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Pietro Santorelli

Publications and source records attributed to Pietro Santorelli.

At least 37 records · Page 2Linked to original sources
arXiv2018

Implications of new physics in the decays $B_c \to (J/ψ,η_c)τν$

We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to cτν$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.

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arXiv2017

Theoretical description of the decays $Λ_b \to Λ^{(\ast)}(\frac12^\pm,\frac32^\pm) + J/ψ$

We calculate the invariant and helicity amplitudes for the transitions $Λ_b~\to~Λ^{(\ast)}(J^P)~+~J/ψ$ where the $Λ^{(\ast)}(J^P)$ are $Λ(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P=\frac12^{\pm},\frac32^{\pm}$. The calculations are performed in the framework of a covariant confined quark model previously developed by us. We find that the values of the helicity amplitudes for the $Λ^\ast(1520,\,\frac32^-)$ and the $Λ^\ast(1890,\,\frac32^+)$ are suppressed compared with those for the ground state $Λ(1116,\,\frac12^+)$ and the excited state $Λ^\ast(1405,\,\frac12^-)$. This analysis is important for the identification of the hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ which were discovered in the decay chain $Λ_b^0~\to~P_c^+(~\to~p~J/ψ)~+~K^- $ because the cascade decay chain $Λ_b~\to~Λ^\ast(\frac32^\pm)(~\to~pK^-)~+~J/ψ$ involves the same final state.

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arXiv2016

On the $h \to V \ell^+ \ell^-$ decays

A set of exclusive decays of the Higgs boson into a vector meson and a dilepton pair ($h\to V \ell^+ \ell^-$, with $V=Υ, J/ψ,ϕ$, and $\ell=μ, τ$) are studied in the framework of the Standard Model. We have evaluated the decay rates, the dilepton mass spectra and the $V$ longitudinal helicity fraction distributions. In the same framework, we considered the exclusive modes $h\to V ν\bar ν$ and the implications of the CMS and ATLAS results for the lepton flavor-changing process $h\to τ^+ μ^-$ on the $h\to V τ^+ μ^-$ decay modes.

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arXiv2016

Four-quark structure of Zc(3900), Z(4430) and Xb(5568) states

We examine the four-quark structure of the recently discovered charged $Z_c(3900)$, $Z(4430)$, and $X_b(5568)$ states. We calculate the widths of the strong decays $Z_c^+ \to J/ψπ^+$ ($η_cρ^+$, $\bar D^0D^{\ast\,+}$, $\bar D^{\ast\,0}D^+$), $Z(4430)^+ \to J/ψπ^+$ ($ψ(2s) π^+$), and $X^+_b\to B_sπ^+$ within a covariant quark model previously developed by us. We find that the tetraquark-type current widely used in the literature for the $Z_c(3900)$ leads to a significant suppression of the $\bar D D^\ast$ and $\bar D^\ast D$ modes. Contrary to this a molecular-type current provides an enhancement by a factor of 6-7 for the $\bar D D^\ast$ modes compared with the $Z_c^+\to J/ψπ^+$, $η_cρ^+$ modes in agreement with recent experimental data from the BESIII Collaboration. In case of the $Z(4430)$ state we test a sensitivity of the ratio $R_Z$ of the $Z(4430)^+ \to ψ(2s) π^+$ and $Z(4430)^+ \to J/ψπ^+$ decay rates to a choice of the size parameter $Λ_{Z(4430)}$ of the $Z(4430)$. Using upper constraint for the sum of these two modes deduced from the LHCb Collaboration data we find that $R_Z$ varies from 4.64 to 4.08 when $Λ_{Z(4430)}$ changes from 2.2 to 3.2 GeV. Also we make the prediction for the $Z(4430)^+ \to D^{\ast\,+} \bar D^{\ast\,0}$ decay rate.

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arXiv2016

On Exclusive $h \to V \ell^+ \ell^-$ Decays

We study a set of exclusive decay modes of the Standard Model Higgs boson into a vector meson and a dilepton pair: $h\to V \ell^+ \ell^-$, with $V=Υ, J/ψ,ϕ$, and $\ell=μ, τ$, determining the decay rates, the dilepton mass spectra and the $V$ longitudinal helicity fraction distributions. In the same framework, we analyze the exclusive modes into neutrino pairs $h\to V ν\bar ν$. We also discuss the implications of the recent CMS and ATLAS results for the lepton flavor-changing process $h\to τ^+ μ^-$ on the $h\to V τ^+ μ^-$ decay modes.

