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Register a new userProbing QCD dynamics and the standard model with $D_{(s)} to P^+ P^0 gamma$ decays
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We compute 10 radiative three-body decays of charged charmed mesons $D^+ to P^+ P^0 gamma$ and $D_s to P^+ P^0 gamma$, $P=pi, K$, in leading order QCDF, HH$chi$PT and the soft photon approximation. We work out decay distributions and asymmetries in the standard model and with new physics in the electromagnetic dipole operators. The forward-backward asymmetry is suitable to probe the QCD frameworks, in particular the $s$-channel dependent weak annihilation contributions in QCDF against the markedly different resonance structure in HH$chi$PT. These studies can be performed with Cabibbo-favored modes $D_s to pi^+ pi^0 gamma$, $D^+ to pi^+ overline{K}^0 gamma$ and $D_s to K^+ overline{K}^0 gamma$ with ${cal{O}}(10^{-4}-10^{-3})$-level branching ratio, which are standard model-like and induced by different hadronic dynamics. Understanding of the latter can therefore be improved in a data-driven way and sharpens the interpretation of standard model tests. Singly Cabibbo-suppressed modes such as $ D^+ to pi^+ pi^0 gamma$, $D_s to pi^+ K^0 gamma$, $D_s to K^+ pi^0 gamma$ with branching ratios within $sim 10^{-5}-10^{-4}$ are sensitive to new physics that can be signalled in the forward-backward asymmetry and in the CP-asymmetry of the rate, ideally in the Dalitz region but also in single differential distributions. Results complement those with neutral $D^0 to PP gamma$ decays.
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The photon polarization in $D_{(s)} to K_1 (to Kpipi) gamma$ decays can be extracted from an up-down asymmetry in the $K pi pi$ system, along the lines of the method known to $B to K_1 (to Kpipi) gamma$ decays. Charm physics is advantageous as partner decays exist: $D^+ to K_1^+ (to Kpipi) gamma$, which is standard model-like, and $D_s to K_1^+ (to Kpipi) gamma$, which is sensitive to physics beyond the standard model in $|Delta c| =|Delta u|=1$ transitions. The standard model predicts their photon polarizations to be equal up to U-spin breaking corrections, while new physics in the dipole operators can split them apart at order one level. We estimate the proportionality factor in the asymmetry multiplying the polarization parameter from axial vectors $K_1(1270)$ and $K_1(1400)$ to be sizable, up to the few ${cal{O}}(10)%$ range. The actual value of the hadronic factor matters for the experimental sensitivity, but is not needed as an input to perform the null test.
The results of searches for $B^{0}_{(s)} rightarrow J/{psi} p overline{p}$ and $B^{+} to J/{psi} p overline{p} {pi}^{+}$ decays are reported. The analysis is based on a data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions, collected with the LHCb detector. An excess with 2.8$,sigma$ significance is seen for the decay $B^{0}_{s} to J/{psi} p overline{p}$ and an upper limit on the branching fraction is set at the 90 % confidence level: ${cal B}(B^{0}_{s} to J/{psi} p overline{p}) < 4.8 times 10^{-6}$, which is the first such limit. No significant signals are seen for $B^{0} to J/{psi} p overline{p}$ and $B^{+} to J/{psi} p overline{p} {pi}^{+}$ decays, for which the corresponding limits are set: ${cal{B}}(B^{0} to J/{psi} p overline{p}) < 5.2 times 10^{-7}$, which significantly improves the existing limit; and ${cal{B}}(B^{+} to J/{psi} p overline{p} {pi}^{+}) < 5.0 times 10^{-7}$, which is the first limit on this branching fraction.
We present a measurement of the $CP$-violating weak mixing phase $phi_s$ using the decay $bar{B}^{0}_{s}to D_{s}^{+}D_{s}^{-}$ in a data sample corresponding to $3.0$ fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not constrain $|lambda|=1$ to allow for the presence of $CP$ violation in decay, yields $phi_s = 0.02 pm 0.17$ (stat) $pm 0.02$ (syst) rad, $|lambda| = 0.91^{+0.18}_{-0.15}$ (stat) $pm0.02$ (syst). This result is consistent with the Standard Model expectation.
Using an $e^{+}e^{-}$ annihilation data sample corresponding to an integrated luminosity of $3.19~mathrm{fb}^{-1}$ and collected at a center-of-mass energy $sqrt{s} = 4.178~mathrm{GeV}$ with the BESIII detector, we measure the absolute branching fractions $mathcal{B}(D_{s}^{+} rightarrow K_{S}^{0}K^{+}) = (1.425pm0.038_{rm stat.}pm0.031_{rm syst.})%$ and $mathcal{B}(D_{s}^{+} rightarrow K_{L}^{0}K^{+}) =(1.485pm0.039_{rm stat.}pm0.046_{rm syst.})%$. The branching fraction of $D_{s}^{+} rightarrow K_{S}^{0}K^{+}$ is compatible with the world average and that of $D_{s}^{+} rightarrow K_{L}^{0}K^{+}$ is measured for the first time. We present the first measurement of the $K_{S}^{0}$-$K_{L}^{0}$ asymmetry in the decays $D_{s}^{+} rightarrow K_{S,L}^{0}K^{+}$, and $R(D_{s}^{+} rightarrow K_{S,L}^{0}K^{+})=frac{mathcal{B}(D_{s}^{+} rightarrow K_{S}^{0}K^{+}) -mathcal{B}(D_{s}^{+} rightarrow K_{L}^{0}K^{+})}{mathcal{B}(D_{s}^{+} rightarrow K_{S}^{0}K^{+}) +mathcal{B}(D_{s}^{+} rightarrow K_{L}^{0}K^{+})}= (-2.1pm1.9_{rm stat.}pm1.6_{rm syst.})%$. In addition, we measure the direct $CP$ asymmetries $A_{rm CP}(D_{s}^{pm} rightarrow K_{S}^{0}K^{pm}) = (0.6pm2.8_{rm stat.}pm0.6_{rm syst.})%$ and $A_{rm CP}(D_{s}^{pm} rightarrow K_{L}^{0}K^{pm}) = (-1.1pm2.6_{rm stat.}pm0.6_{rm syst.})%$.
The first observation of the decays $Lambda_b^0 to chi_{c1} p K^-$ and $Lambda_b^0 to chi_{c2} p K^-$ is reported using a data sample corresponding to an integrated luminosity of $3.0$ fb$^{-1}$, collected by the LHCb experiment in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The following ratios of branching fractions are measured begin{eqnarray*} frac{{cal B}(Lambda_b^0 to chi_{c1} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.242 pm 0.014 pm 0.013 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to J/psi p K^-)} = 0.248 pm 0.020 pm 0.014 pm 0.009, frac{{cal B}(Lambda_b^0 to chi_{c2} p K^-)}{{cal B}(Lambda_b^0 to chi_{c1} p K^-)} = 1.02 pm 0.10 pm 0.02 pm 0.05, end{eqnarray*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fractions of the $chi_{c1}to J/psigamma$ and $chi_{c2} to J/psigamma$ decays. Using both decay modes, the mass of the $Lambda_b^0$ baryon is also measured to be $m_{Lambda_b^0} = 5619.44 pm 0.28 pm 0.26$ MeV/$c^2$, where the first and second uncertainties are statistical and systematic, respectively.
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