[Paper Review] Novel collider signature of $U_1$ Leptoquark and $B o \pi$ observables

Aritra Biswas, Dilip Kumar Ghosh+3 more|arXiv (Cornell University)|Aug 13, 2018

Particle physics theoretical and experimental studies52 references3 citations

TL;DR

This paper investigates the multijet + missing transverse energy ($\mET$) signatures of a vector leptoquark ($U_1$) in proton-proton collisions, demonstrating its potential to mediate both charged and neutral current $b \to c$ and $b \to s$ transitions at tree level. It derives 95% confidence level exclusion limits for the $U_1$ leptoquark at the LHC and evaluates its impact on $B \to \pi$ observables, providing key benchmarks for future discovery.

ABSTRACT

One of the most popular models that is known to be able to solve the lepton flavour universality violating charged ($b o c$) and neutral current ($b o s$) anomalies is the Leptoquark Model. However, collider searches for such leptoquarks till date are only restricted towards their scalar counterpart. In this work we examine the {\it multijet} + $\mET$ collider signatures of a vector leptoquark ($U_1$) which has the potential to mediate both the charged and neutral current processes at tree level. From our collider analysis we derive the exclusion mass limits for the $U_1$ leptoquark at 95\% C.L. at the current and future experiment of Large Hadron Collider. We also calculate the effect of such a leptoquark in $B o\pi$ observables. These can be used as further benchmarks if a hint towards the presence of such a leptoquark is discovered.

Motivation & Objective

• To explore collider signatures of a vector leptoquark ($U_1$) that can mediate both charged and neutral current $b \to c$ and $b \to s$ transitions at tree level.
• To derive 95% confidence level exclusion limits for the $U_1$ leptoquark at the current and future Large Hadron Collider.
• To assess the impact of the $U_1$ leptoquark on $B \to \pi$ observables as a complementary benchmark for experimental validation.

Proposed method

• Perform a collider phenomenology analysis focusing on multijet + missing transverse energy ($\mET$) final states at the LHC.
• Use effective field theory techniques to model the $U_1$ leptoquark couplings to quarks and leptons at tree level.
• Apply Monte Carlo simulations to generate signal events and simulate background processes for signal region analysis.
• Implement kinematic cuts and selection criteria to enhance signal sensitivity in the multijet + $\mET$ topology.
• Calculate the $U_1$ leptoquark contributions to $B \to \pi$ decay observables using effective Hamiltonian formalism.
• Compare theoretical predictions with experimental constraints to derive exclusion limits and benchmark observables.

Experimental results

Research questions

• RQ1 Can a vector leptoquark ($U_1$) explain both charged and neutral current $b \to c$ and $b \to s$ anomalies simultaneously through tree-level couplings?
• RQ2 What are the viable multijet + $\mET$ collider signatures of the $U_1$ leptoquark at the LHC?
• RQ3 What are the 95% confidence level exclusion limits for the $U_1$ leptoquark mass at the current and future LHC?
• RQ4 How do $U_1$ leptoquark contributions affect $B \to \pi$ decay observables such as branching fractions and forward-backward asymmetries?
• RQ5 Can $B \to \pi$ observables serve as independent benchmarks to test the presence of a $U_1$ leptoquark if discovered in collider searches?

Key findings

• The $U_1$ vector leptoquark can mediate both charged and neutral current $b \to c$ and $b \to s$ transitions at tree level, providing a unified explanation for $boc$ and $bos$ anomalies.
• The multijet + $\mET$ final state offers a viable collider signature for probing the $U_1$ leptoquark at the LHC.
• Exclusion limits for the $U_1$ leptoquark mass are derived at 95% confidence level for both current and future LHC luminosities.
• The $U_1$ leptoquark induces non-standard model contributions to $B \to \pi$ decay observables, which can serve as complementary experimental benchmarks.
• The model predicts measurable deviations in $B \to \pi$ observables that could be tested in future flavor physics experiments.