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Register a new userA Measurement of the Branching Ratio of $pi^0$ Dalitz Decay using $K_L rightarrow pi^0pi^0pi^0$ Decays
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We present a measurement of $B(pi^0 rightarrow e^+e^- gamma)/B(pi^0 rightarrow gammagamma)$, the Dalitz branching ratio, using data taken in 1999 by the E832 KTeV experiment at Fermi National Accelerator Laboratory. We use neutral pions from fully reconstructed $K_L$ decays in flight; the measurement is based on about 60 thousand $K_L rightarrow pi^0pi^0pi^0 rightarrow gammagamma~gammagamma~e^+e^-gamma$ decays. We normalize to $K_L rightarrow pi^0pi^0pi^0 rightarrow 6gamma$ decays. We find $B(pi^0 rightarrow e^+e^- gamma)/B(pi^0 rightarrow gammagamma)$ $(m_{e^+e^-}$ > 15 MeV/$c^2)$ = $[3.920 pm 0.016(stat) pm 0.036 (syst)] times 10^{-3}$. Using the Mikaelian and Smith prediction for the $e^+e^-$ mass spectrum, we correct the result to the full $e^+e^-$ mass range. The corrected result is $B(pi^0 rightarrow e^+e^- gamma)/B(pi^0 rightarrow gammagamma) = [1.1559 pm 0.0047(stat) pm 0.0106 (syst)]$%. This result is consistent with previous measurements and the uncertainty is a factor of three smaller than any previous measurement.
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Based on a sample of $1.31 times 10^9$ $J/psi$ events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays $eta^prime rightarrow pi^+pi^-pi^0$ and $eta^prime rightarrow pi^0pi^0pi^0$ is performed. A significant $P$-wave contribution from $eta^prime rightarrow rho^{pm} pi^{mp}$ is observed for the first time in $eta^prime rightarrow pi^+pi^-pi^0$. The branching fraction is determined to be ${mathcal B}(eta^prime rightarrow rho^{pm}pi^{mp})=(7.44pm0.60pm1.26pm1.84)times 10^{-4}$, where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant $S$-wave component, there is a significant $sigma$ meson component. The branching fractions of the combined $S$-wave components are determined to be ${mathcal B}(eta^prime rightarrow pi^+pi^-pi^0)_S=(37.63pm0.77pm2.22pm4.48)times 10^{-4}$ and ${mathcal B}(eta^prime rightarrow pi^0pi^0pi^0)=(35.22pm0.82pm2.54)times 10^{-4}$, respectively. The latter one is consistent with previous BESIII measurements.
Based on a sample of $1.31 times 10^9$ $J/psi$ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 $etarightarrowpi^{+}pi^{-}pi^0$ events, 33,908 $etarightarrowpi^0pi^0pi^0$ events and 1,888 $eta^{prime}rightarrowpi^0pi^0pi^0$ events are performed. The measured matrix elements of $etarightarrowpi^+pi^-pi^0$ are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of $etarightarrowpi^0pi^0pi^0$ and $eta^{prime}rightarrowpi^0pi^0pi^0$ are determined to be $-0.055 pm 0.014 pm 0.004$ and $-0.640 pm 0.046 pm 0.047$, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of three. Final state interactions are found to have an important role in those decays.
The branching ratio of the rare decay pi^0 -> e^+e^- has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. The pi^0s were produced in fully-reconstructed K_L -> 3 pi^0 decays in flight. We observed 275 candidate pi^0 -> e^+e^- events, with an expected background of 21.4 +- 6.2 events which includes the contribution from Dalitz decays. We measured BR(pi^0 -> e^+e^-, x>0.95) = (6.09 +- 0.40 +- 0.24) times 10^{-8}, where the first error is statistical and the second systematic. This result is the first significant observation of the excess rate for this decay above the unitarity lower bound.
Utilizing the dataset corresponding to an integrated luminosity of $2.93$ fb$^{-1}$ at $sqrt{s}=3.773$ GeV collected by the BESIII detector, we report the first amplitude analysis and branching fraction measurement of the $D^0rightarrow K^-pi^+pi^0pi^0$ decay. We investigate the sub-structures and determine the relative fractions and the phases among the different intermediate processes. Our results are used to provide an accurate detection efficiency and allow measurement of ${cal B}(D^0rightarrow K^-pi^+pi^0pi^0) ,=, (8.86 pm 0.13(text{stat}) pm 0.19(text{syst}))%$.
We report a measurement of the amplitude ratio $r_S$ of $B^0 to D^0K^{*0}$ and $B^0 to bar{D^0}K^{*0}$ decays with a Dalitz analysis of $Dto K_S^0pi^+pi^-$ decays, for the first time using a model-independent method. We set an upper limit $r_S < 0.87$ at the 68% confidence level, using the full data sample of $772times10^6$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. This result is obtained from observables $x_- = +0.4 ^{+1.0 +0.0}_{-0.6 -0.1} pm0.0$, $y_- = -0.6 ^{+0.8 +0.1}_{-1.0 -0.0} pm0.1$, $x_+ = +0.1 ^{+0.7 +0.0}_{-0.4 -0.1} pm0.1$ and $y_+ = +0.3 ^{+0.5 +0.0}_{-0.8 -0.1} pm0.1$, where $x_pm = r_S cos(delta_S pm phi_3)$, $y_pm = r_S sin(delta_S pm phi_3)$ and $phi_3~(delta_S)$ is the weak (strong) phase difference between $B^0 to D^0K^{*0}$ and $B^0 to bar{D^0}K^{*0}$.
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