arXiv subjects

Maria Laura Piscopo

Publications and source records attributed to Maria Laura Piscopo.

At least 19 recordsLinked to original sources

arXiv2026

Enhanced Standard Model bound on charm CP violation from QCD penguins

We investigate the impact of QCD penguin operators on direct CP violation in singly Cabibbo-suppressed $D^0$ decays within the framework of light-cone sum rules (LCSR) using pion and kaon light-cone distribution amplitudes. We determine, for the first time, the hadronic matrix elements of the QCD penguin operators for $D^0\to K^+K^-$ and $D^0\toπ^+π^-$ at leading order in $α_s$, employing a three-point correlation function with an artificial momentum to avoid unphysical parasitic cuts. We also compute the matrix elements of the current-current operators using the same framework and compare them with previous LCSR results. We find that the scalar penguin operators $Q_5$ and $Q_6$ can have substantially enhanced matrix elements. We identify two sources of enhancement: quark-condensate contributions, which arise already at tree level and are therefore enhanced by a relative factor of $16 π^2$ compared to the remaining, loop-induced terms in the sum rule; and an annihilation-type contribution from the $\bar u u$ component of these operators, which enters already through twist-three light-cone distribution amplitudes and is of comparable magnitude. While the impact of QCD penguin operators on the branching ratios is negligible, they can enhance the magnitude of the ``penguin-to-tree'' amplitude ratios relevant for direct CP violation. The relevant strong phases, however, remain largely unconstrained within the accuracy of our framework. Assuming maximal relative strong phases, we find that the corresponding upper bound on the Standard Model contribution to charm CP violation can be enhanced compared to estimates based on the current-current operators alone, reducing the gap with the experimental measurement.

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arXiv2026

Charm physics

50 years after the discovery of the first charmed particle, charm physics continues to be an extremely lively field of research and a cornerstone in particle physics. The study of charm, with its unique properties, is characterised by many challenging but also exciting peculiarities, making it an ideal testing ground for Standard Model (SM) predictions and a very sensitive probe of new physics. This chapter is intended to provide a pedagogical introduction to the physics of the charm quark and to its current theoretical and experimental status. Specifically, it discusses the main features of the charm sector of the SM, the theoretical and experimental challenges that arise when dealing with the charm quark, and the methods used to study it. An overview, both from a theoretical and experimental perspective, of fundamental observables such as lifetimes of charm hadrons, $D^0$-meson mixing, charm charge-parity violation (CPV) and rare charm decays is also presented.

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arXiv2026

A Standard Model analysis of $D^0 \to π^- π^+, K^- K^+, K_{\rm S}^0 K_{\rm S}^0$

We investigate the Standard Model (SM) description of the singly Cabibbo-suppressed charm decays $D^0\to π^-π^+$, $D^0\to K^-K^+$ and $D^0\to K_{\rm S}^0K_{\rm S}^0$. Using factorisation together with isospin symmetry, we constrain non-factorisable effects and the associated $U$-spin breaking required by the measured branching fractions. We find that corrections of order $50\%$ are sufficient to describe all modes, which although sizeable, are not unexpected for hadronic charm decays. Using the constraints from the branching fractions, we derive SM predictions for the direct CP asymmetry in $D^0\to K_{\rm S}^0K_{\rm S}^0$, finding it to be at most at the per-mille level in our benchmark scenario, providing motivation for future precision measurements.

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arXiv2026

Predictions for $b$-baryon lifetimes at NNLO-QCD

Motivated by recent and forthcoming experimental progress, we provide updated predictions for the total decay rates of $b$-baryons, their lifetime ratios and their lifetimes normalised to that of the $B^0_d$ meson within the framework of the heavy quark expansion (HQE). We include, for the first time, next-to-next-to-leading-order QCD corrections to the free $b$-quark decay, which significantly reduce the theoretical uncertainties in the total decay rates. In addition, we also include, for the first time, the complete next-to-leading-order QCD corrections to the dimension-five contributions. While these corrections have only a minor effect on the total decay rates, they induce a sizeable shift in the lifetime ratios, improving the agreement between HQE predictions and experimental data. Overall, we find excellent agreement between the HQE predictions and current experimental measurements for both total decay rates and lifetime ratios within the quoted uncertainties.