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arXiv2015

Semileptonic decays $Λ_c^+ \to Λ\ell^+ ν_\ell\,\,(\ell=e,μ)$ in the covariant quark model and comparison with the new absolute branching fraction measurements of Belle and BESIII

We present precise theoretical predictions for the absolute branching fractions of $Λ_c^+ \to Λ\ell^+ ν_\ell\,(\ell=e,μ)$ decays in the covariant confined quark model. This study is motivated by two recent and accurate measurements of the absolute branching fractions of $Λ_c^+ \to p K^- π^+$ and $Λ_c^+ \to Λe^+ ν_e$ by the Belle Collaboration at the KEKB and by the BESIII Collaboration at the BEPCII. Our predictions for the branching fractions are consistent with both experimental results. We also provide detailed numerical results for differential decay distributions and polarization observables.

hep-ph↗
arXiv2015

Towards an assessment of the ATLAS data on the branching ratio Gamma(Lambda_b(0) -> psi(2S) Lambda(0))/Gamma(Lambda_b(0) -> J/psi Lambda(0))

Recently the ATLAS Collaboration at CERN reported on the measurement of the branching ratio R(Lambda_b) = Gamma(Lambda_b(0) -> psi(2S) Lambda(0))/Gamma(Lambda_b(0) -> J/psi Lambda(0)). The measured branching ratio R(Lambda_b) = 0.501 pm 0.033$ (stat) pm 0.019 (syst) was found to be lower than the covariant quark model prediction of R(Lambda_b) = 0.8 pm 0.1 calculated by us recently. We present a detailed analysis of the branching ratio R(Lambda_b) using a model-independent framework for the heavy-to-light form factors based on results from our previos papers.

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arXiv2015

Physical observables in the decay $Λ_b \to Λ_c (\to Λ+π)+τ^{-}+\bar ν_τ$

We analyze the tauonic semileptonic baryon decays $Λ^0_b \to Λ^+_c + τ^{-} +\bar ν_τ$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the $Λ^+_c$ and the $τ^-$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.

hep-ph↗
arXiv2015

The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model

Recently there has been much interest in the tauonic semileptonic meson decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found larger rates than what is predicted by the Standard Model. We analyze the corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) + antinu_tau with particular emphasis on the lepton helicity flip and scalar contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side forward-backward asymmetries. The nonvanishing polarization of the daughter baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two final state decay planes which we specify. We provide numerical results on these observables using results of the covariant confined quark model. We find large lepton mass effects in the q2-spectra and in the polarization observables.

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arXiv2014

On the $ΔA_{CP}$ saga

We discuss a model in which the large SU(3) flavor violations in singly Cabibbo suppressed decays of neutral D mesons are ascribed exclusively to the final state interactions. The agreement with the experimental data on the branching ratios is obtained with large strong phase differences which are also necessary for substantial direct CP violation. While the value of the CP violating asymmetries depends on the strength of the penguin contribution, we predict an asymmetry for the decays into charged pions more than twice larger than that for charged kaons and having opposite sign.

hep-ph↗
arXiv2013

Polarization effects in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi(-> l+ l-) in the covariant confined quark model

We calculate the invariant and helicity amplitudes for the nonleptonic decay Lambda_b -> Lambda + J/psi, psi(2S) in the covariant confined quark model. We discuss joint angular decay distributions in the cascade decay Lambda_b -> Lambda(-> p pi-) + J/psi, psi(2S) (-> l+ l-) and calculate some of the asymmetry parameters that characterize the joint angular decay distribution. We confirm expectations from the naive quark model that the transitions into the lambda_Lambda=1/2 helicity states of the daughter baryon Lambda are strongly suppressed leading to a near maximal negative polarization of the Lambda. For the same reason the azimuthal correlation between the two decay planes spanned by (p pi-) and (l+ l-) is negligibly small. We provide form factor results for the whole accessible q2-range. Our results are close to lattice results at minimum recoil and light-cone sum rule results at maximum recoil. A new feature of our analysis is that we include lepton mass effects in the calculation which allows us to also describe the cascade decay Lambda_b -> Lambda(-> p pi-) + psi(2S)(-> tau+ tau-).

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arXiv2013

CP violation in D meson decays: would it be a sign of new physics ?

