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Register a new userThe search for $D^0to{}e^{pm}mu^{mp}$
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Thomas Bird
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An overview is presented of a method to search for $D^0to{}e^{pm}mu^{mp}$ with LHCb data. In order to reduce combinatorial backgrounds, tagged $D^0$ candidates from the decay $D^{ast+}to{}D^0pi^+$ are used. This measurement is performed with respect to $mathcal{B}left(D^0to{}pi^+pi^-right)$, which cancels uncertainties in the luminosity and $D^{ast+}$ production cross-section. It is estimated that using $3,mathrm{fb}^{-1}$ of LHCb data an upper limit can be attained of $mathcal{O}left(10^{-7}right)$ at a $90%$ confidence level.
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A search for the lepton-flavour violating decays $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions at $sqrt{s} = 7$ TeV, collected by the LHCb experiment. The observed number of $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be $BR(B^0_s to e^{pm} mu^{mp}) < 1.1 ,(1.4) times 10^{-8}$ and $BR (B^0 to e^{pm} mu^{mp}) < 2.8 ,(3.7) times 10^{-9}$ at 90% (95%) confidence level (C.L.). These limits are a factor of twenty lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, $M_{rm LQ} (B^0_s to e^{pm} mu^{mp}) > 107$ TeV/c$^2$ and $M_{rm LQ} (B^0 to e^{pm} mu^{mp}) > 126$ TeV/c$^2$ at 95% C.L., and are a factor of two higher than the previous bounds.
We present a search for seven lepton-flavor-violating neutral charm decays of the type $D^{0}rightarrow X^{0} e^{pm} mu^{mp}$, where $X^{0}$ represents a $pi^{0}$, $K^{0}_{rm S}$, $bar{K^{*0}}$, $rho^{0}$, $phi$, $omega$, or $eta$ meson. The analysis is based on $468$ fb$^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Upsilon(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signals are observed, and we establish 90% confidence level upper limits on the branching fractions in the range $(5.0 - 22.5)times 10^{-7}$. The limits are between one and two orders of magnitude more stringent than previous measurements.
Long-lived particles decaying to $e^pm mu^mp u$, with masses between 7 and $50$ GeV/c$^2$ and lifetimes between 2 and $50$ ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using $5.4$ fb$^{-1}$ of $pp$ collisions collected with the LHCb detector at a centre-of-mass energy of $sqrt{s} = 13$ TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of $125$ GeV/c$^2$, and the charged current production from an on-shell $W$ boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.
A search for the lepton-flavour violating decays $B^+ to K^+ {mu}^{pm} e^{mp}$ is performed using a sample of proton-proton collision data, collected with the LHCb experiment at centre-of-mass energies of $7$ and $8~{rm TeV}$ and corresponding to an integrated luminosity of 3$rm~fb^{-1}$. No significant signal is observed, and upper limits on the branching fractions are set as $mathcal{B}(B^+ to K^+ {mu}^- e^+) < 7.0~(9.5) times 10^{-9}$ and $mathcal{B}(B^+ to K^+ {mu}^+ e^-) < 6.4~(8.8) times 10^{-9}$ at 90 (95) % confidence level. The results improve the current best limits on these decays by more than one order of magnitude.
The decay-time-dependent $CP$ asymmetry in $B^0 to D^{*pm}D^{mp}$ decays is measured using a data set corresponding to an integrated luminosity of $9$fb$^{-1}$ recorded by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7, 8 and 13 TeV. The $CP$ parameters are measured as $ S_{D^*D} = -0.861 pm 0.077,text{(stat)} pm 0.019 ,text{(syst)},, $ $ Delta S_{D^*D} = 0.019 pm 0.075 ,text{(stat)} pm 0.012 ,text{(syst)} ,, $ $ C_{D^*D} = -0.059 pm 0.092 ,text{(stat)} pm 0.020 ,text{(syst)} ,, $ $ Delta C_{D^*D} = -0.031 pm 0.092 ,text{(stat)} pm 0.016 ,text{(syst)} ,, $ $ {cal A}_{D^*D} = 0.008 pm 0.014 ,text{(stat)} pm 0.006 ,text{(syst)},. $ The analysis provides the most precise single measurement of $CP$ violation in this decay channel to date. All parameters are consistent with their current world average values.
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