arXiv subjects

A. C. dos Reis

Publications and source records attributed to A. C. dos Reis.

13 recordsLinked to original sources

arXiv2025

Science Prospects for the Southern Wide-field Gamma-ray Observatory: SWGO

Ground-based gamma-ray astronomy is now well established as a key observational approach to address critical topics at the frontiers of astroparticle physics and high-energy astrophysics. Whilst the field of TeV astronomy was once dominated by arrays of atmospheric Cherenkov Telescopes, ground-level particle detection has now been demonstrated to be an equally viable and strongly complementary approach. Ground-level particle detection provides continuous monitoring of the overhead sky, critical for the mapping of extended structures and capturing transient phenomena. As demonstrated by HAWC and LHAASO, the technique provides the best available sensitivity above a few tens of TeV, and for the first time access to the PeV energy range. Despite the success of this approach, there is so far no major ground-level particle-based observatory with access to the Southern sky. HESS, located in Namibia, is the only major gamma-ray instrument in the Southern Hemisphere, and has shown the extraordinary richness of the inner galaxy in the TeV band, but is limited in terms of field of view and energy reach. SWGO is an international effort to construct the first wide-field instrument in the south with deep sensitivity from 100s of GeV into the PeV domain. The project is now close to the end of its development phase and planning for construction of the array in Chile has begun. Here we describe the baseline design, expected sensitivity and resolution, and describe in detail the main scientific topics that will be addressed by this new facility and its initial phase SWGO-A. We show that SWGO will have a transformational impact on a wide range of topics from cosmic-ray acceleration and transport to the nature of dark matter. SWGO represents a key piece of infrastructure for multi-messenger astronomy in the next decade, with strong scientific synergies with the nearby CTA Observatory.

astro-ph.HE↗

arXiv2020

Multibody decay analyses -- a new phenomenological model for meson-meson subamplitudes

Meson-meson amplitudes are important on their own and also play key roles in analyses of heavy-meson and tau decays. In this work we propose a new phenomenological model suited to all $SU(3)$ mesonic two-body final state interactions up to energies around 2 GeV. It is aimed at replacing those entering the old isobar model, produced in the 1960's, long before the development of QCD. The only similarity between our new proposal and amplitudes used in the isobar model concern vector resonances in the elastic regime. In other situations, especially those involving scalar resonances and coupled channels, the isobar model is not compatible with post-QCD dynamics. In order to support these claims convincingly and to motivate our approach, we consider applications to the $ππ$ amplitude and compare our version with the isobar model in several different instances. We also show that the new model provides a clear indication of the mechanism responsible for the sharp rise observed in the $ππ$ phase around $1\,$ GeV. The phenomenological amplitudes proposed here are suited to any number of resonances in a given channel and rely just on masses and coupling constants as free parameters. Concerning theory, they incorporate chiral symmetry at low energies, include coupled channels and respect unitarity whenever appropriate.

hep-ph↗

arXiv2019

Physics case for an LHCb Upgrade II - Opportunities in flavour physics, and beyond, in the HL-LHC era

The LHCb Upgrade II will fully exploit the flavour-physics opportunities of the HL-LHC, and study additional physics topics that take advantage of the forward acceptance of the LHCb spectrometer. The LHCb Upgrade I will begin operation in 2020. Consolidation will occur, and modest enhancements of the Upgrade I detector will be installed, in Long Shutdown 3 of the LHC (2025) and these are discussed here. The main Upgrade II detector will be installed in long shutdown 4 of the LHC (2030) and will build on the strengths of the current LHCb experiment and the Upgrade I. It will operate at a luminosity up to $ 2 \times 10^{34} \rm cm^{-2}s^{-1}$, ten times that of the Upgrade I detector. New detector components will improve the intrinsic performance of the experiment in certain key areas. An Expression Of Interest proposing Upgrade II was submitted in February 2017. The physics case for the Upgrade II is presented here in more depth. $CP$-violating phases will be measured with precisions unattainable at any other envisaged facility. The experiment will probe $b\to s \ell^+\ell^-$ and $b\to d \ell^+\ell^-$ transitions in both muon and electron decays in modes not accessible at Upgrade I. Minimal flavour violation will be tested with a precision measurement of the ratio of $B(B^0\toμ^+μ^-)/B(B_s^0\to μ^+μ^-)$. Probing charm $CP$ violation at the $10^{-5}$ level may result in its long sought discovery. Major advances in hadron spectroscopy will be possible, which will be powerful probes of low energy QCD. Upgrade II potentially will have the highest sensitivity of all the LHC experiments on the Higgs to charm-quark couplings. Generically, the new physics mass scale probed, for fixed couplings, will almost double compared with the pre-HL-LHC era; this extended reach for flavour physics is similar to that which would be achieved by the HE-LHC proposal for the energy frontier.

