NLO pQCD underestimates the data by a factor of four.
• Azimuthal correlations $d\sigma/d\Delta\phi^{\mu\mu}$ show that JB and KMS UGDs reproduce the D\O data, while the parametrization (11) underestimates the data at small $\Delta\phi^{\mu\mu} \sim 0$, indicating importance of $\alpha_S^n \ln^n(1/x)$ contributions.
• The $k_T$-factorization approach predicts a broad distribution in $\Delta\phi^{\mu\mu}$, unlike the sharp peak at $\pi$ expected in LO pQCD, due to initial-state gluon transverse momentum.
• Theoretical predictions for muon-muon and muon-jet cross sections at the LHC ($\sqrt{s} = 14\,\text{TeV}$) are provided, with curves showing sensitivity to the UGD model used.
• The study concludes that JB and KMS UGDs are more reliable than other parametrizations for describing $b\bar{b}$ production and correlations, especially in the small-$x$ regime.