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arXiv2026

$B$-meson decay width up to $1/m_b^3$ corrections within and beyond the Standard Model

Starting from the most general effective $|ΔB| = 1$ Hamiltonian describing non-leptonic $b$-quark decays $b\to q_1 \bar q_2 q_3$, we compute analytic expressions for all matching coefficients of the two-quark operator contributions in the heavy quark expansion~(HQE) of a $B$ meson, up to mass-dimension-six. In addition, we calculate the weak-annihilation contributions, which enter the matching of four-quark operators in the HQE at dimension-six and were previously missing. Our results complete the calculation of beyond Standard Model (BSM) effects in non-leptonic, tree-level, $b$-quark decays relevant for $B$ meson lifetimes and lifetime ratios such as $τ(B^0_s)/τ(B^0_d)$. Such BSM contributions naturally arise in generic extensions of the Standard Model (SM) that aim to address the observed tensions between experimental measurements and theoretical predictions based on QCD factorisation in several colour-allowed non-leptonic $B$-meson decays. As a by-product of our calculation, we also determine the matching coefficients in the HQE induced by the QCD-penguin operators within the SM, including both the interference between current-current and penguin operators and the contributions quadratic in the penguin operators. Owing to the suppression of the QCD-penguin Wilson coefficients within the SM, these effects are typically regarded as corrections of order $α_s$ and $α_s^2$ in the strong coupling, respectively. Our results reproduce the known expressions at dimension-three and provide new results for the coefficients of the chromomagnetic operator at dimension-five and of the Darwin operator at dimension-six.

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arXiv2025

Standard Model Benchmarks for $D^0\to K^- K^+, π^-π^+, K^0_{\rm S} K^0_{\rm S}$ Decays

The non-leptonic $D^0\to K^- K^+$ and $D^0\to π^-π^+$ decays are powerful probes of the Standard Model and are related to each other through the $U$-spin symmetry of the strong interaction. Using lattice QCD inputs we calculate the corresponding colour-allowed tree amplitudes in factorisation and demonstrate that non-factorisable contributions and $U$-spin-breaking effects at the level of 50% allow us to accommodate the measured branching ratios in the Standard Model. An exciting direct probe of such non-factorisable and $U$-spin breaking effects is provided by the $D^0\to K^0_{\rm S} K^0_{\rm S}$ channel. This decay is governed by non-factorisable exchange topologies and essentially vanishes in the $U$-spin limit, although it is experimentally well established with a prominent branching ratio. Extrapolating our $D^0\to K^- K^+$ results using the isospin symmetry, we find a consistent benchmark picture. Specifically, we can accommodate the measured $D^0\to K^0_{\rm S} K^0_{\rm S}$ branching ratio with $U$-spin-breaking effects at the 50% level and exchange amplitudes at the level of 50% of the colour-allowed $D^0\to K^- K^+$, $D^0\to π^-π^+$ tree contributions. Finally, we explore the resulting range for direct CP violation in $D^0\to K^0_{\rm S} K^0_{\rm S}$, obtaining upper bounds in our benchmark scenarios of a few per mille, offering an exciting target for future measurements.

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arXiv2025

Physics Briefing Book: Input for the 2026 update of the European Strategy for Particle Physics

The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisioned for the near-, mid-, and long-term future. All submitted contributions are evaluated by the Physics Preparatory Group (PPG), and a preliminary analysis is presented at a Symposium meant to foster a broad community discussion on the scientific value and feasibility of the various ideas proposed. The outcomes of the analysis and the deliberations at the Symposium are synthesized in the current Briefing Book, which provides an important input in the deliberations of the Strategy recommendations by the European Strategy Group (ESG).

