Application of large-area avalanche photodiodes to X-ray spectrometry of muonic atoms

Large-area avalanche photodiodes have been investigated as 1.9-keV X-ray detectors for the muonic hydrogen Lamb-shift experiment. We report experimental tests carried out for evaluation of the avalanche photodiode capabilities for X-ray detection in the intense radiation and low counting rate environment of experiments with muonic atoms. Several muonic atoms were used and it was shown that the electronic background of muonic atom X-ray spectra can be reduced simply by timing the X-ray signal against the gate signal produced by the muon entrance. Furthermore, the background can be eliminated using coincidences between the X-ray signal and the signal resulting from the electron due to the muon decay. This coincidence discrimination results, however, in a reduction of the X-ray detection efficiency.http://www.sciencedirect.com/science/article/B6THN-4B6608X-11/1/4bb8c2b08d267e2eba00e1ae64b143a

Study of coherent J/ψJ/\psi production in lead-lead collisions at sNN \sqrt{{\mathrm{s}}_{\mathrm{NN}}} = 5 TeV

International audienceCoherent production of J/ψ mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 μb$^{−1}$. The J/ψ mesons are reconstructed in the dimuon final state and are required to have transverse momentum below 1 GeV. The cross-section within the rapidity range of 2.0 < y < 4.5 is measured to be 4.45 ± 0.24 ± 0.18 ± 0.58 mb, where the first uncertainty is statistical, the second systematic and the third originates from the luminosity determination. The cross-section is also measured in J/ψ rapidity intervals. The results are compared to predictions from phenomenological models.[graphic not available: see fulltext

Search for CP violation in D(s)+→h+π0 {D}_{(s)}^{+}\to {h}^{+}{\pi}^0 and D(s)+→h+η {D}_{(s)}^{+}\to {h}^{+}\eta decays

International audienceSearches for CP violation in the two-body decays ${D}_{(s)}^{+}\to {h}^{+}{\pi}^0$ and ${D}_{(s)}^{+}\to {h}^{+}\eta$ (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 ${D}_{(s)}^{+}\to {K}_{\mathrm{S}}^0{h}^{+}$ to cancel the production and detection asymmetries. The CP asymmetries are measured to be${\displaystyle \begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}{\pi}^0\right)=\left(-1.3\pm 0.9\pm 0.6\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}{\pi}^0\right)=\left(-3.2\pm 4.7\pm 2.1\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}\eta \right)=\left(-0.2\pm 0.8\pm 0.4\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}\eta \right)=\left(-6\pm 10\pm 4\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}{\pi}^0\right)=\left(-0.8\pm 3.9\pm 1.2\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {\pi}^{+}\eta \right)=\left(0.8\pm 0.7\pm 0.5\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}\eta \right)=\left(0.9\pm 3.7\pm 1.1\right)\%,\end{array}\end{array}\end{array}\end{array}}$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 ${\mathcal{A}}_{CP}$ in these decay modes to date.[graphic not available: see fulltext

Searches for 25 rare and forbidden decays of D+D^{+} and Ds+ {D}_s^{+} mesons

International audienceA search is performed for rare and forbidden charm decays of the form ${D}_{(s)}^{+}\to {h}^{\pm }{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{\left(\prime \right)\mp }$, where h$^{±}$ is a pion or kaon and ℓ$^{(′)±}$ is an electron or muon. The measurements are performed using proton-proton collision data, corresponding to an integrated luminosity of 1.6 fb$^{−1}$, collected by the LHCb experiment in 2016. No evidence is observed for the 25 decay modes that are investigated and 90 % confidence level limits on the branching fractions are set between 1.4 × 10$^{−8}$ and 6.4 × 10$^{−6}$. In most cases, these results represent an improvement on existing limits by one to two orders of magnitude.[graphic not available: see fulltext

Test of lepton universality in beauty-quark decays

International audienceThe Large Hadron Collider beauty collaboration reports a test of lepton flavour universality in decays of bottom mesons into strange mesons and a charged lepton pair, finding evidence of a violation of this principle postulated in the standard model

Search for CP violation in D(s)+→h+π0 {D}_{(s)}^{+}\to {h}^{+}{\pi}^0 and D(s)+→h+η {D}_{(s)}^{+}\to {h}^{+}\eta decays

International audienceSearches for CP violation in the two-body decays ${D}_{(s)}^{+}\to {h}^{+}{\pi}^0$ and ${D}_{(s)}^{+}\to {h}^{+}\eta$ (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 ${D}_{(s)}^{+}\to {K}_{\mathrm{S}}^0{h}^{+}$ to cancel the production and detection asymmetries. The CP asymmetries are measured to be${\displaystyle \begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}{\pi}^0\right)=\left(-1.3\pm 0.9\pm 0.6\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}{\pi}^0\right)=\left(-3.2\pm 4.7\pm 2.1\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}^{+}\to {\pi}^{+}\eta \right)=\left(-0.2\pm 0.8\pm 0.4\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}^{+}\to {K}^{+}\eta \right)=\left(-6\pm 10\pm 4\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}{\pi}^0\right)=\left(-0.8\pm 3.9\pm 1.2\right)\%,\\ {}\begin{array}{c}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {\pi}^{+}\eta \right)=\left(0.8\pm 0.7\pm 0.5\right)\%,\\ {}{\mathcal{A}}_{CP}\left({D}_s^{+}\to {K}^{+}\eta \right)=\left(0.9\pm 3.7\pm 1.1\right)\%,\end{array}\end{array}\end{array}\end{array}}$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 ${\mathcal{A}}_{CP}$ in these decay modes to date.[graphic not available: see fulltext