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1. The pion beta and radiative electronic decays

   https://doi.org/10.21468/SciPostPhysProc.5.024  

   Pocanic, Dinko (January 2021, SciPost Physics Proceedings)

   As the lightest meson, pion offers unique opportunities for measuring parameters and testing limits of the Standard Model (SM). The PiBeta experiment, carried out at PSI, focused on SM tests accessible through the pion beta, \pi^+ \to \pi^0e^+\nu_e(\gamma) π + → π 0 e + ν e ( γ ) , and electronic radiative, \pi^+ \to e^+\nu_e\gamma π + → e + ν e γ , decay channels. We review the PiBeta experiment, and update the pion beta decay branching ratio B^{\text{exp}}_{\pi\beta}=1.038(6)_{\text{tot}}\times10^{-8} B π β exp = 1.038 ( 6 ) tot × 10 − 8 , along with the corresponding derived value of the Cabibbo-Kobayashi-Maskawa matrix element V_{ud} = 0.9738(28) V u d = 0.9738 ( 28 ) . 

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2. Search for CP violation in $$ {D}_{(s)}^{+}\to {h}^{+}{\pi}^0 $$ and $$ {D}_{(s)}^{+}\to {h}^{+}\eta $$ decays

   https://doi.org/10.1007/JHEP06(2021)019  

   Aaij, R.; Abellán Beteta, C.; Ackernley, T.; Adeva, B.; Adinolfi, M.; Afsharnia, H.; Aidala, C. A.; Aiola, S.; Ajaltouni, Z.; Akar, S.; et al (June 2021, Journal of High Energy Physics)

   A bstract Searches for CP violation in the two-body decays $$ {D}_{(s)}^{+}\to {h}^{+}{\pi}^0 $$ D s + → h + π 0 and $$ {D}_{(s)}^{+}\to {h}^{+}\eta $$ D s + → h + η (where h + denotes a π + or K + meson) are performed using pp collision data collected by the LHCb experiment corresponding to either 9 fb − 1 or 6 fb − 1 of integrated luminosity. The π 0 and η mesons are reconstructed using the e + e − γ final state, which can proceed as three-body decays π 0 → e + e − γ and η → e + e − γ , or via the two-body decays π 0 → γγ and η → γγ followed by a photon conversion. The measurements are made relative to the control modes $$ {D}_{(s)}^{+}\to {K}_{\mathrm{S}}^0{h}^{+} $$ D s + → K S 0 h + to cancel the production and detection asymmetries. The CP asymmetries are measured to be $$ {\displaystyle \begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}{\pi}^0\right)=\left(-1.3\pm 0.9\pm 0.6\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}{\pi}^0\right)=\left(-3.2\pm 4.7\pm 2.1\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}\eta \right)=\left(-0.2\pm 0.8\pm 0.4\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}\eta \right)=\left(-6\pm 10\pm 4\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}{\pi}^0\right)=\left(-0.8\pm 3.9\pm 1.2\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {\pi}^{+}\eta \right)=\left(0.8\pm 0.7\pm 0.5\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}\eta \right)=\left(0.9\pm 3.7\pm 1.1\right)\%,\end{array}\end{array}\end{array}\end{array}} $$ A CP D + → π + π 0 = − 1.3 ± 0.9 ± 0.6 % , A CP D + → K + π 0 = − 3.2 ± 4.7 ± 2.1 % , A CP D + → π + η = − 0.2 ± 0.8 ± 0.4 % , A CP D + → K + η = − 6 ± 10 ± 4 % , A CP D s + → K + π 0 = − 0.8 ± 3.9 ± 1.2 % , A CP D s + → π + η = 0.8 ± 0.7 ± 0.5 % , A CP D s + → K + η = 0.9 ± 3.7 ± 1.1 % , where the first uncertainties are statistical and the second systematic. These results are consistent with no CP violation and mostly constitute the most precise measurements of $$ {\mathcal{A}}_{CP} $$ A CP in these decay modes to date. 