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arXiv2024

Total decay rates of $B$ mesons at NNLO-QCD

We update the Standard Model (SM) predictions for the lifetimes of the $B^+$, $B_d$ and $B_s$ mesons within the heavy quark expansion (HQE), including the recently determined NNLO-QCD corrections to non-leptonic decays of the free $b$-quark. In addition, we update the HQE predictions for the lifetime ratios $τ(B^+)/τ(B_d)$ and $τ(B_s)/τ(B_d)$, and provide new results for the semileptonic branching fractions of the three mesons entirely within the HQE. We obtain a considerable improvement of the theoretical uncertainties, mostly due to the reduction of the renormalisation scale dependence when going from LO to NNLO, and for all the observables considered, we find good agreement, within uncertainties, between the HQE predictions and the corresponding experimental data. Our results read, respectively, $Γ(B^+) = 0.587^{+0.025}_{-0.035}~{\rm ps}^{-1}$, $Γ(B_d) = 0.636^{+0.028}_{-0.037}~{\rm ps}^{-1}$, $Γ(B_s) = 0.628^{+0.027}_{-0.035}~{\rm ps}^{-1}$, for the total decay widths, $τ(B^+)/τ(B_d) = 1.081^{+0.014}_{-0.016}$, $τ(B_s)/τ(B_d) = 1.013^{+0.007}_{-0.007}$, for the lifetime ratios, and ${\cal B}_{\rm sl} (B^+) = (11.46^{+0.47}_{-0.32}) \%$, ${\cal B}_{\rm sl} (B_d) = (10.57^{+0.47}_{-0.27}) \%$, ${\cal B}_{\rm sl} (B_s) = (10.52^{+0.50}_{-0.29}) \%$, for the semileptonic branching ratios. Finally, we also provide an outlook for further improvements of the HQE determinations of the $B$-meson decay widths and of their ratios.

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arXiv2024

Towards a SM prediction for CP violation in charm

We provide an overview of the current experimental and theoretical status of charm CP violation and discuss recent progress in obtaining a Standard Model prediction for $Δa_{\rm CP}^{\rm dir}$ using the framework of light-cone sum rules. Furthermore, we present new results for the ratios of the direct CP asymmetries and of the branching fractions for the modes $D^0 \to π^+ π^-$ and $D^0 \to K^+ K^-$.

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arXiv2023

Two body non-leptonic $D^0$ decays from LCSR and implications for $Δa^{\rm dir}_{\rm CP}$

Motivated by the recent measurements of CP violating effects in singly Cabibbo suppressed $D^0$ decays, we revisit the theoretical predictions of these channels. Using up-to-date values for the decay constants and form factors, we find already within naive QCD factorisation surprisingly good agreement between the central values of the branching ratios and the corresponding experimental data. We further extend the study of these modes by employing the method of light-cone sum rules (LCSR) with light-meson light-cone distribution amplitudes. Using for the first time this framework to compute the leading contribution to the decay amplitude, we can again describe well the experimental branching ratios for the modes $D^0 \to π^+ K^-$, $D^0 \to K^+ K^-$, $D^0 \to π^+ π^- $ and $D^0 \to K^+ π^-$. The combination of our results with known predictions for the penguin contributions, obtained with LCSR, leads to an upper bound for the value of direct CP violation expected in the Standard Model of $|Δa_{\rm CP}^{\rm dir}| \leq {2.4} \times 10^{-4} \,,$ which is approximately a factor six smaller than the current measurement.

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arXiv2023

Non-factorisable effects in the decays $\bar B_{s}^0 \to D_{s}^+ π^-$ and $\bar B^0 \to D^+ K^-$ from LCSR

In light of the current discrepancies between the recent predictions based on QCD factorisation (QCDF) and the experimental data for several non-leptonic colour-allowed two-body $B$-meson decays, we obtain new determinations of the non-factorisable soft-gluon contribution to the decays $\bar B_{s}^0 \to D_{s}^+ π^-$ and $\bar B^0 \to D^+ K^-$, using the framework of light-cone sum rule (LCSR), with a suitable three-point correlation function and $B$-meson light-cone distribution amplitudes. In particular, we discuss the problem associated with a double light-cone (LC) expansion of the correlator, and motivate future determinations of the three-particle $B$-meson matrix element with the gluon and the spectator quark aligned along different light-cone directions. Performing a LC-local operator product expansion of the correlation function, we find, for both modes considered, the non-factorisable part of the amplitude to be sizeable and positive, however, with very large systematic uncertainties. Furthermore, we also determine for the first time, using LCSR, the factorisable amplitudes at LO-QCD, and thus the corresponding branching fractions. Our predictions are in agreement with the experimental data and consistent with the results based on QCDF, although again within very large uncertainties. In this respect, we provide a rich outlook for future improvements and investigations.

