arXiv subjects

Roberto A. Morales

Publications and source records attributed to Roberto A. Morales.

15 recordsLinked to original sources

arXiv2025

Quantum Information meets High-Energy Physics: Input to the update of the European Strategy for Particle Physics

Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown and has gathered the attention of the scientific community. For the range of particles and fundamental interactions involved, particle colliders provide a novel environment where quantum information theory can be probed, with energies exceeding by about 12 orders of magnitude those employed in dedicated laboratory setups. Furthermore, collider detectors have inherent advantages in performing certain quantum information measurements, and allow for the reconstruction of the state of the system under consideration via quantum state tomography. Here, we elaborate on the potential, challenges, and goals of this innovative and rapidly evolving line of research and discuss its expected impact on both quantum information theory and high-energy physics.

hep-ph↗

arXiv2025

HEFT's appraisal of triple (versus double) Higgs weak boson fusion

Multi-Higgs boson interactions with massive gauge bosons are known to be tell-tale probes of the vacuum manifold of electroweak symmetry breaking. Phenomenologically, a precise determination of these parameters is hampered through increasingly rare processes at the presently available energy frontier provided by the Large Hadron Collider. Contact interactions of three Higgs bosons with the $W$ and $Z$ bosons seem currently well out of experimental reach due to an irrelevant SM production cross section. From a theoretical perspective, in perturbative extensions of the SM such interactions are suppressed by weak loops and further diluted in a priori sensitive processes like weak boson fusion (WBF) when they admit a dimension-six Standard Model Effective Field Theory description. In this work, we identify scenarios that can indeed lead to large, and perhaps even observable modifications of WBF triple Higgs production most directly parametrised by Higgs Effective Field Theory. We critically analyse these enhancements at the LHC and future colliders from the perspective of unitarity and demonstrate the radiative stability of such analyses under QCD corrections at hadron colliders. Taking into account the restrictions from unitarity, we finally study the expected sensitivity to the electroweak triple Higgs production within HEFT, considering $HHVV$ and $HHHVV$ effective couplings, at both future hadron and lepton colliders. Particularly, we present numerical predictions for LHC, FCC, CLIC and muon colliders.

hep-ph↗

arXiv2024

Machine-Learning Performance on Higgs-Pair Production Associated with Dark Matter at the LHC

Di-Higgs production at the LHC associated with missing transverse energy is explored in the context of simplified models that generically parameterize a large class of models with heavy scalars and dark matter candidates. Our aim is to figure out the improvement capability of machine-learning tools over traditional cut-based analyses. In particular, boosted decision trees and neural networks are implemented in order to determine the parameter space that can be tested at the LHC demanding four $b$-jets and large missing energy in the final state. We present a performance comparison between both machine-learning algorithms, based on the maximum significance reached, by feeding them with different sets of kinematic features corresponding to the LHC at a center-of-mass energy of 14 TeV. Both algorithms present very similar performances and substantially improve traditional analyses, being sensitive to most of the parameter space considered for a total integrated luminosity of 1 ab$^{-1}$, with significances at the evidence level, and even at the discovery level, depending on the masses of the new heavy scalars. A more conservative approach with systematic uncertainties on the background of 30\% has also been contemplated, again providing very promising significances.

hep-ph↗

arXiv2024

Tripartite entanglement from experimental data: $B^0\to K^{*0}μ^+μ^-$ as a case study

We develop an angular analysis based on the reconstruction of the helicity amplitudes from dedicated experimental data corresponding to the tripartite state composed by one qutrit and two qubits, which arises in the three-body decays of a spin zero particle into one vector and a fermion pair. Starting from the associated spin density matrix of the final state, entanglement quantifiers were investigated and the corresponding significances were determined up to second order in the error propagation of the uncertainties of the angular measurements. As an application of our analysis, we performed a full quantum tomography of the final state in the $B^0\to K^{*0}μ^+μ^-$ decays using data recorded by LHCb collaboration. We found the presence of genuine quantum entanglement of the final state and also in both kaon-muon and di-muon subsystems. In recent years, $B$ meson decays received significant attention from both experimental and theoretical sides, and the proposed observables provide novel perspectives for studying them. Furthermore, this analysis could be also applied to other several processes if the complete experimental data were available for the helicity amplitudes reconstruction.