hep-ex↗

arXiv2018

Multi-Meson Model for the $D^+\to K^+K^-K^+$ decay amplitude

We propose a novel approach to describe the $D^+\to K^+K^-K^+$ decay amplitude, based on chiral effective Lagrangians, which can be used to extract information about $K\bar{K}$ scattering. Our trial function is an alternative to the widely used isobar model and includes both nonresonant three-body interactions and two-body rescattering amplitudes, based on coupled channels and resonances, for S- and P-waves with isospin $0$ and $1$. The latter are unitarized in the $K$-matrix approximation and represent the only source of complex phases in the problem. Free parameters are just resonance masses and coupling constants, with transparent physical meanings. The nonresonant component, given by chiral symmetry as a real polynomium, is an important prediction of the model, which goes beyond the (2+1) approximation. Our approach allows one to disentangle the two-body scalar contributions with different isospins, associated with the $f_0(980)$ and $a_0(980)$ channels. We show how the $K\bar{K}$ amplitude can be obtained from the decay $D^+\to K^+K^-K^+$ and discuss extensions to other three-body final states.

hep-ph↗

arXiv2016

Multi-Meson Model applied to $D^+ \to K^+ K^- K^+$

Matrix elements of weak currents involving light multi-meson states are important in many hadronic decays of both heavy leptons and heavy mesons. In this paper we focus on the latter case where the current size of the data set demands better models. The specific case of three-kaon weak matrix elements is considered and expressed as a relatively simple structure, which generalizes naturally the concept of form factor. We propose a model for the decay $D^+ \to K^+ K^- K^+$ as an alternative to isobar model, with free parameter predicted by the theory to be fine-tuned by a fit to data. An important qualitative outcome is that we encompass naturally all final states topologies, which involve necessarily proper multi-particle structures and cannot be decomposed into simpler two-body processes. This aspect represents a significant improvement when compared to isobar model, often employed in analyses of heavy-meson decay data.

hep-ph↗

arXiv2014

Final state interaction in $D^+\to K^-π^+π^+$ with $Kπ$ I=1/2 and 3/2 channels

The final state interaction contribution to $D^+$ decays is computed for the $K^-π^+π^+$ channel within a light-front relativistic three-body model for the final state interaction. The rescattering process between the kaon and two pions in the decay channel is considered. The off-shell decay amplitude is a solution of a four-dimensional Bethe-Salpeter equation, which is decomposed in a Faddeev form. The projection onto the light-front of the coupled set of integral equations is performed via a quasi-potential approach. The S-wave $Kπ$ interaction is introduced in the resonant isospin $1/2$ and the non-resonant isospin $3/2$ channels. The numerical solution of the light-front tridimensional inhomogeneous integral equations for the Faddeev components of the decay amplitude is performed perturbatively. The loop-expansion converges fast, and the three-loop contribution can be neglected in respect to the two-loop results for the practical application. The dependence on the model parameters in respect to the input amplitude at the partonic level is exploited and the phase found in the experimental analysis, is fitted with an appropriate choice of the real weights of the isospin components of the partonic amplitude. The data suggests a small mixture of total isospin $5/2$ to the dominant $3/2$ one. The modulus of the unsymmetrized decay amplitude, which presents a deep valley and a following increase for $Kπ$ masses above $1.5$ GeV, is fairly reproduced. This suggests the assignment of the quantum numbers $0^+$ to the isospin 1/2 $K^*(1630)$ resonance.

hep-ph↗

arXiv2014

Heavy meson decay in three-mesons and FSI

The final state interaction (FSI) contribution to charged $D$ decay into $Kππ$ is computed within a light-front framework, considering $S$-wave $Kπ$ interactions in $1/2$ and $3/2$ isospin states. The convergence of the rescattering series is checked computing terms up to the third perturbative order. The role of the resonances above $K^*_0(1430)$, and the contribution of the $Kπ$ $3/2$ isospin channel to charged three-body $D$ decays, are studied against the available phase-shift analysis.

