LHC constraints and prospects for $S_1$ scalar leptoquark explaining the $\bar B \to D^{(*)} \tau \bar\nu$ anomaly

TL;DR

This paper investigates the constraints and future detection prospects of the scalar leptoquark S_1 at the LHC, which could explain B meson decay anomalies, by analyzing current data and simulating future searches.

Contribution

It provides the first detailed analysis of LHC constraints and discovery potential for the S_1 leptoquark explaining B decay anomalies, including future prospects at 14 TeV.

Findings

Current LHC data constrains S_1 mass below 400-640 GeV.

Future 14 TeV searches can probe S_1 masses up to 600-800 GeV.

The S_1 leptoquark can explain B decay anomalies within certain parameter ranges.

Abstract

Recently, deviations in flavor observables of B -> D(*) tau nu have been shown between the predictions in the Standard Model and the experimental results reported by BaBar, Belle, and LHCb collaborations. One of the solutions to this anomaly is obtained in a class of leptoquark model with a scalar leptoquark boson S_1, which is a SU(3)_c triplet and SU(2)_L singlet particle with -1/3 hypercharge interacting with a quark-lepton pair. With well-adjusted couplings, this model can explain the anomaly and be compatible with all flavor constraints. In such a case, the S_1 boson can be pair-produced at CERN's Large Hadron Collider (LHC) and subsequently decay as S_1 -> t tau, b nu, c tau. This paper explores the current 8 and 13 TeV constraints, as well as the detailed prospects at 14 TeV, of this flavor-motivated S_1 model. From the current available 8 and 13 TeV LHC searches, we obtain constraints on the S_1 boson mass for M_{S_1} < 400 GeV - 640 GeV depending on values of the leptoquark couplings to fermions. Then we study future prospects for this scenario at the 14 TeV LHC using detailed cut analyses and evaluate exclusion/discovery potentials for the flavor-motivated S_1 leptoquark model from searches for the (b nu) (b nu) and (c tau) (c tau) final states. In the latter case, we consider several scenarios for the identification of charm jets. As a result, we find that the S_1 leptoquark origin of the B -> D(*) tau nu anomaly can be probed with mass less than around 600/800 GeV at the 14 TeV LHC with 300/3000 fb^-1 of accumulated data.