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Creating plasmonic nanoparticles on a tapered optical fiber tip enables a remote SERS sensing probe, ideal for challenging sampling scenarios like biological tissue, specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Here, we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands (NIs) with varied geometric parameters, directly contacting the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark Rhodamine 6G molecule and Serotonin, a neurotransmitter with high relevance for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, for serotonin we observed a different behavior linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, we believe our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provide new clues to discover and understand the intricate plasmonic-driven chemical reactions.

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 $\Delta a_{\rm CP}^{\rm dir}$ 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 $D^0 \to \pi^+ \pi^-$ and $D^0 \to K^+ K^-$., Comment: 8 pages, 1 figure, Contribution to the Proceedings of the 20th International Conference on B-Physics at Frontier Machines (Beauty 2023), 3-7 July 2023, Clermont-Ferrand, France

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 $D^0 \to \pi^+ K^-$, $D^0 \to K^+ K^-$, $D^0 \to \pi^+ \pi^- $ and $D^0 \to K^+ \pi^-$. 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 $|\Delta a_{\rm CP}^{\rm dir}| \leq {2.4} \times 10^{-4} \,,$ which is approximately a factor six smaller than the current measurement., Comment: 22 pages, 2 figures, 1 table

Artificial intelligence has emerged as promising tool to decode a phase image transmitted through a multimode fiber (MMF) by applying deep learning techniques. By transmitting tens of thousands of images through the MMF, deep neural networks (DNNs) are capable of learning how to decipher the seemingly random output speckle patterns and unveil the intrinsic input-output relationship. High fidelity reconstruction is obtained for datasets with a large degree of homogeneity, which underutilizes the capacity of the combined MMF-DNN system. Here, we show that holographic modulation can be employed to encode an additional layer of variance on the output speckle pattern, improving the overall transmissive capabilities of the system. Operatively we have implemented this by adding a holographic label to the original dataset and injecting the resulting phase image into the fiber facet through a Fourier transform lens. The resulting speckle pattern dataset can be clustered primarily by holographic label (rather than the image data), and can be reconstructed without loss of fidelity. As an application, we describe how colour images may be segmented into RGB components and each colour component may then be labelled by distinct hologram. A UNET architecture was then used to decode each class of speckle patterns and reconstruct the colour image without the need for temporal synchronisation between sender and receiver

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 $\bar B_{s}^0 \to D_{s}^+ \pi^-$ 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., Comment: 45 pages, 4 figures, 2 tables

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., Comment: 8 pages, 3 figures, 5 tables. Contribution to the Proceedings of 8th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2022), 7-11 November 2022, Baden-Baden, Germany

In the 1990s, very low experimental values for the lifetime ratio $\tau (\Lambda_b)/\tau(B_d)$ 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 $\tau (\Lambda_b)/\tau(B_d) = 0.969(6)$. 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 $\tau (\Lambda_b)/\tau(B_d) = 0.955(14)$, $\tau (\Omega_b^-)/\tau(B_d) = 1.081(42)$, and $\tau (\Xi_b^0)/\tau (\Xi_b^-) = 0.929(28)$., Comment: 36 pages, 3 figures, 8 tables

With the aim of measuring the $^{235}$U(n,f) cross section at the n\_TOF facility at CERN over a wide neutron energy range, a detection system consisting of two fission detectors and three detectors for neutron flux determination was realized. The neutron flux detectors are Recoil Proton Telescopes (RPT), based on scintillators and solid state detectors, conceived to detect recoil protons from the neutron-proton elastic scattering reaction. This system, along with a fission chamber and an array of parallel plate avalanche counters for fission event detection, was installed for the measurement at the n\_TOF facility in 2018, at CERN. An overview of the performances of two RPTs - especially developed for this measurement - and of the parallel plate avalanche counters are described in this article. In particular, the characterization in terms of detection efficiency by Monte Carlo simulations and response to neutron beam, the study of the background, dead time correction and characterization of the samples, are reported. The results of the present investigation show that the performances of these detectors are suitable for accurate measurements of fission reaction cross sections in the range from 10 to 450~MeV.

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 $\tau (B^+)/\tau (B_d)$ and the experimental bound on the semi-leptonic CP asymmetry $a_{sl}^d$, provide strong, complementary constraints on some of the NP Wilson coefficients., Comment: 29 pages, 3 figures

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 $\Gamma (B^+) = (0.58^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, $\Gamma (B_d) = (0.63^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, $\Gamma (B_s) = (0.63^{+0.11}_{-0.07}) \, \mbox{ps}^{-1}$, and for the lifetime ratios $\tau (B^+) / \tau (B_d) = 1.086 \pm 0.022$, $\tau (B_s) / \tau (B_d) = 1.003 \pm 0.006 \, (1.028 \pm 0.011)$. The two values for the last observable arise from using two different sets of input for the non-perturbative parameters $\mu_\pi^2(B_d)$, $\mu_G^2(B_d)$, and $\rho_D^3(B_d)$ 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 $\tau (B_s)/\tau (B_d)$ when considering the second set of input parameters. Specifically, this observable is extremely sensitive to the size of the parameter $\rho_D^3 (B_d)$ and of the SU(3)$_F$ breaking effects in $\mu_\pi^2$, $\mu_G^2$ and $\rho_D^3$; hence, it is of utmost importance to be able to better constrain all these parameters. In this respect, an extraction of $\mu_\pi^2 (B_s), \mu_G^2 (B_s), \rho_D^3 (B_s)$ 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 $\rho_D^3 (B)$ extracted from fit, would be very helpful in reducing the corresponding theory uncertainties., Comment: 35 pages, 5 figures, 7 tables