hep-ph↗

arXiv2013

D+ -> K- pi+ pi+ : heavy meson decays and final state interactions

We show that final state interactions are important in shaping Dalitz plots for the decay $D^+ \rar K^- \p^+ \p^+$. The theoretical treatment of this reaction requires a blend of several weak and hadronic processes and hence it is necessarily involved. In this talk we present results from a calculation which is still in progress, but has already unveiled the role of important dynamical mechanisms. We do not consider explicit quark degrees of freedom and our study is performed within an effective hadronic framework. In spite of the relatively wide window of energies available in the Dalitz plot for the $D^+$ decay, we depart from $SU(3)\times SU(3)$ chiral perturbation theory and extend its range by means of unitarization. Our present results, which concentrate on the vector weak vertex, describe qualitative features of the modulus of the decay amplitude and agrees well with its phase in the elastic region.

hep-ph↗

arXiv2012

Second Generation of 'Miranda Procedure' for CP Violation in Dalitz Studies of B (\& D \& τ) Decays

The `Miranda Procedure' proposed for analyzing Dalitz plots for CP asymmetries in charged B and D decays in a model-independent manner is extended and refined. The complexity of CKM CP phenomenology through order $λ^6$ is needed in searches for New Dynamics (ND). Detailed analyses of three-body final states other great advantages: (i) They give us more powerful tools for deciding whether an observed CP asymmetry rep- resents the manifestation of ND and its features. (ii) Many advantages can already be obtained by the `Miranda Procedure' without construction of a detailed Dalitz plot de- scription. (iii) One studies CP asymmetries independent of production asymmetries. We illustrate the power of a second generation Miranda Procedure with examples with time integrated rates for $B_d/\bar B_d$ decays to final states $K_Sπ+π-$ as trial runs with comments on $B^{\pm} \to K^{\pm}π^+π^-/K^{\pm}K^+K^-$.

hep-ph↗

arXiv2012

Towards three-body unitarity in $D^+ \to K^- π^+ π^+$

We assess the importance of final state interactions in $D^+ \rar K^- \p^+ \p^+$, stressing the consistency between two- and three-body interactions. The basic building block in the calculation is a $Kπ$ amplitude based on unitarized chiral perturbation theory and with parameters determined by a fit to elastic LASS data. Its analytic extension to the second sheet allows the determination of two poles, associated with the $\k$ and the $K^*(1430)$, and a representation of the amplitude based on them is constructed. The problem of unitarity in the three-body system is formulated in terms of an integral equation, inspired in the Faddeev formalism, which implements a convolution between the weak vertex and the final state hadronic interaction. Three different topologies are considered for the former and, subsequently, the decay amplitude is expressed as a perturbation series. Each term in this series is systematically related to the previous one and a re-summation was performed. Remaining effects owing to single and double rescattering processes were then added and results compared to FOCUS data. We found that proper three-body effects are important at threshold and fade away rapidly at higher energies. Our model, based on a vector weak vertex, can describe qualitative features of the modulus of the decay amplitude and agrees well with its phase in the elastic region.

hep-ph↗

arXiv2011

Three-body FSIs in D+ ---> K- pi+ pi+

We stress the importance of three-body final state interactions in $D^+ \to K^- \p^+ \p^+$. The basic building block is the $Kπ$ amplitude with parameters determined by a fit to elastic LASS data. Based on a vector weak vertex, we can describe the $Kπ$ phase production experimental in the elastic region.

hep-ph↗

arXiv2009

On a CP Anisotropy Measurement in the Dalitz Plot

We describe a novel use of the Dalitz plot to probe CP symmetry in three-body modes of $B$ and $D$ mesons. It is based on an observable inspired by astronomers' practice, namely the significance in the difference between corresponding Dalitz plot bins. It provides a model independent mapping of local CP asymmetries. We illustrate the method for probing CP symmetry in the complementary cases of B decays, where sizable or even large effects can be expected, yet have to be differentiated against leading Standard Model contributions, and $D$ decays, where one cannot count on sizable effects, yet has to deal with much less Standard Model background.

hep-ph↗

arXiv2003

Asymmetries in the Production of Lambda0 in 250 GeV/c pi+-, K+- and p -- Nucleon Interactions

Using data from Fermilab fixed-target experiment E769, we have measured particle-antiparticle production asymmetries for Lambda0 hyperons in 250 GeV/c pi+-, K+- and p -- nucleon interactions. The asymmetries are measured as functions of Feynman-x (x_F) and p_t^2 over the ranges -0.12<=x_F<=0.12 and 0<=p_t^2<=3 (GeV/c)^2 (for positive beam) and -0.12<=x_F<=0.4 and 0<=p_t^2<=10 (GeV/c)^2 (for negative beam). We find substantial asymmetries, even at x_F around zero. We also observe leading-particle-type asymmetries. These latter effects are qualitatively as expected from valence-quark content of the target and variety of projectiles studied.

hep-ex↗