We present a new determination of the parity of the neutral pion via the double Dalitz decay pi0-->e+e-e+e-. Our sample, which consists of 30,511 candidate decays, was collected from KL-->pi0pi0pi0 ...decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative pi0 parity and place a limit on scalar contributions to the pi0-->e+e-e+e- decay amplitude of less than 3.3% assuming CPT conservation. The pi0gamma*gamma* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase-space distribution. Additionally, we have measured the branching ratio of this mode to be B(pi0-->e+e-e+e-)=(3.26+/-0.18)x10(-5).
We present a measurement of B(π0→e+e-γ)/B(π0→γγ), 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 KL decays in flight; the measurement is based on ~60 thousand KL→π0π0π0→γγγγe+e-γ decays. We normalize to KL→π0π0π0→6γ decays. We find B(π0→e+e-γ)/B(π0→γγ) (me+e->15 MeV/c2)=3.920±0.016(stat)±0.036(syst)×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(π0→e+e-γ)/B(π0→γγ)=1.1559±0.0047(stat)±0.0106(syst)%. This result is consistent with previous measurements, and the uncertainty is a factor of 3 smaller than any previous measurement.
We present a measurement of B(π0→e+e−γ)/B(π0→γγ), 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 KL decays in flight; the measurement is based on ∼60 thousand KL→π0π0π0→γγγγe+e−γ decays. We normalize to KL→π0π0π0→6γ decays. We find B(π0→e+e−γ)/B(π0→γγ) (me+e−>15 MeV/c2)=3.920±0.016(stat)±0.036(syst)×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(π0→e+e−γ)/B(π0→γγ)=1.1559±0.0047(stat)±0.0106(syst)%. This result is consistent with previous measurements, and the uncertainty is a factor of 3 smaller than any previous measurement.
A
bstract
We study the constraints that electroweak precision data can impose, after the discovery of the Higgs boson by the LHC, on neutrinophilic two-Higgs-doublet models which comprise one extra ...SU(2) × U(1) doublet and a new symmetry, namely a spontaneously broken
ℤ
2
or a softly broken global U(1). In these models the extra Higgs doublet, via its very small vacuum expectation value, is the sole responsible for neutrino masses. We find that the model with a
ℤ
2
symmetry is basically ruled out by electroweak precision data, even if the model is slightly extended to include extra right-handed neutrinos, due to the presence of a very light scalar. While the other model is still perfectly viable, the parameter space is considerably constrained by current data, specially by the
T
parameter. In particular, the new charged and neutral scalars must have very similar masses.
The KTeV E799 experiment has conducted a search for the rare decays KL→π0π0µ+µ- and KL→π0π0X0→ π0π0µ+µ-, where the X0 is a possible new neutral boson that was reported by the HyperCP experiment with ...a mass of (214.3 ± 0.5) MeV/c2. We find no evidence for either decay. We obtain upper limits of Br(KL→π0π0X0 →π0π0µ+µ-) < 1.0 x 10-10 and Br(KL→ π0π0µ+µ-) < 9.2 x 10-11 at the 90% confidence level. This result rules out the pseudoscalar X0 as an explanation of the HyperCP result under the scenario that the d¯sX0 coupling is completely real.
A
bstract
If the neutrino analogue of the Mössbauer effect, namely, recoiless emission and resonant capture of neutrinos is realized, one can study neutrino oscillations with much shorter baselines ...and smaller source/detector size when compared to conventional experiments. In this work, we discuss the potential of such a Mössbauer neutrino oscillation experiment to probe nonstandard neutrino properties coming from some new physics beyond the standard model. We investigate four scenarios for such new physics that modify the standard oscillation pattern. We consider the existence of a light sterile neutrino that can mix with ν
e
, the existence of a Kaluza-Klein tower of sterile neutrinos that can mix with the flavor neutrinos in a model with large flat extra dimensions, neutrino oscillations with nonstandard quantum decoherence and mass varying neutrinos, and discuss to which extent one can constrain these scenarios. We also discuss the impact of such new physics on the determination of the standard oscillation parameters.
Using the complete KTeV data set of 5,241 candidate K(L)--> pi(+) pi(-) e(+) e(-) decays (including an estimated background of 204 +/- 14 events), we have measured the coupling g(CR)= 0.163 +/- ...0.0149(stat) +/- 0.023(syst) of the CP conserving charge radius process and from it determined a K(0) charge radius of <r(2)(K(0))> = -0.077 +/- 0.007(stat) +/- 0.011(syst)fm(2). We have determined a first experimental upper limit of 0.04 (90% C.L.) /g(e1)/ / /g(M1)/ of the couplings for the E1 and M1 direct photon emission processes. We also report the measurement of /g(M1)/ including a vector form factor /g(M1)/(1 + (a(1)/a(2))/((M(2)(p)-(M(2)(k))= 2M(K)E(gamma*)), where vector /g(M1)/= 1.11+/- 0.12(stat) +/- 0.08(syst) and a(1)/a(2) = -0.744 +/- 0.027(stat) +/- 0.032(syst) GeV(2)/c(2). Finally, a CP-violating asymmetry of 13.6 +/- 1.4(stat) +/- 1.5(syst)% in the CP and T odd angle phi between the decay planes of the e(+) e(-) and pi(+) pi(-) pairs in the K(L) center of mass is reported.
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