arXiv subjects

Fernando Barreiro

Publications and source records attributed to Fernando Barreiro.

3 recordsLinked to original sources

arXiv2012

Transverse Energy-Energy Correlations in Next-to-Leading Order in $α_s$ at the LHC

We compute the transverse energy-energy correlation (EEC) and its asymmetry (AEEC) in next-to-leading order (NLO) in $α_s$ in proton-proton collisions at the LHC with the center-of-mass energy $E_{\rm c.m.}=7$ TeV. We show that the transverse EEC and the AEEC distributions are insensitive to the QCD factorization- and the renormalization-scales, structure functions of the proton, and for a judicious choice of the jet-size, also the underlying minimum bias events. Hence they can be used to precisely test QCD in hadron colliders and determine the strong coupling $α_s$. We illustrate these features by defining the hadron jets using the anti-$k_T$ jet algorithm and an event selection procedure employed in the analysis of jets at the LHC and show the $α_s(M_Z)$-dependence of the transverse EEC and the AEEC in the anticipated range $0.11 \leq α_s(M_Z) \leq 0.13$.

hep-ph↗

arXiv2011

Improved sensitivity to charged Higgs searches in Top quark decays $t \to bH^+ \to b (τ^+ν_τ)$ at the LHC using $τ$ polarisation and multivariate tecnniques

We present an analysis with improved sensitivity to the light charged Higgs ($m_{H^+} < m_t-m_b$) searches in the top quark decays $t \to b H^+ \to b (τ^+ν_τ) + ~{\rm c.c.}$ in the $t\bar{t}$ and single $t/\bar{t}$ production processes at the LHC. In the Minimal Supersymmetric Standard Model (MSSM), one anticipates the branching ratio ${\cal B} (H^+ \to τ^+ν_τ)\simeq 1$ over almost the entire allowed $\tan β$ range. Noting that the $τ^+$ arising from the decay $H^+ \to τ^+ν_τ$ are predominantly right-polarized, as opposed to the $τ^+$ from the dominant background $W^+ \to τ^+ν_τ$, which are left-polarized, a number of $H^+/W^+ \to τ^+ν_τ$ discriminators have been proposed and studied in the literature. We consider hadronic decays of the $τ^\pm$, concentrating on the dominant one-prong decay channel $τ^\pm \to ρ^\pm ν_τ$. The energy and $p_T$ of the charged prongs normalised to the corresponding quantities of the $ρ^\pm$ are convenient variables which serve as $τ^\pm$ polariser. We use the distributions in these variables and several other kinematic quantities to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we have calculated the BDT(D)-response functions to estimate the signal efficiency vs. the rejection of the background. We argue that this chain of analysis has a high sensitivity to light charged Higgs searches up to a mass of 150 GeV in the decays $t \to b H^+$ (and charge conjugate) at the LHC. For the case of single top production, we also study the transverse mass of the system determined using Lagrange multipliers.

hep-ph↗

arXiv2010

Prospects of measuring the CKM matrix element $|V_{ts}|$ at the LHC

We study the prospects of measuring the CKM matrix element $\vert V_{ts}\vert$ at the LHC with the top quarks produced in the processes $p p \to t\bar{t}X$ and $p p \to t/\bar{t} X$, and the subsequent decays $t \to W^+s$ and $\bar{t} \to W^- \bar{s}$. We insist on tagging the $W^\pm$ leptonically, $W^\pm \to \ell^\pm ν_\ell$ ($\ell =e, μ, τ$), and analyse the anticipated jet profiles in the signal process $t \to W s$ and the dominant background from the decay $t \to W b$. To that end, we analyse the $V0$ ($K^0$ and $Λ$) distributions in the $s$- and $b$-quark jets concentrating on the energy and transverse momentum distributions of these particles. The $V0$s emanating from the $t \to W b$ branch have displaced decay vertexes from the interaction point due to the weak decays $b \to c \to s$ and the $b$-quark jets are rich in charged leptons. Hence, the absence of secondary vertexes and of the energetic charged leptons in the jet provide additional ($b$-jet vs. $s$-jet) discrimination in top quark decays. These distributions are used to train a boosted decision tree (BDT). Using the BDT classifier, and a variant of it called BDTD, which makes use of decorrelated variables, we calculate the BDT(D)-response functions corresponding to the signal ($t \to W s$) and background ($t \to W b$). Detailed simulations undertaken by us with the Monte Carlo generator PYTHIA are used to estimate the background rejection versus signal efficiency for three representative LHC energies $\sqrt{s}=7$ TeV, 10 TeV and 14 TeV. We argue that a benchmark with 10\% signal ($t \to W s $) efficiency and a background ($t \to W b$) rejection by a factor $10^3$ (required due to the anticipated value of the ratio $\vert V_{ts}\vert^2/\vert V_{tb} \vert^2 \simeq 1.6 \times 10^{-3}$) can be achieved at the LHC@14 TeV with an integrated luminosity of 10 fb$^{-1}$.

hep-ph↗