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arXiv2023

Status of the lifetimes of heavy hadrons within the HQE

We present the theoretical status of the lifetimes of weakly decaying heavy hadrons containing a bottom or a charm quark, and discuss the current predictions, based on the framework of the Heavy Quark Expansion (HQE), for both mesons and baryons. Potential improvements to reduce the theoretical uncertainties are also highlighted.

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arXiv2023

Quark-hadron duality at work: lifetimes of bottom baryons

In the 1990s, very low experimental values for the lifetime ratio $τ(Λ_b)/τ(B_d)$ triggered a considerable amount of doubt in the applicability of the heavy quark expansion (HQE), which is based on the assumption of quark-hadron duality (QHD) for inclusive total decay rates. However, these low values turned out to be the result of purely experimental problems, and the current HFLAV average reads $τ(Λ_b)/τ(B_d) = 0.969(6)$. In this work, we present the Standard Model predictions for the $b$-baryon lifetimes within the framework of the HQE. In particular, we include for the first time the contribution of the Darwin term and we update the estimates for the matrix elements of the dimension-six four-quark operators. Within experimental and theoretical uncertainties, we find excellent agreement between the data and the HQE predictions, and thus no indication for any visible violation of QHD. Our numerical results can be summarised by the ratios $τ(Λ_b)/τ(B_d) = 0.955(14)$, $τ(Ω_b^-)/τ(B_d) = 1.081(42)$, and $τ(Ξ_b^0)/τ(Ξ_b^-) = 0.929(28)$.

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arXiv2022

Taming New Physics in $b \to c \bar u d (s) $ with $τ(B^+)/τ(B_d)$ and $a_{sl}^d$

Inspired by the recently observed tensions between the experimental data and the theoretical predictions, based on QCD factorisation, for several colour-allowed non-leptonic $B$-meson decays, we study the potential size of new physics (NP) effects in the decay channels $b \to c \bar{u} d(s)$. Starting from the most general effective Hamiltonian describing the $b \to c \bar{u} d(s)$ transitions, we compute NP contributions to the theoretical predictions of $B$-meson lifetime and of $B$-mixing observables. The well-known lifetime ratio $τ(B^+)/τ(B_d)$ and the experimental bound on the semi-leptonic CP asymmetry $a_{sl}^d$, provide strong, complementary constraints on some of the NP Wilson coefficients.

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arXiv2022

Disintegration of beauty: a precision study

We update the Standard Model (SM) predictions for $B$-meson lifetimes within the heavy quark expansion (HQE). Including for the first time the contribution of the Darwin operator, SU(3)$_F$ breaking corrections to the matrix element of dimension-six four-quark operators and the so-called eye-contractions, we obtain for the total widths $Γ(B^+) = (0.58^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, $Γ(B_d) = (0.63^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, $Γ(B_s) = (0.63^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, and for the lifetime ratios $τ(B^+) / τ(B_d) = 1.086 \pm 0.022$, $τ(B_s) / τ(B_d) = 1.003 \pm 0.006 \, (1.028 \pm 0.011)$. The two values for the last observable arise from using two different sets of input for the non-perturbative parameters $μ_π^2(B_d)$, $μ_G^2(B_d)$, and $ρ_D^3(B_d)$ as well as from different estimates of the SU(3)$_F$ breaking in these parameters. Our results are overall in very good agreement with the corresponding experimental data, however, there seems to emerge a tension in $τ(B_s)/τ(B_d)$ when considering the second set of input parameters. Specifically, this observable is extremely sensitive to the size of the parameter $ρ_D^3 (B_d)$ and of the SU(3)$_F$ breaking effects in $μ_π^2$, $μ_G^2$ and $ρ_D^3$; hence, it is of utmost importance to be able to better constrain all these parameters. In this respect, an extraction of $μ_π^2 (B_s), μ_G^2 (B_s), ρ_D^3 (B_s)$ from future experimental data on inclusive semileptonic $B_s$-meson decays or from direct non-perturbative calculations, as well as more insights about the value of $ρ_D^3 (B)$ extracted from fit, would be very helpful in reducing the corresponding theory uncertainties.