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3. Observation of the doubly charmed baryon decay $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{\prime +}{\pi}^{+} $$

   https://doi.org/10.1007/JHEP05(2022)038  

   Aaij, R.; Abdelmotteleb, A. S.; Abellán Beteta, C.; Abudinén, F.; Ackernley, T.; Adeva, B.; Adinolfi, M.; Afsharnia, H.; Agapopoulou, C.; Aidala, C. A.; et al (May 2022, Journal of High Energy Physics)

   A bstract The $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{\prime +}{\pi}^{+} $$ Ξ cc + + → Ξ c ′ + π + decay is observed using proton-proton collisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5 . 4 fb − 1. The $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{\prime +}{\pi}^{+} $$ Ξ cc + + → Ξ c ′ + π + decay is reconstructed partially, where the photon from the $$ {\varXi}_c^{\prime +}\to {\varXi}_c^{+}\gamma $$ Ξ c ′ + → Ξ c + γ decay is not reconstructed and the pK − π + final state of the $$ {\varXi}_c^{+} $$ Ξ c + baryon is employed. The $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{\prime +}{\pi}^{+} $$ Ξ cc + + → Ξ c ′ + π + branching fraction relative to that of the $$ {\varXi}_{cc}^{++}\to {\varXi}_c^{+}{\pi}^{+} $$ Ξ cc + + → Ξ c + π + decay is measured to be 1 . 41 ± 0 . 17 ± 0 . 10, where the first uncertainty is statistical and the second systematic. 

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4. Measurement of CP observables in B± → D(*)K± and B± → D(*)π± decays using two-body D final states

   https://doi.org/10.1007/JHEP04(2021)081  

   Aaij, R.; Abellán Beteta, C.; Ackernley, T.; Adeva, B.; Adinolfi, M.; Afsharnia, H.; Aidala, C. A.; Aiola, S.; Ajaltouni, Z.; Akar, S.; et al (April 2021, Journal of High Energy Physics)

   A bstract Measurements of CP observables in B ± → D (*) K ± and B ± → D (*) π ± decays are presented, where D (∗) indicates a neutral D or D ∗ meson that is an admixture of meson and anti-meson states. Decays of the D (∗) meson to the Dπ 0 and Dγ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the D meson are reconstructed in the K ± π ∓ , K + K − , and π + π − final states. The analysis uses a sample of charged B mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb − 1 taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed B ± → D (*) K ± and B ± → D (∗) π ± with D → K ∓ π ± decays are the first of their kind, and a first observation of the B ± → $$ {\left(D{\pi}^0\right)}_{D^{\ast }}{\pi}^{\pm } $$ D π 0 D ∗ π ± decay is made with a significance of 6.1 standard deviations. All CP observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle γ . 

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5. A \(\beta \)-decay Study of the Low-spin Structure of \(^{98}\)Zr

   https://doi.org/10.5506/APhysPolBSupp.18.2-A21  

   Mashtakov, KR; Garrett, PE; Olaizola, B; Andreoiu, C; Ball, GC; Bender, P; Bildstein, V; Chester, A; Cross, DS; Dawkins, H; et al (February 2025, Acta Physica Polonica B Proceedings Supplement)

   A high-statistics \(\beta \)-decay experiment was conducted at the TRIUMF-ISAC facility using the \(8\pi \) \(\gamma \)-ray spectrometer and its ancillary detectors to study the low-spin structure of \(^{98}\)Zr. The analysis of \(\gamma \)–\(\gamma \) and \(e^-\)–\(\gamma \) coincidence data is presented. New measurements of \(\gamma \)-ray branching ratios and mixing ratios are reported for four \(J^{\pi } = 2^+\) states located above 2 MeV excitation energy in \(^{98}\)Zr. Based on these measurements, ratios of \(B\)(E2) values for transitions to lower-lying levels are determined, highlighting the preferential decay paths of these \(2^+\) states. AbstractPublished by the Jagiellonian University2025authors 

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