hep-ph↗

arXiv2024

Bosonic multi-Higgs correlations beyond leading order

The production of multiple Higgs bosons at the LHC and beyond is a strong test of the mechanism of electroweak symmetry breaking. Taking inspiration from recent experimental efforts to move towards limits on triple Higgs production at the Large Hadron Collider, we consider generic bosonic deviations of $HH$ and $HHH$ production from the Standard Model in the guise of Higgs Effective Field Theory. Including one-loop radiative corrections within the HEFT and going up to ${\mathcal{O}}(p^4)$ in the momentum expansion, we provide a detailed motivation of the parameter range that the LHC (and future hadron colliders) can explore, through accessing non-standard coupling modifications and momentum dependencies that probe Higgs boson non-linearities. In particular, we find that radiative corrections can enhance the sensitivity to Higgs-self coupling modifiers and HEFT-specific momentum dependencies can vastly increase triple Higgs production thus providing further motivation to consider these processes during the LHC's high-luminosity phase.

hep-ph↗

arXiv2022

LHC search strategy for squarks in higgsino-LSP scenarios with leptons and $b$-jets in the final state

The higgsino Lightest Supersymmetric Particle (LSP) scenario opens up the possibility of decays of strongly produced particles to an intermediate neutralino, due to the Yukawa-suppressed direct decays to the higgsino. Those decays produce multijet signals with a Higgs or a $Z$ boson being produced in the decay of the intermediate neutralino to the LSP. In this paper we study the discovery prospects of squarks that produce $b$-jets and leptons in the final state. Our collider analysis provides signal significances at the 3$σ$ level for luminosities of 1 ab$^{-1}$, and at the 5$σ$ level if we project these results for 3 ab$^{-1}$.

hep-ph↗

arXiv2021

Hunting Squarks in Higgsino LSP scenarios at the LHC

The assumption that strongly interacting sparticles will decay directly to the LSP plus jets breaks down in situations where those decays are Yukawa suppressed. That occurs when producing the first two generations of squarks and when, at the same time, there are several electroweakinos lighter than those squarks. In this paper we analyze the signal of pair production of squarks that subsequently decay to an intermediate neutralino ($\tildeχ_3^0$) plus jets. The neutralino will then decay to the LSP (mainly higgsino) and a Higgs. We have simulated the events and designed a discovery strategy based on a signal of two jets, four $b$-quarks and missing transverse energy. We obtain very promising values for the LHC sensitivity at 14 TeV and 300 fb$^{-1}$.

hep-ph↗

arXiv2021

One-loop renormalization of VBS with the electroweak chiral Lagrangian in covariant gauges

This work presents a first full one-loop computation of vector boson scattering (VBS) within the non-linear effective field theory given by the bosonic sector of the usually called electroweak chiral Lagrangian (EChL). The computation is performed in the most general case of covariant $R_ξ$ gauges and is compared through all this work with the Standard Model case, whose computation in these covariant gauges is also novel and is presented also here. The calculation of the one-loop VBS amplitude is performed using the diagrammatic method by means of the one-particle-irreducible (1PI) Green functions that are involved in these scattering processes. The central part of this work is then devoted to the renormalization of all the n-legs one-loop 1PI Green functions involved. This renormalization is performed in the most general off-shell case with arbitrary external legs momenta. We then describe in full detail the renormalization program, which within this context of the EChL, implies to derive all the counterterms for both the electroweak parameters, like boson masses and gauge couplings, and those for the EChL coefficients. These later are crucial for the renormalization of the new divergences typically appearing when computing loops with the lowest chiral dimension Lagrangian. We present here the full list of involved divergences and counterterms in the $R_ξ$ gauges and derive the complete set of renormalization group equations for the EChL coefficients. In the last part of this work, we present the EChL numerical results for the one-loop cross section in the WZ channel and compare them with the SM results.

hep-ph↗

arXiv2021

Search strategy for gluinos at the LHC with a Higgs boson decaying into tau leptons

