22 research outputs found
Search for the dark photon in decays
A sample of fully reconstructed
decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is
analysed to search for the dark photon () production in the decay followed by the prompt decay. No signal is observed,
and an exclusion region in the plane of the dark photon mass and
mixing parameter is established. The obtained upper limits on
are more stringent than the previous limits in the mass range
9~
m MeV/c^2<70~
m MeV/c^2. The NA48/2 sensitivity to the dark
photon production in the decay is also evaluated
Order p^6 chiral couplings from the scalar K Pi form factor
Employing results from a recent determination of the scalar KPi form factor
F_0^KPi within a coupled channel dispersion relation analysis \cite{JOP01}, in
this work we calculate the slope and curvature of F_0^KPi(t) at zero momentum
transfer. Knowledge of the slope and curvature of the scalar KPi form factor,
together with a recently calculated expression for F_0^KPi(t) in chiral
perturbation theory at order p^6, enable to estimate the O(p^6) chiral
constants C_12^r=(0.3 +- 5.4)10^-7 and (C_12^r+C_34^r)=(3.2 +- 1.5)10^-6. Our
findings also allow to estimate the contribution coming from the C_i to the
vector form factor F_+^KPi(0) which is crucial for a precise determination of
|V_us| from K_l3 decays. Our result F_+^KPi(0)|_C_i^r=-0.018 +- 0.009, though
inflicted with large uncertainties, is in perfect agreement with a previous
estimate by Leutwyler and Roos already made twenty years ago.Comment: 19 pages, discussion of scale dependence of the chiral couplings
added; version to appear in JHE
ChPT tests at the NA48 and NA62 experiments at CERN
The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of
rare kaon decays in the Ke4 modes: Ke4(+-) ()
and Ke4(00) () with nearly one percent
background contamination. The detailed study of form factors and branching
rates, based on these data, has been completed recently. The results brings new
inputs to low energy strong interactions description and tests of Chiral
Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new
data support the ChPT prediction for a cusp in the invariant mass
spectrum at the two charged pions threshold for Ke4(00) decay. New final
results from an analysis of about 400 rare
decay candidates collected by the NA48/2 and NA62 experiments at CERN during
low intensity runs with minimum bias trigger configurations are presented. The
results include a model-independent decay rate measurement and fits to ChPT
description.Comment: XIIth International Conference on Heavy Quarks and Leptons 2014,
Mainz, German
First observation and study of the decay
The NA48/2 experiment at CERN reports the first observation of the decay based on a sample of 2437
candidates with 15% background contamination collected in 2003--2004. The decay
branching ratio in the kinematic region of the squared dilepton mass above
~GeV is measured to be . The
extrapolation to the full kinematic space, using a specific model, is found to
be , in agreement with chiral perturbation
theory predictions.Comment: 16 pages, 9 figure
Search for the dark photon in decays
A sample of fully reconstructed decay candidates collected by the NA48/2 experiment at CERN in 2003--2004 is analysed to search for the dark photon () production in the decay followed by the prompt decay. No signal is observed, and an exclusion region in the plane of the dark photon mass and mixing parameter is established. The obtained upper limits on are more stringent than the previous limits in the mass range $9~{\rm MeV}/c^2m_{A
Searches for lepton number violation and resonances in K± → πμμ decays
The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003--2004. A new upper limit on the rate of the lepton number violating decay is reported: $\mathcal{B}(K^{\pm}\to\pi^{\mp}\mu^{\pm}\mu^{\pm}
Measurement of the form factors of charged kaon semileptonic decays
A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 106K± → π0e±νe (Ke3 ±) and 2.3 × 106K± → π0μ±νμ (Kμ3 ±) decays collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the Ke3 ± and Kμ3 ± modes is also presented. © 2018, The Author(s)