Many extensions of the Standard Model include the possibility of light new particles, such as light Higgs bosons or dark matter candidates. These scenarios can be probed using the large datasets ...collected by B factories, complementing measurements performed at the LHC. This review summarizes recent searches for light New Physics conducted by the BABAR and Belle experiments.
Baryon pair production in two-photon collisions is studied with the L3 detector at LEP. The following reactions are identified:
γγ →
p
p
,
γ → Λ
Λ
,
γ → Σ
0
Σ
0
and
γγ → Λ
GS
0 + Σ
0
Λ
. The analyses ...are based on data collected at e
+e
− center-of-mass energies from 91 GeV to 208 GeV, corresponding to an integrated luminosity of 844 pb
−1. Their cross section is measured as a function of the the two-photon center-of-mass energy and the production polar angle. The results are compared to the predictions of the quark-diquark and handbag models.
This review briefly describes light dark matter searches performed by the BABAR experiment. Although dark matter candidates have traditionally been associated with heavy particles appearing in ...extensions of the Standard Model, a lighter component remains a well motivated alternative, and many scenarios of light dark matter have been recently proposed. Thanks to their large luminosities, B factories offer an ideal environment to probe these possibilities, complementing searches from direct detection and satellite experiments.
The SuperB project is an asymmetric e super(+)e super(-) accelerator of 10 super(36)cm super(-2)s super(-1) luminosity, capable of collecting a 50 - 75 ab super(-1) data sample in five years of ...running. The SuperB electromagnetic calorimeter (EMC) provides energy and direction measurement of photons and electrons and identification versus other charged particles for electrons. A matrix of 25 LYSO crystals has been tested at the Beam Test Facility at Frascati in May 2011 at energies between 100 MeV and 500 MeV. Results from this test will be presented. Design and Monte Carlo studies for the general EMC system will also be presented.
We report the observation of the decay $B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}$ based on $342 \mathrm {\,fb}^{-1}}$ of data collected at the $\Y4S$ resonance with the BABAR ...detector at the PEP-II $e^{+}e^{-}$ storage rings at SLAC. A simultaneous fit to three $D^{+}_{s}$ decay chains is performed to extract the signal yield from measurements of the squared missing mass in the B meson decay. We observe the decay $B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}$ with a significance greater than five standard deviations (including systematic uncertainties) and measure its branching fraction to be $\BR(B^{-} \rightarrow D^{(*)+}_{s} K^{-} \ell^{-} \bar{\nu}_{\ell}) = 6.13^{+1.04}_{-1.03}(\mathrm{stat.})\pm0.43(\mathrm{syst.}) \pm 0.51(\BR(D_{s}))\times10^{-4}$, where the last error reflects the limited knowledge of the $D_{s}$ branching fractions.
We report the measurement of the Cabibbo-Kobayashi-Maskawa CP-violating angle $\gamma$ through a Dalitz plot analysis of neutral $D$ meson decays to $K_S^0 \pi^+ \pi^-$ and $K_S^0 K^+ K^-$ produced ...in the processes $B^\mp \to D K^\mp$, $B^\mp \to D^{*} K^\mp$ with $D^* \to D \pi^0,D \gamma$, and $B^\mp \to D K^{*\mp}$ with $K^{*\mp} \to K_S^0 \pi^\mp$, using 468 million $B\bar{B}$ pairs collected by the BABAR detector at the PEP-II asymmetric-energy $e^+e^-$ collider at SLAC. We measure $\gamma=(68 \pm 14 \pm 4 \pm 3)^\circ$ ({\rm mod $180^\circ$}), where the first error is statistical, the second is the experimental systematic uncertainty and the third reflects the uncertainty in the description of the neutral $D$ decay amplitudes. This result is inconsistent with $\gamma = 0$ (no direct CP violation) with a significance of 3.5 standard deviations.
We report a direct measurement of $D^0-overline{D}^0$ mixing parameters through a time-dependent amplitude analysis of the Dalitz plots of $D^0 \rightarrow K_S^0 \pi^+ \pi^-$ and, for the first time, ...$D^0 \rightarrow K_S^0 K^+ K^-$ decays. The low-momentum pion $\pi_s^+$ in the decay $D^{*+} \rightarrow D^0 \pi_s^+$ identifies the flavor of the neutral $D$ meson at its production. Using 468.5 fb$^{-1}$ of $e^+e^-$ colliding-beam data recorded near $\sqrt s = 10.6$~GeV by the BABAR detector at the PEP-II asymmetric-energy collider at SLAC, we measure the mixing parameters $x= 1.6 \pm 2.3 ({\rm stat.}) \pm 1.2 ({\rm syst.}) \pm 0.8 ({\rm model}) \times10^{-3}$, and $y= 5.7 \pm 2.0 ({\rm stat.}) \pm 1.3 ({\rm syst.}) \pm 0.7 ({\rm model}) \times 10^{-3}$. These results disfavor the no-mixing hypothesis with a significance of 1.9 standard deviations, and provide the best measurement to date of $x$.
We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V_cb| and the form-factor slope rho^2 in Bbar -> Dl- nubar decays based on 460 million BBar events recorded at the ...Upsilon(4S) resonance with the BaBar detector. BBar -> Dl- nubar decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure the differential decay rate and determine G(1) |V_cb|= (43.0 \pm 1.9 \pm 1.4)\times 10^{-3} and rho^2 = 1.20 \pm 0.09 \pm 0.04, where G(1) is the the hadronic form factor at the point of zero recoil. We also determine the exclusive branching fractions and find BF(B^- -> D0l- nubar) = (2.31 \pm 0.08 \pm 0.09)% and BF (B0bar -> D+ l^- nubar)=(2.23 \pm 0.11 \pm 0.11)%.
Using 467 $fb^{-1}$ of $e^+e^-$ annihilation data collected with the BaBar detector, we measure $\frac{{\cal{B}}(\tau^- \to \mu^- \bar{\nu}_\mu \nu_\tau)}{{\cal{B}}(\tau^- \to e^- \bar{\nu}_e ...\nu_\tau)} = (0.9796 \pm 0.0016 \pm 0.0036)$, $\frac{{\cal{B}}(\tau^- \to \pi^- \nu_\tau)}{{\cal{B}}(\tau^- \to e^- \bar{\nu}_e \nu_\tau)} = (0.5945 \pm 0.0014 \pm 0.0061)$, and $\frac{{\cal{B}}(\tau^- \to \K^- \nu_\tau)}{{\cal{B}}(\tau^- \to e^- \bar{\nu}_e \nu_\tau)} = (0.03882 \pm 0.00032 \pm 0.00057)$, where the uncertainties are statistical and systematic, respectively. From these precision measurements we test the Standard Model assumption of $\mu$-$e$ and $\tau$-$\mu$ charged current lepton universality and also obtain a value for $|V_{us}| = 0.2255 \pm 0.0024$, which is consistent with the prediction from the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.
We report an analysis of tau- decaying into omega.pi-.nu_tau with omega -> pi+pi-pi0 using a data sample containing nearly 320 million tau pairs collected with the BABAR detector at the PEP-II ...B-Factory. We find no evidence for second-class currents and we set an upper limit of 0.69% at 90% confidence level for the fraction of second-class currents in this decay mode.
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