The possibility in supersymmetric scenarios that the dark matter candidate is a Higgsino-like neutralino means that its production can be associated with Higgs bosons. Taking advantage of this fact, we propose a LHC search strategy for gluinos with $τ$ leptons in the final state, coming from the decay of a Higgs boson. We consider the strong production of a pair of gluinos, one of which decays into the Higgsino plus jets while the other decays into the bino plus jets. In turn, this bino decays into the Higgsino plus a Higgs boson which finally decays into a $τ$-lepton pair. Therefore, the experimental signature under study consists of 4 jets, 2 $τ$ leptons, and a large amount of missing transverse energy. Our cut-based search strategy allows us to reach, for a LHC center-of-mass energy of 14 TeV and a total integrated luminosity of 1 ab$^{-1}$, significances of up to 2 standard deviations, considering systematic uncertainties in the SM background of 30\%. The projections for 3 ab$^{-1}$ are encouraging, with significances at the evidence level, which in more optimistic experimental scenarios could exceed 4 standard deviations.

hep-ph↗

arXiv2021

Novel Higgsino Dark Matter Signatures at the LHC

In the LHC searches for gluinos it is usually assumed that they decay predominantly into the lightest neutralino plus jets. In this work we perform a proof-of-concept collider analysis of a novel supersymmetric signal in which gluinos decay mostly into jets and the bino-like neutralino ($\tildeχ_3^0$), which in turn decays into the lightest Higgsino-like neutralino ($\tildeχ_1^0$), considered the dark matter candidate, together with the SM-like Higgs boson ($h$). This new physics signal then consists of an LHC final state made up by four light jets, four $b$-jets, and a large amount of missing transverse energy. We identify $t \bar t$, $V$+jets ($V$= $W$, $Z$), and $t \bar t + X$ ($X$ = $W$, $Z$, $γ^*$, $h$) productions as the most problematic backgrounds, and develop a search strategy for the high luminosity phase of the LHC, reaching signal significances at the evidence level for a luminosity of 1000 fb$^{-1}$. The prospects for a luminosity of 3000 fb$^{-1}$ are even more promising, with discovery-level significances.

hep-ph↗

arXiv2020

Anatomy of Higgs decays into $γγ$ and $γZ$ within the EChL in the $R_ξ$ gauges

In this work we study the Higgs boson decays into two photons and into one photon and one $Z$ gauge boson within the context of the non-linear Effective Field Theory called the Electroweak Chiral Lagrangian. We present a detailed computation of the corresponding amplitudes to one-loop level in the covariant $R_ξ$ gauges. We assume that the fermionic loop contributions are as in the Standard Model and focus here just in the computation of the bosonic loop contributions. Our renormalization program and the anatomy of the various contributions participating in the $R_ξ$ gauges are fully explored. With this present computation we demonstrate the gauge invariance of the EChL result, not only for the case of on-shell Higgs boson, but also for the most general and interesting case of off-shell Higgs boson. We finally analyse and conclude on the special relevance of the Goldstone boson loops, in good agreement with the expected chiral loops behaviour in Chiral Lagrangians. We perform a systematic comparison with the corresponding computation of the Standard Model in the $R_ξ$ gauges and with the previous EChL results in the unitary gauge. This work represents the first computation within the EChL of these Higgs observables to one-loop in the most general $R_ξ$ gauges and with a full renormalization program description, not yet fully explored in the previous literature and which is different to the most frequently used in the linear Effective Field Theory (SMEFT).

hep-ph↗

arXiv2020

Flavor techniques for LFV processes: Higgs decays in a general seesaw model

Lepton flavor violating processes are optimal observables to test new physics, since they are forbidden in the Standard Model while they may be generated in new theories. The usual approach to these processes is to perform the computations in the physical basis; nevertheless this may lose track of the dependence on some of the fundamental parameters, in particular on those at the origin of the flavor violation. Consequently, in order to obtain analytical expressions directly in terms of these parameters, flavor techniques are often preferred. In this work, we focus on the mass insertion approximation technique, which works with the interaction states instead of the physical ones, and provides diagrammatic expansions of the observables. After reviewing the basics of this technique with two simple examples, we apply it to the lepton flavor violating Higgs decays in the framework of a general type-I seesaw model with an arbitrary number of right-handed neutrinos. We derive an effective vertex valid to compute these observables when the right-handed neutrino masses are above the electroweak scale and show that we recover previous results obtained for low scale seesaws. Finally, we apply current constraints on the model to conclude on maximum Higgs decay rates, which unfortunately are far from current experimental sensitivities.