Ascribing the large SU(3) violations in the Cabibbo forbidden decays of neutral D mesons to the final state interactions, one gets large strong phase differences, necessary for substantial direct CP violation. While the absolute value of the CP violating asymmetries depend on the uncertain strength of the penguin contribution, we predict an asymmetry for the decays into charged pions more than twice as large and having opposite sign with respect to that for charged kaons.

hep-ph↗
arXiv2013

Rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma : Differential and total rates, lepton- and hadron-side forward-backward asymmetries

Using the covariant constituent quark model previously developed by us we calculate the differential rate and the forward-backward asymmetries on the lepton and hadron side for the rare baryon decays Lambda_b -> Lambda l+ l- (l=e, mu, tau) and Lambda_b -> Lambda gamma. We use helicity methods to write down a three-fold joint angular decay distribution for the cascade decay Lambda_b -> Lambda (-> p pi-) + J_eff (-> l+ l-). Through appropriate angular integrations we obtain expressions for the rates, the lepton-side forward-backward (FB) asymmetry and the polarization of the daughter baryon Lambda leading to a hadron-side forward-backward asymmetry. We present numerical results on these observables using the covariant quark model and compare our results to the results of other calculations that have appeared in the literature.

hep-ph↗
arXiv2012

Light baryons and their electromagnetic interactions in the covariant constituent quark model

We extend the confined covariant constituent quark model that was previously developed by us for mesons to the baryon sector. In our numerical calculation we use the same values for the constituent quark masses and the infrared cutoff as have been previously used in the meson sector. In a first application we describe the static properties of the proton and neutron, and the $Λ$-hyperon (magnetic moments and charge radii) and the behavior of the nucleon form factors at low momentum transfers. We discuss in some detail the conservation of gauge invariance of the electromagnetic transition matrix elements in the presence of a nonlocal coupling of the baryons to the three constituent quark fields.

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arXiv2012

Form factors for semileptonic, nonleptonic and rare $B\, (B_s)$ meson decays

We provide new values for the model parameters of the covariant constituent quark model (with built--in infrared confinement) in the meson sector by a fit to the leptonic decay constants and a number of electromagnetic decays. We then evaluate, in a parameter free way, the form factors of the $B(B_s)\to P(V)$-transitions in the full kinematical region of momentum transfer. As an application of our results we calculate the widths of the nonleptonic $B_s$-decays into $D_s^- D_s^+,$ $D_s^{\ast\,-} D_s^{+}+D_s^- D_s^{\ast\,+}$ and $D_s^{\ast\,-} D_s^{\ast\,+}$. These modes give the largest contribution to $ΔΓ$ for the $B_s-\bar B_s$ system. We also treat the nonleptonic decay $B_{s}\to\Jpsiϕ$. Although this mode is color suppressed this decay has important implications for the search of possible CP-violating New Physics effects in $B_s-\bar B_s$ mixing.

hep-ph↗
arXiv2011

One-photon decay of the tetraquark state $X(3872) \to γ+ J/ψ$ in a relativistic constituent quark model with infrared confinement

We further explore the consequences of treating the X(3872) meson as a tetraquark bound state by analyzing its one-photon decay X => γ+ J/psi in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the X(3872) meson with its four constituent quarks by using the P-exponential path-independent formalism. We calculate the matrix element of the transition X => γ+ J/psi and prove its gauge invariance. We evaluate the X=> γ+ J/psi decay width and the longitudinal/transverse composition of the J/psi in this decay. For a reasonable value of the size parameter of the X(3872) meson we find consistency with the available experimental data. We also calculate the helicity and multipole amplitudes of the process, and describe how they can be obtained from the covariant transition amplitude by covariant projection.

hep-ph↗
arXiv2011

Determining alpha_s from the hyperfine splitting mUpsilon(1S)-mEta(b)

The measurement of the eta_b mass, together with a QCD result for the hyperfine splitting E_{HFS}=M_{Upsilon(1S)}-M_{eta_b}, allows us to determine the strong coupling constant alpha_s at a low energy scale. The result alpha_s(M_{Upsilon(1S)})=0.197\pm 0.002_{Delta E_{HFS}^{exp}} \pm 0.002_{scheme} \pm 0.002_{delta } \pm 0.006_{delta m_b} \pm 0.005_{ho}, alpha_s(M_{Z^0})=0.124\pm 0.001_{Delta E_{HFS}^{exp}} \pm 0.001_{scheme} \pm 0.001_{delta } \pm 0.003_{delta m_b} \pm 0.002_{ho}, is compatible with the current world average of alpha_s reported by the Particle Data Group, and shows that the experimental lowest-lying \bar b b hyperfine splitting can be reproduced in terms of a perturbative and nonperturbative QCD contribution.

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