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arXiv2021

Higher Order Corrections To The Lifetime Of Heavy Hadrons

In this work we discuss the theoretical status for the study of the lifetime of heavy hadrons. After presenting some introductory topics like the effective weak Hamiltonian and the heavy quark effective theory (HQET), we describe the construction of the heavy quark expansion (HQE), which constitutes the theoretical framework to systematically compute the total decay width of heavy hadrons, in terms of an expansion in inverse powers of the heavy quark mass. The structure of the HQE is discussed in detail, and the computation of the lowest dimensional contributions, explicitly outlined. Particular emphasis is put in describing the expansion of the quark propagator in the external gluon field using the Fock-Schwinger (FS) gauge, which represents a fundamental ingredient of the calculation. Moreover, the main result is the computation of the dimension-six contribution due to the Darwin operator, only recently determined and found to have a sizeable effect. Finally, we consider two phenomenological applications of the HQE in the charm sector, namely the study of the lifetime of charmed mesons and the analysis of the Glashow-Iliopoulos-Maiani (GIM) cancellations in neutral $D$-meson mixing. By comparing our results with recent measurements performed by the LHCb, Belle-II and BESIII collaborations, we conclude that the HQE is able to reproduce, within large theoretical uncertainties, the experimental pattern for the lifetimes of charmed mesons and we discuss a potential solution for the discrepancy of previous theoretical determinations of $D$-mixing with data.

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arXiv2021

Revisiting Inclusive Decay Widths of Charmed Mesons

Determining for the first time the Darwin operator contribution for the non-leptonic charm-quark decays and using new non-perturbative results for the matrix elements of $ΔC=0$ four-quark operators, including eye-contractions, we present a comprehensive study of the lifetimes of charmed mesons and inclusive semileptonic decay rates as well as the ratios, within the framework of the Heavy Quark Expansion (HQE). We find good agreement with experiment for the ratio $τ(D^+)/τ(D^0)$, for the total $D_s^+$-meson decay rate, for the semileptonic rates of all three mesons $D^0$, $D^+$ and $D_s^+$, and for the semileptonic ratio $Γ_{sl}^{D^+}/Γ_{sl}^{D^0}$. The total decay rates of the $D^0$ and $D^+$ mesons are underestimated in our HQE approach and we suspect that this is due to missing higher-order QCD corrections to the free charm quark decay and the Pauli interference contribution. For the $SU(3)_F$ breaking ratios $τ(D_s^+) / τ(D^0) $ and $Γ_{sl}^{D_s^+}/Γ_{sl}^{D^0} $ our predictions lie closer to one than experiment. This might originate from the poor knowledge of the non-perturbative parameters $μ_G^2$, $μ_π^2$ and $ρ_D^3$ in the $D^0$ and $D_s^+$ systems. These parameters could be determined by experimental studies of the moments of inclusive semileptonic $D$ meson decays.

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arXiv2021

Contribution of the Darwin operator to non-leptonic decays of heavy quarks

We compute the Darwin operator contribution ($1/m_b^3$ correction) to the width of the inclusive non-leptonic decay of a $B$ meson ($B^+$, $B_d$ or $B_s$), stemming from the quark flavour-changing transition $b \to q_1 \bar q_2 q_3$, where $q_1,q_2 = u, c$ and $q_3 = d, s$. The key ideas of the computation are the local expansion of the quark propagator in the external gluon field including terms with covariant derivative of the gluon field strength tensor and the standard technique of the Heavy Quark Expansion (HQE). We confirm the previously known expressions of the $1/m_b^3$ contributions to the semi-leptonic decay $b \to q_1 \ell \bar ν_\ell$, with $\ell = e, μ, τ$ and of the $1/m_b^2$ contributions to the non-leptonic modes. We find that this new term can give a sizeable correction of about $- 4 \, \%$ to the non-leptonic decay width of a $B$ meson. For $B_d$ and $B_s$ mesons this turns out to be the dominant correction to the free b-quark decay, while for the $B^+$ meson the Darwin term gives the second most important correction - roughly 1/2 to 1/3 of the phase space enhanced Pauli interference contribution. Due to the tiny experimental uncertainties in lifetime measurements the incorporation of the Darwin term contribution is crucial for precision tests of the Standard Model.

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