hep-ph↗

arXiv2019

Model-independent search strategy for the lepton-flavor-violating heavy Higgs boson decay to $τμ$ at the LHC

In this work we present a model-independent search strategy at the LHC for heavy Higgs bosons decaying into a tau and a muon, $H/A \rightarrow τμ$, showing a plausible tendency to improve the sensitivity obtained by the present experimental limits. This search strategy is performed for the Higgs boson mass range 1-5 TeV and uses as the most relevant kinematical variables, in order to discriminate signal against background, the transverse momenta of the muon and the tau together with the missing transverse energy. We estimate the exclusion limits at 95% C.L. and the significances for evidence and discovery at $\sqrt{s}$ = 14 TeV with $\cal{L}$ = 300 fb$^{-1}$, observing a growth in the sensitivities for high Higgs boson masses. Moreover, since the Higgs boson decay into a $τ$-lepton pair may mimic our LFV signal, we also study the impact of the ditau channel on the exclusion limits and the significances for evidence and discovery. In particular, the impact on the exclusion limits of LFV heavy Higgs boson decays is significant when the ditau rate begins to compete with the corresponding to the $H/A \rightarrow τμ$ decay.

hep-ph↗

arXiv2019

Constraining R-axion models through dijet searches at the LHC

The search at hadron colliders for new massive resonances of a few 100 GeVs that couple effectively to colored states is an extremely challenging issue, due principally to the presence of large QCD multijet backgrounds at this energy, rendering the searches at the LHC particularly difficult. Recently, it was realized that these large backgrounds could be overcome by demanding one high-$p_T$ jet from initial-state radiation (ISR) and by means of novel jet-reconstruction techniques through which the resulting hadronized products of the massive resonances are reconstructed as a fat-jet, a unique large-radius jet. The ATLAS and CMS Collaborations have recently reported searches for the experimental signature of a single fat-jet in association with an ISR jet. Models of dynamical supersymmetry breaking with an spontaneously broken R-symmetry give rise to the appearance of a pseudo-Nambu-Goldstone boson called the R-axion, which naturally tends to be light. In the parameter space regions where the anomalous R-axion coupling to gluons is boosted, these models can be tested against these new LHC dijet searches. Taking into account the CMS search, we apply the $q_μ$ statistical method to the signal events against the background-only expectation and obtain the 95\% C.L. exclusion limits on the most relevant model parameters for a particular messenger sector, namely, the R-axion mass $m_a$, the decay constant $f_a$, and the number of color messengers $N$, being these limits suitable to be applied to more general models with axion-like particles.

hep-ph↗

arXiv2018

Search strategies for pair production of heavy Higgs bosons decaying invisibly at the LHC

The search for heavy Higgs bosons at the LHC represents an intense experimental program, carried out by the ATLAS and CMS collaborations, which includes the hunt for invisible Higgs decays and dark matter candidates. No significant deviations from the SM backgrounds have been observed in any of these searches, imposing significant constraints on the parameter space of different new physics models with an extended Higgs sector. Here we discuss an alternative search strategy for heavy Higgs bosons decaying invisibly at the LHC, focusing on the pair production of a heavy scalar $H$ together with a pseudoscalar $A$, through the production mode $q \bar q \to Z^\ast \to HA$. We identify as the most promising signal the final state made up of $4b + E_T^\text{miss}$, coming from the heavy scalar decay mode $H \to hh \to b \bar b b \bar b$, with $h$ being the discovered SM-like Higgs boson with $m_h=125$ GeV, together with the invisible channel of the pseudoscalar. We work within the context of simplified MSSM scenarios that contain quite heavy sfermions of most types with ${\cal O}(10)$ TeV masses, while the stops are heavy enough to reproduce the 125 GeV mass for the lightest SM-like Higgs boson. By contrast, the gauginos/higgsinos and the heavy MSSM Higgs bosons have masses near the EW scale. Our search strategies, for a LHC center-of-mass energy of $\sqrt{s} =$ 14 TeV, allow us to obtain statistical significances of the signal over the SM backgrounds with values up to $\sim$ 1.6$σ$ and $\sim$ 3$σ$, for total integrated luminosities of 300 fb$^{-1}$ and 1000 fb$^{-1}$, respectively.

hep-ph↗